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,ELECTROFISIOLOCIA Y ACCIOil DE LA EOi-iiA 3&L CORAZQN

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I I A R C A P A C O C

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/' /AWlENDARB _- CORDOVA F A B I A N

ROBLES DIAZ LAURA ISABEL

A U W A DEL COMZON

E1 corazón es e l órgano propulsor de l a sangre; debe bombear sangre en cantidades y a presión suficiente para cubrir las hecesidades de las células corporales y -- mantener l a sangre en movimiento constante dentro de los vasos, imprime a esté liquido- su movimiento constante a través del cwppo. Ea un órgano hueco, muscular, que en e l a- dulto pesa unos 255 gr. Está situado en l a parte u d i a del pecho, algo inclinado a l a - izquierda. entre las dos pleuras y envuelto por e l pericardio, se encuentra dentro de - l a cavidad torácica. Alrededor de los dos tercios del corazón se encuentran a l a izquierda de l a linea media y l a punta descanaa iobre e l diafragma. Puede senterse e l choque de l a punta entre l a quinta y la sexta cost i l la sobre l a línea que pasa por e1 centro- de l a clavfcula izquierda. La base o extremidad ancha del corazón se encuentra inmediatamente arrilia de l a tercera cost i l la .

r Posician del corasbn en el torax

E l corazón esta aplanado en dos caras; una es convexa, hacia arriba y a l a dE recha, y l a otra ea c6ncava y ae encuentra abajo y a l a izquierda. Bat¿ dividido por dos surcos circulares.

El surco transversal es e l m4s profundo y divide a l corazón en dos porciones de las cuales, l a que ocupa l a parte superior constituye las AUPICUUS y la otra los VBRIñI- - CULOS.

E l aurco longitudinal devide este 6rgsno en COMZOt4 DERECHO y C O W O N IZQUIXiw, de suerte que corprende cuatro partes: dos aurfcuha y dos ventrícuios. Las dos auriculas reciben sangre que ae d i r í e a1 corarón. y l a arirfcula derecha es mayor que l a izquierda.- poro tiene paredes más delgadas. Loa ventriculvs. de mayor tameao y paredes 4 s gruesas,- bombean l a aangre hacia fuera de l corasbn. Cada uno de e l los tiene una capacidad de alrededor de 05 m l de sangre.

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Las dos partes que constituyan e l ccrazdn derecho comunican entre s i por e l orL

f icto ~ u p ~ c r m ) - v ~ # ~ ~ ~ c ~ ~ & t (A. v.), de igual modo, l a auricula izquierda comunica con e l ventriculo izquoerdo; pero las auriculas no comunican entre si y l o mismo sucede con los vantrfculos. Loa or i f ic ios de counicación eaten cerrados por unas valvulas i i auda s : - l a del corazóa derecho VALWU TRIWSPIDB y l a del corazón izquierdo VALVULA MITRAL.

La valvula tricdapt.de (tres hojas o cuspides), se abre para permitir que f lu- ya sangre de l a auricula hacia e1 ventriculo. pero dcspues se cierra para impedir f lujo- retrógzado delventr icula hacia l a auricula. La cara inferior de cada hoja se encuentra- adherida a 1aa parodes del ventrfculo por rerirtentes cordonea llamdos C ü m S lpmINOSAS que estan conectadas con elevaciones de l a musculatura ventricular que se denominan HüS- CULOS PAPILARES.

La válvula bicdspide o mitral se encuentra en e l o r i f i c i o entre l a auricula y- e l ventriculo izquierdo# e impide fugar retrógradar de sangre hacia l a auricula. Como l a vAlvula tricdspide, sus hoja. se f i j an a las pardes del ventriculo por las cuerdas tm- dinoaas que nacen de los d scu los papilarer.

B1 corazón se encuentra dentro de una bolsa ligeramente mayor de tej ido f i b o SO resistente y blanco l l u v d o R U I O I O . 8stA cubierto de una doble capa de tej ido see ros0 cuya capa interna f o r u l a capa exterior del corazáa m i n i o , que ae llama HPICARDIO. Entre astaa dos capas se encuentran de 30 a 50 m l de lfquido transparente qua l ibr ica l a superficie e impide frikciones por roce cuando el corazón se contrae.

Bajo e l epicardio se encuentra l a capa principal del corazón, e l MIOCABDIO, que en los ventrfculos esta distribuida an puentes cruzados denminados 'RMECUUS CARNOSAS. Eat8 compuesto por múrculo cardiaco y forma la masa de l a p a r d cardiaca. La tdnica que - reviste las cavidades cardiacas es una oabrana duominada XDOCABDIO; estA compuesta - por endotelio y se contináa con e l endotelio que cubre a todo e l sistema vascular.

Las auriculas presentan, en au parte superior, una pequeña pro lmac ión llamada APENDICE AURICULAR o SENO, A i seno de l a aur€cuia derecha afluyen l a VENA CAVA SUPERI OR y l a VENA CAVA INPBRIOR. en e l de la auricula izquierda 66 encuentran los or i f ic ios - de las V U A I PUMONAUS DgagCHA e IZQUIBILM. t

La ARTWUA PUUIONAR deaembo8a en e l ventriculo derecho, La ARTERIA AORTA e l e l ventriculo izquierdo. Cada una de estas arterias esta provista de tres válvulas llamadas SIGUOIDEAS o SIOXIUJNAiUS, destinadas a cerrar l a abertura de esos vasos.

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La fanción principal del corazón es crear un gradiente de presión para e l novi miento de liquido. Por tanto, l a sangre es expulsada a las grandes arterias elásticaa ho cia vasos que l a distribuyen por los tejidos. La pared gruesa y muscular del corazón se- contrae y re la ja en forma rítmica, y recibe y expele sangre continuamente. Las dos auriar: culas se llenan de sangre a partir de SUS venas respectivas J l a e w i i n a través de lor- or i f ic ios auriculoventriculares hacia los ventriculos. Cuando las paredes de los ventrfculos se contraen, l a sangre es expelida bajo presión hacia l a aotta y l a arteria pulmonar. Cuando las vi lvolas tricdspide y mitral ae cierran, producen e l primer ruido card- co de tonalidad grave. E l cierre repentino de las dos válvulas sa i lunares producen e l - segundo ruido cardiaco de tonalidad aguda.

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Cow ya se d i j o e l corazón es un bobba pursatil de cuatro cavidades, dos surf- las y dos ventriculos. le función aurfcular es principalmente de entrada s los ventrícu-- los , pero también impulsa débilmente l a sangre para desplazarla a través de las aurfculas hacia los ventrfculos. l os vantrículos son los que proporcionan l a fuerza principal e im- pulsan l a sangre a través de los pulmones y de todo e l sistema circulatorio periferico.

' FISIOGOGIA DEL MJSCULO CAPDIACO

E1 corazón está formado por tres ti&s principales de músculo. MISCULO AURICU-- LAP, MIJSCUU) V ~ I C ü I A R y FIBBAS ESPECIALIZADAS para excitación y conducción; estas fi-- bras especializadas solo se contraen debiliente porque contienen m y pocas f ibras contra: t i l e s , pero brindan un sistema excitatorio para e l corazón y un sistema de tran8if8i6n po ra l a rapids conducción del impulso a travis del mismo.

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E1 olaculo cardiaco es ESTRZADO, y contiene míofibri l las tfpicas que contienen- filamentos de ACTINA y XIOSINA. estos filamentos se interdigitan y se deslizan uno8 sobre otros durante e1 proceso de contracción. E l d s c u l o cardiaco contiene además unas iineas- angulares llamada8 DISCOS INTBRCALAüBS, que son mambraaas cdlulares que separan unas de - otras las células nosculare8 cardiacas, que son células conectadas en serie unas con otras Por l o tanto desde e1 punto de vista funcional los iones fluyen con relativa facilidad SL guiendo elaeje de las f ibras musculares cardiacas, de manera que los potenciales de acci- 6n pasan de una c i iu ia u r cu i a r cardiaca a otra y atraviesan rlr a l l á de 108 discos int- calares, de mamara que lar células musculares cardiacas estan tan estrechamente unidas -- que cuando una es excitada e l potencial de acción se difunde a todas pasando de célula a- c i lu la a través de las interconecciones.

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Mdsculo Cardíaco

WTKNCIALES DE ACCION EN EL IYlJSCULO CIUilDIACO

Hay potenciales eléctrico8 a travéa de las i d r a n a s de practicamente todas las células corporales; algunas células colo las nerviosas y mmculares, son excitables. o -- sea, capaces de transmitir impulsos electroquimicos a l o largo de sus membranas. " _

Para hablar de potenciales recordsrcms que los lfquidos, tanto dentro como --- fuera de l a célula, son soluciones de alectr6litos que contienen aproximadamente 155 meq/ l i t r o de aniones y l a misma concentración de cationes. En general, se acumula un exceso -

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de ioiies negativos (anionas) inmediatamente dentro de l a membrana celular, y un námero - igual de ioncs positivos (cationea) por fuera de l a membrana. E l resutado es e1 desarro- 110 de un m C l b l DE HR4BBANA.

Los dos medios bdsicos por medio de los cuales pueden desarroiiarse potancia-- les de membrana son: Transporte activo de iones a través de la membrana. creando un des' qu i l i b r io entre cargas negativas y positivas a uno y a otro lado de la membrana. Y Difu- sión de iones a través de l a membrana. como consecuencia de una diferencia de concentraei ciones, creando tambien un desequilibrio de cargas.

Mientras l a membrana de l a f i b r a nerviosa no sufre parturbaciones, e l potencial de membrana se conserva en aproximadamente -85 mV. valor denominado POTENCIAL DE REPOSO.

B1 potencial de membrana en reposo, medido en diferentes f ibras musculares y -- nerviosas, es generalmente entre -75 y -95 mV., con -85 IN. COIO valor promedio probable- de las diferentes mediciones.

Cualquier factor que aumente bruscamente l a permeabilidad de l a membrana para- e l sodi tiene tendencia a desencadenar una seria de cambios rapidos en e l potencial de - membrana, que dura una fracción de segundo, seguidos inmediatamente de l a vuelta del pot$" cia1 de membrana a su valor de reposo. Esta sucesión de Cadi06 recibe e l nombre de P O - CUL DE ACCION.

Algunos de los factores que pueden desmcadenar e l potencial de acción son l a - estimilación electrica de l a acmbrana, e l f r i o , e l calor o cualquier factor que perturbe- Poientdneammte e l estado normal de reposo de l a membrana.

B1 potencial de a c c i h se presenta en dos etapas separadas, denominadas DESPOG RIUCIOti y REPOLARIZACION, Cuando e l estado de l a membrana es de reposo, se encuentra con negatividad dentro y positividad fuera. Cuando l a permeabilidad de l a membrana para los-*io iones de sodio aumenta bruscamente, muchos iones de sodio penetran en e l interior de l a - f ibra l k a n d o consigo suficientes cargas positivas para causar una BESlWA8UMIOü total del potencial normal de reposo, y generalmente gargas bastantes para desarrollar un estado positivo dentro de l a f ibra ea lugar del estado negativo normal. E l estado positivo -- dentro de l a f ibra recibe e l nombre de POTENCIAL IiWEitTIW.

Casi inmediatamente después de producida l a despolarización los poros de l a m- brans vuelven a se1 casi total-te impermeables a los iones de sodio. En concecuencia e l potencial invertido dentro de las f ibras desaparece, y se restablece e l potencial no ru l - de membrana en reposo. Esto recibe e l nombre de PPPOLARIZACIüt?.

Sucesión de Potenciales

E1 potencial de l a membrana m reposo del músculo cardiaco normal es de aproxi- nudamente de -80 a -85 mV, y a p r o x i ~ d a ~ m t o do -90 a -100 4, en las fibras conductorand E1 potencial de accibn total dol d s c u l o cardíaco es de unos 105 mV, l o cual signif ica u- M inversi6n de potencial, o bien un "esceso", más a l l á del potencial de reposo de unos - 20 mv.

E l músculo cardiac0 t i m o un tipo pecl l iar de potencial de acción. Despuas de 4 l a ospiga in i c i a l l a membrana se encuentra dupolarizada durante 0.15 a 0.30 de segundo,- manifestando una merota, reguido. a l termino do l a misma, de una brusca repolarizacibn. - La presencia de osta m e t a .II e l potencial de acción hace quo inre dura de 20 a 25 vecon más on e1 d i c u l o u rd i aco que en e1 d r c u l o uqueletico.

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Potenciales de acci& regbtrados en una f ibra de Purkinje y en una f ibra u s cu l a r ventricular.

IRIDCIDAD D1 COIIDUCIOU EN EL l IuSclM CIBDuCo

La volocidad de concuccion y e1 potencial de acción de l a musculatura, t a t o -- aurfcular como ventrfcular, on de aproxiudannte 0.3 a 0.4 m por segundo. Li velocidad - de c d u c c i ó a en 01 s i r t u eapecialixado 8610 varía de una p q u M a fracci6n de mtros a- varios motros por soptdd, n.pQi l a parte del sistema.

m o m i w u c u u o DPL NUSCUII) cap~uco

i l . u 8 b : e C c o ~ i t d $ i d & d a i t a b b l . , es rofractario a l a nuwa ostimula-- e i h durani0 l a uplga dol potaicial de acción rápida. ün e s t í a l o e l k t r i c o oxtraordins- riamait. intenso puede iniciar a veces una BUWA o r p i y d a t r a s todavía persiste l a moa2 t a del primor p o t a c i a l do acción, pero e l impulso cordiaco nom1 no t i n e l a utraordi - naria in ta s idad de UD u t í m l o eláctrico de a l to voltajo. y no piiodo excitar nuevomeate- 01 rlaculo ardiaco mtcr de haber terminado l a m o t a . üu cmsecuaiicia, e l periodo refrcc tar io dol corazbn suele considerarse en tárminos de PEüIQo lgUcEhlf0 ?üIlCIWAL, OCUSCII-

e l intervalo de tiempo durante e l cual un potencial de acción do otra parte del corazón - no es capaz de excitar nuevamente una zona ya oxcitada del d s c u l o cardíaco. E1 periodo - refractario frmcinal normal del ventrfculo es de aproxipidaimte 0.25 de segundo, Hay un- PlOuOLiO REFRACTAR1 I i M R w ) adicional, de aproximadawmte 0.05 de sogundo, durante e l --- cual e l dnc u l o es más d i f i c i l de excitar quo normalmente.

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E l periodo refractario funcional del dncu lo auricular es de aproximadameata -- L 0.15 de segundo, y con un periodo refractario relativo do 0.03 de segundo.

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l o es o1 mopio potencial de accidn e l que hace que las i i o f i b r i l l a s del máscu- l o cardiaco se contraiga. t s el movimiento de los iones de calcio penetrando en lar iio-- f i b r i l l a s . Esto ocurre cuando e l potencial de accióa v i a j a por e l músculo y origina una - corriente eléctrica y e s t l a su vez l ibera iones de calcio derdc e1 retfcuio sarcoplásti- co longitudinai situado a l o largo de las miofebrillas. Prtós €mes de calcio $e- tipidameate a l interior de las miof ibr i l las , u a l l í c a t d i r l n las reaccsfones qufmicas - que estimilan e l deslizamiento de los filamentos de actin. y de miosina unos contra Otro8 esto, a su vez, hace que e l músculo se contriga. Inmediatamente despuás, ya terminado e l potencial de accidn, l os iones de calcio empiezan a f i j a r r e una vez mAs a l retfcuio longitudinal, de manora que en unas pocas mil68iM8 de segundo l a densidad de l o s iones de- calcio cae por debajo de l o necesario para &servir l a contracción; en consecuencia, e l músculo se re la ja .

Cuanto mayor e l volta je del potoncia1 de acción, y myor su du rac ih , mayor es también e l trabajo producido por l a contracción del pdsculo cardiaco. La raaon es que e l aumento el l a duraci6n del potacial de aCclll0,y &-irrato del volta je , increwmtan la- cantidad de iones do calcio liberada hacia e l interkor de las f ibras musculares, l o cual estimula las reacciónes qufmicas del propio proceso contráctil.

E l músculo cardiaco empieza a contraerse unas pocas mil6sismas de segundo des- pués que empieza e i potencial de acción, y siporcontraido una8 milésimas de segundo dez pu6s que dicho potencial de accidn termino. Por l o tanto, l a duracion de l a contraccibn- del &culm cardiaco em h c i ó n principalmente de l a duracidn del potencial de acción, - aproximadamente 0.15 de segundo ea e l másculo auricular y 0.3 de segundo e l ventricular.

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Contracción del corazh stl, UrrDO->

CICU) CARDIAC0

E1 periodo que va desde e l f i na l de una contracción hasta e l final de l a contra= ción siguiente se denomina UaLO CARDIACO. Cada c ic lo se inicia por l a generación espontá- nea de un pot.ncial de accidn en e l nodo SKNO-AüXKULAR (S.A.). Este nodo se hal la localizado en l a pared posterior de l a auricula derecha, cerca de l a abertura de l a vena cava u- superior; e l potencial de acción v ia ja rápidamente desde e l nodo S. A. por ambas auricu- l a s , y desde ahí , a t r a d s del nodo AUBICULO-VSMTBICULAR (A.V.) y del HAZ AWCULO-VIWTBI- C W , hacia l os ventrfculos. S i n embargo, debido a una disposición especial del sistema - de conducción desde las aiirículas a l o s ventrículos, hay un retraso de más de un decimo de segundo entre el paso del impulso cardiaco a través de las auriculas y lullgo a través de - ~

los ventrículos. Esto permite que las auriculas se contraigan antes que los ventrlculos,- con l o 1~41' impulran sangre a los ventrículos antes de ptmducircc l a contracción o e n t r i z l a r enérgica. Por l o tanto las auriculas mctuan como bombas de cebamiento para los ventriculos, y estos luego proporcionan l a fuerza mayor para desplazar l a sangre por todo e l si: tema vascular.

E l c i i l o card&aco completo se compone de dos fases: Contracción "SISTOLE" y le - lajación "DIASl9J.E". Cuando l a frecuencia cardiaca es de 72 latidos ppr minuto, hay un ci- c lo aproximodamente cada 0.8 de segundo. En este tiempo ocurre l o siguiente:

Sfstole Ventricular: E1 músculo ventricular se contrae y hace que se eleve marc2 damente l a presión de l a sangre dentro de los ventrfculos, en e l ventrdculo izquierdo a -- aproximadamente 120 mm tig y en e l ventrfculo derecho a alrededor de 26 mm Hg. Laa u P h 1 & s a AV se cierran antes de comience l a s fstole ventricular. pues l a presión auricular cae por- debajo de l a presión ventricular antes de que los ventriculos comiencen a contraerse. Es - neceuario que se cierren para impedir f l u j o retrógrado de sangre hacia las auriculas.

Las válvulas semilunares se abren cuando l a presión ventricular se hace mayor -- que l a presión en l a aorta y en l a arter ia pulmonar. La sangre es expelida hacia las dos - arter ias . l a mayor parte durante e l primer tercio de l a s fstole ventricular.

Diástole Ventricular: DespuCs de l a faae de eyección. l a presidn ventricular de- crece marcadamente cuando e l músculo entra en fame de relajacibn. Cuando l a presión de los ventrfculos cae por debajo de l a presión en l a aorta y l a arteria pulmonar, las válvulas - semilunares se cierran repentinamente en chasquido e impiden f l u j o retrógrado hacia los -- ventriculos . I-

Mientras tanto, las auriculas se han llenado de sangre que proviene de las venas y l a presión en estas CAmaras comienza a elevarse durante l a ultima parte de l a s€atole q-

ventricular. Cuando l a presión ventricular cae por debajo de la*> auriculas, las válvulas - AV se cierran y se inicia de nuevo otro cic lo .

Hay un lapso de 0.4 de segundo en e l ciclo<; durante e l cual tanto lor vmtrfculos como las aurículas están en diástole. Este lapso es llamado PERIODO DE REPOSO durante e l - cic lo de trabajo del músculo cardiaco.

Debemos subrayar que loa ventrículos cstan llenos a los dos tercios de BU capaci dad cuando l a s aurfclaa entran en sistb*e. Ea decir, los ventrfculos se llenan rápidamente durante e l primer tercio de l a diástole ventricular y hay un pequeño llenado adicional durante l a contracción auricular. Durante e l periodo de llenado rápido puede escucharse un - tercer ruido cardiaco.

La duración de l c ic lo cardiaco varía segdn l a Frecuencia; a medida que aumenta - l a frecuencia, l a fase s is tó l ica y l a diastólica se hacen más breves. La cantidad de sangre que expele e l corazón en cada lat ico se llama VOLllwEN SIS1ioLICo y suele ser de alrededor - de 70 m l , pero este volumen puede variar en ciertos estados f isiologicos. Se calcula e l -- GASTO CARüIACo multiplicando e l número de latidos por minuto y e l volumen de sangre expul- sado en cada latido, 6 sea. l a frecuencia cardiaca por e l volumen sistól ico. De este modo, a una frecuencia de 70. e l gasto cardiaco es de 4 900 m1.

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TUBAJO DEL CORAZON

E l trabajo de l corazon es l a cantidad de enería que e l corazón transfiere a la - sangre a l mandarla a las arter ias . La energía es transferida a l a sangre en dos formas:

En primer lugar, en au mayor parte para moverla desde las venas de presión ba ja - hasta las arterias de presión a l ta . Bsta es ENBRGIA FOTBNCIAL DE PPaSION.

En segundo lugar, UM proporción menor de l a energía se ut i l i za para acelerar l a sangre hasta su velocidad de salida a través de las válvulas pulnonar y aórtica. Esta es - ENBüGIA CINKTICa DKL FLUJO SANWINBO.

E1 trabajo efectuado por e l ventriculo izquierdo para aumentar la presión de l a - sangre en cada latido equivale a l gasto s istól ico por presión media de vaciamiento ventricular izquierdo menos presión de aurfcula izquierda. Análogamente, e l trabajo efectuado-. por e l vcntrlculo derecho ára elevar l a presión de l a sangre equivale a gasto s istól ico -- por (presión media de vaciamiento ventricular dercho menos preeión en aurfcula derecha). - E l trabajo da vaciamiento del ventrfculo derecho suele ser l a séptima parte del correspondiente a l ventrfculo izquierdo, por l a diferencia de presidn s ist6l ica contra las cuales - han de trabajar uno y otro ventriculo.

E l trabajo necesario del ventrículo para crear energfa cinética de la sangre que circula e8 proporcional a l a masa de sangre expdaada multiplicada por e1 cuadrado de l a - velocidad de salida. De ordinario, e l gasto de energfa del ventriculo izquierdo necerario- para crear l a energla cinética del f l u j o de saagre constituye de l dos a l cuatro por ciento del trabajo ventricular total. La mayor parte de esta energla r e necesita para producir l a ripida aceleracidn de l a sangre durante e l primer cuarto de l a s l s to le .

E l máaculo cardiac0 ut i l i za energla qufmica para efectuar e l trabajo de contra= ción. Esta energfa proviene principalmente del metabolismo de glucosa y licido graso en el- oxigeno y , de mucho menor grado de otros nitrientes eo e l oxigeno.

La cantidad de energfa gaatada por e l corazon guarda relación con au carga de -- trabajo en l a siguiente forma: La epergfa gastada ea aprexiudaunte proporciail a l grado- de tensi6n generado por l a Ptaculatura Cardiac. durante l a contracci6n, multiplicada por - el tiempo durante e l cual se soatiene l a t ens ih .

Durante l a contracción macular . l a u y o r parte de l a energfa qufmica se convieK te en calor; una poeporción mucho menor en trabajo* La proporcih de trabajo a .aersfa qPd mica producida recibe e l nombre de eficacia de l a contraccibn cardiaca o s i m p l u a t e BPI- CIA DEL WMZüN. Bn e1 coraaón norm1 que late contra una carga normal suele ser muy baja, del orden de 5 a 10 por ciento. Sin embargo durante au trabajo rlximo se eleva haata 15 a 20 por ciento m corazones normales.

RXGULACION DE U ?üNíXON CIIPDIACa

Cuando una perdona se ha l la en reposo. e l corazón esta obligado a bombear 8610 - cuatro a 8ei l i t ros de sangre por minito; en ocacióil de un ejercicio ma intenso pude te ner que impulsar hasta cinco veces este volumen.

Los dos medioa biaicos por virtud de loa euales M r-la l a acción de la bomba- del corazón son: Autoregulación intrfnseca m respuesta a cambio. de volumen de sangre que fluye penetrando ea e l coraz6n, y Control re f l e jo del corazbn por e l sistema nervioso ve=

- tstivo.

Uno de l o a principalea factores que rigen el volumen de sangre impulaada por -- e l corazón cada minuto ea la intenaidad de l a penetración de sangre en e l corazón, procs dente de las venas, el llamado RETORNO VENOSO. Cada te j ldo periférico de la econoaia controla su propio riego danguineo, y aea cual sea el volumen de sangre uqe fluye a través - de l o s tejidos perif4t)ocalas venas regresa a l a auricula derecha. E l corazón, a 8u vez,? impulsa autodtisamente esta sangre que entra en é l , mandlndola a las arterias de la gran circulación, de manera que pueda soguir de nuevo e1 circuito vascular. h i , pues, e l cor2 zón debe adaptaree en cada momento, incluso cada segundo, a l o s ingresos muy variables de sangre, que a vocea alcanzan ci fras tan bajaa como dos o tres l i t ros por minuto y otras - veces ae elevan hasta 25 o mAs l i t r o s por minuto.

Bata capacidad intrinaeca del corazón de adaptarse a cargas cambiantes de san-- gre que l e llegan, recibe el nombre de FRANK-STARLIG.

Blsicamonte l a ley de Starling afirma que cuanto IPS ae llema el corazón dura2 te la diAatole mayor es e l volumen de sangre impulsado hacia la aorta. En otras palabras e l corazón pude impulsar un pequeño volumen de sangre o un voluien considerable, aegán l a cantidad que l e l lego por las venaa; automáticamente se adapata a l a carga que l lega , ai- pre que t a l carga total no paoe de un limite f iaiológico que el corazón pueda impulaar.

P1 mecanismo primario por virtud del cual e l corazón se adapta a los volumenail- variantes de . ingreao de sangre ea: Cuando e l músculo cardiaco es distendido, como ocurre- cuando penetran cantidades extra de sangre en las csvidades cardiacas, e l d a cu l o a t contrae con una fuerza muy aumentada, lo cual autoillticamente mania sangre extra hacia las - arterias. la capacidad del músculo distendido para contraerse con mayor fuerza ea caract2 r iat ica de todos los pilaculos eatriados, no simplemente del míaculo cardiaco. Como senala- moa anterior-mente, la mayor fuerrsa de contracción depende de que los filameates de actina y mioaina llegan a un grado óptimo de interdigitación. Esta capacidad del corazón para cog traerse con fuerza creciente se conoce c o w AU'RXREGüí.4CION EETJ2RC"RICA DXL COWON.

I

-

- CONTROL NERVIOSO DEL CORAZON

El corazón este bien inervado por f ibras tanto simpática8 como parasimpáticas. - gatos nervios afectan l a bomba cardiaca de dos maneras: Cambiando l a frecuencia del ritmo, y Cambiando l a fuerza de l a contraccih cardiaca.

- La estimilación paraaimpltica disminuye l a frecuencia cardiaca, y l a simpltica - la aumenta. le amplitud mAxim.9 de control ea desde cero latidos cardiacos por minuto hasta una ciSra tan a l ta como 250 o , 300 latidos por minuto.

En genera1,:cuantas p4a veces ae contrae el corazón por minuto, mayor volumen de sangre pude impulsar, pero hay limitacione8 importantes de este efecto. Una de esta8 es c~ ando l a frecuencia cardiaca ha subido por encima de un valor cr i t ico , disminuye l a fuerza- de l a contracción, probablemente por utilización excesiva de l o s aubstratoa metabólicoa - en e l d a c u l o cardiaco. A d d s , el periodo de dillstole entre las contracciones ae cmh C-

que l a sangre no tiene tiempo de fliir adecuadamonte dasde las auriculas hasta l os v u i t r e culos. Por estos motivos, cuando l a frecuencia cardiaca se eleva artificialmente por csti- unalación eléctrica e l corazón tiene capacidad máxima par impulsar grandes vólumenes de sa0 gre con una frecuencia de aproxinadamente 150 latidos por minuto. Por otra parte, cuando - 8u frecuencia ea muy a l ta por eatimulación simplltica, alcanza su capacidad elxima de imml Ear sangre con frecuencia8 de aproximadamente 200 latidos por minuto. E l motivo de esta d i ferencio e8 que l a eatimulación simpltica no a610 aumenta l a frecuencia aardiaca sino tam- bián l a fuerza de l a contracción.

- - I

I

Las dos auriculas están inervadas por gran nóaero de f ibras simpáticas y p a r a s i t páticas, pero los ventr€culos reciben casi exclusivamate f ibras nerviosas simpáticas. Por tanto, en l a práctica e l efecto global de l o s iervios neurovegetativos sobre l a fuerza de- l a contracción depende fundomentaliwnte de los nervios simpáticos.

En general, l a estimulacidn simpática iumenta l a fuerza de coatraccidn del m d s c ~ l o csrdiaco, mientras que l a estimulacidn parasimpAtica l a disminuye.

En condiciones normales, las fibra6 nerviosas simpáticas p8ra e l corazdn descar- gan continuamente con ritmo lento, conservando una fuerza de contracción dentricular aproximadamente 20 por ciento por encima de su fuerza en ausencia de entimulacidn simpática. - Por l o tanto, un d t odo por e l cual es sistean nervioso pude disminuir la fuerza de l a con- tracci6n ventricular es simpleunte haciendo más lenta o interrumpiendo la transmisi6n de- l o s impulsos dimpáticos del coraz6n. De otra parte, l a est imlición simpática máxima puede aumentar l a fuerza de l a cantracci4n ventricular hasta aproximadamente e l doble de l a normal.

La estimlacidn parasímpltica mAxima de l corarón disminuye la fuerza contráctil- vontricular quiza en 10 o 30 por ciento. Por tanto, v a r n t e p6ca importancia.

&&ZlXCiOü PIMICA DIL

e l efecto parasimpático, tiene r e l a t i

E1 corazón está dotado do un sisteaa especial para generar r€ tdcauo t e impulsos que produzcan l a coatraccidn periódica del d r cu l o cardiico. y para conducir estos iipul-- so8 a todo e l corazón.

Cou, ya dijimos e1 corasdn h u n o adulto n o r u l u a t e se contrae r f t d camate unos 72 veces por mínuto. I1 sistema onpecial de excitaciom y conducción que controle 0st.s m- erne&41.s cardiacas ost. constituido de l a siguiente manera: a l lodo 8aeAur i cu l a r en - e1 cual se gena. e1 impulso r i t d c o -nul autoexcitaterío. L1 Nodo AurLcaieVentricular- en e l cual e l impulso procedente de l a mr fcu la se rotrasa antes de.pa8.r a1 ventriculo.- E1 ñaz Aariculo-Vonrricular qqe conduce el impulso desde las auriculas a lor ventriculos,- y Los Haces Derecho e Ixquierdo de ?lbras de Purki#&e que conducen e l impulso cardiac0 a - todas las partes de los ventriculos.

, 'A

Sistema especial de excitacion y conduccion del corazón,

E1 nodo amoauricular (S-A9 es uaa pequaa t i r a de adsculo especialirado, de a- proximadamente 3 mm de ancho y & cm de largo; se hal la localizado en l a pared superior de l a aurfcula derecha inmediatamente por detrás y por dmtro de l a abertura de l a vena cava superior. Las f ibras de este n6dulo sólo timen tres a cinco micra8 de diámetro. Sin em-- bargo, las f ibras del S-A se contindan con las f ibras auriculares de manera que cualquier potencial de accibn que comiara a e l nodo S-A se difunde inmediatamente a las aurfculas.

E l potencial em reposo de las f ibras S-A es m y bajo, sólo de 55 a 60 mV. La cag sa de este bajo potencial de reposo es una permeabilidad muy elevada de l a a rb rana de ese tas f ibras para e l sodi&, l o cual permite e l escape rápido del sodio a través de l a misma. Bs eta fuga de sodio l a que también origina la autoexcitarión de las f ibras sC;t.

Cada vez que un impulso rftmico es generado en una f ibra aislada del nódulo --- S-A, se difunde inmediatamente a l m usculo auricular vecino, y es conducido en todas dire2 ciones con velocidad de aproximadamente 0.3 m por segundo.

wando e l impulso cardiaco atraviesa las aurfculas, e l músculo auricular se contrae mandando sangre a trav6s de las válvulas auriculwantriculares hacia los ventrfculos.

~l sistema de conducción estd organizado de t a l forma que e l impulso cardiaco no v ia ja desde las aurfculas a l o s vmtrfculos con daasiada riipidez, l o cual permite que las aurfculas vacfan eu conteoido em los ventrfculos antea que anpiece l a contracción de estos Son primeramente e l nodo A-V y sus f ibras de conduccih asociadas las que retrasan l a tr- m i s i h del impulso cardiaco de las aurfculas hasta los vantrfculos.

E l impulso después de atravesar e l músculo auricular alcanza el nodo A-V aproxir madamente 0.04 de segundo dupuós de su origen a el nodo S-A. Sin embargo, entre este -- tiampo I el tiempo en que sale el impulso en e l haz A-V transcurre 0.11 de segmdo. La mL tad de este tiempo transcurre en las f ibras de unih que son f fbras muy delgadas que us- nen las f ibras auriculares normales con 1aa f ibras del propio nódulo.

Organización del nodo A-V

ki velocidad de conducción en estas f ibras es de 0.05 m o ma108 por segundo, lo- cual retrasa considerablemente l a penetración del impulso en e l nodo A-V. Después de entrar en e1 nodo, l a velocidad de conducción en las fibra6 nodales es todavía my baja. Por l o - tanto se produce un nuevo retraso en l a transmisión cuando e l impulso v ia ja a través del m nodo A-V hacia l i s f ibras de transición y , finalmente, por el haz A-V. Las f ibras aur icu la res van a parar a las pequelim f ibras de unibn, luego hay un agrandamiento progresivo de - las f ibras nuevamente cuando se dispersan por todo e l nodo, a trave6 de l a región de tran- sición y hacia el haz A-V.

~

... .

...

..

Las f ibras

Esquema funcional de l a región nodal A-V

Purkinje que van de l noso A-V a través del haz A-V hasta los ven-- t fculos tienen caracteristicas funcionales totalmente diferentes de las correspondientes - a las f ibras de l nodo A-V; son fibras muy voluminosas, incluso mayores que las f ibras mu8-

culares r o n t r i d a r e s normales, y transmiten impulsos con velocidad de 1.5 a 2.5 m por segundo, y 40 veces mayor que en las f ibras de unión. Esto permite una transmisión casi inmediata del impulso cardiaco - a traves de todo e l sistema vascular.

aproximadamente seis veces mayor que en e l m6sculo cardiaco

Las f ibras de Purkinje despues de originarse e i e l nodo A-V forman e l haz A-V, - que pasa entre las válvulas del corazón y desde ah2 a l tabique ventrlcular, E l haz auric: loventricular se divide casi inmediatamente en RAMA IZpUIQM p UIU DERECHA situadas por debajo de l endocardio en l a s partes respectivas de l tabique. Cada una de estas ramas sique hscia abajo en dirección de l a punta del ventrfculo correspondiente, luego se encurva rod: ando e l extremo de l a cavidad ventricular y , finalmente, regresa hacia l a base cardiaca si guiendo l a pared externa. A l a tercera parte, aproximadamente, e l camino de l a parte alta- de las paredes ventriculares, l a s dos rama de l haz l e dividen en muchas pequeñas ramas de- f ibras de Purkinje, que se d spersan en todas direcciones por debajo del endocardio ven-- tricular. Las f ibras terminales de Purkinje penetran en e l mdsculo ventricular desde l a 6%

perf ic ie endocárdica y terminan en las f ibras musculares. A l l legar a término e l impulso- cardiaco pude pasar rApidamente de las f ibras de Purkinje a l a f ibra muscular del corazón- pero, p1 impulso no pude pasar en sentido retrógrado desde e l mdsculo hasta las f ibras de- Wrk in j e.

Desd e l momento en que e l impulso cardiaco penetra an e l haz A-V hasta que a k a 2 e l tietnpo transcurrido total es solamente

cuando un impulso cardiaco ha penetrado en e l sistema - a todo e l endocardio de los ventrfculos.

za las ter i inactows de las f ibras de Purkinje, de 0.03 IC segundo; por l o tanto, de Purkinje, se transmite inmediatamente

Una vea que e l impulso cardiaco ha alcanzado los extremos de las f ibras de Purkic Je, se transmite a traves de l a masa iniscular ventricular. La velocidad de transmisión C-- ahora es de solamente 0.3 a 0.4 m por segundo, o sea, l a sexta parte que en las f ibras de Purkinje.

E l d s c u l o cardiaco está dispuesto en repiolinos con tabiques fibroso8 entre &%os

por l o tanto, e l impulso cardiaco no via ja necesariamente en forma directa hacia fuera, - dirigiendose a l a Superficie del corazón, sino que forma ángulos hacia l a superficie Sig' endo las direcciones de los remolinos. En consecuencia, l a transmisión desde la superficie endocárdica a l a superficie epicárdica del ventrfculo necesita hasta 0.03 de segundo más.- E l tiempo total de transmisión del impulso cardiaco, desde e l origen del sistema de Purki' j e hasta las ultimas f ibras musculares wentriculares, es de aproximadamente 0.06 de segundo.

Por l o dicho puede verse que l a primera parte de l a masa muscular ventricular - que es excitada es e l tabique; esto va seguido rdpidamente de las superficies endocárdicas de l o s vértices y de las paredes laterales de los ventriculos y , finalmente, de las super- f ic ies epicárdicas del ventrfculo.

Interoalos de tiempo para dittuiún del impulso en las diferentes superficies- anterior y posterior del epicardio.

COEpraOL DE LA EXCIT*CICW Y CCñDUCCION EN EL CORMON

En l o dicho sobre g h e s i s y transmisión del impulso cardiaco del corazón, se -- afirma que e l impulso nace normalmente en el nodulo S-A. Esto es por que l a frecuencia del nodo 8-1 ea considerablemente mayor que l a del nodo A-V y a l a s f ibras de Purkinje. Cada - vez que e l nódulo S-A descarga SU impulso va a parar a1 nodo A-V y a las f ibras de firkin- j e , descargando sus membranas excitables. Luego todos estos tejid6s empiezan un cic lo de - recuperación. Pero en nodo S-A se recupera mucho d a rlpidamente que ninguno de los otms- dos, y emite otro impulso antes que niasuno de aquellos iuya alcanzado supropio umbral de- autoexitación. 31 nuevo impulso descarga nuevamente e l nodo A-V y las f ibras de ?urkinje.- Este procesl cont ine una y Otra ver; e l nódulo S A va excitando conatantemente estos otros tejido. potencialmente autoucitables antes que pueda producirse una verdadera autoexcita- ción .

.

Aaf, pues , e l nodo S A controla e l latido del corar6n porque SU frecuencia de -- descarga rftmica es uyur que l a de ninguna otra parte del coramón. Pa consecuencia, se -- dice que q l nbdulo &A es el IURWASO n o r u l del corazón.

En ocaciones, alguna otra parte del corazfi desarrella descarpa rftmicas d s J-

rápidamente que e l n6dulo S-A. Esto ocurre frecuent-nte en e l nódulo A-V o en l as f ibras de hirkinje. En ambos casos e l marcapaso del corstón se desplaza deade e l nódulo S-A hacia e l nodo A-V, por las f ibras excitables de Purkinje. En raras circunatancias un punto en l a

musculatura auricular o ventricular presenta una excitabilidad excesiva y se transforma en msrcapaso.

un marcapaso situado en otro lugar que no s u e1 nódulo S-A se denaina M C I I A - SO ECTOIICO, est6 origina una aucenión anormal de contracción de l a r diversas partes del - corazón.

la estimulación de los vagos, los nervios paraaimpáticoa del corazón, hace que - se l ibere acetilcolina de las terminaciones vagales. l a cual tiene dos efectos sobre e l cz razón; dinminuye l a rApidea del ritmo del nodo S-A y disminuye l a excitabilidad de las f i - bras de unión A-V entre l a musculatura auricular y e l nodo A-V, con l o cual hace i 1 s lenta l a transn~isión del impulso cardiaco hacia los vmtriculos. Una estimulacióa muy enérgica - de los vagos puede parar coapletaiante l a contración rítmica del nodo S-A o bloquear por - completo l a transmisión del impulso cardiaco a trsvéz de l a unión A-V. En ambos casos los- impulsos rftmicos ya no non transmitidos a los ventrfculos. Estos dejan de l a t i r durante - 10 segundo, pero luego algün punto de las f ibras de Purkinje desarrolla un ritmo esponeir- neo y origina contracción ventricular. este fenomono se denomina ESCAPE VENTRICULAR.

i

La acetilcolina liberada ai l as terminaciones vagales aumenta considrrablemente- l a permeabilidad de las membranas de las f ibras para e l potasio, l o cual permite rApido e2 cape de potasio hacia e1 exterior. Esto incremmta l a negatividad en e l interior de las f i bras, este efecto se conoce como H I ~ P O L A R i U C I O N . que hace mucho menos excitable e l t e j i do excitable.

Pn el nodo A-V e l estado de hiperpolarización hace d i f i c i l que las pequeñas f i i u

bras de unión. que sólo puede generar pequeflas contidades de corriente durante e l potenci- a l de acción, urcitai las f ibras nodales. Por l o tanto, e l factor de sapridad para l a t r a p misión del impulso cardiaco a través de las f ibras de unión y hacia e l interior de las nodales disminuye . Con una disminución moderada simplemente retrasa l a conducción del impulr so, pero una disminución del factor de sapridad por debajo de l a unidad bloquea totalmen-

. te l a conducción.

la estimulaclón siip4tica causa sobre e l corazón esencialmente los efectos opuez tos a los producídoi pur l a estimulación vagal; aumenta l a intensidad de l a descarga S-A- nodal, también aumenta l a excitabilidad de todos los procesos del corazón y aumenta cons i d e r a b l e mte l a fuerza de contracción de toda l a usculatura cardiaca, tanto auricular co-

‘

” mo ventricular.

La estimulación de los nervios simpiticos l ibera l a hormona noradrelina a nivel- de las terminaciones nerviosas simp&icas, está a n t a l a permeabilidad de l a -&rana de la f ibra para e l sodio. En e l nodo S-A un aumento de permeabilidad para el sodio causarfa- aumento de l a tendencia del potencial de i r b r a n a an reposo a disminuir hasta valor de u= bra1 para autoexcitación, l o cual w ida r tewate acelerarfa el comienzo de l a autoexcitación después de cada latido sucesivo y , por l o tanto aumentarfa l a frecuencia cardiaca.

.

En el nodo A-V e l aumento de permeabilidad para e l sod io harfa nAs f á c i l que cs- da f ibra excitase l a siguiente. Por l o tanto, las pequefias f ibras de unión de l a región n% da1 A-V podrfa excitar fácilmente las f ibras nodales, disminuyendo e l tiempo de conducción desde las aurfculas a los ventrfculos.

- E1 electrocardiograma, o LCC, es registro de los potenciales elóctricos que

genera e1 corazón. Un h r o rducido de ut01 impulsos eléctricos, que c a i a u a n en e1 - nodo S A y viajan por todo e l d s c u l o cardiaco a través del s i s t c u de conducción son c- ducidos a l a superficie del cuerpo por los 1fquíl.s tisulares. De este d o , 6 i se Colo-- can electrodos en l a p i e l a u11 lado y a otro del corazón, pueden registrarse esto6 impulsos. este registro de denomina ELIIcIpocABDIoGwU.

Electrocardiograma ?+orma1

CILpIILcTppISTICAS DE UN HiSCTlWARDIoGsann E l electrocardiogsama está formado por una onda P, un complejo QRS y onda T.

E l complejo QRS en realidad incluye tres ondas aeparadas, l a Q, la B y la S ; todas e l las están cauaadas por e l paso del impulso cardiaco a travós de los vmtrfculos. Ihr e l e l e s trocardiograma normal la6 ondas Q y S suelen 6er mucho menos prominentes que l a onda B,- a veces Incluso faltan; a pesar de todo l a onda sigue conociéndose como complejo OM.

La onda P depende de corrientes eléctricas generadas cuando las aurfculas s e despolarizan antes de l a contracción, y e l complejo QRS es producido por corrientes unci das cuando los vcmtrflculos se despolarizan antes de contraerse. Por l o mismo, tanto la- onda P c- los coopanantes del cwpie jo QXS son (RIDILS de DESPOUüIZACIOH. la onda T e2 U causada por corrientes nacidas cuando io6 vent r fa los se recuperan del estado de des- polarización. Este proceso ocurre en e l d s c u l o ventricular aproximadamente 0.25 de s b - gundo después de l a dupolaritación, y esta onda se conoce c o o GtiDA de BIIPOLABIWCI0N.- hi, p w ~ , e l electrocardiogram6 está formido por ondas, una de despolarizacióo y une de rcpolarización.

Durante el proceso de despolarización e l potencial negativo normal dentro de - las f ibras de pierde, y m1 poteacial de l a -rana en realidad se invierte, este proce- 60 va viajando de izquierda e derecha, y l a primera oítad de l a f i b ra YA esta de6polSri- zada mieatras la mitad restante todavia sigue polarizada. Por l o tanto si se colocan unos electrodos a l a derecha y a l a izqaierda de esta orbrana, e l electrodo izquierdo colocado sobre e l exterior de l a f ibra se halla en zona de n-atividad, mientras que e l e l es trodo derecho se hal la ea UM zona de positividad. e l ud i do r conectado e estos electrodos por l o tanto marcara e l registro posit ivauate, i b d p d m La.ta deApoUbituot+i ierextioude a toda l a f i b ra muscular, y e1 registro en e l medidor pasa a la cero por que a h o s electrodos se hallan ahora en zona da negatividad igual. La oada completa es una onda de de2

polarización porque depende de l a difusión del proceso de despolarización a todo l o largo- de l a f ibra muscular. Ya a este nivel l a repolarización ha 1l.gado s mitad del camino rn - toda l a f ibra de izquierda a dercha, en este punto el electrodo izquierdo se hal la en una- zona de positividad, mientras que e1 derecho se hal la en una ZOM de negatividad, en cons2 cuencia el registro en e l medidor de los electrodos se hace negativo. Finalmente toda l a - f ibra mscular se ha repolarizado y ambos electrodos se hallan 611 zonas de positividad de- manera que no se registra diferencia de potencial, y por l o tanto e1 potencial vuelve a -- repolarización sobre l a f ibra muscular cero, esta ando es una onda de depende de l a difusión del proceso de

1, iLI de .--- - - _ _ _ _ _ - ,~.

- - _ _ _ ... *-I it''----- --== -

. . * 1 .- 1- -+t A C + a + _ . . + C - _ - - - - -

v _._.- - - _ _ .-<.I 1- * + d i .-,*A+++-.+ - 0 3 0 d r ,e

Bogistro de las diferentes ondasdde despolarización y repolarización.

E l potencial de acción monofAsico del m6sculo ventricular, normaliwnte solo du-- ra de 0.25 a 0-30 de somndo. Est6 en e l registro del electrocardiograma hace un desplaza- miento hacia a r r i beque s 4 a el proceso de despolarizaciónl l a vuelta del potencial a l a linea basal es el proceso de repolarización. Por otra parte, no se registra ninsQn pot-- cia1 en e l electrocardiograma cuando e l aúsculo ventricular esta coopletamate po la r i s sde o completamente deapolarirado, solaamnte cuando el músculo está polarizado en parte y en - parte despolarizado hap corriente que fluye de una a otra zona de los ventriealos y , por-- lo tanto, también va a parar a l a superficie del cuerpo, dando lugar a l electrocardiograna.

Potencial de acción monofAsico en una f ibra muscular ventricular, electro-- cardiograma.

" -

h t e s que pueda producirse l a contraccibn del músculo, una onda de despolariza-- ción debe difundirse a todo l o largo del mismo para iniciar los procesos qufmicos de l a -- contraccibn. La onda P resulta de difusión de l a onda de despolarización a travás de l a s - aurfculas, y l a onda Q.6 de difusión de l a onda de despolarizacidn a través de los ventrfculos. Por l o tanto l a onda P ocurre a l principio de l a contracción de las aurfculas, y l a onda QS tiene lugar a l principio de l a contracción de los ventrfculos.

Las auriculas se repolarizan aproximadamente 0.1 a 0.2 de segundo despu6s de la- onda de despolariracibn. Sin embargo, es precisamente en este momento en que se registra * l a onda QRS an e l electrocardiograma. Por l o tanto, l a onda de repolarizaci6n auricular, - conocida c o w onda T aurfcular suele quedar totalmete enmascarada por l a onda QüS, mucho- d s importante.

La onda do rqo ía r i rac i6n v a t r f cu l a r es la onda T del electrocardiograma normal. De ordinario e l d s c u l o ventricular empieza a repolarizarse en algunas f ibras aproximadameg te 0.15 de segundo después de iniciarse l a onda de despolarizaci6n, y completa su papola- rización m todas las f ibras 0.30 de segurido después de c-zada l a despolarizacidn. As f , pues, el proceso de repolarización se extiende durante un tiempo largo, aproximadamente de 0.15 de segundo.

VOLTAJE Y WBRACIOII cilOMWGICa DEL ELBcmoc11pDIoO1ullA

Todos l os regiatros de electrocardiograma se efectñan con líneas de calibración- adecuada m e l papel de registro. O bien estas 1Zneas de calibración 8st.h impresas en e l - papel, como ocurre cuando se u t i l i z a un electrocardiógrafo de pluma, o sean marcan en e l - papel a l mismo tiempo que se registra e l electrocardiograma.

Las lfneas de cal ibraciói horizontal están dispuestas de manera que 10 pequeñas- divisiones (1 cm) en d i r e c c i b vert ical del Ql8CtrOCardiOgraM estdndar reprerentan el equi valente a u11 milivoltio.

Las l i m a s verticales del electrocardiograma son lfneas de calibraci6n cronol6gL ca. Cada pulgada (2.54 cm) del e l ec t roca rd iog r~a eatáudar corresponde a un s w n d o . Ca p& pulgada a su vez, suele estar dividida en cinco segmentos por lfneas verticales obscuras;- l a distancia entre cada una repreaenta 0.20 de segundo.

los intervalos entre las lfneas verticales obzcuras están separados en cinco - pequeflos intervalos por lfneas finas; l a distacia entre cada dos de éstas líneas represan- t a 0.04 de segurido.

Voltaje8 Uormales en e l Electrocardiograma. los voltajes de las ondas del elec-- trocardiogruaa normal depend- de l a manem como se han aplicado los electrodos a l a SUME

f i d e corporal. Qundo se coloca UD electrodo directamente sobre e l corazh y e l segundo- en cualquier otra parte del cuerpo e l vo l ta je de l complejo QW puede ser hasta de 3 a 4 -- milivoltios, incluso este vo l ta je reaulta muy pequoño en comparaci6n con e l potencial de- acción monofiísico de 135 mi? cuindo se registra directamate del corar6n.

Cuando los elsctrocardiogramas ae registran con electrodos colocados an los dos- brasos, o un brazo y una pierna, e1 vo l ta je del coiplejo QRS suele hallara. aproximadamete m 1 i V del vdrtice de l a onda B hasta e1 fondo de l a onda S; e1 vo l ta je de l a onda P va-

r f a entre 0.1 y 0.3 de milivoltio. yeel de l a d a T antre 0.2 y 0.3 de milivoltio.

... .

Intervalo PQ. E1 tiempo qua transcurre antra a1 coiianzo da la onda P y a i cobc m i m o de l a onda QRS es e l intervalo que tramcurre antre e1 codOEao de l a contracción - de l a aurícula y a l copieuzo de l a contracción .delvantrfculo. Este lapso recibe e1 nom-

bre da1 intervalo PQ. De ordinario esta in tuva io os de aproxiudauote 0416 da segundo A veces recibe e1 nombre da inta 'valo P-P porque l a onda Q uchas veces no Uriste.

IliTERVU.0 Q-T. La contracción del vetrfculo dura esmcia lwntr ( ~ t r e onda Q y a i f inal de l a onda T. Pate intervalo de tiuipo recibe e l nodre de intervalo Q-T; do ordinario dura aproximadamaate 0.30 de segundo.

P r w u a c i a cardiaca d e t e d n i d s sagtin e l alectrocardiogrsu. t. frecuencia de loii latidos cardiacos pude deteninarre f ó c i l i a t a con e1 electrocardiogram, ya que e1 inte- valo entre dos latidos sucesivos es el corrupandiata a1 valor ionrerro de l a fracuencia- cardiaca.

Si e1 intervalo a t r e don latidos determinidos srgdir las lfneas de ti- 0s d r ap rox i u da mte 0.8 de aegundo u t 6 cornrponde a 1u1. freuuaeia cardiaca de 75 latidas ?- por minuto.

Wtodor pira obtmer e loct rourd iograu i . U s ce r r i a t e s el6ctricas genoradar w

por e1 s8sculo cardiac0 con cada latido del cora%ón a vaee8 cambian e l potencial y l a por- laridad en -8 de 0.03 de regundo. Por l o tmto, .o esencial que cualquier aparato pap- ra registrar e i . s m r c n l 6 0 ~ s poda rupso*rr muy ripidamante a estos cambios de potan- cia1 eléctrico.

En general, para e l l o se emplean dos tipos diferentes de aparatos de ragidtro:-- P1 registro de P lum: estos escriban e1 electrocardiograma con una pluma directamente sobre una t i r a de papel qua se desplaza. 1 e l Registro de Electrocardiogramas con Osciloicopio*

Registro del electrocardiograma

PASO DE U CORRIñIITB ALRBDBM)II. DEL CQWVBN

Registro de los potencialas electricos. Antes de l a est imlación, toda l a parte- exterior de las células musculares era positiva y l a interior negatiua. S i n embargo, tan -

EL CICLO CARDIAC0

#

pronto como una zona del s insit io cardiaco es despolarizada, cargas negativas escapan ha* cia l a parte externa de dicha zona, haciendo que l a superficie correspondiente 888 =lec-- tronegativa, y se representa por signos negativos, con respecto a l resto de l a superficie- del corazbn, que todavia sigue polarizada normalmente, y se representa por signos pos i tb - vos, Por l o tanto, un medidor conectado con su terminal negativa a nivel de l a zona de deg polarización, y su terminal positiva en una de las zonas todavfa polarizada, registrara una corriente positiva. Como e l proceso de despolarizaci6n se difunde en todas dirocciones dec de e l corazón, las diferencias de potencial solo duran unas pocas mil€simas de segundo.

Flujo de Corrientes El6ctricas en e l Torax alrededor del Corazbn. l o s ventrfculos cardiacos dentro del torax. Incluso los pulmones, aunque están llenos de a i re , conducen bien l a electricidad y los lfquidos de otros tejidos que rodean a l corazbn l a conducen d s - facilmente todavl. Por l o tanto, el coraz6n se hal la en realidad suspaidido en un medio -- conductor. Cuando una parte de los ventriculos se vuelve electronegativa con respecto a l - resto, fluye corriente el6ctrica de l a zona despolarizada a la zoma polarizada.

Como ya se menciono e l impulso cardiaco primero l lega s los ventríctilos e l las - paredes del tabique, y casi i d i a t a m m t e despuls a l a su e r f i c i e andocárdica del resto - de los ventrfculoa. esto provoca electroneptividad en las parten internas de los ventríc2 los y electropositividad en las paredes externas de los mireas. S i se establece el valor- algebrico medio de todas las 1fneas.de f l u j o de corriente, se comprueba que e l f lu jo medio de corriente es desde l a base del corazón hacia l a punta.. Durante l a mayor parte del res- to del c ic lo de despolarización l a corriente sigue fluymdo en esta dirección cuando e l iz pulso difunde desde l a superficie del endocardio hacia afuera a través del pdrculo vent- cular. Sin eabargo, inmediatamante antes que l a onda de despolarización haya conplatado su curso a trav6s de los vQptr€culos, l a d i r e c c i h del f lu jo de corriente se invierte durante apriximadamonte una centésima de segundo, y va desde e1 vértice hacia l a base, porque la- óltima parte del corazón que ea deapolarizada son las paredes externas del ventriculo cerca de su base,

I

”

Ad, pues, e l corazón normal puede canriderre que l a corriente fluye de l a base.’ hacia l a punta durante todo e1 c ic lo de despolarización, exceptuando su parte f ina l .

A l tomar registros electrocardiogrdficos se uti l izan varias posiciones e s thda r - para colocar los electrodos; que l a polaridad del regiatro durante cada ciclo cardiaco sea positiva o negetira d e m e de l a orimtacichi de los electrodos con respecto a l f l u j o de - corríoutes an e1 mismo corazón.

*

.

DPPTVACICüBS ~ ~ I ~ I W

DPPIVACION I. A i rogistrar l a deivación L de oxt r r i idadu la terdnii n o g a t i w del eiectrourdi6grafo se conecta a1 brazo derecho, y l a t e rdnn l positiva a1 brazo i y u i - arde. Por l o tanto, cuando e1 p a t o del t6r.x donde e1 brazo d a d o se une a1 tdrax es - electronylativo con r e spc to a1 punto .ID que e1 brizo i yu í e rdo se une a1 tórax, e l .lec-- trocanl iagrau resistra UII d W p h Z A i i ~ t 0 positivo.

D E U W X O W 11. A l registrar 1s dorivaci6n I1 de oxtroddaden. l a tatifnil negatA va del electrocardibpafo re conecta a l brazo derocho y l a positiva a l a pierna izquierda. A d , cuando e l b r i r o dercho es negativo con reiaci6n a l a pi- izquierda e l eiectrocsr-- d i 6 g a f o registra positivaiiunte.

I

DERIVACION 111. Para registrar l a derivación 111 l a terminal negativa del elec-

cardiógrafo se une a l brazo !.zquierdo, y l a terminal positiva a l a pierna izquierda, e s t e da un registro positivo en e l electrocardiógrafo cuando e l brazo izquierdo es negativo en- relación a la pierna de l mismo lado

m m DE EXNTHOVlW. Rodea l a zona cardiaca; este es un medio esquedtico para- señalar que los dos brazos y l a p erna izquierda forman l o s vértices de un triángulo que - rodea e l corazón. Los dos ángulos de l a parte a l ta del triángulo representan los puntos a- los cuales se conectan eléctricamente l o s dos brazos con l o s lfquidos que rodean e l corazón e l 6ngulo inferior es e l punto donde l a plerna izquierda se conecta eléctricamente con los líquidos de l a base del corazón

La ley de Einthoven dice simplemente que s i se registran l o s potenciales eiéctricoc de dos cualesquiera de las tres derivacjónes electrocardiogreficas estándar, l a tercera -

puede deducirse matedticamente de las dos primeras, simplemente sumandolas.

Los electrocardiogramas normales registrados con l as tres derivaciones estándar -- son muy parecidos entre s f , ya que todos registran ondas P positicas y ondas T positivas,- y l a mayor parte de l complejo QRS es positivo en cada uno de los electrocardiogramas.

'

I - La a n a l i i w los tres electrocardiogramas puede comprobarse, mediante mediciones - cuidadosas, que en cualquier momento l a suma de l o s potenciales en derivaciones I y 111 -- equivale a i potencial en derivación 11, demostrando l a valides de l a ley de Einthoven.

?

DBPIVACIOUES

A I 8..

I

~ l r i án ju lo de Einthwen

Electrocardiogramas normales registrados en las tres derivaciónes electrocardiográficas estándar

I

,-

DERIVACIONES PBECOBDIALES: Muchas veces se registran electrocardiograms con un - electrodo colocado en la cara anterior del torax encima del corazón. Este electrodo se conecta a la terminal positiva del electrocardiógrafo, y el electrodo negativo, denominado - ELECTROW INDIPEBEñiE, se conecta a través de resistencias eléctricas al brazo derecho, el el izquierdo y la pierna izquierda similtáneammte. Genetalmente se registran seis deriva ciones torácicas estándar a nivel de la pared anterior del torax. Las diferentes derivacic nes registradas por el método se denominan V, , V, , V, , V., , Vsy V,.

Coma la superficie del corazón está cerca de laapared torácica, cada derivación tc rácica registra principalmente-el potencial eléctrico de la musculatura cardiaca inmediata Pante por debajo del electrodo. Por l o tanto anomalias relativamente pequefias en los vent- culos, sobre todo en la pared ventricular anterior, suele causar cambios muy intensos en - l o s electrocardiogramas obtenidos mediante derivaciones torácicas.

En derivaciones V, y V, los registros QRS son principalmente negativos porque, e&,%, electrodo del torax en estaa derivaciones se halla i p s cerca de la base del corarb que la de la punta, que es la direcci6n de la electronegatividad durante la mayor parte del procz so de despolariraci6n ventricular. Por otra parte, l o s complejos QRS en las derhaciones VI V, y Vg son principalmente positivos porque el electrodo torácico en estas derivaciones se halla cerca de la punta, que es la dirección de la electropositividad durante la despolar& zaci6n.

Electrocardiogramas registrados el las seis derivaciones torácicas.

Derivaciones unipolares aumentadas de miembros: Otro sistema de derivaciones, muy- empleado, es la Derivación Unipolar Aumentada de miembro, en este tipo de registros se conectan dos de las extremidades mediante resistencias eléctrica8 a la terminal negativa del electrocardiógrafo, y la tercera extremidad se conecta a la terminal positiva. Cuando la - terminal positiva se halla en el brazo derecho, esta derivación se denomina aV,; cuando en el brazo izquierdo, derivación aVL; y cuando en la pierna izquierda, derivaci6n s k .

l o s registros normales de las derivaciones unipolares aumentadas de los miembros - son todas similares a los registros estlndar de extremidades, excepto por el hecho de que en derivación aVK el registro esta iiliartiQ0,iel motivo de esto es que la polaridad del -- electrocardiógrafo se conecta en direccidn inversa del curso principal de la corriente en- el corazón durante el ciclo cardiaco.

Cada derivación unipolar aumentada de extraidad en realidad registra el potencial del corazón en el lado d ls cercano de la extremidad correspondiente. Asf. cuando se registra una derivación aVxuna curva negativa, esto significa que el lado del corazón que se - halla cerca del brazo derecho en negativo en relación con el resto del órgano; cuando el - registro en aVF eo positivo, equivale a decir que la punta del corazón es positiva con re: pecto al resto del órgano.

Electrocardiogram registrados en las derivacionea unipolares aumenta¿as de -

~ extremidades.

I ~ k ~ S T A C i O I p ELEcRochlDIOGUFIC4 . ~ W A L I S I S ImCTOILW..

Por loa dicho sobre transminión del impulso s través del corazón, se deduce clara- mente que cualquier cambio de la misma puede originar corrientes eléctriuas anormales en - los liquido8 extracelulares que lo rodean; en consecuencia, puede alterar las formas de las ondas del electrocardiograma. Por tal motivo, caai todas las anomalfas graves del másculo- cardiaco pueden describirse analisando l os contorno8 de las diferente8 ondas en varias - de las derivaciones eiectrocardiogrAfica8.

*

Ptincipio de Analisi Vectorial de Electrocardiogramas. a t e s de poder comprendor - c h las anomalías cardiacas modifican los contornos de las ondas electrocardiogrlficas, - hablaremos del concepto de vectores J del analisis vectorial aplicado a las corriente8 e l 4 tricas que fluyen alrededor del corazón.

Anteriormente se d i j o que l as corrientes del corazón van en una direccidn particular segbn los mooIcotos del c i d 0 cardiaco. Un vectoe es una flecha dirigida en e l sentido de l a corriente con l a punta en dirección positiva. T a m b i b por conveccidn, se dibuja l a longitud de l a flecha proporcional a1 volta je generado por e l f l u j o de l a corriente.

Bn una masa s inc i t ia l del d s c u l o csrdiaco, cada vector va desde negativo a posit% vo y l a longitud de cada vector es proporcional a l a carga que produce e l f l u j o de corri- te.

Vectores indicadores del f l u j o de corriente en e l d s c u l o cardiaco.

E l vector sumado en e l corazobn en un momento dado. En l a despoliriracidn del tabique ventricular p parte de las paredes endoc;lrdicas laterales de los ventrfculoi, fluyen corrientes el6ctricas del tabique y de las paredes endoclrdicas laterales hacia l a -- parte extema del corazón, tambib fluye corriente dentro de l a s cavidadea cardiacas d i - rectamente de l a s zonas despolarizadas hacia las zonas polarizadas, ests pequafia cantidad de corriente se di r ige hacia arriba dentro del corazón. pero es mucho mayor l a dirigida hc cia abajo, hacia l a punta. Por l o tanto, exciste un vector que representa l a SUN de l a r - corrientes en este noraato particular, que va del centro de los ventrfculos en dirtcción- de l a base a l a puata del coratbn.

Pate vector que atraviesa e1 corazón tambi& se piede localizar a l a derecha o a-- l a izquierda del corazón y en eitos lugares tienen e l diu, signif icad, por que un vector- 6610 indica l a dirección del f l u j o de corriente y e l potencial causado por l a corriente, - Entonces mientras l a dirección sea l a a d e m i s y aíwlongitud sea l a correrpondiente, e l - vector colocado en e l centro, a l a derecha o a l a izquierda del corazón tmdra e l misw si& ni f icado .

Vector sumado a través de un corazdn.

..

r

I.

Indicacion de l a dirección de un vector en grados. Cuando un vector es horizontal- y se d i r ige hacia e l lado izquierdo de l paciente, se dice que se extieade en dirección de- cero gradoa. Partiendo de este punto de referencia cero, l a escala de vectores g i r a en s- t ido de l a s manecillas de l r e l o j ; cuando un vector se extiende de arriba hacia abajo, tiE ne 90. de dirección; cuando se extiende de izquierda a derecha de l paciente tiene una dire: cidn de 180', cuando se extiende hacia arriba tiene una dirección de -90..

En un coraz6n normal, l a dirección media de l vector cardiac0 durante l a difución - de la onda de despolarización es de ap rox i udumte 59.. Esto s igni f ica que durante l a mayor parte de la onda de despolatiaación, l a pufitagOde~z$$yazón r e mantiene positiva con re i pecto a la barre.

3 90' Vectores roprerentando d i recc iaes de flUjo de corriente y potenciales

.- -.

"Ilje" de cada m a de l a s derivaciones. Cada derivación en realidad es un par de - electrodos colocados en lados opustos del corazón, y l a direccidn del electrodo negativo - a l positivo recibe e l nombre de EJE DEL COWOiI de derecha a izquierda del sujeto se dice que tiene O * , y l o s gvados se miden luego en d reccidn de las agujaf del r e l o j , La derivación I se registra con dos electrodos colocados, respectivamente, en los - dos brazos; como los brazos se hallan en dírecci6n horizontal con delectrodo positivo a- l a izquierda, e l e j e de l a derivación ed de 0..

Un eje horizontal

A l registrar l a derivación I1 se colocan los electrodos en e l brazo derecho y en t l a pierna izquierda El brazo derecho se conecta a l tronco en e l ángulo derecho alto; l a - Pierna zquierda, en e l ángulo Inferior izquierdo. Por l o tanto, la áirecci6n de esta de- vación es de aproximadamente 60'.

Con anál is is aimilar puede compiobarse que l a derivación 111 tiene un e j e de aprei ximadamente 120. La derivación ave, de 30.; l a aV,, de 90* , y l a aV, , de 30'.

Cuando e l vector en e l corazón se hal la en una dirección casi perpendicular a l e je aei órgano, e l voltaje registrado en l a derivación correspondiente es muy pequefm, s i e l - vector tiene casi exactamente e l mismo e j e que l a derivación, se registrará prácticamente- todo e l volta je del vector

En e l anal is is vzcrtorial de potenciales de las tres derivaciones estándar I , I1 y- 111, e l registro es positivo porque los vectores resultantes quedan en direcciones positivas a l o largo de los ejes de las derivaciones. E l potencial en derivación I es aproximad? mente l a mitad de l vector a traves de l corazón; en derivación I1 casi exactamente igual -_ que e l de l corazón, y en derivación IIi es aproximadamente la tercera parte que e l del co-

razón.

l o s e f e c t o s producidos por trnstorno? en el .sistema de c onducc ih fue-

r on not ido? nor lo? doctores mucho rn t es nile nud~ieran F e r explica.d.os

E l médico Aleman b¶a.rcPs Gerbezius, nue murio en 1718, e s c r i b i o .acerca

de un naciente con un aulso t;m l e n t o , n u e entre do?, !a t idos , e' cora-

zón de iini persona normal hubiese l a t i d o DOT l o menos t r e s veces. Duran

t e 7~0s s i g a i e n t e 150 añn:. todos :o? dem6.c fenomenos a:.,ocii.dos con fa.--

1.l.a~ en l a conducción fueron reaort idR? como: Pocos b t i d o s , Mucho? T a

t i d o c , Lat idos inregul-ares y o t r o i . Pero ninguna exa l i cac i ón e ra nocri-

b l e hasta n r i n c i o i o s delL nresente s i g l o , cuando l o s a.nxtomicitas descu-

b r i e r on 1.o~ caminos del sistema de conduccián del corazón v ! o s na.r t i -

da r i o s d e l ECG mostraron como esqs camino? eran transitados.

E l b1.ocueo ca.rdiaco, o sea e?. impalso l e n t o mo?trn.do nor Gerbeizius,-

se d e r i v a de una f a l l a en e l nodo A-B para conducir e 1 im.wlso de l as

nur i cu i r s a 10:. ven t r í cu l os , l o s v en t r í cu l o s entoces se contren a sus

pro.:io r i t n o , más l e n t o , de 21)':a 45 por minuto. La f a L l a a su vez pug^:

de sex debida a la. ausencia. d.e f i b r a s , un d e f e c t o gongenito, o una, es - caces en el abastecimiento de sangre. En casos muy r a r o s puede per de - bido a narasieos, tumores o una mala c i rug ia .

F i e l suministro de sangre hacia e l nodo 4-V y a1 haz de h i s e s r e c o r

tedo, entoces todo e l sistema v en t r i cu l a r es a i s l ado , s i l a i r r i g a c i 6 n

a l as f i b r a s conductqras e? reducida e1 sistema e s afectado.

-

1.a conducaión a t r a v é s d e l area de l a unión A-V puede ha'larse r e ta r -

dada o bl-oaueada por f a c t o r e s nue e levan e l tono vagal ( en t r e e s t os - se incluyen l o s e f e c t o s de c i e r t a s drogas, asf corn cardionat ias is--

ouemicas, es tenos i? o ocusiSn coronar ia ) , l o s re tardo€ de conducción

e __-

o blonueos Dueden uroducirse también en una o anbas raman fasc iculares .

Se han ideado t6cnicac nue nermitan registrar l o s impulcoc de l a re--

gión d e Ir u n i ó n . >.-V y del si;stema de c~nd.J ,cc : i~~u! fihrr? de I>i;rk:inje - e l e lec trocar- 1. ?. s C 2 . r P í i c ' c : r >p r ~ ~ i ~ r -? :.~-r',?~.;.: f-.ir :'cfl.<:,::j s )

diograma. En ePtas t é cn i cas se ao l i c an microe lectrodos para r e g i s t r a , r

lo? po tenc ia l e s a través de 1.,2 membrana, en e l nodo A-V. Tambikn ?e -- dispone de t e cn i cas nue regi'tran electrograma? d e l haz do h i ? y de

svs ramas en su j c t os h w a n ' c .

. I

O 1 0 GSTILIULAUOBES EUCTXLCOS ( URCAPLPASO)

El marcapaso cardiaco e s y estimulador e l e o t r i c o que produce puisos e l é c t r i c o s per iodicos que son conducidoe a e lectrodos que est+ loca l i zados ya sea en l a super f ic ie muscular d e l corazon (miocardio) o dentro de l a vavidad car- diaoa.

Hoy en d í a l a insenciÓn,de un marcapaso cardiaco e s probablemente l a operación mas communmente $ealizad? en corazones enfermos. Yambien es una de l a s pro tes i s mas exi to- seniente implantadas. Aun cuando e l estudio de l a anatomía y f i s i o l o g f a de l sistema conductor d e l corazón se remonta a muchos años atras, e l uso de un rnarcapaso e lectrónico para remediar una conducción defectuosa en pacientes e s de o r i - gén reciente.

Practicamente todo paciente que en l a actualidad recibe un iaplante de marcapaso padece de bloqueo $ardiaco debido a alguna enfermedad en ar te r ias CoronaEias, mas l o s primeros marcapasos fueron usados principalmente para defectos conge- n i t o s en e l septo interventr icular . Pue en 1957 que un e l e c - trodo fue por primera vez implantado en un corazón humano y conectado a un marcapaso externo para e l tratamiento d e l b lo- queo cardiaco debido a un defecto en e l septo interventr icu lar En gran numero de l o s casos e l bloqueo cardiaco era temporal

y e l e lectrodo pudo ser renovido de l miocardio despues de 3 semanas.

Pronto de descubrio que mi les de pacientes con bloqueo cardiaco completo debido a ar te r ioscreros i s coronaria po- dian benef ic iarse con estos e lectrodos conectados a iiiarcapa- sos enternos. A f i n a l e s de l a decade de l o s cincuentas &ran numero de pacientes con bloqueo cardiaco ar ter iosc2erot ico tenian e lectrodos conectados a marcapasos externos trancis- torizados. Estos marcapasos eran l levados externamente y tenian un tamaño poco maJor que una c a j e t i l l a de c igarros y obviamente e l e lectrodo ten ia que atravesar l a pared toraci- ca, por l o cual l a in fecc ion era e l pr inc ipa l poblema de estos pacientes y e l desarro8A.o de un marcapaso cardiaco completamente implantable en 1960 fue un gran,avance en esta rama. En l a s primeras tecnioas de irnplantaci.cn de marcapasos,

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se rea l i zaba una toracotomia izquierda y los dos e lectrodos se implantaban en l a super f ic ie d e l ventr iculo izquierdo. Los electrodos a su vez se conectaban a un marcapaso que se acomodaba subcutaneaaente en l a esquina superior izquierda de l a pared abdominal. Uebido a l a l t o r iesgo qhe e x i s t i a en l a s operaciones a torax abierto se ten ia mayor in te res en l a implantacion de electrodos en el ventr iculo derecho por ru- t a intravenoea. Aotuai mente se han mejorado tanto l a s tac- nicas de implantacion como l o s materiales con que se fabr i ca el marcapaso evitando a s i e l r i esgo $e que se deter iore el d i s o s i t i v o o en l a misma intervencion a l momento de colocar- lo P 2).

Cier to numero de ondas de impulso son ut i l i zadas corrien- temente; l a d s comun es una onda diferenciada., b i f a c i ca y asimetrica de 1 a 2 me de duracion, con una fase estimuladora negativa y una fase d s larga de recobro posi t iva. Se ha encontrado que e s Lias ventajoso hacer que e l e lectrodo implantado en e l endocardio sea el cdtodo, ya sea en un sistema unipolar y l o mismo en uno bipolar.

Un impulso con duración de 1 a 2 us es usdo en l a mayo- r i a de los marcapasos permanentes y en l a mayoria de los casos, el umbral i n i c i a l para l a estimulacion d e l endocardio es de 0.5 ma o 0.5 volts. i31 umbral para el estimulo debe entonces elevarse hasta d iez veces en l a s sgguientes 2 a 4 semanas, pero en es te punto por l o regular se establece a menos que se presente f i b r o s i s acentuada alrededor d e l electrodo

n ib l ee y en gran parte son altamente confiables. l o s mds comunmente u t i l i zados se describen acontinuacion:

MARCAPASO DE BITiUZO FIJO; Es el mas simple de todos desde el punto de v i s t a de l a c i r cu i t e r i a y puede ser usado e f e c t i - vamente para l a mworia de los pacientes con bloqueo cardiaco completo cronico. Algunos de estos marcapasos tienen un ritmo que es preestablecido de fabr ica, en otros e l ritmo puede ser alterado por un inductor var iable o un switoh mag- netico.

idxisten d i ferentes t i pos de marcapasos comunmente dispo-

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URCAPASO SINCHübICO: En los pacientes de mayor edad con bloqueo cardiac0 permanente, un maroepaso de ritmo f i j o e s su- f icientemente sa t i s fac tor io , y s i l a act iv idad f i s i c a se in- crement., l a respuesta cardiaca se ad.pta con un n i v e l de volumen mas alto. Para los pacientes mas jovenes, gue t ienen una act iv idad f i s i c a mayor, e s d s ventajoso usar un marcapaso eincrónico o marcapaso accionado por onda P. Con es te t i p o de marcapaso, un te rcer eleotrodo ea implantado en l a auricula, desde donde detecta l a s ondas P y despues programa un retardo e lectronico auricular de 120 ma de 2.1 manera que e l impulso de estimulo e s disparado despues de un retardo t o ta l , e lec tronico y f i s i o l o g i c o , de 180 us. date disposi- t i v o t i ene una velocidad f i j a base de 60 pulsaciones por min y opera s i l a onda P no e s detectada o s i ae presenta una f ib r i l ac ion .

m un cuando este t i po d& marcapasos t iene algunas venta- jas obvias, es mucho más complicado en su c i rdu i te r ia y t i e - ne un rango de error d s a l t o que e l de ritmo f i j o . l'anbien ordinariamente se requiere de una toracotomia para e l implan- t e de l e lectrodo auricular y e l gasto de l a ehergfa de l a hater ia e s mayor.

ax i s te un considerable numero de pacientes que t ienen bradicardia temporal o intermitente y w e requieren un t i po d i ferente de uarcttpasos a los descr i tos anteriormente, ya qu ex i s t e algun r iesgo a l competir e l estimulo natural d e l sistema de conduccion de l corazón con e l de marcapaso a r t i - f i c i a l .

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UillRC~PdSíl ud UA~ANUA: x x i s t e n dos t i p o s de e s t o s marcapasos de demanda o espera , ambos monitorean l a onda H usando un e lectrodo v e n t r i c u l a r , que almismo tiempo s e n s a l a onda H y e s t i m u l a e l v e n t r í c u l o . da llamado i n h i b i d o r de l a olida B, la onda v e n t r i c u l a r i3 inhibe el generador de p u l s o , pa@ e s t i m u l a solo cuando e l i n t e r v a l o R-B excede o i e r t c l i m i t e p r e e s t a b l e c i d o . Ha habi- do algunos problemas un aislar es te c i d c u i t o de campos elec- t r i o o s e x t e r a o s que tambien pueden i n h i b i r e l generador de

dn un t i p o de marcapaso de deman-

pulso. (11)

Un segundo t i p o de marcapasos de espera es llamado marcapaso estimulado p o r onda B. ds disparadopor l a onda R e inmediatamente a c c i o n a un impulso de r e t a r d o dentro d e l complejo qBS. S i e l i n t e r v a l o B-B excede 0.86 seg., l a unidad d ispara as incronicamente un r i tmo f i j o de 7 0 - 72 latidos por minuto. el i n t e r v a l o E-R es menor de 0.86 seg., l a unidtld dispara s incronicamente . Asta t i p o de marcapasos dispara continuamente y no puede s e r i n h i b i d o por campos e l é c t r i c o s ex ternos .

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Actualmente l o s marcapasos mencionauos son onstante conf iables y han disminuido ttn gran medida l a martaliaad en pacientes con bloqueo ctlrdiaco. mque e l promedio de v ida de una bater ia en un marcapaso interno 13s solamente de dos anos, esperanzadoramente descubrimientos s i gn i f i ca t i vos muestran l a manera de eliiuinar l a pecesiaad de reemplazar e l marcapaso completo cada dos anos.

blema de l reemplazo frecuente de marcapases. Una tecnica ha sido e l uso de una unidad alimentada por frecuencia de redio. En este sistema , l a unidad transmite señales atruve de una antena conectada a l a p i e l d e l torax directamente si& bre una unidad receptora implantada. &ita a su vez es conectada a l miucardio por medio de cablee.

Otro remedio a l problema de l a s bater ias es e l uso de unas recargubles de niquel y cadmio, auque no es muy recomen- dable por algunos inconveniezites como su rapida descarga y darlos $n l a p i e l .

internos puede bien ser l a energia nuclear. t a l e s marcapasos son posibles a l conectarse una fuente nuclear a un marcapaso disponible de los sn t e s mencionados.

.a t re l a s curacter ist icus que debe tener un marcapaso existen e l t i po de onda que se pretende disparar, a s i como l a magnitud de l a corr iente a enviar. Axiste por ejemplo l a pos ib i l idad s i e l impulso e s mucho mas largo de 5 ms de causar f i b r i l a c i ó n ventricular. Eambian hay @ e estar concientes que

u l s o s mas largos causan raduccion en l a v ida de l a bater ia

&l hecho de enviar un corr iente conocida a l corazón ser ia pract ico usando una fuente de vo l t a j e de ba ja impe-

dancia s i supiecemos l a s impedamcias Pucay exactas en e l c i r cu i t o f i s i o l i g i c o . Pueden ser medidas y son var iables de paciente en paciente, l a menos var iable de estas imp dancias e s l a impedancia d e l corazón (7).

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dxisten d i ferentes posibi l idades de minimizar e l pro-

Finalmente l o ultimo en fuentes de poder . a ra marcapasos

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Sxamineuios ahora con un joco de mayor de ta l l e cada uno de los elementos componentes de l sistema que implica un rnarcapaso a r t i f i c i a l :

PUd' l 'd U8 PODER; l a fuente de poder uas frecuenteuLnte usada en marcapasos implantable e s la bater ia de celdad de mercurio de a l t a cal idad ( 6 ) que pueden ser conectadas en se r i e para obtener una fuente de 6 a 9 volts. bn l a pract ica estas celdas son frecuentemente descargadas erL dos años, l o cual se debe regularmente a l temprano deter ioro de l a misma ce l lda ocacionada por un mal empaque.

Los marcapasos implantables tambien pueden ser alimenta dos por fuentes externas,como ya habiamos mencionado, por medio de radio transmisores.

vIHCUITO Lid TI l i idPO; fi l a parte de l d ispos i t ivo que de encarga de generar e l p8lso que se dara a l corazon para estimularlo y en general aumenta de coupiejedad a medida que se requiere 5 i e r t a regulacion dependiendo de l comporta- miento de l corazon en c i eL to tiempo.

CIECUIrO DS SALIDA; .&1 c i r cu i t o de sal ida de un marcapaso ampl i f ica l a serlal que aebe ser enviada a los electrodos consta de un tranakstor operado por un switch y un apropiado acoplamiento a l o s electrodo8 . pasos e l generhdor se coloca a c i e r t a distancia d e l corazón debe haber buena conduccion para l l e v a r e l estimulo hasta e l lugar apropiado. LOS cablcs u t i l i zados para conectar a la unidad con los electrodos no s o l o deben ser capaces de soportar las sacudidas de l o s l a t i dos de l corazon , sino tamLien l os movimientos de l r es to de l cuerpo d e l pacnente que l o posee, debe soportar torceduras en d i ferentes posiciones y presienea.

l o s primeros consisten en dos e lectrodos conectados en e l corazon mientras que l o s segundos solo t ienen un e lectrodo conectado a l corazon otro en algun lado de l cuerpo para cerrar e i c i r cu i t o ( 5 7 (9).

C A L L S Y d L & C i w U u S ; couio en la inayoria de l o s marca-

dxisten dos t i pos de marcapasos, bipolares y unipolares

a- ,

A l i gua l que l i s cables, e l mater ia l q a i que estan fabr icados l o s e l ec t rodos es muy im$ortante, es tos deben s i e ubre e s t a r en su lugar apesar de l a intensa ac t i v i dad meca- n ica que t i ene e l corazon, a s i como es ta r hechos de ua t e r i a l e s que no se disuelvan despues de e s ta r por lar80 tiempo imklantados y no c rear reacciones e i e c t r o i i t i c a s ai s e r l e s ap l icado e l est imulo correspondiente. Para s a t i s f a c e r e s tas caractu i s t i c a s los e l e c t r odos son fabr icados de los misrnos mater ia les que los cables. por ejemplo. de p l a t i no qu e s quimicamente iner te .

íUEERiNC IBS

1.- Remo bed in i , Graziano Pa l a g i , k o l o & m i n i . xbi IiliPHOVhD IblS'I'RU&NT POR PACE&RiUZR ANALISIS &¡SEU Oil CCD TNHNIQUE IEEE Trans Biomed Eng Vol. bme-29 #3 1982 p 209-215

2.- b r e d i k i s Yu. Yu., E. P. S t i r b i s . OPTI~~ALATION OF BNDW CaaDIAL ELECTXODES GEONETRY AND CONTACT SURFACE AlUA. B i o idea Eng vol. 14 #7 y980 p 85-88.

OP PACEMAKER EWCTRODES: I& VITRO STUIIIS SII~ULATING 3.- B. Fischler, H. P. Shcwan. POLbpISAI'IOil I@BI)U&CE OF

PRACTICAL OPi3i¿ATIOlJ. &ed B i o l &ng Comput Vol. ig #5 1981 p 579-588

4.- G. Hoffmonn de Visme, A. Purness. MINIMJM dN&KGY PUL- SIilG BY CARDIAC PACEUKER. IEEE Trans Homed Eng vol. Bm-29 #7 1982 p 546-549

5.- P h i l i p Hurze ler , V. de Caprio, S. Purman. kiiOPOS8U CARUIAC PUCB-R SYST8IIIL COMBINING UNIPOLBR STIIYNU- T I O N WHITH BIPOLAR SENSIbG. IEEE Trans biomed Eng voa. ~ m - 2 6 #7 u 7 9 p 440

6.- H. Matschiner, K. B. Otte, S. Rudolf , K. Wiesener. SFEECT OF WATBR VAPOR ON A&~RCURY@'LINC CALLS I N 3LBC- TlIICAL P A C 5 N R S . Biomed dng Vol. #5 1979 p 252-256

7.- L. fYgrkrid, O-J. Ohm, E. Hammer. d1GluAL SüUiidb Ii4ed:U~N- CE k'OR I&??PLKNWU PxCdL<ix&iR dUCTiIOUBS SST 1~UiUL~'lliü PliOud &SP&CTlUL i U T I O bETWdbli LOADEU AND UNLOAMD i3UCTROGRAiIIS I N MAN. PKed B i o l 5ng Comput vo l 18

8.- A. I. Sheremet'ev, S. S. Grigorov. dVALUaYIOEJ üP IiIHti: SUITABILITY OF AN BUCTKODWIOSIGNAL FRü& THd RIGHT

STIiulULATOR. Biomed bng vo l 14 #3 1980 p 89-91

1982 p 223-232

VdNTRICULAR SNIIOCARIIIU~ TO COni'I'ROL KIU dL&CTROCfiRL)IO-

9.- G. S. Smith, J. C. Toler. ANALYSIS OF YHd COUPLING OE

&KBRS. Ued B i o l Eng oomput vol. 19 ,$ 1981 p 97-109

dng Comput vol. 18 1980 p 109-113

ASYDJCHRONOUS CAHUIS~'IWLKTORS. Biorned bng vo l 12 #4 1978 p 206-208.

~LdCTHüithübl&TIC 1IUTdILL"dRENCE TO UPI IPOLILB C&I .J IAC PBCE-

10.- Tech i ca l Note. €AC&LSB~~~R VfiCTUR CnKUIOGAAPH. dlied B i o l

11.- G. V. L U S W ? INClUASI&ü INSd€U'liRdiVCE IBhfU&ITY OF

BLBLIOGEAFIA

BASoS FISIOLOGICAS DE LA PRi3C'PICA &UICA Jhon B. Brobeok Best y Taylor.

The HART Donald Long more World Univers i ty Library

udUlCaL 1NSTRUiIIANYxTlL)N APPLICx'PlON ANU UdSIGN John G. Webster Houghton Miffl in Company

iMGIM!dHlNG 11v YiiJ PRhCTICd OV &dlClN& B o r n a l d L. Segal, uevid ti, Kilpatriok. "he Williams Bc Wilkins Company

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I :n!ent

I is s 0 cm ’0 cm , , I

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,:c,rii~w;tors, Ihe I I I : : S ~ I I C C of conductors wii t in thr fields will (:auoi, ,I meiisiirenic lit artifact. Ttie only soliiiion to this prob- ]err ,., t o k,r?p c<:miiuctors away from the scirch coil and use loc. I: .,ense coils .is inri I ttie search coil as posi;.ble.

iiCKNOWLEDGMENT

V’i: ,would ‘likr t i , t h m k A. C. Ziminsky, S:. for helFi in the :‘;ihr.:iition of the ,c¡r,:uits, and A. G. Lasker of the Johns Hop- .!ns !;chool of Meiliciie for suggesting the limiter circuits.

ILEFERENCES

11 I ~ . . Collewijn, “E ,‘e ind head movements in freely mwing ixabbits,” .I. Physiol.,vd. l66. pp. 471-498, 1977.

21 1.1. Collewijn. F. Van der Mark, and T. C. lamen, “Precise recard- r ig of human c y riovemenb,” Vision Res., vol. 15, pp, 441-450, 1975.

,‘31 .A, F. Fuchs and D. A. Robinson, “A method for measuring hori- !ental and vcrt;al eye movements chronically in the monkey,”

J. Judge, U. .I. Richmond, and F. C. Chi!, “lmpiantation of riagnetic searct c d s for measurement of eye position: An improved method,” Vsioti Res., yol. 20, pp. 535-538, 1980.

51 .I. G. McEüigoti, V.. H. Loughnane, and L. E. Mays, “The use of iynchronous dr.modulation for the measurerrient of eye movements by me.ani d’ an ocular magnetic search coil,” IEEE Trans. .Biomed. Eng., v:tl HME-26, pp. 370-374, 1979.

161 :I). A. Robinson. “,$ method of measuring eye movement using a icieral search c d i i a magnetic field,” IEEE lrans. Biomed. Eng., id. BME.10, pp. 1187-145, 1963.

171 .\I. I. Sullivan s:id A. Kertesz. “Signal detection via phase-lacked wnpüng in a magnetic search coil eye movement monitor,” IEEE i”mm Biomed. .Eng., vol. BME-26, pp. 50-52, 1979.

[8] L.. R. Young and D. Sheena, “Survey of eye movement recording methods,” B<hai~. Res. M., vol. 7, pp. 397-429, 1975.

Appl. Physhl., vd. 2 1 , pp. 1068-1070, 196f..

An Improved Instrument for Pacemaker Analysis Based on the CCD Technique

REMO BEDINI. GR4ZIANO PALAGI, AND PAOLO MANCINI

,zlbirmet-The insi:niment deser ia in a previous paper, “A new method for utilizing, a standard elstmendiograpli for in vivo clinical pai:mnnker analysis” [3 ~ h a been improved with l.he utilization of the chiul:e.coupled device.

Iliiii device, used here PP in d o g shift reglster of 10% cells, permita tho di~pliy of the piceinaker pulse with a standard electrocardiograph in I high-resolution tinte course; the same time coum can be trans. mitliA by telephone for remote uinlysih

I‘iirthermoie, our technique permits an automatic serinluing of the stnea:hed pncemnkei pdse and ita induced cardiac rhythm on the same LnOt .

Ilr! low-power circuits wed by the authors enable operation with a ba’ttwy supply which iniplies high noise immunity, safety PñUIrance For thi: patient, and portability of the instrument for its utilization throu@ thi! public telephone neiwork.

‘it.inuscript recciwd January 12, 1981; revised October IS, 1981. 1 work was suppori.ed by the lrtituto di Fisi,>Iopia. Chica CNR,

:,I...>< Italy. K. Ikdini is with SORIN SPA Salupgh and the lstituto di Fisiologia

1:. Pdilagj is with üic lbtitutu di Fisiologka Clinica CNR, Pis*, Italy. 1’. Mancini is with the Scuola Normale Supcriorc and the lstituto di

C h u a CNR, Pisa, l l a ly

hi<ili>gia Chica CNR, Pisa, llaly.

INTKODUCTION Pacemaker carrying patients are northally submitted t o

periodical check 121 in specialized clinics to analyze the status o f their prosthesis from two points o f view: 1) clinical effectiveness o f the pulse and 2) electrical life expectancy; both depend on residual battery charge, circuit efficiency, and catheter and electrode conductivity.

Generally, the electrical analysis is performed by means o f ECG and oscilloscope; the oscilloscope dkplays the pacemaker (PM) pulse time course. The instrument presented in this paper is based on the previous instrument I31 with improved implementation through the CCD technique I1 l.

The previous instrument samples the PM pulse time course on 20 analog memory cells &e, , capacitors) at a sampling rate o f 200 &sample, then resolves the PM signal at a scaled rate (10 Hz) on a standard electrocardiographic recorder.

This apparatus presents two practical problems: i ) The stretched PM pulse on the electrocardiographic paper

is reproduced with Large waveform distortion due t o the low number of samples.

2) The amplitude peak evaluation can be obtained, not directly, but by means of an extrapolation of the staircase waveform o f the reproduced PM pulse.

In the new instrument presented here, the number of the samples has been increased from 20 t o 256. This fact prevents the above-mentioned inconveniences and permits a continuous waveform of the stretched PM pulse to be displayed on electrocardiographic paper. The new instrument embeds a charge- coupled device (CCD) for sampling the pacemaker pulse and performing the necessay stretching action t o display the pacemaker pulse on a standard electrocardiograph. The use of the CCD technique automatically allows the stretched pacemaker artifact and induced cardiac rhythm in real time t o be serialized on the same trace.

Furthermore, the new electronics of the instrument permit battery powering and high noise immunity. Safety assurance for patient and portability are, consequently, obtained. A single-channel transmission of the processed ECG signal on the standard public telephone network is provided, using frequency modulation of an acoustic hand carrier and acoustic coupling with the telephone headset 141.

METHOD AND MATERIALS The analog memory of the instrument, based on charge

coupled devices (SAD 1024 by Rethicon), is used as an apalog shift register o f 2 X 512 cells operated in the differential mode and with a twin clock phase. This way o f operation gives 256 useful samples.

The use o f charge-coupled devices (CCD) presents various advantages over the capacitor analog memory and digital memory for pacemaker analysis.

1) High ratio “memory size/volume” compared t o discrete capacitor memory.

2) Natural real-time processing capability, lower number of chips, and lower power circuits compared t o the equivalent method based on A/D conversion, digital storing on RAM, digital recall, and D/A conversion.

The CCD analog shift register is used under control of a timing clock which masters the sampling process of the analog signal operating on a bucket brigade base.

In this application, two sudden clock frequency changes are necessary to obtain a stretching action on PM pulse and resolve it at an underscaled rate:

i ) A first increase in clock frequency when PM pulse is present at the input of CCD (from 1 kHz t o 125 kHz);

00i8-9294/82/0300-0209$00,75 O 1982 IEEE

210 IEEE 1RANSACT)DNS ON BIOMEDICAL ENGINEERING, VOL. BME29, NO. 3. MARCH 1982

o- m- 111 T

01 Fig. I. Block diagram of the new instrument: EA is the ECG inpt

adapter, PA is a pacimaker input adapter, AS is an analog switch, NI and N 2 are inverting unit gain amplifiers, S1 -S2- S3 aro sum- mators, OA is an output adapter, FMM is a voltapcontrolled as&* lator, SY is a synchronism circuit. SCL is the system control iopc circuit, CK is the system clock, and BL is a baselinecorrectioncircuit.

2) a subsequent decrease m clock frequency (from 125 kHr to 1 kHz) to display the sampled signal at scaled rate for bandwidth compression

The high frequency sampling period results m 2 ms which covers everv actual pulse duration of the ?M delivered by the market.

The hi& samolinn freauencv is related to the bandwidth of PM pul&; the iowsampiing fkequency has bebn choosen com- patible with the minimum clock requirement of the C C D integrated circuit used. This choice permits stretched PM pulse width to be displayed as durations on the order of 100 ms, which gives the physician a waveform comparable to a typical QRS.

Fig. 1 shows the entire block diagram of the implemented instrument.

The inout ECG simal is orocessed bv two different inDut - interfaces:

1) A low-noise high-amplification (=500) narrow-band (100 Hz) amplifier for standard ECG detection, (EA block),

2) a low-amplification (=2) high-bandwidth (100 kHz) pacemaker input adapter block for pacemaker detection (PA block). A manually operated switch can be provided to increase the amplification of the PA block for a factor of IO for bipolar PM analysis.

These two input channels are necessary due to the large difference between the amplitude range of the detected PM signal (200 mV for unipolar PM and 20 mV for bipolar ones) and of the ECG signal ( I mV) and the limited signal dynamic

Some important remarks must be made about when the CCD circuit is used with sudden changes o f the Flock frequency. Typical distortion on the output signal is present when the

I . clock frequency changes from 1 kHz to 125 kHz and vice versa. In the present application, the distortion assumes particular importance when the clock frequency switches from the high to low vaiue for displaying the sampkd PM artifact at scaled rate.

'

' ' range (70 dB) of the CCD.

Two types of distortion are contemporaneously present. I ) A first one is a glitch (glitch distortion), corresponding

to the first high-frequency sample, detectable.only on the first low-frequency sample (after clock switching) with a random amplitude comparable to the full dynamic range of the CCD.

2) A second one is a stepwise distortion which affects the reproduced signal present on the CCD oul!put during low- frequency timing for the period corresponding to the high- frequency sampling.

The second distortion has been corrected by means of a purposely generated bias, during high-frequency sampling, obtained as a first-order correction of the above-mentioned distortion (¡.e., a srep with a superimposed ramp).

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Fig. 2. ñactical stepwise correction parameters for three different sampler of SAD IO24 CCPintsgrated circuits: CHI and CHZ are referred to Uie two CO-distinct 8ections in the same chip.

Fit. 3. Pacemaker input adapter block. PM is the pacemaker input signal, A is a larle band input buffer, CCD is a 256-1.t~ delay Une, SY- synchronism flag, FD= 1 MH2 clock input to the delay Une, PM' delayed PM pulse, and dt = delay between PM and PM'.

Fig. 2 shows typical values of the parameters of the correction &al in the practical cases for three different integrated circuits.

The f b t distortion (glitch distortion) cannot be corrected due to its random nature, but its effect on a stretched PM pulse may be avoided with a suitable choice of stretching phase with respect to PM pulse timing. For this reason, a special purpose preprocessin6 circuit of the PM signal is included in the input PA block (Fig. 3).

The PA4 input &ai has been buffered by a large bandwidth amplifier A (100 kHz) which delivers a signal SY to start high- frequency sampling, and drivea a CCD delay line clocked by a stationary delay frequency FD (in practical implementation FD = 1 MHz and the CCD delay line present, 256 delay cells corresponding to 256 ps of deliy).

The delayed PM signal is buffered by the B amplifier to drive the subsequent stretching block.

With this preprocessing block, the PM pulse to be stretched is purpasely displaced in time with respect to the glitch distortion, permitting a noise-free reproduction o f the waveform.

Referring to Fig. I , an analog switch (AS) operates the switching of the stretching CCD block input adapter circuits (block N i , S 1 , S2) between ECG signals and pacemaker pulse.

The signal delivered from the AS block is processed by two complementary channels (Ni +S1 and S2) working with a bandwidth of 60 kHz, related to the sampling frequency of 125 kHz used here. These Unes drive two distinct complementary sections of the CCD stretching block. A trigger circuit SY, supplied by the PA block, provides

synchronism with the pacemaker pulse event and drives a system SCL-control logic which controls all the functions of the system.

In particular, the SCL block controls the position of the AS-analog switch connected to the input adapten. Further- more, it switch= CK-clock block sampling frequencies between the two values: 1 kHz for ECC sampling and 125 kHr during PM pulse event. Timing is provided to permit a stretching action of one PM pulse every three events.

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IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. B M E 2 9 , NO. 3 , MARCH 1982

Fig. 4. Time axis transformation performed by the instrument: P, Q, R, S, and T are the standard ECG wave identifications. I'M is the pacemaker pulse. followed by induced QRS complex. The delay effect of the PA black is not considered here.

(b) Fig. 5. (a) The prototype near a standad telephone headsct for stretched

pacemaker pulse transmission. (b) The prototype in conjunction with a standard electrocardiograph for ambulatory pacemaker chock.

During high-frequency sampling, a special output signal from the SCL block controls the BL block which provides the signals to correct stepwise distortion. Four trimmed functional regulations are necessary for presetting the correction parameters due t o the variability of the CCD employed. The cor-

I

1 1

I

1 1

(b)

result with il synchronized-type pacemaker. Fig. 6. (a) Typical result with a demand-type pacemaker. (b) Typical

rected signal is delivered t o the two input lines o f the CCD stretching block; this device is operated in differential mode in order to increase the signal-to-noise ratio. Through the inverting buffer NI and summator S3, the CCD stretching block provides two complementary outputs which supply an output adapter (OA) and a voltage-controlled oscillator in the acoustic band (FMM block).

A schematic time diagram o f the input and output signals is shown in Fig. 4. The output signal presents a delay of 256 ms with respect t o the input signal during and foilowing the S wave, for example, the delay shown from a t o a '. A compression is performed on the position of the signal preceding the pacemaker event, due to high-frequency sampling on the pulse (b - c, b' - c'): a 1 : 125 stretching action is obtained on the pacemaker artifact when the sampling frequency has been switched from 125 kHz to 1 kHz (c - d , c' - d') ;an unchanged QRS wave follows the stretched pulse. in this way, the bandwidth necessary for describing the pacemaker pulse is reduced by a factor of 125.

RESULTS Fig. 5(a) and (b) shows the practical prototype in conjunc-

tion with the standard electrocardiograph and telephone a p paratus for transmission o f the pacemaker stretched pulse. The system is powered by two 9 V miniature batteries. Two electrodes are provided for one lead ECG detection and a miniaturized loudspeaker generates a 125 mW audio signal for telephonic transmission.

Fig. 6(a) and (b) shows practical results on eiectrocardio- graphic paper o f a synchronized [Fig. 6(b)l and o f a demand type [Fig. S(a)l pacemaker carried by two different patients; some QRS events, with and without artifact stretching, may be

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IEEE TRANSACTIONS OIY BIOMEDICAL ENGINEERING. VOL. BME29. NO. 3, MARCH 1982

J.,

Fig. I. Typical peak distortion of PM pulse due to lead electrode-skin impedance. Continuous Line represents PM pulse waveform, dotted h e represehts PM pulse dittorteiiby lead coupling. Vi= peak amplitude of ori$nai PM pulse, Yo = pcLk amplitude of distorted PM pulse, and Td = d&y time induced by lead-coupling time constant.

'I"

r ootion is orovided in order to aenerate a O V functions resultinn in the followinn n ' base line for reierence Purpose, immediately before the

stretched pacemaker pulse time cousse. A good stability of functional adjustment of stepwise distor-

tion has been evaluated over a long period of use (¡.e., >2 yemi.

- - ai mula:

Vo = A exp (-mor) + B exp ( - w ~ f ) + C e x p (-w2f)

+D exp(-w,t) (1) where . .

Several important considerations must be made in order to evaluate quantitative results o f any PM waveform analysis System especially related to peak amplitude measurements. The four most impottant sources of distortion wili be considered and modeled:

I) Variability of ro time constant of PM pulse; it is related to ac coupling o f the myocardium electrode. Ranges between

.' . 0.8 and 1.2 ms. 2) Variability o f rl skin-lead time constant; ii is related to

the equivalent RC at lead electrode-skin contact (Fig. 7 shows typical peak dist.ortion and Fig. 8 shows somenumericalresults in the practical range of electrode-skin impedance). T I ranges between 2 and SO gs.

3) Stretcher transfer function, which is approximated by a fist-order low-pasa fiiter with r2 - 2.6 ,D.

4) Electrocardiographic transfer function, which is approximated by a first-order low-pass filter with r3 ranging between 0.3 and 3.18 ms, corresponding to a bandwidth between S O and 200 Hz.

Fig. 9(a) shows a schematic model of all the processing blocks involved in PM peak distortion.

The time course of the output voltage Vo, without loading effect between the stages of the model depicted in Fig. 9(n), can be easily obtained ay the convolution of four exponential

.'

,.,

I ,

wi = i/ri i = O, 3 and A , B , C, and D are computed functions of T,. Fig. 9(b), (c), and (d) shows percentage error

(2) computird respectively versus ro, r l , and T , varying in the following practical ranges:

E% = ((To - Vi ) /Vi ) x 100

71 2.6 /i~

800 < ro < 1200 w 2 < r 1 <48w

0.8 < TJ < 3.18 ms. The magnitude order o f the total percentage error results, in

the practical case, to be 5.5 percent. Worth noting is the fact that the measurement system gives a

iyrtematic error and the display unit introduces a constant error; these errofs can be corrected by calibration. On the contrary, the variability of PM pulse and lead-coupling time constants induces random errors.

The maximum contribution to valuable error on PM peak amplitude due to the PM pulse time constant changing is, in

(21

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,N' ,.i~''I'lONS O N BIOMEDICAL ENGINEERING, VOL, BME-29. NO. 3, MARCH 1982 2 1 3

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P U L S E COUPLING SYSTEM UN11

Fig. 9. Percentage error on peak PM pulse amplitude evaluation in practical case related to measure transfer function parameters of overall system: (a) Schematic diagram for transfer function evaluation: Vi = true PM pulse and Yo = measured PM pulse. (b) Percentage error versus PM pulse t h e constant (71 = 5 us, 72 = 2.6 us, and 73 = 1.6 ms). (c) Percentage enor versus lead-coupling time constant ( T ~ = 1000 us, TI = 2.6 us, and r3 = 1.6 ms). (d) Percentage error versus display unit bandwidth (TO = IODO us, TI = S us, and 72 = 2.6 PS).

1 A more 5 CI ., e f j t z t on PM peak evaluation is given b y a bad lead 1 i~i in fact, we can see in Fig. 9(c) that the percentage I . isel 'ram 5.5 to 15 percent when the lead- 1 ip::.i: t i r i e constant changes from 2 io 48 ps. in practical c e! . d I i .I lead capacity of 100 pF, w e have an expected i IC I.,,: it, error of I O percent when lead contact resistance i i f ! , [om 20 io 500 kfl. On t h e other hand, we must com- I n .tiat t 'iese last two types of errors are common i o every > tc I , . of P M pulse analysis; in particular t h e last one, which is I: f , thi. by an accurate o ' a: I : , m w t procedure.

I ' t:;tiL:al case, less then 2 percent [Fig. 9(6)1. electrocardiograph for in vivo clinical pacemaker analysis," IEEE Trnns. Biomed. Eng., vol. BME22, pp. 281-286, July'1975.

[41 P. Manchi, R. Bedini, G. Pakgi, and C. Contini "A new method for complete in-vivo pacemaker analysis for ambulatory and telephone-home check," in Proc. San Diego Biomed. Symp., vol. 15,pp, 17-21, 1976,

crucial, may be avoided Maximum Frequency indication: M i h a Counting versus zero-crosing counting

ALLEN BECKER AND R. STUART MACKAY ACKNOWLEDGMENT

:k :,ut I I : ~ thank Prof. C. Contini of Patologia Medica I of Abs,mer-Certun Dopplei now ue done by I > iiiversity of Pisa for his preliminary clinical evduation of extrscting the pnamt fiquenw; dtpnih 1 :> 1. :ser tsd instrument and Miss S. C. Dryburgh for the ren- me,,,,,,, involving munth of ,,,inhi is prerented, dong with a circuit :i n , i ' thc English manuscript. type that directly produces a volumeindicating integral.

REFERENCS If a Doppler flow probe is aimed through a large curved blood vessel, the signal will show a variety of frequencies corresponding to flow at various angles and speeds through the sensitive region. If only instantaneous maximum frequency is recorded,

11 ,.J. hangster and K. Teer. "Bucket-brigade electronics: New i ,-sibili:.ies for delay, time axis conversion, and scanning," IEEE ' ~'o>li.l-.iiore Circuits, vol. SC.4, pp. 131-136, June 1969.

Kntii. ky, R. McDonald, and G. Sloman, "A method of testing ylanlcd cardiac pacemakers," Bnr. Heari J., vol. 27, pp. 483-

Uaiic ni and R. Bedini, "A new method for utilizing a standard

: ' Manuscript received July 14, 1981;revised September 22 , 1981. The authors are with the Department of Biology, Boston Universit' , I ,:!I< 1')i.S.

' : Boston. MA 02215.

0018-9294/82/0300-0213$00.75 O 1 9 8 2 IEEE

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0pTIMIZATION OF ENDOCARDIAL ELECTRODES' GEOMETRY AND

CONTACT-SURFACE AREA

Yu. Yu. Bredikis, P. P. Stirbis, A. S. Dumchyus, R. P. Veteikis, I. Yu. Skuchas, V. I . Korolev, and P. F. Yarmiiko

UDC 615.472:616.12-089.- 28-77 :621.3.035.2

One of the most frequently encountered complications during constant endocardial electric stimulation of the heart is electrode dislocation, which is observed in 8.8-23.8% of cases [l-31.

Various aspects of the problem of reliable fixation of the electrode in the endocardium have been studied. The creation of a silicon cuff or a conical cap on the end o f the electrode has allowed us to decrease the number of dislocations to 4.5-7% [4-51.

in order to eliminate electrode dislocations, new electrodes with fixating mechanisms have been devised [6, 71. These electrodes are chiefly intended for stimulation of the cardiac auricles or markedly dilated ventricles. However, when they are used for a long time, frequently such an increase of the stimulus threshold is observed that the electrocardiostimulator is noc capable of causing a propagated excitation wave [71 and besides, isolated electrode dislocations have been noted [ E ] . The fixation of such an electrode in the wall of the heart occassionally requires several attempts. Schmidt's whisker electrodes 191 are well known, as well as the hook-shaped electrodes that Irnikh supplied, whose advantage is the possibility of inserting them without a guiding catheter. When they are used, the fixation of the electrodes in the atrial wall presents definite difficulties. If thehooks are too long the danger of perforating the wall is present, and in contrast, if they are short, the electrode is unreliably implanted. In the Soviet Union a hook-shaped electrode with remote control has been supplied [U]; however, clinical experience with its use has not yet been accumulated.

A corkscrew-shaped electrode which is secured in the myocardium without the use of su- tures has been supplied by the firm "Medtronic" for myocardial stimulation. This has defin- itely stimulated the development o€ a new generation o€ corkscrew-type endocardialelectrodes. The firm "Vitatron" in particular supplied the screw-in electrode "Khelifiks" which was test- ed on experimental animals, and on patients [12-14land proved less traumatizing than the 'Wed- tronic" firm electrode already mentioned. The catheter electrode 1151 secured by a balloon which inflates between the endocardial trabeculae deserves mention. For the time being, it is impossible to give the electrodes which have been enumerated a final appraisal, since the periods of their clinical use have been too short.

functioning time. lation energy, the most important has to do with decreasing energy loss in the electrode- tissue contact and with related matters - choosing a corresponding electrode contact-surface alea and geometry 110, 16, 171.

trode design which would ensure reliable original fixation in the endocardium. We also hoped that our design, by creating a contact surface of a particular geometrical form, would ensure a decreased expenditure of electrical energy.

Intensity and simultaneously would ensure reliable fixation proved to be a complex problem.

and this allowed us to decrease the percent of dislocations (see Table 1).

When implanting an eiectrocardiostimuiator the most important goal is to increase its Among the basic trends in the study of possible ways to save electrostimu-

Our investigations into electrode optimization were directed towards choosing an elec-

The development of an electrode which would create a sufficiently high electric field

in order to improve rhe fixation properties, electrodes were designed which had cuffs, Then three proto-

electrodes were developed. The first, a polyhedral electrode having from 6 to 20 edges,

Kaunas Medical Institute, Special Design Bureau of the Cable Industry, Kamenets-Podo1'- ckiY. article submitted April, 9 1979.

Translated from Meditsinskaya Tekhnika, No. 3, pp. 9-13, May-June, 1980. Original

0006-3398/80/1403-00B5$07.50 Q 1981 Plenum Publishing Corporation 85

TABLE 1. Dislocation of Electrodes o f Different Design

number o € percent of electrodes dislocation electrode .type

- ordinary electrode" eLectrode with a cuf f , hook-shaped e lec trode" split electrode ,siclrle-shape electrode

49 12.2 210 4.28 48 2.08

8 63

- -

"The ordinary electrode liad a smooth stimulating head surface and did n o t have any attachments for fixation. :hook-shaped electrode of the firm "Biotronic".

Fig. 1. Polyhedral endocardial

allowed us to increase the electric field intensity. Its contact-surface area was 24 mm2. One of the variants of this electrode i s shown in Fig. 1.

connective tissue into the cracks between the wires was created on the basis of data of mor- phological investigations. soidal form in the cardiac cavity as a result of bending of a bunch of thin wires joined at the top. 'The diameter o f the thin wire is 0.25 mm, and the contact-surface area is 17.8 mm'.

The electrode with a securing device that we call sickle-shaped I181 is also prototypic. The contact part of the electrode has t w sharpened sickles displaced 180' relative to each other (Fig. Zb). The length of the sickle handle is 0.7 mm, which limits the depth of pene- tration of sickle-shaped elements into the wall of the atrium OK ventricle. The flexure of the sickles does not exceed the diamete]: of the electrode, which is equal to 2.5 mm. contact-surface area of the electrode is 10.4 mm2. alloy, brand 40 KKh27MNTA.

out on small strips of mycrcardium (2 x 2 em) in conditions approximating those o f the live organism. 500 mm Hg column. trical current I, and charge Q of single threshold electrical impulses (the last value was necessary for an estimate o f the energy expenditure of the electrocardiostimulator [lo]; it was calculated by an integration of the impulse current).

dium showed that for electrodes with a small contact-surface area (sickle-shaped, hook-shaped, and split) the dependence of threshold voltage and current on the impulse length was less fully expressed than for oecassionally employed hemispherical and cylindrical electrodes. For example, for a sickle-shaped electrode a decrease of impulse length from2.0to 0.25msec results in an increase of threshold volt<agga f r m 320 f 23 to 510f47 mV, that is, results in a 60% increase. A similar impulse length decrease for hemispheric electrodes (contact surface area 24 mm') results in an increase of the threshold voltage from 630 ? 135 to 1544' 286 mV, that is, a 145% increase (Pig. 3 ) .

Polyhedral electrodes proved more effective than hemispherical and cylindrical electrodes with an identical contact-surface ares (see Fig. 3).

electrode.

An electrode with a split contact head (Fig. 2a.) which is secured due to growth of

The contact part having a diameter of 4.5 nun attains an ellip-

The The electrode is prepared from a special

In order t o establish values of threshold stimuli, electrical stimulation was carried

For this an oxygenated Tyrode's solution was used at 37OC, pH 7.4, with a pOz of Using monopolar endocardial elec- The speed of perfusion was 20 mllmin.

stimulation from an electrostimulator type ESL-2, we determined threshold voltage U,

The study of threshold values of voltage and current on isolated small strips ofmyocar-

b

For example, with an impulse length of

86

..

d

L 1

iei

F i g . 2 . a ) s p l i t and b ) s i c k l e - shaped e l e c t r o d e s .

F ig . 3 . Threshold values o f v o l t a g e ( a ) , current ( b ) , and charge i(c) f o r endocardial e l e c t r o d e s with a s t i m u l a t i n g impulse o f var ious lengths . On t h e a b s c i s s a i s the length o f t h e s t i m u l a t i n g impulse ( i n msec). 1 ) Hemispherical e l e c t r o d e , 2) c y l i n d r i c a l e l e c t r o d e , 3 )polyhedra l e l e c t r o d e , 4 ) s ickle-shaped e l e c t r o d e . The c o n t a c t s u r f a c e area o f t h e s ickle-shaped e l e c t r o d e i s 10.4 mmz and t h a t of t h e remaining e l e c t r o d e s i s 24 mmz.

0 . 2 5 msec t h e threshold charge f o r a hemispherical e l e c t r o d e was equal t o 0 . 6 2 f 1 5 vC, and f o r a polyhedral e l e c t r o d e with t h e same impulse length t h e threshold charge was 0 .31 * 0 . 0 4 u C. Hemispherical and c y l i n d r i c a l e l e c t r o d e s with a contac t - sur face area from 11 to 20 proved l e s s e f f e c t i v e than s p l i t , s i ck le -shaped, and hook-shaped e l e c t r o d e s i n the c a s e of such a contac t - sur face a r e a and an impulse length o f 0 .25 msec.

For wider c l i n i c a l a p p l i c a t i o n we chose the s ickle-shaped e l e c t r o d e , which possesses a s e r i e s o f advantages: r e l i a b l e f i x a t i o n i n the endocardium, a small contac t - sur face a r e a , and minimal magnitudes o f s t imulus threshold. In electrical energy requirements t h e s i c k l e - shaped e l e c t r o d e i s l i k e t h e polyhedral one.

The method of i n s e r t i n g t h e s ickle-shaped e l e c t r o d e i s f a i r l y simple. The e l e c t r o d e i s introduced i n t o t h e lumen of t h e guiding c a t h e t e r (2-3 m s h o r t o f approaching i t s end). The i n i t i a l form of t h e guiding c a t h e t e r depends on t h e p l a c e of e l e c t r o d e i n s e r t i o n - e i t h e r the r i g h t atrium o r the r i g h t v e n t r i c l e . t u r n s the f r e e endof t h e e l e c t r o d e l o c a t e d i n theguiding c a t h e t e r four t o f i v e revolut ions ( u n t i l the c o n t a c t end wi th t h e s ickle-shaped elements begin t o move). with t h e e l e c t r o d e i s introduced i n t o t h e heart through t h e e x t e r n a l o r i n t e r n a l j u g u l a r v e i n according t o a g e n e r a l l y accepted method. Under x-ray c o n t r o l t h e opt imal p o s i t i o n o f the end o f t h e e l e c t r o d e i s e s t a b l i s h e d a f t e r w h i c h i t i s pushed out of t h e guiding c a t h e t e r and 1s turned 180”. Being convinced of i t s r e l i a b l e f i x a t i o n , one removes the guiding c a t h e t e r . I f the p o s i t i o n o f t h e e l e c t r o d e i s u n s a t i s f a c t o r y , i t i s necessary t o turn it four to f i v e revolut ions counterc lockwise . to t h e method descr ibed above without removing t h e e l e c t r o d e from t h e h e a r t .

The i n i t i a l threshold magnitudes o f v o l t a g e and current f o r t h e s ickle-shaped e l e c t r o d e average o f 0 . 5 V and 0 .42 mA.

I n our c l i n i c t h e s ickle-shaped e l e c t r o d e was used i n 6 3 c a s e s ( 3 5 e l e c t r o d e s were i n - ser ted i n the a t r i a l and 2 8 were i n s e r t e d i n t h e v e n t r i u c l a r p o s i t i o n ) .

two y e a r s no c a s e s o f d i s l o c a t i o n were observed.

In accordance with t h e d a t a of I r n i k h and with our r e s u l t s f o r e l e c t r o d e s w i t h a small

As regards the

P r i o r t o i t s in t roduct ion i n t o t h e lumen o f the ve inone

L a t e r , t h e guiding c a t h e t e r

A repeated f i x a t i o n of t h e e l e c t r o d e i s accomplished according

In t h e course o f the

‘OntaCt-surface a r e a , t h e dependence o f threshold values of vo l tage and current on the impulse length i s less marked t h a n for e l e c t r o d e s w i t h a l a r g e contac t - sur face area .

,

87

influence of electrode geometrical form on energy parameters, investigations have shown that current density on the electrode surface is highest in those places where the bending of the electrode surface is most highly marked 116,171.

We obtained low energy threshold values when investigating the sickle-shaped electrode. It is necessary to accumulate data about the changes of electrical parameters during lengthy use of electrodes when connective tissue covers the contact part.

At the present time mass production of the sickle-shaped electrode has been readied and the possibility of its wider use is being realized particularly for atrial stimulation. Thanks to the reliability of initial fixation of the sickle-shaped electrode, patients from the first day after the operation do not need bed rest, and can avoid repeated operations related to dislocation.

.

f Both these facts prove economically beneficial.

LITERATURE CITED

1.

2.

3.

4. 5. 6. 7.

8.

9.

10.

11. 12.

13.

14.

15.

16. 17.

18.

88

L. Bette, P. Doenecke, and G. Rettig, et al., in: Advances in Pacemaker Technology, M. Schaldach and S . Furman, eds., New York (1975), pp. 75-90. P. Kalmar, K. von Bally, N. Bleesr. et al., in: Advances in Pacemaker Technology, M. Schaldach and S. Furman, eds., New York (1975), pp. 153-174. M. Bilitch, Advances in Pacemaker Technology, M. Schaldach and S. Furman, eds., New York (1975), pp. 91-97. U. Wende and M. Schaldach, Dtsch. Med. Wschr., 9, 2026-2031 (1970). V. Parsonnet, in: Cardiac Pacing , H. J. T. Thalen Assen, ed., (19731, pp. 41-48. M. Schaldach and O. Franke, Acta Medicotech., 12, 2-9 (1969). W. Irnich, in: Advances in Pacemaker Technology, M. Schaldach and S. Furman, eds., New York (1975), PP. 241-251. .. K. A. Rosenkranz, in: Advances in Pacemaker Technology, M. Schaldach and S. Furman, eds., New York (1975), pp. 503-529. K. Braun and G. Schmitt, in: Cardiac Pacing, H. J. T. Thalen Assen, ed., (1973). pp. 279-281. W. Irnich, Elektrotherapie des Herzens: Physiologische und Biotechnische Aspekte, Berlin (1976). V. N. Trubkin and S. S. Grigorov, Inventor's Certificate 476877 (USSR). G . C. Timmis, S. Gordon, and J. HeLland, in: Fifth International Symposium on Cardiac Pacing. T. Togawa, K. Suma, Y. Fujimori, et al., in: Fifth International Symposium on Cardiac Pacing. H. J. Bisping and M. Rupp, in: Fifth International Symposium on Cardiac Pacing. Abstracts of Free Conunications, Tokyo (1976), p. 17. R. Harper, G. Sloman, G. Mond, et al., in: Cardiac Pacing, Y. Watanabe, ed., Amsterdam (1977), pp. 548-553. S. Furman, P. Hurzeler, and B. Parker, J. Surg, Res., 2, 149-154 (1975). H. T. Thalen, in: Pacemaker Colloquium. Proceedings, J. Norman and A. Rickards, eds., Arnhem (1975), pp. 39-48. V. P. Sol'ts, V. I. Sharikov, V. I. Korolev, et al., Inventor's Certificate 521349 (USSR).

Abstracts of Free Cnmunicaitions, Tokyo (1976), pp. 14-15.

Abstracts of Free Comunications, Tokyo (1976), p. 15.

, .. Polarisation impedance of pacemaker electrodes:

' . in vitro studies simuPatínig practical operation . . ..

.A.

. . . H. Fischler' H. P. Schwan . . : : j Wpannnnt of Bwn.y.ntwring. unt~eoi iy 01 ~eniisvivmia. ~hiweiphhia. ~ennrvlraii~a 19m:u.s.a ' ~. ~

." . . . . .. Abstract-The elecrricalproperrier of pacemaker elecrrodes were siudied in vitfo under condmons prevailing

in pracricalpaiernaker operalmn. Emp:iad was m d tin a ciear d,strncrion between lhe changing modes ofrhe pacemaker acrwn. Durmg setsing, the elecirode can be reoreSenled b y an a.c. sertes pdarisarion resistance and capaciiance, generally accepted for biological elecrrodes obeying lúiearltvrules. Qurmgsrimularion. lhe eleclrode "Perales in rhe non-linearregion. A nearly consranr. vonage. short rectangularpulse wphedd,.ectly ro rhe electrode-hearrsyrrem. causesine eiecrrode vollage and curren,t lo respond as a l w w r n r exponenr,aI. characterisedapprarl-nsie.y bv ¿I smgie h e constanl. This response allows m n d e h g of r+e d s. equiialenr circuir of :he e,rc:iode. ir) the form of n polaensalrivt capacilmce with a sinaii restslarce in series. shunred by B para/W res;srance. Formulae were derivrdfor calculation olfhese elementi. The response afthe 6leCtrode-h?3rt sys~cm roasinglesrirnulus wasrestedasa function ofrheernplitude anudurarion ofrhc app!;edpti!se. Also. rhe effecr ofrepeririv? srirnulaliom was checkedai a normal pacing rare. A nearly consrani. voltage pacing Suurce, as compared w,lh 8 conslanl-currenl one. appears 10 .$e advantageous for presewafion of the l ongwry of rhe electrods.

. . .: ,. 1; . : . 1 ::. -.

" , ~~ . .

.. .?.. ..'. 5 < 1 .

1

i- ! \

~ .'i .. " 4 < -

Keywords-A. C. p0l?risarioi? impedance. Cardiac pacing. Q. C. 'polarisaflon impedance. 2ecrrode ,

? i . . polmisarion. Paceniaker electrodes I . .

I Introduction

(controlled) pacing applications. fulfil 3 dual function 0íalterna:ively sensing the intracardmc heart activity and stimulation of the cardiac muscie. Each ni these tasks is being performed under conipletel) different operating conditions, which affect thc polarisation impdance of the electrodes to an extreme e~.teni. One has to be aware of these qualities while analysing the períormance of the heari-pacemaker interkicc. to evaluate correctly the contribution of the electrode to ihe transfer characteristic oí the interface.

On the one hand, the sensed heart potentials (R-waves) present low amplitude. of the order of a íew to IOmV, a.c. sipnais (CHARTERJEE cr al.. 1968; GoRDoNc!~~~ . , 1968; P A R K E R C . ~ ~ 1969: F L R M A K C I al.. 1977). with the maiii frcquenc) content between 10-40Hz ( M Y E R S et d. i9781 and tils upper cut-oK limit of IOOHz (LAMP.\UICS and PKLER. t977: ~ ~ Y E R S e: ul.. 1978). On the other hand. the pacing stimuli are delivcred ai minimuin intermis of 833 ms

THE PACEMAKER electrodes used in demand

.. . . , The present study aims at modelling the electrical in

r i m bchaviour of conventional pacemaker elecirudes in simulated practical operating conditions. and i t working out methods for e\aluation oiihe elemer,ts oí the equiuient electrode polarisation impedance. Thi. sensins di;iractcristics =?re in\cbtigaied bx using Iii$li$ ;uinple\ bridge in>irumentotion. T u ,:mulate pacing conditions. a time-dorriain procedure \<as elaborated. The experimental technique and the impedance formulae. derived in this stud!. enable a realistic estimation ofthe elecrrcde's part in any pacing system, íora pdrticuiar pacemaker-slectro& set-up. ai a variety of operative conditions. A phenomenological approach has bccn adopted to

assess the influence of the st~mulation partimeters on theelectrodebehaviour at pacing. \iithoutgoir.- intoa correiatire self-search of the electrochemxi! proccsse, eoverning this txhaviour. Honcver. our tindiqs ~ e r c discused in connection with other stiidicr In the field.

on average. in the form of narrou ii2.5 I..: ?.Oms, rectangular pii!ser of 4- 6 V (or X- I ? m.4 I. at current densities of up tl, ~ o o ~ A ~ ~ ~ 2 electrodes,, * A l preseronr: Dcpammanr of Membrane Research. The Wetimann Imtaure of Socnce. Rehovot lsrael

Fitsf received 22nd May and ,n fmal form 7th November f980.

0140-0118/811050579+10 191.50/0

2 Materials and %lethods Tuo types of commercial endocardial unipolar

electndes were examined:

( u ) oí - 75ohms lead resistance. uith 3 platinum-.

(b ) of - IOOohms lead resistance. with 3n Elgil03 flat

- iridium (Pt . - ir) flat tip oí 11 mm?:

O IFMBE: 1981 tip oí 10mm'. ,

Medical li Biological Engineering li Computing . .

679 September 1981

-? .4

! i

: I

... i

' 3 * a

5

The electrode 1issi:e iiitcrl,ic:e arid t i le ti,*iie resist:inc were Gniu1:itcd hy ijnmcr\in; ;ne electrudc into ii fresh OY,, NnCI (ph>s¡ol< with the :x(iis perpeiidicui:tr I chloride TAg,A$'Il rclcrcnce elccircide 2 i n i apiiri. The reícrcnce clectrnrlc wits mide of 1: foil of 0.00h3iii.. w i t h 3 Iot.iI iictivc h u r l

ClilorideiI at Z m A c n - ' to a charge of '300mC c u - 2 . Its polarisation impedance, measured ( w i t h a Wayiie-Kerr UN2 autohalaice transforiner ratio arm hridgc) as ii function of hequeni). at ii currcnt dcn5itj D I Xlii\ciii ~' , (ueii in the linear region). shiiwed a series rcsistiince oí O.2R at 2WHr. dropping to - 0-01 R i i t IOkHz. and a capacitance oí IíKx)pI and 75OpF. respectiielg. Thus. lbs impedancc compmcnts of the relerence electrode are 500 to loo0 times loser thari tiiu~e of the examined pacing Ieids Iprcsetited in the íullouin~). and can he neglected in the nieasurenienis n i the pacemaker electrodes.

The actual 'tissue' (salinc solufiori) rcsi~tai~ce of the measurings)'stem depends on i h r i:rtiie wrl'xce area uf

. the electrode examined. but not on itr iiiateri:iI (POLLAK, 197-1i.Itcanbsappro~imatcdti~ihaiofritip with an equivaleiii spherical Chape of rxlius r. hy

I R, = 1, . -- 4nr

wherep is the-esistiiity oítheslectrolyte. Considering the saline lo he a homogeneous medium of p = 75ohriwciii . R,hecomes - 65ohtniforiiothrhe PI-Ir and EIgili>y rlectrudes iired here. Hcweber. in iii rico electrode implantations. ihc he: i t tisrue is nonhomogcnaxs, presentins ii tiiixturc of heart muscle oí 6, - 1000ohms.cin and of blood of - iWohms'cm (SCIILVSN and K f r . lYi:l. uhich yields a ;compound resistancc hipher than that of pure saline. In pacing studies. 350 to %I) ohnir are ;enirall) accepted for the total electrode~~hetirt loid. To compensate fur the diíierence between t t e iii i-iiii and the iri rirm tissue resistance% an external X i h h m resistor was connected in serics w i t h the: elecrrode.

The measurements of the electrode po1;irisatioii impedance at sensing were iindertak.cn in the lrequency dnnioin, by usinp a Wa)ni:~~Kerr B U ? autobalance transformer ratio iirm bridge. I.ow amplitude a.c. s i g s l s inre applied to I h r clectrode system (?OmV pe;ik-to-peah, maximum current density oí - 0 4 m A cm ~'1:xtiich f i t the conditions o! intracardiac hensing (see introductory ri:mai ir). The instrument provides an accuriiq uf +0.5';,,, and an excellent resolotinn kind reproducibility üriiing the hridge from i n ex!ernal generator (e.p. G.K. I31 I ).and using a 1iine:ible detector ?or frequency discrimination 1e.g. G.R. 1232-Al. the rnensiiring ran:!c i s covered from 2M) to IIXXXI Hz. txtrapolaticin -:is iipplied to the lower frequencies. In il neuer hridga: model. i t i s possibletogodownto 50tlrwliichisqiiiiecluietotlic

intrinric yxcirum oíthe w x d K - u a \ c ~ i I $ \ t i , \ i l i !

ouicomc. :hc \i:ics K :ind <' corny, me;iured clectrodc .cy+xn :ire p i ~ v idcY thc serie, x c . p<iI;iriiaiion clcmeiits R,. :inJ ( ' ..: :! .. clectrodi: x l w c ihc leii:.i and i i ~ e re>i>tu subtracted l v i i 1 the inessurin? íewlt-.. Thr :issw rcli\!ancc I> equal to il cncd approyi thai. uf the e1::ctrodc ,)stem measured IS(.ii\\ *s. l % . ~ J .

i h c meaiurcmenis oí the electrode pulJriwi,,:, iir.pe,loiiic .it paii i ig y.crc undertiikci? i:, ti:; :.,aC. duniaiii.. 1,) appljii ig a ringle. cun.tani-ii,,iagc*. rectanp1::r pulx to the electrode s!steni. as \ h m n L , ,

Fig. 1 (thc electrode i s dread) presented h! I\\

equivalent circuit derib~ed from i r i r ihcr condcra:iiu:Al. A S-44 Grass stimulator u iih .in SI(:: stimulus isuliition unit of E, emf . acti\.~!c\ inc electrode \!>:cm through R, 1220Rl simi!.iiiiii. rl:c output resi,tacce o¡ i normal piicem;iL:r. R , prcscniinf t!ie elccrrode-le3d resistiince. 2r.d R,? (XNOI compensating for the 'rissue' resistan,:>c:p: i S W Telitroiiix. with 5448 amplifieri. and phcios: with a Polaruid camera iFig. ?I: ( '11 the elei potential I,. including the voltage drop on R,. R: .mi R., and (hl the simultaneous electrode ci!rreni I ,

presented by the ioltagedropacross R,. Using pruhc, withan input of 10\Inand II-5pF.enaurssne~li~ihlr. shunting oí the electrode system. The espenmenti were performed by first recording the r, m d i. baselines íO?,andOi,.respecti\.el?Iand inct;yul..-iai open s~itcl i S,J then. dosing S3*. the !,. and :, :iw displayd In each cabe. the respnse &\as z h d k e d ¡or 4

single pacing pulse. except stated otherii;.e. ;8!tu allowing the elcctrode to rest for at Ie-st 'iliiiin iiiicr the preceding stimulus. From our e s ~ ~ r i c : : ~ ~ . . ih ih

..

680 Medical & Biological Engineering Pi Computing September 1981

limn2 p i - i r ICnirn2 Elgiloy

Ea-2 OV-!

Using thc samcnieaiuriiig arrangement of Fig. 1. tile eNect of rcpctiiiuc siimtilations on the rlcctrode characteristics was investigated. The response to repetitive stimuli was recorded on 1:he same photographic plate. by !raving the camera's lid open for the stimulation period. For comparison, thr electrode responses io

stimulation by constant-curren: pulses were also studied. excliaiigin-. the signal wurce of Fig. ! for an $44 Crrass stiniulatoÍ i i i th a PSl l :6 stirnuilk isol:il ion

further applied to the electrode system. pruiidiiig h

negligible inaccuracy.

3 Results The resul1sofa.c. polarisation nieasurenient «I Pt-Ir

and Elgiloy electrodes are shown in Fig. i. The Kr and C , series elements are presented a, a hincrion of

creyueiic). as are also tie reactance X, = ~--: and rhc

absolute iinpcdancr lZ,J = ~ RD T X; , The o anglr, concems ~lir pliiise 'hiit bet~reer. the R.. :?id !he

1

?>< ,,

resultiint vector Z,. Fig. 2 denionstrates the r,. and ie responsrs of Pi-Ir

and Elgiloy electrodes IO stimulation b) cim*taiit- voltage pulses of E, = 2 V and duration r,. = 4 nis. Both rc .and 'i, relax exponentia!!! with an approximately single time constant. epproadiing a steady constant lciel a: the end o: the pulse. I t is worthy of note that the steady ce does not reach f!ir E, level, and that the i, áecrcases to a conitan: but not zero now. Also. the initial currents 1,101 for Pt-Ir 2nd Elgiloy are diííerciit, althdtqh ihr tests were pir'imned under practisail) identical conditionj.

Fig. 4conip;iics :he I,, ctirbcs for u r j m g te ,in<! r,. li can be seen that the time constant 7 < , o! the electrode response w r i e h inverse¡) \villi E, =: P6ms lor 1.5V: - 08ms for 3.01': and - 0-4ms for h V ) For higher pulses and or of longer durations. the r. shape becomes distortcd. There appears 3 second exponential swing with a time constant o1 v hich in turn approaches a steady constant Ic\cl. The íii is laryrr than 7,:: it also i,aries inierc i ) with E,

A family ofthc I,. ciirtes. as a function of E,; \ar)ins in :.teps oí 0-25 Y. is depicted in Fis. 5. .\ 2r:idual n;irrouing oí tie cur\c-spdcing, and,cr dist6rtioils.

$00 ,000 loo00 Frlpu.ni".HI

Fig, 3 A.C pr,!iii-i.soric,~,~horurrrri.~rirr~i/Pi-lruii~lElyi!u~ I 7 r i 4ms 'Or = 3-0v: -. Zms lor 6v'.

i > L 1 ~ ~ ,,,,, kCr , , ,P<.IrV~~ ,,,, c,b ,,,, Ll i<, , , cq.jre ,!,, ~ .,,<.y. ~ < ~ , ~ ~ ~ ~ d 1,) ,I,<, i;,,p,,I. r e q ~ , l ~ t , ,,,, t,~i,q~~I,.s ,:, he,l.,i,tr, eimdirioii.>

Medical & Biological Engineering & Computing Septembsr 1981 581

!+ i

B

can be distinguished w i t h E, riqe and . . wi ih Fig. 7 presents a family of thc r ' , curves. diw 10 prolongation <if ihc stiinulur. i l q u ~ l spdcing !s cor.snnt-corrent 1, pticing. as aiiinctiuii ol1,chaiisiny preserved up to about E, = 0-5 1'(c,, 2 O 1 V) and in steps of 0.5 and I4mA. Equal curie apdciiig is

preserved up to I, = 1.OmA (I , z 0 4 V ) :ind 1 i

t, = 2am. . .

E9'30V

EP'60V

Fig. 60 shows consecutive dispkiys o f the u,,, resulting from repetitive 75 h.p.ni. >tinulatiocs hy constani-voltage pulses throughout a 15s period. taken on the Siime photwraph. For longer duration and higher strength pulses 1c.g.. ,i arid 16mt. at 3 and 6V). there i s a recogiiisabledrilt oftbc I , . , fo~etlier uith a change (second exponeiitiall in their shapc. The response stabilises w i i h tinic fsee Fig. 6h. after 1 minute of pJcing).

r," = 0 4 ms. With higher I,, and longer l p . the spaciop narrow gradually and or distoriiens begin to appear.

The ellect o1 repetiiive 75b.p.m. stimulation by constant-curreni I,. pulses on the I.., potentinis is demonstrated in Fig . 8. A drift o1 the I.,, is alread! recognisihle at low 1,s and short rps 12 mA. I.6msi: i t rises considerably lor higher currents and durations. Also, changes in shaix of the rr hecome much pronounced at longer. higher magnitude pulses. üc

compared with those during repetitive constant- voltage stimulations (see F i g . 61. The second . exponential component of the i; appears earlier with each consecutive pulse. and the tiine-consrant of thc exponential hortens.

4 Modelling clrctrodr-tissue interrace at ihr pacing operation mode

Presenting a hiological electrode by a series of R,,--C,, equivdlent polarisation impedances IFRic-xi. 1932: SCHWAN, IY63: S C H W A N . 1968: GEDDíC. 19731 proved to he of wide utility in studyin: electrupliysiolo~ical phenomena of an B.C. naturc. including the sensing 01 the heari potentials. In this

582 Medical & Biological Engineering E Computing September 1981

i

m ~ t ni;iti.ri:!i< 1,:- %!r ,,thcruix iit i~!~.:i!iciiI ton

I,:,, et p:~ri i i x coiitrol!in!! ihr : , in; . , ~ m i i i ~ ~ mmincc n,,, dcirrmirics thc i 1 o R - m ~ - , t ~ l d - > t : i i c ci~irrcnt.

By mmlysiiis the shape 31 thc exponenti:il rcsponic or i:ii s l ~ : i ~ d c t<: ;I puciiig pulse IF::. 2). i t ciin be seen th.it i! cxhihiii to a fiist approrim;ttion :i rel:ixation

ingle tit7:cconsta:it. Inured. this IS thc (lowe:lE,,sandshort ii\ l a f cw msI.as With vxying E,. the time conatant

changes inversely. For higher and longer ¡,,s the :,tc;id> clcctrodi. potentid sv.:i!gs a 'aLcuciu!ation' p-nod. exhibiting a second exponentini r;x. uliich seems to indicate the formalion of a ~upplemcntar~ pnlurisation capxitancc. To account h r thesi .:Tects. thc polarisation componnh in Fig. I were designated a:$ lunctioiis of t i c si!rnu!us strcngt!? E, (it niay be substituted by the current density j,r and duration I,. For practical pacing conditions Ispecific E</. t , shorter than 2 ms). the polarisation elements are constant and rndeyendent o1 time. and :he elec:mde equi\aient lends itsell readily to circuli anai?sis.

I t msy be argued thiit the exponential chxxtcrisiis

' k(eeirode.Thcy m y ¡cad tocoriiusing&lts %!?en the

) . i?.s&w,qo.mcdel araiioble w:hic!, u~>uld :wl:mint lor i :'b6ih 'the lincar and noii.:iri~z.~r k:x~viou~ of the ..,~cksgrodesin thcircquency ;ind !iniedi'.niiin. We have n%%iihgled~oui. thrreiore. the pacing cabe its a typical non- Se hktirspplication in ~ i e w olthr high current densities c a ~ s s i q 1' rlirough the electrode and. somewhat :i.l+beliicf&ntly. l i n i i t d ourselics io the Iinipier qu iw ie i i i arrcirsuit. which simulates airnost exacti] :he tiectrode

Accepting the equivalent network 01 Fig. I as valid dor electrode operation during paciilg. rnethcdr of lumpxl circuit analysis were applied to the me:isurirq system. to formulate mathematically ttc ciec!rode response to stimulation by recttingular pulses.

E~ Designating the series equivalent rt:sistance vi the pacing circuit

i 3 p:[inwritj wnditior! isnot ililislied.Tlieivqp 1 I ;, .,,..

! I Y-brtnaciour during pacing

j 1. *

n, = n,+R,+iz+n, . . . . . (2) according to Kirchhoffs loop lau

E, = n ~ i c + ~ , p ( i ~ - i D ) . .

Applying Thevenin's theorem : configuration - -. . .

. .

to the

uherrr < . l I . . , "i ~. . . .

. interface . .

Introducing cqn. Y into eqn. S ri\c.s

The eisctrudc current feci¡ is pruportiunal IO [he potential drop 3cross the K.. Practi;;ili> honeier. when the c!sctrodr is implanted within the bod). it Is

whcrc: .... ..- <: - '

, .. .~ easiei to monitor the rJ!L potential ai the proximd end ofthe dectrode. ni:huut niaking circuit dtcrations \

,6J

+ i ; h I , ' , i ' +R,,$,)' cp,, . i . . . R'. K,,. 7 *',',....-

! . :' (&,+.R,, in the pacing path. This ma) br expressed b! . .

is elfective time constant oí the pacing circuit. WI = fiq-i,.w.ng . . . . . (121 r ~ . . . . %.

~" . - < ~ .,. .~

1 Medical k Biological Engineeriw ík Computing September 1981 ! 684 .-

pacemaker It ISCHL~~K. igíg!. .. . . . . I ~.

i' ..,, - , c, = .~ . . . . . . . ' ¡ 161 Coninnrinc Pt-Ir and Eleilo~ mater13Is ¡or stnsiny

1181

when t,, is taken on the exponential part of the c6.1fI dkpkd y:

R,,,=<.,.R,-R, . . . . . . 1191

(20)

Knowing the parameters of the measuring system: E, R and R",. measuring ihc R, i R , from the d.c. im&:tnce at IOkHz (see remark3 in Section 2 abovel. andme~suringih-i-,(01.i- , .(xland i,,lifljfrc~mtt!:l,itl display of the teitcd electrode -thc components of the pacemaker electrode po1:irisation irnped:iiice citii he calculated froiii eqns. 19. ?O and 21. For the best resolution. i t is suggested to choose at about 1,3 to 112 01 the expoiicntial wing inicrwi. The resistance components can be calciil3icd with i n accuracy of f IO>" (piilse generator's ;ind oscilloseope.5 5t;ihiIitj. observation error). The c:ip;ii:it:incc IS ;in ai)l)roiimiiti. value (results from presenting ihc electrode response

into use in the k is t years For sabing enerp! c\ptildiiure of the pxemukrrs. An escessiw aitmuation o¡ the heart signals rrulting from a higher p4.1ris1tion impedance negatiiei) a k t s the rsnsinc process

With reference to pacing. ilic rsliabilit? and versatilit) of the proposed d.c. electrode polarisation model IFi;. I I cait he jiidgcd b) i t ? ~ & t p ~ a h ~ l ~ t ! 10 represent eiecirrdcs oi d3ertiii >h&w,. iiítij ami materials. üt spLTifx operation points. Indeed. the inclusion ofihe R?:, in ih~ccapaciti\erquii~lsiii brüiieh ensures not oni) a faithful reprodwtion a? the form j¡ the exponential ciecirode response. but also d gcnuins discrimina!ion het,.\sefi T ~ I I the coniti!ueni clements taking pari in hh:iping this rsspo;is~. The .?:,r ii absolutcl) necewr) in the case of Elgilo, ?.:¡! is of the order 0 1 t h ~ K,. R , and R, resi5tancei. \\ iiich rnaker i t a deterniiiiaiii ¡actor in setting the initial current I~IVI. i n thec;ise:cfPt~ Ir.R,.,.is~er)smail~~ifthrorderofsin~le ohnirl. and a simple parallel R-C circuit ii:i$lii rer\e as ii sood :?pproximarion for the electrode" cuiii,. aleni.

re of dependahili!! o[ thc cicc:rode pacing model iFig. 1 i. is the d c ~ r e c tu uhich the conktiruen! cisments of t model reflect !he i-.kilin of electro-cireniical proce taking p l xe .I: the electrode-tisiir interface. There is :f b:iiic ;igresmenf aniong ~pecialists in the field (es. GK\H\\IL 195:: Dyvo\t). iY76l. thnf in the c ~ s e 01 met:ii electrodes. the electric chxge can be carried throuFh the interface

( FtSCIi LEX. 1 9 3 I.

Medical & Biological Engineering & Computing September 1961 585

---T

t, .. ' A,,, . I !

fiikii I ig. 9. 'ike 'K>;, .o1 t.l,ciloy a> a lunction ( d E,, b$;ivei sinriliirly io ih;iI 1'1 Ir. hui i$ considcrahlg

,;\..A V i Tlic ( ' ,; i ,oíl~lgiloy is loucr th:in ihxt of Pi-Ir, a,+J drops Curter in the cpcraiiori r;in-e. 'The K,,,,i*

?&).ohms lor Etgilh). l h c higher d.c. pdarisdtion irnyic<l;iiice oí,F.Igik)j, oixcrvcd a lm by C;RL:ATHKH

wi!rm t Fig. 61. Thib mi> he expieincd h! ihc f ~ i c t t i i . i r : 111 cnnsfiinbiolt;i~c ~t i tnul~t ion. iiitcr l h c p.ii,ii .i &:tier tliri,iighnut !ni prxtic::l c7pcriitioii iwi;gc ce i i~c~ . the pr1l:tris:ition c : tp : ic~t , r~~c di,

/ . ihroush the piiciiiy circuit duritis ik niter-paLc : iiitcrval. This a l l o~h lor thr. reverw 0 1 th: cu~i:nt in j .~ p c t m i i y ~ C M for pi ~ r . nut aniwnts to a b u t : t~iccicc:rode-tisiue inicrfiicc ( F ~ F . 21. iir<i:igi:, return

10 cquilihriutn. The relati!d> small ci!miit dtiinng the ! loti: ia\t;ngtnter-pncc pcriodcompenutt\ t i > r l t le:i?t a

(IYúx)iind J , A R O ~ L ' I u/. (iYshYi. means . p.trtixl cxtcnl for the eficct eicricd during i h i \nmt p;icin$ energy to the ti\rue. and strong :,timuIus. In Lontrast. in con*tan-currcnt lctynnrgin 01 pJcing' íFisciii.tu. stiniuiaison the current prescne, ~ i*> orr$ind . .

'.. iY7Yl. rec tmghr form, liillina at ihe mu to IC;'<>. ritthout L . i'erlain conchusion< can he dr&,wn from thc reversil. .Thure is virtually no-compensation phase:

I& each consecutive pulse adds to thc driít uhich remaiiied lrom the preceding stimulus. The driit at lower currents (Fig. ~lindicatesanincrea,e in the R,,

. ! .chan&cs nt tke:bkCtrode .tissue interhce. The cliarge constant only slightly. At hiphcr current.i and i duiations. thc pseudocapacitance seems to domin;?is: 1 with rdch pacing pulse. the capaciriw chkirge herins .v earlier. The delorméd snd driftinp electrods poisnri:ils

may he a symptom 01 accelerated dcciroc!:cmicrl * intdrpreted as lk pseudoc;ip;icitance postulated by reactions.

: 8 DVMOND (1976). itss<u.iatcd uith gas c\oluiion Comparison hetueen the a\ailahle supplies for

I . pactmakers points to the advantngs of ths nc.ii" constant-voltagc generator. Its intrinsic ierirure of

' -! rwersinp the current flow during the inter.pacing 1 interval allou.s lor at Least a partial compsnii:ion OS I irom~~con~fant-Furrenl sburci. íF.ig. X I appears eiirlier the eiectrochemicdl changes taking plncs at the

electrode interface during the pacing pulsc. This ma! explaintheobservationOg hlE4Rsand BROU\IIY:I I that increasine the capaciike part oithe tmal eisdrods current minimises electrode damage. One ma! argue that this task is provided hg th.: couplin: ca;xitor which is normally interposed beiueen the p¿csm.iiir'í output and the electrode. There :ire. hosieitr. indications from practice. that the coupling c.ipci!or does not always enwre z reall) passi\e bshd\iour of the eiectrcdss. Several :mons can be sn\i,ag-a. ' 1 1 1 ~ output resistance of the p~,ierna~ergeiieratvr i> <o high thxt the coupling capacitor does not affxt practica¡i> the shape of the electrode current. When the Faradiiic part of the current is relatively large. the inicr-pace resting period may he ton short to allmi fc: a full

I

~: ; *' ; . . t.

i .~ ,

ohicii~tionid'~thcelcctmdc potentials in ri:,ponse to p'cing hy single: Kigli.arnplitudc. long lasting pulses (Isg.i-4). The appearsnce of the second exponriitial .. ; swing pmumahty reflects charge accumuiation and R,{>íFig. 11 uith p~l,e repetition. alleciing ine time

flo.li ili the case oí heart kiting is much higher than in othi;r' hiological irimuiations, so the accumulative dckming cllcct becomes easily discernihle. and its imfl;>ct is quantuiili\*eIy h i g e r . The e k t might be

r lhcdrilt ofelectrode po~tCn1i;ils (Figs. 6 arid X I u hen ihc pacing I>ulse~ccomerepctiti\~e~!. at the hc,ii.l rille. i t is yscritioi to note that-thc drift 111 tiectrodes driven

hm lor a constant-voltage

,at,,g of rcr~~d*hversdloUienrsuefoipacrog lo lhar.nin,mum required lo ow^^ thqlpqCi,ng lhreshold

.... c -a

-. .. -

10000 g .- - o o

5OC'O u % compensation of the charge flow during ;he pacing c pulse. This may he specially truc for demand o .- - : o

0" .-

2

pacemakers during intermittent pacing. U hen the electrodes are lrequentl) driven out oí equilibrium. The non-linear operation of the electrodcs add:. 13

complexity of the problem. causing inequalities in resistance olthe heart-pxeinaker path throughout the

500 5 pacing cycle. Also. paradoxical anodal corrobioii niii! arise lrom the averaging clTect~ O( thc coupiitig capaCltor I ~ R L \ T H A T C I I el d.> 156Y). from F¿r:&ic rectification during a cathodal pulse IGRE\TB \ ~ ~ c ~ I I c,:

d.. 1955: I>!\loui~, 1976) and Srom a gal\iitiic c.iupic creared hy dissiniilx electrode metals (GR t,\Ti%.$.r(H

- o

- o

0 0

Pocemoher-generotor open vuiioqe(v) ,*'. ín, O

i FiK. 9 ~aC.diol~i~r~,tiiin'<.iiiii<ii.r<.i.i,li~ o f P i - I r iiid Elgilo) et '11.. 1969 ).

p<i<.<.inu~w.',<lli.~~~l~,li.r: it.; /i,iwr;oi, u rzr<,riy coiisl'iiii-,.<ilr<it,~~ PLKii'l, I>i'l..C o,rlpii<iiiit.

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546 IEEL TRANSACCTIChS Clbl BIOMEDICAL ENGINEERING, VOL. BME-29, NO. 7, IULY I982

consistent with the equal anisotropy assumption. These parameters were also measured by Roberts ef d i . [ S I , but their results depend on the incorrect interpretatipn of the fosr- electrode formula as applying to an anisotropic bulk monc- domain, and hence must be regarded cautiou$y; the resu1ts.h any event, are substantially different from iClerc’s. Conre- quently, the extent to which the equal anisoOopy assumption is satisfactory for a cardiac muscle preparation is uncertain, based on current limited data.

monodomain, even though anisotropic? Not in general. particular, For tissues with equal anisotropy ratios, unless t F e conductivities normal to the orientation of the four electrodes are equal, the measurement will not evaluate the root mean of bulk conductivities in those two directions. That is, nixording to (46). the correct formula is

Can tissue being examined still be viewed

when an x-oriented four electrode lies on the srrface of a semi- infinite tissue.

Extensive experimental evidence from cardiac üssue prepa- rations used for many diffmnt purposes h y made it certain that an intracellular domain exists in close proximity to, but separate from, an interstitial domain within cardiac muscle. Although the physical siruciure of the muode is complex, it seems likely that the ideaüzed bidomain dodel is a much better approximation for modeling the eleciridal characteristics of the muscle than an idealized monodomaid model that has intracellular and extracellular domains cansidered to be merged. What is important, in the senenlc&, is to recogniee

. ~ that if the bidomain model is a good approxwation, then the existence of two separate (although coup1ed)anisotropic OW-

ducting regions must be taken into account in interpreting four-electrode conductivity measurements. This paper bas

~ shown how such an interpretation of the mtasurements m be achieved for the u s e of equal anisotropy ratios, and has shown that the results are not what would bdobtained from a monodomain model whem the conductivitiespion&!x.y, and z are the intra- and extracellular ones in pawel . Since the derivations break down for the more general ibidomain model that has unequal anisotropy nitias, the c o q c t means of interpretation of four-electrode resistivity measprements, in general, in terms of the six basic conductivitiesbf the bidomain ’ model, remain unknown and, in fact, may not.exist.

ACKNOWLEDGMENT

The suggestions, support, and encouragement of Dr. M. S. Spach, Duke University Medical Center, Durham, NC, are

’ - gratefully acknowledged.

REFERENCES

Ill R. Plonsey, Biwiectric Phenomena. New York: McGraw-HU, 1969, p. 358.

(21 H. P. Schwan and C. D. Ferris, “Four-elcctr e null techniques for impedance measurement with high rea$ution.” Rev. Sei. Insrrurn.,vol. 39, pp. 481-485, 1968.

131 S. Rush, I. A. Abildskov. and R. McFee. “Resistivity of boáy times at low frequenciei,” Cbc. Res.. vol. 12, pp. 40-50, 1963.

I41 L. Gcddes and L. E. Baker, ‘The specitii reaimnee of biological material: A compendium of data for tbe biom(dica1 engineer aid physblogisf,”Med. Biol. Eng.* vol. 5, pp. 271-293, 1967.

[S I S. Rush, “Methods of maniring the ruistivi les of anisotropic conducting media in situ,” J. Res. NBS, vol. i6C, pp. 2i7-2Z2, 1962.

’

,~

. 161 L. Clerc, ”Directionil differences of impulse spread in trabecular muscle from mammalian heart,” J. Phyriol. (London). vol. 255. pp. 335-346.1976.

[ I ] A. L. Muler uid U. S. Markin “Electrical properties of anise tropic nerve-muscle syncytia: 11. Spread of flat front of excitation,”Biofizika. vol. 22, pp. 518-522. 1977.

[ 81 D. E. Roberts, L. T. Hersh. and A. M. Schcr, “Influence of fiber orientation on wavefront voltage, conduction velocity. and time redtivity in the dog,”Circ. Res., vol. 44, pp. 701-712, 1979.

[ e ] O. Schmitt, “Biological infomation processing using ihe concept of the interpenetrating domains,” in Informorion Pmcessing in the Nervous Sysrem, K. N. Leibouic, Ed. New Yort: Springer- Verlag, 1969,pp. 325-331.

[ 101 W. T. Miller and D. B. Cestlowitz. “Simulation rtudies of the elstrocardiwam.” Circ. Rea, vol. 43, pp. 301-315.1978.

[ 111 L. Tung, “A Womain model for dexnbing ischemic myocardial d.c., potentials,” Ph.D. dissertation, Maacachusetts Inst. Technol., Cambridge, 1978.

[ 121 A. Van Oorntom, ‘The intramural resistivity of cardiac t h e , ” Meü. Biol En& Compur.,voI. 17,pp. 337-343,1979.

[ 131 A. L. Hodgkin and W. A. Rushton, “The electrical constants of a crustacean nave fiber,” Roc. Roy. Soc., vol. B133, pp. 444- 479.1946.

[ 141 R. Plonsey and R. E. Collins, Rincipiesand Applicarionr ofElec- rromagneric Fields. New Ywk: McGraw-Hill, 1961, pp. 323-324.

Minimum Energy F‘uWg by Cardiac WamaLns

C. HOFFMANN DE VIGME AND A. FURNESS

Alaflct-In detnnming niitabk cardiac pacemaker w m f m s it is aOwbIe to conudqr I) w m f a n i r which cowme leaat asigy fmn tM p.oaiaker batOw, and 2) wmformr which dbsipah least en- In the eiid*e circuit conktent Hiih effective pacing In geneml, the tam rqukmenta I d to different wwefonn specüicationn in thb paper, a sipple electriul e<luivainit is assumed for the cardiac

cktuit, WJ Eubr’s variational e q u a t h is used to derive voltage and cumnt puke w d o m of delined duntion which d e h r the least m&hicai energy to the c h i t whUe raising the voltage the cii- cuk’s captcitive component to a d á m d level.

INTRODUCTION In a paper entltled, “An optimally energized cardiac pace-

maker,’’ Klafter [ 1 I assumes the electrical model for the all dbcnbed by Myers and Parsannet [21, T h i s comprises a capacity smunted by a resistance. By treating this as the load for a cardiac pacemaker, Klafter determines the cumnt waveform i(t) which 4as to be driven through it to raise the voltage across it from O to V in time d, the waveform having the property that .ft iz df is a miiimum. He describes the waveform % “optimal,” asserting that it is the one which consumes the least energy from the pacemaker battery, while raising the load voltage to the required threshold level Y. In a subsequent paper, Xlafter ef o/. (31 give cums showing pacemaker pulse e n t r a plotted against pulse duration for pulses of various shapes wed to pmduce actual pacing in a live animal, and they indude a corresponding theoretically derived curve based on klefter’s original “optimal” current waveform and assumed equivalent circuit.

The present paper assumes B slightly more realistic equiva- l e i t circuit, and derives waveforms which are optimal in each of the two quite distinct senses:

Nanuiiript received August 11, I98I;revised February 5,1982. This wotk wec supported by thc British Heart Foundation under Grant 817.

The authoIs arc with thc W. E. Dun“ Unit of Cardiology. Univorrity of Keele, Staffordshhiro, Icngland.

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i-'-I

I -J I I 7

Sin= u = O at t = O, and u = Vat f :~ d,

sinh (f/f) sinh (d/T)

u = v

Therefore,

and

V(R + R l ) sinh (r/T) R sinh (d/T)

u1 = u + i l R l =

CVRl cosh (t/T) +- T sinh(d/T) '

.-- 1 1 - Fig I. Equiidi n circu t of pacemaker lo; d.

Making the following substitutions,

x = (t/d), m = (d/T), k = ( R I / R ) , sinha =fi, I ilissipatio- c f least eiiwrgy in the load I consurnpi 211 of least ,,nerg).ifrom the bitteiy.

1 1 ik:r's "opti irI" wavela rm, lrased csn the minimiza1 on of and ' :2 31, is not 11 timal in E ither 3S these senses.

I IIF.IVATION 11 WAVEI:<#RM TWSIPA~ING LEAST EN !<GY We get

cosh u = m, . (

I N THE LOAD .el Fig. 1 re1 resent the eectriwl load presented by th pa =-

I ~Icei'. Thf! vi kige and mrrent Cppüeil to the load ire ', and respectively a i d the vwtage I across the capa:ity is l ' i e cne

i ,iiried to in¡ ia:e pacing. We =quire evaluatitig (8, ( ; ) id ']) : .,:h ,:hat 5; u i l df shall #ie a riinimum, while voltagp r8ri;es !: in O at f .= O :c Vat f =: ,.'.

:Are have i , = I / P + C(dii, if) ar d

' I -.tiiig b f o r d /c f, power 1 is giren by

i ' 8 ,w : r p is an E ir licit funciion o0 u and ;>, and Eiiler's e< iatlon , I rciibing the r;dectoIy ir7ining points (O, O ) and (d, V jn :he , u plane ove \rhich df is stationary (in t1.k D ~ S B . m..ni- . ~ 1 1 1 i s

ap 2 R + R i : i C ( R + 2 . R l ) . u,

-. = - , I + aL8 R2 R

u + 2C2RIÜ. R

V cosh (mx +u)

R s i n h a i n h m sinh m V coshu sinh (mx t - a)

il = and u, =

(O < x ?< 1).

We see that the point (il , u l ) lies on the hyperbola

I ( i I /V)JRs inhus inhmlZ - l(ul/Vcosho)/sinhml' I. 1

whose asymptotes are given by u1 F F i l and

While the value of T i s determined by the parameten of the equivalent circuit. the value of d may be varied at will. We therefore wish to find the value of m = dJT which rninirnizes the energy supplied to the circuit during the interval O to d.

3 ! whose vertices are given by il = t V / R R I smh rn

V' cosh u power p = u1 i, = cosh (mx +u)

R sinh u sinh' m

sinh (mx + a )

V z cosh a 2R sinh a sinh' m

sinh 2(mx +u) - -

Therefore,

energyE= l d p d f = d

V2 T cosh a 4 R sinh u sinh' m

{cosh 2(m + a ) - cosh 2 a ) . - -

Calling the energy of the fuliy charged capacity Eo, Eo = 4 <CY2, and E becomes

Eo { c o s h Z ( m + a ) - cosh2u

2 sinh' m í lhu!;, the ri:qL rid ira.iectc'ry is j$ven by If we substitute n for 2m and b for Z a , the foliowing very

simple expression for EJEo emerges: C(JZ + 2 R l ) . u i - 2 C L R , Ü , 2 ( R + R 1 ) ,.. C ( R + ; R l ) ;-

R = A! R E cosh (n + b) - cosh b ... , - = Eo cosh n - 1

[where n = 2 d / T and b = 2 s i n h - l ( R 1 / R ) ] . ü = T'u,, uhere T' =CR X C { -1, RR 1 R + R . I . - - - I ,

I 'ie solution c this equabon IS

u = A cosh t / T ) + B SIJ h ( t / í ' )

Fig. 2 shows how E/Eo varies with n. We see that E/Eo has no true minimum. it has its least pos-

sible value of e b , however, for n = -, i .e . , for infinite pulse

$48 IEEE TRANSACTIONS ON BIOMEOICAL ENGINEERING, VOL. BME-29, NO. 7, JULY 1962

I b

Fig. 2. Variation of pulse energy with pulse duration.

' I ? i : y ? ..L.u~~dNZ5j , .ci-r Fii. 3. Optimum pulse waveforms (as quoted in the text).

duration. In the case considered by Klafter, R i , = O . Thus, . . T = O , and 4 = b = O , and the current pulse, optimal in this

sense, becomes an infinite impulse, while the optimal voltage < . pulse is an impulse of height V, and E/Eo = I , as expected.

example, suppose C = 0.5 pF, R = 6 kfL, and R i = 800 51. Then T = 1.029 msand k = 0 . 1 3 3 . Tllur,\/k=O.365 and 4 = 0.3575. Let m = 2a = 0.715. Then the pulse duration d = m T = 0 . 7 3 6 m s . Ako,n=Zm= 1 . 4 3 0 , a n d b = 2 4 = 0 . 7 1 5 .

As

Then

E Eo

= 24 cosh 2.145 - cosh 0.715 cosh I .43 - 1

_ - -

(the least possible value o f E/Eo is eb = 2). The optimal current is

i l = V 0.736 I + 0.357S) 6000 X 0.365 X 0.778

= 0 .587V cosh (0.972f + 0.3575) mA

and the optimal voltage is

Y X 1.065 I .I u1 = sinh (0.7 I S -

0.778 0.736

= 1.369Vsinh (0.972t t 0.3575) V

' 'where f is measured in milliseconds and O < f < 0.736. Note that i l at f = O is 0.625 V mA, and at f = 0.736 is

0.958V mA, while uI at f = O is 0.5 Y V, an4 at I = 0.736 is 1.766Y V. Fig. 3 shows ul and i l plotted with, respect to time

,., ,, for Y = 1 V. Figs. 4 and 5 show the influence upon the optimum voltage waveforms for differing values of load parametes. Fig. 4 shows the optimum voltage waveforms for d/T = 0.5 and R , / R = 0.1 and 0.5. Fig. 5 shows the optimum voltale

.., , waveforms for R 1 /R = 0.1 and 0.5 and d /T = 2.

Fig.4. Variation in optimum pulse waveforms due to differing RiIR ratios and a pulse duration d = OST. (Ri = 500 R, R = 1000 and 5000 S i , C= 0.5 pF.)

I 4 .i .A .¿ .1 >"

t - 21

Pi. 5. Variation in optimum pulSS waveforms due to differing Rp/R (R1 = 500 R, R = 1000 and I tios and a pulse duration d = 2T.

5300 si. C = 0.5 pF.1

COMPARISON OF CURRENT WAVEFORMS ARISING FROM KLAFTER'S ANALYSIS AND THE PRESENT ANALYSIS

The waveforms derived by Kkfter are based upon the mini- mization of fi i: dt in a load consisting of R and C in parallel, .whUe those of the present analysis are based upon the mini- mization of s: u l l l df in the load of Fig. 1. Fig. 6 shows the

,wmparative current waveforms for d = CR and: 1 ) R I = 0.1R a n d 2 ) R I =O.SR.

The relevant equations are

( O < x smh I

sinh hx + h cosh hx sinh h present analysis: y =

( O < x < l )

where x= ' / d and h = d w Thus, for R l = O . I R , h-m, and for R I = 0 . 5 R , h = ,.h. F o r R l =w, h = I , and the two equations become identical.

PULSE WAVEFORM FOR LEAST CONSUMPTION OF BATTERY ENERGY

it is not possible to derive the energy supplied by the battery i@ raisins the capacity voltage from O to Y without knowing tiis circuit used for producing the pulse. However, beanng in m a d th;it the battery is (approximately, at least) a source O f mastant voltage ubs the power supplied by the battery is ub

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and not allowing time for the sample and hold t o acquire tho new pulse height

The operation of hold and peak detect signals is illustrated in Fig. 4. generated by the pulse stretcher Da, C3, and R,.

The necessary overlap between these two signals ir;

REFERENCES

[ I ] H. E. Kubitshok, “Counting and sizing micra-organisms with the Coulter counter,.l in Merhods in Cell Biology, 1. R. Norris and D. W. Ribbon& Eds. London, England: Academic, 1969, pp. 593-610.

[2] S. J. Rackham. “A pulse height analyzer for displaying particle size distributions,” M.Sc. th&, Univ. Waikato, Hamilton, New Zea- land, 1977.

Proposed Cardiac hcemaker System Combining Unipolar Stimulation with Bipolar Sensing

PHILIP HURZELER, V. DE CAPRIO, AND S. FURMAN

A&tmct-Reaent cardiac pacemaker deaigns use either uNPoLv or bipolar electrode sysianr Advantages of unipolar electrodes for atMu- Istion are list+ then -menta in favor of bQdar elecboder for seming are cited. A propord ayaiem combine# uNpdar atimulstion with bipohr sensing and may be implemented by adding a differentid- input stage to the rming ampliTLi. .

STIMULATION In unipolar stimulation, while the cathode is in contact with

the myocardium and connected t o the pulse generator through an insulated lead wire, the anode forms part or all of the exterior package o f the implanted pulse generator and, being relatively distant from the myocardium, is the “indifferent” electrode. The significant voltage loss that is characteristic of anodes during stimulation, is minimized by the large anodal surface area. In bipolar stimulation, where the anode is also in the heart and must be kept physically small, voltage stimulation thresholds are greater [ I ] . Further advantages o f unipol;ir stimulation are increased reliability due to absence of a lead wire, and avoidance of anode-to-myocardium contact with conceivable attendant fibrillation hazard [21.

. .

SENSING

For sensing of myocardial depolarization t o achieve non- competitive pacing, bipolar electrodes offer the advantage of improved rejection of electromagnetic and skeletal muscle artifact due t o a more restricted lead field or “antenna” [31. Chatterjee e t al. [41 report greater signal-to-noise ratios for both ventricular and atrial sensing, using their new catheter with bipolar electrodes. Ongoing research at this institution also suggests that the b i p o k s i g n a i is greater than the unipolar signal in amplitude, unless the bipolar axis is perpendicu

Manuscript received February 23, 1976; reviscd December 11, 1978. This work was supported in part by the United States Public Health Service under Grant HL 04666-16. P. Hurzeler is with Cardiac Datacorp. Inc.. Bloomfield. CT 06002. V. De Caprio is with Becton-Mckinson, Inc., Fairfield, NJ 07006. S. Furman is with the Division of Cardiac Surgery, Montefiore Hos.

pital and Medical Center, New York. NY 10467.

lar to the direction of propagation o f the depolarization wave. However, new bipolar electrode geometries such as coaxial or tripod arrangements suggested by Siegel et al. [ 5 1 may be devised t o overcome the directionality problem. A past con- straint on such designs has been a minimum surface area of some I O mm’ for the proximal electrode since it is also the stimulation anode.

THE COMBINATION In the proposed system, one pole, say the tip, of an intra-

cardiac bipolar electrode serves as both the stimulation cathode and as a sensing electrode, as in conventional systems. The other half of the bipole is connected only t o the other input of the differential sensing amplifier, while an indifferent electrode serves as the stimulation anode. In this way the advantages of both systems are retained.

An alternate way t o effect the combination is t o use the isolation afforded by an output transformer in the pulse generator in lieu of a push-pull differential stage in the input amplifier.

As the second half of the bipole is no longer used as an anode, its surface area may be made as small as is convenient, and designs featuring hooks to attach catheter tips to the myc- cardium, such as described by Irnich [ 11, may be more valuable. A central tip, forming one pole, surrounded by a tripod o f hooks forming the other pole, may overcome the directionality problem as well as avoiding dislodgement. This combination should be particularly helpful for atrial sensing.

In conventional designs, the sensing amplifier input impedance is shunted by the OFF output impedance of the stimulator circuit, whereas in the proposed design the differential input impedance is not shunted. This further removes contraints on sensing electrode surface area. Also, the polarization voltage that persists after each stimulus pulse is conducted directly t o a conventional single-ended sensing input, whereas in the proposed design the anodal portion of the polarization voltage, which Irnich [ I ] suggests is the larger portion in bipolar systems, appears as a common-mode input voltage. A further advantage is that a redundancy feature of the bipolar system is retained, to wit-in the event of a single lead wire fracture, the surgeon has the option of changing to a uniuolar confieuration t o maintain pacinp: without implanting - . - . a new electrode.

Finally. the concept need not be confined t o systems which sense and stimulate from the same electrode tip. For instance, bipolar atrial sensing may be combined with unipolar ventricular stimulation.

REFERENCES [1] W. Irnich. “Engineering concepts of pacemaker electrodes.” in

Advances in Pacemaker Technology, M. Schaldach and S. Furman, Eds. New York: Springer-Verlag. 1975.

[2] T. A. Preston, “Pacer induced ventricular tachycardia,” in Modem Cardlac Pncing, S. Furman and D. I. W. Escher, E&. Bowie, MD: Charles Press. 1975.

[3] A. R. Kahn and R. I. Schlentz, “Design and construction methods for protecting implanted cardiac pacemakers from electromagnetic interference,” in Cardiac Pacing, H. J. Thalen, Ed. Assen. The Netherlands: Van Corium, 1973.

[4] K. Chatterjee, H. J. C. Swan, W. Ganz, R. Gray, H. Loebel, I. For- rester. and D. Chunette. “Use of a balloon-tipped notation elee trode catherer for cardiac monitoring,” Amer. J. Cardiol., vol. 36. pp. 56-61. 1975.

IS] L. Siegel, E. B. Mahoney. I. A. Manning, and S. Stewart.“Conduc- tion cardiograph-bundle of His detector.” IEEE 77ans. Bioinrd. Eng., vol. BME-22. pp. 269-274, July 1975.

00i8-9294/79/0700-0440$00.75 O 1979 IEEE

-7 - -

the os-250 (250-w channel) has a higtier a x i a l :L;L$ht intensiGY (approximately 33%) i n corn- parison w i t h the condenaer systeq comprising ai€@hericai lenses. The l ight -opt ics system of the os-150 and OS-250 have a somewhat smlli3r v a i w f o r the in t eg ra l l i g h t f l u x i n cop parison with other comparable i l luminators. spec ia l l y mnufactured, i l lumination modules ciYmprising a KGI-150 and a 48-m re f l ec tor , manufactured i n the USSR, are used.

end face o f the l ightguide cable, i s reconwended for the improvement O f l i ght ingeng ineer int character is t ics o f l i ght -opt ics illumination-m0dule systems, which relies on the improved u t i l i z a t i o n o f the l i g h t spot i n the image plane.

erected a t an angle o f 10-12' t o the o p t i c a l arie i s recommcnded t o e l iminate the dip in t)u centra l por t ion of the curve depLcting the l ight - intens i ty d i s t r ibut ion of the light-opti- system using an i l lumination module.

njis i s because mass-produced, as Opposed

3. m e adaptation o f ana ly t i c lenses wich V .I n r ins ta l l ed i n f ront of the entrance

4 . T i l t i n g the entrance ehd face o f a l l ghtguide cable so that i t s perpendicular is

LITERATORE CITED

1. V. N. Sazontova, Nov. Med, Priborostr. , No. 1. 113 (1972). 2. M. E. Nemirovskii, Nov. Med. Tekh., No. 2. 31 (1976). 3. A. S. Ivantsev and L. N. Semenova, Sve to tkh . , No. 11, 4 (1976). 4. V. B. Veinberg, G. Ya. Konaeva, and D. K. Sattarov, Geliotekhnika, No. 2, 9 (1965).

EFFECT OF WATER VAPOR ON MERUCY+ZINC CELLS IN ELECTRICAL PACEMAKERS

H. Matschiner, K. B. Otte, S. Rudolf, and K. Wiesener

1IDC 615.472:616.12-089.28-77 :621.3.035.2] .014.4

Mercuryz inc c e l l s are onq of the pr inc ipa l energy sources f o r e l e c t r i c a l pacemakers. In 1977, f o r example, over 90% qf a l l the pacenakers i n operation were provided with these c e l l s despite the fac t that theae were mre pdtuerful sources such as rad io isotope batteries and l i th ium c e l l s . according t o a l l indications they w i l l continue t o be used as the energy sources f o r pacemakers.

However, an in t r ins i c disadvantage of marcury-zinc cel ls i s the l im i t ed c l i n i c a l service l i f e (averaging 3-4 years) which does no t correspond t o the rated value. Their opera- t i on was studied using the RMCC-1 ba t t e r i e s mmufactured by the Mallbry Company (USA) and showed that the c l i n i c a l se rv i ce l i f e i s neduaed p r inc ipa l l y because the f lu ids circulatinc i n the organism penetrate in to $he pacemaker, tliereby producing pa ras i t i c leakage current that resu l t s i n a reduction in the cell's capacity 121.

a t h o d s are discussed belqw f o r reducina the ef fect o f the i n f i l t r a t i n g water vapors on the leakage current through the insulat ion o f the e lec trodes , on the self discharge, on the capacity, volume, and mass o f the c e l l s .

The leakage current i s defined as the current passing through the outside insulation o f the c e l l ' s terminal (see Fig. 1).

The o r i g i n o f the causes f o r current leakage were f irst studied i n d e t a i l i n connec- t i on wi th the untimely removal of pacemakers du@ to the deple t ion o f the bat tery . found that the rubber gasket o f the ce l l was oovered wi th an e l e c t r o l y t i c f i l m [31. i l a r f i l m makes i t s appearance during the s torage of c e l l s i n a i r .

. Owing t o the service l i f e , $eliabil ity, and low cost o f these c e l l s ,

It Was A Sip

It i s caused by the

Martin Luther University, Halle-Wittenberg, German Dcmocratic Republic.

TranslaPe$ frmm Mdits inskaya Tekhnika, Vol. 13, No.

People's Enterprise "Ultrashultekhnik." $a l le . German kmcratic Republic. Dresden, German Democratic Republic. 5, PP. 38-42, September-October, 1979.

Technical IhiiversitY,

Or ig ina l a r t i c l e submitted January 23, 1979.

252 0006-3398/79/1305-~~~~$07.50 O 1980 Plenum Publishing Corporation

midation i Jr, form.

Zhe c Wct the ( E

fD l l0WS . 1. I

ruched, tii b e c e l l . bakage o:

2. 1 promotes i h pressure is &e rubber

3. 7 mre made t dirough ti e ptted i n e ilong witt: ib geometu *her. 'Ei i d 1eakaf:e bgaohme L e

In <.r h g e s tt.e Vdroxide, WrimenLs

u controls 5% and t1.e +US conta 'f these re. @re observ 'ere then f Uine. LV, ator, an¿, odium hydn

to 5.11 han down o lbii were

The ra robably i,ea

In or< insuiat:

bur c e l l s 3

3. 2 8

4 Fig . 1. Cross s e c t i o n o f a type RMCC-1 ce l l : (1) Zinc anode; (2) cap o f c e l l ; (3) rubber g a s k e t ; ( 4 ) s e a l i n g r i n g ; (5)

ca thode ; (8) e l e c t r o l y t i c absorber and s e p a r a t o r ; ( 9 ) i n s u l a t i o n ; (10) e x t e r n a l s h e l l ; (11) i n s u l a t i o n h o l d e r ; (12) anode i n s u l a t i o n .

5

0 - i n n e r s h e l l ; ( 6 ) s l e e v e o f adapter ; (7)

7

8 '

9 ' ID I I 12

i n t h e seal o f sodium oxide which, after combining with carbon dioxide from t h e air, forms sodium carbonate .

t ec t t h e c e l l a g a i n s t t h e escape o f e l e c t r o l y t e . follows.

1. When a c e r t a i n i n t e r n a l pressure i s reached, t h e hydrogen should spontaneously emerge through a v a l v e l o c a t e d i n t h e bot ton o f the cel l . However, as a result o f t h e excess pressure o f hydrogen t h e r e i s always a small leakage o f gas which Fa accompanied by t h e escape o f t h e very l i q u i d e l e c t r o l y t e s .

?romotes t h e p e n e t r a t i o n o f water from t h e surrounding medium. ?ressure i s i n c r e a s e d , thereby causing e l e c t r o l y t e t o emerge through t h e s a f e t y v a l v e and the rubber gasket .

I! 3. The i n c r e a s e in t h e anode volume during discharge. Experimental i n v e s t i g a t i o n s !! uere made t o evaluate t h e effect o f i n d i v i d u a l f a c t o r s on t h e amount o f leakage current

1' lotted i n epoxy r e s i n . 1; along wi th t h e e l e c t r o d e b l o c k s and d i v i d e r s . i :he geometr ic p o s i t i o n o f t h e cell's housing, rubber g a s k e t , and cap relative t o one an-

~ sther. 1 and leakage current at a v o l t a g e o f 1.35 V. ' gigaohrmneter using a mCc-1 ce i i as w external v o l t a g e s o u r c e ,

1 , :'ages t h e i n s u l a t i o n resistance or t h a t t h i s is a s s o c i a t e d wi th t h e exudation o f sodium !' -?droxide, s ix cel ls were i n v e s t i g a t e d i n t h e first series o f tests. Before s t a r t i n g the txperiments t h e i n s u l a t i o n r e s i s t a n c e was mfasured and found t o be ( 3 . 2 ... 6.7).109n. Then

1 iJur c e l l s were f i l l e d wi th a 40% s o l u t i o n o f sodium hydroxide. The two o t h e r c e l l s served Is contro ls . The ce l ls were kept f o r 28 days a t 37OC in a i r having a r e l a t i v e humidity o f

The d a t a t h a t were presented i n d i c a t e t h a t t h e seal employed does not adequately pro- The reasons f o r t h i s phenomenon are as

The l i b e r a t i o n of hydrogen i n s i d e t h e cell .

2. The p e n e t r a t i o n o f water i n t o t h e cel l . The extremely hygroscopic e l e c t r o l y t e As a r e s u l t the i n t e r n a l

:hrough t h e i n t e r n a l e l e c t r o d e i n s u l a t i o n . They were performed on ce l ls t h a t had been B e f o r e s t a r t i n g t h e i n v e s t i g a t i o n s t h e bottom o f a cell was removed

Care was taken t h a t t h e r e was no change i n

This c e l l preparat ion was necessary i n order t o measure t h e i n s u l a t i o n r e s i s t a n c e The i n s u l a t i o n resistance was measured w i t h a

In order t o determine whether it i s o n l y water absorpt ion by t h e epoxy r e s i n t h a t

and then t h e i n s u l a t i o n r e s i s t a n c e was measured aga in . B e f o r e t h e measurements, t h e

No d i f f e r e n c e s conta in ing the sodium hydroxide s o l u t i o n were c a r e f u l l y washed and d r i e d . The r e s u l t s

:: these measurements gave i n s u l a t i o n res i s t :ances o f (1.1 . . . 2.3)*109n. '%e observed between t h e c o n t r o l ce l l s and those c o n t a i n i n g t h e s o l u t i o n . w e then f i l l e d aga in with t h e s o l u t i o n and. s t o r e d for 275 days a t 3 7 ° C i n p h y s i o l o g i c a l laline. I tor , and then measured for r e s i s t a n c e .

* t o 5.10'R.

u k i were:

The four c e l l s

Every 20 days, on t h e average , t h e ce l ls were c l e a n e d , d r i e d for 18 h i n a des ic -

hydroxide after 114 days t h e i n s u l a t i o n r e s i s t a n c e dropped abrupt ly from 10' t o lo9 It was found t h a t i n one o f t h e ce l ls f i l l e d with

I n another c e l l o f t h i s group a f t e r 205 days t h e i n s u l a t i o n r e s i s t a n c e down t o 8.106n. After 560 days t h e i n s u l a t i o n r e s i s t a n c e s o f t h e sample w i t h the

8.Z*105, 2.7.10' . 6.1*10*, and 1.5-10'R.

The r e s i s t a n c e s o f t h e sample without t h e a l k a l i went down t o 3.8.10' and 7.8'1O7n,

I n order t o e v a l u a t e t h e e f f e c t o f d ischarge-current magnitude on p o s s i b l e changes i n

because water vapors permeated throilgh t h e epoxy r e s i n .

.. -'e insula t ion r e s i s t a n c e , w e took two group:; o f s i x c e l l s each. 'ne c e l l s o f the first

I "

.n

TABLE 1, and o f Re la t i ve Bumidity o f the Air

Self Discharge as a Runctim o f the Storage Periods

25 1071*2¿3 ioo(li.14 9&' E I no 9 4 9 i l l Capacity. m A * 11

Capacity decrease.

Average =If-discharge

1038238 981C45 - 2? 45 - 57 89 - 5,o 5.1 - I O , ? 13,O

25 I o0 25

I mA

current. PA I TABLE 2. and the Re la t i ve Humidity o f the Air

Capacity as a Function o f the Discharge Resistance

Discharge n- i buradon of di? 1 Capacity. A' h Cell number I aiatance, kn I charge, days I I - I

Relative humidity of air 20 . 30 %

1,031f0,0?8 238.5 I ,15OfO,O41

I , 121f0.040 411,8 43'9 I 21-26 1- L$ 53-58

111-116 I 12.00

Relative humidity of au 10%

27-32 43.9 I .038*0,038 239.3 1 1.154*0.029

117-122 4w,3 I .085*0,030

group were f u l l y discharged through a resistance of 1.33 kn ( in t h i s case the current magnitude was 1 mA) and then stored f o r 90 days zi,t a temperature o f 3 7 O C i n a i r having a r e l a t i v e humidity o f 100%. per iod with a res is tance o f 67 kQ ( the discharge current was about 20 UA). as indicated above, were prepared and the insulation resistances were measured. age f o r a l l the c e l l s i n the f isst group was (2.3 + 0.7)*10sn and f o r those i n the secon6 group (2.0 f 1.7)*10'R.

f o r s i x c e l l s o f one production.series.

a f t e r s i x months o f storage a t 3 7 O C i n a i r having a r e l a t i v e humidity o f 25 and 100% and a f t e r 12 months o f s torage under the same conditions.

V. discharging proceeded under i d e i t i c a l conditions, the ca lculated average self-discharge current characterizes with s u f f i c i e n t accuracy the sel f discharge. stood t o be the f low o f current through the i j t e r n a l e l ec t rode insulation.) t h e results o f the measurements, Note the substantial d i f f erence between the sel f-discharge currents with 25 and look r e l a t i v e h m i d i t y o f the a i r .

The e f f e c t on the capacity due t o the penieation o f water vapors was studied by usinr. measurements o f the charge madeion c e l l s that were not pot ted i n epoxy res in , a t a temperature of 3i°C i n a i r with a r e l a t i v e humidity o f 25 and 100%. Before beginning the measurements the open-circuit vo l tage and short -c i rcq i t current were measured, as i s usually done when pacemakers are de l ivered. accord with de l i ve ry conditions. The short -c i rcui t current was measured f o r 2 sec through a load of O.].:?. 0.9 v.

and the r e l a t i v e humidity o f the a i r , s i x c e l l s were discharged through loads o f 1.33. 6-8' and 1 2 kn. The average discharge currents i n these cases were 1, 0.2, and 0 . 1 mA.

The c e l l s o f the second group were loaded during th i s same .

.

Then a l l ce l l s . The aver-

The e f f e c t on the self discharge due t o the permeation o f water vapors was determined

They were discharged immediately a f t e r $e c e l l s were rece i ved from the manufacturer.

, .

All c e l l s were discharged a t 37OC throu@ a 1.33 kn r e s i s t o r down t o a vo l tage of 0.3 The charge was calculated from the current charac te r i s t i c during the discharge. Since

(Self discharge i s idcr-

Table 1 shoxs

.

,

The open-circuit vo l tage was measured with a voltmeter i n

A charge measurement was stopped when the bat tery vo l tage f e l l IC

In order to, dete-ne the useful charge as a function o f the duration o f the discharre .,

254

Th, current ., #&ed i' but i s p:

To: tween thl

Ge< md showt Usigni f:

It feal b a k i periods,

The s r c u r y l of par t i c i

The have no 5:

sistance i tent haste

Hove the trans: 12 )LA. 2 the s e l f c observable discharge that f o r i l i e f valve

ASSU

terna1 cur txplainei'

The leakage cu Current t i vapors an? h i s confc Capacity J

9 the res.

A co: :hat the )f the ce l . :rease of be discha:

to the IPparen t 1:: :he ce l l ' s 'f the eiec ,inc i n an

The

ad no ob,, n mass o: f the l i s < ealed . i f ference Yte, w i t h he retarea

there

c

1 1 :.liarge w w imea:;iir.i:d irii. .i :ect..y b y man8 o.€ t i m e aric irrei": ineasurerneiits. The .. .,:I , i i , measuri:.I w i t l i a d i g i t a l vo : . tmt i i r . An a n a l y s i s c.! tie n:: . iults, w h i c h a r e pre- ,: .: I'able 2 , , ; ' iov.ad t:iat t ie c a p a c i t y i s a funct ion oi t d u r x i o n o f t h e d ischarge '. ;.: 1 1 ' i : t i c a l l y :i.iidepi:nd,::;i$ of t i e i .elat:ive humidity.

o f cIi,sides i i i thf volime and mass i t 1s ~ces:;ar:9 t o d i s t i n g u i s h b e - ,\ II : : ; t r , a i g h t ii:~scliai.g<: pherioixnor and 'the e f fec t o f e n v i , ,nmeiit 711. condi t ions .

,. 1 ctr.ic cel : . d:iini:r.s.lons wen? miasurod with i i micromete beforr, and a f t e r d i s c h a r g h g / I :si . t h a t the :.ncri:iisi! i n the dizmeter compared with t h e hange o f the h e i g h t was 11 l ; i ~ I . a n t . The 1-e:iiii ivii hmidj.i:y b a d nu observable e f E e c t n dimensions.

1: !i d i f f e r e r . t w i t h c t iwges :.n the IELSS o f similar (cel l Measurements with a <:hen- :: :! :it1 :, tie d u r a t i c r o f the. ddsc'hai:ge, mil also the relative : m i d i t y .

,! L X '-2 cc ce l ls c f pacemakers. 'The l eakase c u r r e n t through he e l e c t r o d e i n s u l a t i o n i: i ar i.( lar importance.

'.i reasurements i n d i c a t e that: water absorpt ion by t h e el xy r e s i n and d ischarg ing I. ! n, s . enif icant e f f e c t on the t r a n s f e r resistance o f the i r d a t i o n . .! in ? j 1 3.6.10' and 7.8'10'Q r e s u l t : ; i n a c u r r e n t flow o f I LO-' JA, which t o some ex-

, ! I h. ; ! I i s t h e cel l 's d ischarge .

i ~ i i i ier , when the sodium hydrt:sxidc s o l u t i o n exudes from i 2 c e l l i n t o the i n s u l a t i o n , .f :ri I:: i ?r resistan-e i s redyced : iubsi :ant ia l ly so t h a t t h e d i :harge c u r r e n t goes up t o

L. 'I- i s c o n d i t i o 1 a1:ro :onfirms t h e r e s u l t s o f measurement obtained i n the study o f f ;e. : Lscharge ami c a i ~ a c i t y as funct ion of r e l a t i v e humidit . The environment had no : 'vi y . ? zffect on 'capacity durin:g, a per iod o f 4oy) days. On ' ie o t h e r hand, t h e s e l f -

; E

.a fi E v.: v i .md i n t o .:lie rubber gasket of ' t h e c e l l s s t o r e d i n t h humid environment.

- r , I

I: :.,. c e b e f o r e :.:XI i f t e . r d i s c h x g e showed a clear depende- e o f t h e mass on t h e st.ornFe

L C study resdts confirbi the comples nature o f t h e i n f l - nce o f water vapor on t h e

The drop i n re-

. .

ai :y i igure f o r l i torage i n an <!avri.onmelit with 100% r e l a t i , ! humidity was n e a r l y twic? 1 ib, and heire there was s i i : n i f j . c a n t exudat ion o f e l e c t : , l y t e both through t h e r e -

,i I Ling t h a t t h e s e l f dkscharge is t o a c o n s i d e r a b l e deg: e independent o f the ex- )..: 'imt f low 1.1: car. be a n c l i i d e d t h a t measured l o s s o f c .rgc i s almost e n t i r e l y '

i ip i i i : I: :I the p a r w i t i c c u r r e n t s j u s t desc.tibed through t h e ec torde i n s u l a t i o n . I

4

:I e i i ant i ty o í measurements made does not permit t h e v a r ' , us f a c t o r s t h a t affect thi? :I ! ge it11 r e n t t o be. eva luated furt ' : ier. : c ' : n t i:l. itugh t h e External e l e c t r o i e inaula . t ion i s caused by . e combined effect o f water . 3 ! s !I( t.he exudation of e l e c t r o l j t e . I t s maximal value was 2 VA i n t h e experiment. L :I : i t c the energy source [ 3 , 4 1 .

I However, w e ,can now ci ' clude t h a t t h e leakage

2.0 I f ] UIS the propos i t ion t h a t 1e:akage c u r r e n t can reduce SI. s t a n t i a l l y t h e u s e f u l

T i! cnsequences o f t h e water-vapor in f luence on t h e c e l l '

A :#:I 3arison o f t h e average val.ues for t h e difference i n t .: e l e c t r o d e diameters shows

! 1: 's housing. Thi' pre9ence of ;in e l a s t i c rubber gasket is r e s p o n s i b l e f o r an in-

e l e c t r o l y t e a r e t r a c e d : ? I ? s i I t s o f volume and mass mea.surciments.

!

iif :hi ii irease i s r e l a t l v e l y small.. : I t i s evident t h a t it i s r e s t r i c t e d by the p rope r t i c s

::i ! 1' : I ) to 10% in t h e h e i g h t o f t h e cell's housing. The de; ;mdence o f t h i s value on L: . . S I : i i l i :e current i n d i c a t e s t h a t the p r o c i s s e s causing t h e v.'Lume i n c r e a s e , which are : I 1: .roceed mo:ce i n c e n s i y e l y ; i t a higher c u r r e n t dens i ty . The smaller i n c r e a s e In :.

,I:. ti limensions (during a p r e l i r i n a l ' y s t o r a g e per iod i s exp: tined by t h e p a s s i v a t i o n t

f I !

, 3

1 t ' t ! : :rode bloclrii with tin+? and a1s.o as a r e s d t o f t h e t h !modynamic i n s t a b i l i t y of

I C 11 -1 queous so:Liitiori and ' the iiinaller l i b e r a t i o n o f hydrog : . . The r e l a t i v e humidity c !i.! ,-Jable eff6ii:t on celL dimeiisicns. The clear dependen- , , o f t h e average d i f f e r e n c n

I cel l when s t a r t i n g end when depleted on the s t o r a g e arge as w€!l . l as: on r e l a t i v e hurnidi.ty i n d i c a t e s t h a t

e r i o d s and the durat ion e ce l l i s not t i g h t l y

I1 I . Wh I:<: :i with r e l . i . t i v e l y dry a i r water i s exuded from t h e ct' 1 as a consequence o f t h e

€!tween the par t ia l psessui:e of water vapors i n t h e ei.. ironment and the e l e c t r o - d :i c i s t air t h e oppos i te e f f e c t is obperved.

: t , a : :li ion o f the volume increase? ani the s u b s t a n t i a l i n c r e c e i n t h e mass when i n

i .f I e n I!

The a p p a r w t incons is tancy between

nio:ist a i r i s explained by the f a c t that the cmrging e l ecúro ly te being deposited on the rubber gasket i s takeri in to the mss maaureideot. The change i n the mass of c e l l s that st.i,red before being d i scbrged ' ind ica tes t h a t discharging has l e s s e f f e c t on the mass than the enIironment.

10:;s due to the act ion o f water vapors on meccury-zinc ce l ls by preventing the leakage of the e l e c t r o l y t e and thus the occurrence o f pa ras i t i c currents through the e lec trode insulation. This requires matching the p a r t i a l pressures of the water vapors of the environment and of the e l e c t r o l y t e . Since the pa r t i a l pressure of the e l ec t ro ly te ' s water vapors a t 37'C is about 1.7-10' Pa, the requirement i s met when the r e l a t i v e humidity o f the a i r i s 27% [5]. Meeting th i s requirement i n the production 161 o f pacemakers i s an important prerequis i te for the f u l l u t i l i z a t i o n of a cell's chabge ind thus an inproved c l i n i c a l s e r v i c e l i f e for pacemakers.

In conclusion if can be ra id that i t hi- been showi.possible to reduce the discharging

LITERATURE CITED

1. H. Matschiner, K.-B. Otth. S. Rudolf, e t a l . , Medizintechnik, g, 74 (1977). 2. 3. 4 . 5. Wissenschaftl iche TabelLen, Basel (1969). 6.

K.-B. Ot te and J. Witte, Dtsch. Gerundh. Wes., 32, 2218 (1977). G. Wickham and T. B. Ca&mill, Pkd. J. Aust., 2, 138 (1971). K.-B. Otte, R. Richwien, and H. Matschiner, Wiss. 2. Univ. Halle, 2, 5 (1976).

H. Matschiner, K.-B. Otte, and R. Richwien, DL-WP, 116, 753 (1975).

2 5 6

QURI~:

pp.Os''..

achie:-e "te :<

7 for ciie tissue. a l ly re of iricr tion. the end the las rate in 8UPPlY the u l t cation

A achieve destruc changed

k countrit acope CI

rhage a: the per: >ver tht Lnstrum ares i r i i f icant Lng the 17 the c !yes of iully as

Le ,rradiat n the c egimes. nations his l ea Ontinuo he ther luminm

Th * The )Wer in

- A l .

:atislati : t i c l e :

3 ' 5 higher :l and 24h ~i 2nswere fli soaking Tagation at lemimature .tit ballwas id irrnalin. eported in- itic arterial I t king to t i l wall is

W. ,F. and u¡< on and Y Y ~ :harar- lings. IEEF

P '(19791 IS. !TP""ill

J. D. and ' tht . aorta ir ,"#"p.

BoURLANt,.

i ( "Ipul.,

scattering .<=dings,

*ition and IUS'" 'acked

:h".l80

Signal source impedance of implanted pacemaker electrodes estimated from the spectral ratio between loaded and unloaded electrograms in man L. Morkr id O-J. Ohm E. Hammer Seslion of Midkal R-mirch. MadiUI Depanmeni A. Univerritv School o1 Medicine Hauheland Syhehus. Norway and The Chr Mtchelrr Insifl~le. Depanmeni of S S Y W ~ and Technolow Nvpaiardigl 114 5000 Beroan Norway

Abatrsct-The Signal source impedance Z of implantedpacemaker electrodes plays an importanr rui<' for adequate sensing of electrogram signals and has so far been little explored. A frequenci, domrin method for the in vivo calculation of i is described. Electrogram signals picked OD between two elecirodes were recorded unloaded, and loaded with resistors and capacnors. then amplified. and stored O n magnetic tape. Aiter time sampling and a.d. conversior. the signds were readinto a digital computer as discrete time vectors with 2' samples. Each vecim was subjected to a fast Fourier transform / f . f r . } , and the ratio H(jwJ between the transformed loaded and unloaded vectors was calculated, For the electrode impedance Z a linear model was chosen that consisted of the tissue and electrode resistonce R ,, in series with a parallel coupling betwei?n Faradayresisrance RF. andHelmholtz capacitance CI. By nonlinear regressiorr analysis the paiametefs ( ) in this model were estimated from the ratios H(jw,l obtained in patients with Permanent pacemaker electrodes, and in patients with temporary multicore wire electrodes after open h e m surgery. As an'estimale for R T was also used the voltagelcurrenr ratio R ' , , 90 p into the stimulation pulse from an external variable parameter pulse generaror The 3-component impedance modeldescribed the essential features of the electrode impedance in the ffequencv range UP to 100 Hz. If was found that e,, decreased slightly with increarmg frequency. and that R , in general was larger than R' ,. A moditied model with frequency dependent para,neters was found to obtain a better approach to the experimental data.

Kaiywordr-~Ieceogran;. Frequency analysts, Nonlinear regression analysis. Pacemaker electrode impedance

I Introduction IT HAS recently been suggested that the electrode impedance may play an important role with respect to both energy and to signal transfer between the pulse generatoi and the heart muscle ( K L A ~ R , 1973; OHM et al., 1977). Mismatch between the output impedance o f the pulse generator and the electrode impedancemay result in stimulation failure (exit block) as well as increased current drain of the batteries. On the other hand, i f the input impedance of the.pulse generator's Sensing circuit is low compared with the ekctrode source impedance, attenuation of the heart signal will take place. This may in turn lead to Sensing failure (entrance block).

Various definitions have been given of the pacemaker electrode impedance, and several methods have been proposed for its measurement both in vitro and in uivo. Some investigators have measured this impedance during stimulation as the voltage/ current ratio a fraction of a millisecond into the

Received l¶h March 1979

014M1181801020223-11 O1 5010

Q I F M E E . 1980

pacemaker pulse or on its leading edge (BAROLD and WINNER, 1976). The values found by this me1h.x indicate the magnitude of the impedance at high frequencies only. In general, the electrode impedance is a complex quantity, a function of frequency and voltage (DYMOND, 1976). The equivalent,electrode resistance defined a$ the ratio between mean voltage and mean current during stimulation (IRNICH. 19761 has been suggested as a more easily understood parameter. This resistance, however, depends upon the shape and duration of the pacemaker pulse. A more attractive approach has been to represent

the electrode impedance by an elecirical equibaleni model with a limited number of discrete components (BAKER, 1971). The values of the components can then be found by parameter esiimation Using a time-domain method, KLAFTER et al. (1974) found that a 4-component model was a good approximation to the electrode impedance during excitation experiments in physiological saline.

The validity of this model outside the range o1 frequencies contained in the pacemaker pulse during heart stimulation may, however. be questioned Because of the complex nature of the electro- chemical process occurring in the electrode/tiswr

Medical & Biologicil Engineering & Computing March 1980

. /

223

intciface and the presence oi two clccrrodes that may dilicr in size üiid mdcriai coiiipositinn, one would expect that ii simple dircrcte rnndcl with a moderate number of components viouiu only fit over a rather lirnitcd range of frequencies. Another complicating Factor is the heterogcncous structure o f the components in the tissue h o w e n the two electrodes. The frequency conlent of ihe stimulation pulse lics in a region well above the frequency spectrum of cardiac potentials picked. up by a pacemaker system. The electrode model derived from stimulation experiments using ordinary paccnisker pukes should therefore in general not bt used to calculate the electrode signal source impedance relevant to sensing problems. I n h c t , no simple discrete model describes adequately the electrode impedance over a broad spectrum of frequencies. Using sinus wave excitation i n physiolopicdl Saline and in the cat gluteus muscle, MUNU ei al. (1976) found that the following function could be used to express the impedance of smooth surface electrodes for high frequencies

Z=Z.(f/fo)'P'"" . . . . . . ( I )

where - l < y c - O . S and Zo,=IZ1 at f = f o . Although simple in form, this function cannot be simulated by a simple discrete network with frequency-independent components.

The signal source impedance of implanted pacemaker electrodes does not seem to have been thoroughly investigated. The object of this paper is to describe a frequency-domain method for determining the impedance of pacemaker electrodes in the frequency range of endocardially and iniramyo- cardially recorded signals. A %-component modei (Fig. 1) described by MINDT and SCHALDACH (1975) has been used for 2. On certain assumptions this is also valid for a nonsymmetric electrode pair (Appendix I). The model consist!; of a parailel coupling between Faraday resistance Rf and Helmholtz capacitance C,,. This parallel ceupling is connected in .series with the tissue and electrode resistance R,. Preliminary studies h.ave shown that this model exhibits the essential features of the

CU

Fig I The 3-component model of the elecrrode and tissue impedance, loaded wilii an exlernal impeaance'2,. For explanalmn of symbols. see fexi

eiecirode imprimice in the frequciicy ranpc I J ~ . !o0 Hz. its relation to the model in eqii. i ulii !.. discusied.

2 >Methods

2.1 Theory Notation

A = denotes statistical estimates I = time

U ( I ) = diRerentia1 potential generated by thc heart muscle fibres between the two pacemaker electrode poles

i ( t ) = noise potential u , ~ U' = unloaded, and loaded potential

j-4-1 f = frequency o = 2n f = angular frequency s = jo = parameter in Laplace trans-

ü(s), Ruco) = Laplace transform of u({). modulus of forms

UI jo) T = length of time vector

At, = start mint differences of discrete time vectors

o, = ZniIT = ith harmonic Y; = L~Lijm,)/~xCjo,) = experimental

transfer function H(jo,) = theoretical transfer function. depen-

dent upon model parameters (¡.e. Rr, R r , CHI see below)

1 I = modulus of complex quantity 6, = error in statistical model; i = I , 3 ... n II = number of regression points S = sum of squared errors

Z, = impedance of the tissuelelectrode

2, ZN = electrode signal source impedance. interface

' source impedance of noise ZL = load impedance

C,, Cr = Helmholtz capacitance, load capacitance

c, = (i/C,+ I/C&' cr = CH+CL

R,, RL = Faraday resistance, load resistance RT = tissue and pacemaker lead resistance

Rr' = initial voltage/current ratio of a stimulation pulse

Rs = RT+ R L Rp = (I/Rs+ l/Rr)- '

R,, T, y = transfer resistance, time constant and exponent parameter in impedance model (see text)

d(x) = 1/(2ns) f - L = d(Rr CP) fa = ~ ( R F Cn)

224 Medical & Biological Engineering & Computing March 1980

,. . ." , .-_<"I_ . ., , . ~ . , . , . ~ , _ . . I ...,.,. ,

,y te . o

:a .

4s of

ti l

x n - (I+

.. n

%

IC%.

ci-

ice a

i d :e

O

c, k = electiode capacitance, conductance per unit arca

d = effective electrode circumference I , , I2 = exposed electrode lengths I... = (I//,+

lenglh = equivalent electrode

The most useful and common definition of i m p dance is the ratio between volta& and current amplitudes in the frequency domain. It is therefore convenient to work with the complex frequency components of the signals involved. A much used mthod for the assessment oi signal source impedance is to load the signal with a known impedance ZL. The source impedance Z may then be calculated from the resulting voltage drop. If Kirchhoñs law is used (KREYSZIG, 1967) .with the arrangement shown in Fig. I , the signal over the load impedance can be written

LPL(jw) = U ( j w ) Z , / ( Z + Z , ) . . . : (2)

The unloaded signal U,(jw) can be obtained by making ZL9 Z (that is by recording the source signal with an amplifier of very high input impedance:).

(3) U d j o ) z t r ( jo) . . . . . . . Taking the ratio between eqns. 2 and 3, one has

udjo)/u,(jo) % ZL / ( ZL+Z ) = i f( jo) . (4)

The left-hand side of eqn. 4can be found by taking the Laplace transformation of each sipnal uL(t), u=(i)

~ ( s ) = [ expí.-e)u(f)dr . . . . . (5) =

right Icp was used as a reference point. Thc recordings were ohtained from permanent paamakcr systems and during temporary pacing in patients undergoing open heart surgery. With permanent systems the following electrode pair wniigurations were used: (u) bipolar endocardial electrodes and (b) unipolar endoimyocardial electrode against the indifferent lead (capsule, plate) of a pulse generator. During new pacemaker implantations and replacc- ments.the indifferent elecirode was simulated by a dummy (a pulse generator with all. the electronic equipment removed). A lea8 attached to the inside was used as electrical contact to the indifferent electrode. The dummy was placed in the pacemaker pocket. During open heart surgery two multicore adequately insulated stainless-steel or platinum- iridium wires were used as pacemaker leads, one fastened in the myocardium and the other in the pericardium or surrounding tissue. The leads were drawn through the upper abdominal wall .and fastened to the skin.

Signals picked UP by the electrodes were recorded unloaded and loaded -with a series of different resistors and capacitors. Via insulation transformers (Analogue Devices 272 I) the signals were fed into a differential amplifier (input impedance 10 MQ, amplification 100 times). The amplified.signals were stored on magnetic tape (Tandberg analogue instrumentation recorder, Type TTR 115). Tape speed was usually 3tin/min, and input Sensitivity could be varied stepwise from 0.5 to 20.V full scale. The overall frequency response of the system was flat from 1.5HztoZKHrwitha -2OdB/decaderoIl-off below 1 .5 Hz and 40 dB/decade roll-off above 2 KHz.

o The recordings were replayed on a Could Brush putting recorder and inspected visually. Curved parts with

evident noise or very iriegular heart rhythm were excluded from the subsequent data analysis. s = j o

and performing the division between the two resulting Fourier transforms. With a Deriodic 2.3 onalWis digitised signal this process may be re.placed by the

. discrete Fourier- transform Of time segments equal to the cycle length of the signal (COCHRAN el al.. 1967). Th-e mathematical expressions of the theoretical transfer function H ( j o ) with the 3somponent model in Fig. 1 and with resistive and caDacitive

. A Standard Fortran program that allowed reading of-two simultaneous signal channels from the tape recorder was developed. The s iaals were digitised in a 12 hit a.d. convertor (Zeitcx Mod ZD 462) and read into a NORD-I computer. The sample time

loads, are calculated in Appendix 2. The following statistical model was found to be appropriate for the estimation of the network parameters (RF, Cm and Rd:

Y, = IH(jo,)l +e, i = 1,2, ..., n . . . (6) Here I; is the -amplitude ratio between the ith harmonics of the loaded and the unloaded signal. TP

2.2 Insfrumenrotion Fig. 2 Selec1,on of consianf lengfh ims vectors horn a

record with valving R.R interval T = /moth ni ~S -.

vecfors (bold trace). T. = time needed for storage on magnefic plate disc, TP I trigger point in the QRS complex, A T = specified waif fo.inifiafe sampling of a new vector

The cardkc signals were recorded by measuring the differential voltage between a pair of implanted electrodes. A skin electrode usually placed on the


.~

r

" .

. .

7 7 - , . -_I c

equations. Instead simple search routinc? were uaed. Attention was paid to the lac1 that 01 frequciicies f > I/(ZnH, CH) the resistance Itr could be omitted from the equivalent diagram. In ^is frequency range the parameter values R, and CI, were determined as shown in Appendix 3. Using the-value determined for K,. the combination E, and CH was -found that gave minimum sum of squared errors over the frequency range 0-10 Hz with a .resistive signal load. The magnitude o f the load impedances was chosen so as to give the greatest stability of the utimates. 'This was achieved in practice by ensuring that lH(jw,)l was not too close to zero or one along its main course.

3 Results

lntramyocardially recorded electrograms from three patients with temporary pacemaker leads implanted during open heart surgery are shown in Fig. 3. The differences in. frequency content between the three corresponding periodograms support the impression one gets from visual inspction o f the original electrograms. Examples of the exlxrimental transfer functions Y, ( jo ) , which result from capacitive and resistive loading of intramyocardially recorded signals, are shown in Fig. 4. 'The parameter values Br, & and C,, for chis recording which was done in a patient the first day postolmratively, are listed in Table 1 (GS), togeiher with the results obtained from six other patients, three of uhom were investigated with permanently implanteij systems (long-term electrodes). Four different values are given for C,. One was calculated with a capacitive load in the frequency interval [ZO, 401 Hz rind one in the 160, WIHz, and one from a resistivdy loaded signal. in the frequency interval [O, IO1 Hz. The remaining fourth capacitance value was d,etermined together with RT when using a resistwe load. This value reflects the capacitance over a frequency inter-

val from IS HZ ícf. Apwndix 3) and upwards to a point where the tr;insler function uscd lor the calculation of R, levels OR (see Fig. 4).

I t is seen from Table i that the C,, values were much larger for the temporary myocardial wire electrodes (typical areas - 50-1 SO mm') than for the permanent electrodes (areas -&12mmz). An increase in CH is to be expected with increasing electrode area, whereas an inverse relation holds for R,:The dependence of. C,, and R p on the I.,. of a wire electrode pair was clearly demonstrated in

1.0 IH(jw)I 1

100 HZ

50

Fig. 4 Experimentaltransfer functions betweenresistive loaded (filled symbols), capacitive loaded (open symbols) and~unloaaed eleclrograms (palient GS. cl. Table 1). Three different resistive loads are shown. The model parameters C,. Rf and R, eslimated'from eqn. 6 are given in. Table 1. line 2. Solid lines rapresent the theoretical model given in eqn. 12 wifh R, = 10 KQ T = 0.11 s. andy = 0.94

Table 1 . Parameters of the 3-component electrode impedance model R,(n). C&F) and R , ( k Q ) Bsfimated by regression analysis on the ratio belween fase Foürier transforms of loaded and unloaded eleclrogram signals . " .

Type of R, c, e, e, R, e" Patient electrode R L (15+ 100) CI (2040) (60-90) R, (0-10) A P Q D + G 307 1-0 :370 4.8 5.0 5.1 - 5.0 10-2 6.1 G S I D + G 304 1.0 :319 8.6 5.0 9.4 9.0 5.0 4.5 10.7 KF i Pt-Ir 222 1.0 :310 19.9 10.0 20.9 - 2.0 3.9 31.2 NH j E 144 1.0 '184 14-2 10.0 15.1 11.7 2-0 7.3 18.4 JS C322-462 1100 2.0 1:334 1.4 2.0 1.4 1.1 10-5 50.9 2.1 GE i C322-620 625 2.0 1:396 1.3 0.9 1.5 1.3 11.0 54-4 1.5 TK = M69D7 500 3.0 817 1.7 1.0 1.9 1.7 11.0 37.1 2.0

. .

" . R'r(R) = voltagelcurrent ratio 90 FS into the stimulation pulse (initial impedance) RL(kR) = load resistance, C,(pF) = load capacitance Numbers in parentheses are the frequency rringes in HZ where the parameters were calculated . D + G = Davis+GeckR. Pt-Ir = platinum-iiidium. E = EthiconR; long multicore wire electrodes. analyses made the first postoperative d e after open heart surgery. C = Cordisn. M = MedtronicR electrodes. - = values not determined owing to noise in the signals

Medical & Biological Engineering & Computing March la60 227

. ,

one patient who had two stainless-steel pacemaker leads implanted in the myocardium. The two noninsulated exposed pairs of the metal wires measured 58.2 and 34.7mm. The length of the indifferentlead(apericardialelectrode) was 51.2mm. According to eqn. A.1,lZ in Appendix 1 the corresponding I.,.. for the two pair configurations: myocardial-pericardial, should be 27.2 and 20.7 nun. The corresponding valuu for CH in the frequency interval [20,40]Hz were 17.9 and 13.9 /rF, giving capacities per unit lengih of 0.66 and 0.67mF/m which are almost the Same &pres.' Estimation of Rr in the frequencyinterval [O. IO] yielded the values 3.1 and 3 .6kn . Conductanas per unit length, 0.01 28 and 0.01 29 Sjm, are quite comparable figures. For the wire electrodes it was found that C H was increasing linearly with Adopting the first-order regression model C, = a + b 4.. ,+E, and exa.mining .fourteen EthiconR electrode pairs from patients who had undergone open heart surgery, capacitance per unit length, 6 was found to be 0.54mFjni in the frequency ranpe [20,40] Hz at electrode remdval. (correlation coefficient r = 0-95, p <

4 Discussion

The validity of the results obtained with <he present method for calculation of the electrode impedance will depend upon.(a) the sensitivity, and the accuracy of the estimation procedure, (b) the statistical properties of the electrogram signals. including stationarity and noise and (c) how well a 3component linear model approximates the true electrode impedance. These factors will be d:iscussed briefly.

(a) T.0 test the recording system and the computer program a long record of an unloaded electrogram signal was replayed from a tape recorder, attenuated to the original mi! range and fed through an electrode impedance model with the following three components: Rr = IWR, Rr = 5.0kR. and C, = 9.8 #F. This in vino network represented the patient. The Signal was then loaded, amplified and recorded in the same manner a d w i t h the same equipment as during the in vivo measuremeiits. The subsequent parapeter estimation-on the digital computer gave: RT = 1 M 1 0 7 R: CH (15+ Hz) = 9.1-9.6/rF: CH ~ 2 l U O H z ) = 9.7fiF; -CM (6 ^ H z ) = ? . 6 p F ; CH (&10Hz)= 8.8-9.21iF. and RF = 4.9-5.0 k?. These values were in good agreement with the true model parameters. The procedure was repeated on another occasion with different tMes of simals. and showed the same degree of .. - . . precision.

(b) The estimates of the impedance model will k representative only if the frequency content of the P, QRS and T complexes are stationary with respect to time, since the loaded and unloaded signals have to be recorded at different points of time. It is known that a number of factors may modulate the

individual cardiac cyclei. \u<h as respir:i,L.ty n l I > C .

iocnl(. drugs. changes in acid-base I electrolyte disturbances. The rapidly changing injury potential during the initial phase of sn acutely

respect to stationarity. To obtain consistent estimates. with small variances the impedance parameters should be calculated as means from a numher of cardiac cycles. The effectiveness of this procedure - ~ : is clearly demonstrated in the following example of ten successive determinations .of the Helmholtz cipacitana. The difference between the estimates may indirectly indicate the variability in amplitudej frequency content of the electrogram segment from oneheartbeat to another. Each capacitance value was calculated from a pair of cardiac cycles, one taken from a long record of an unloaded signal and the other froma capacitance loaded signal. The individual estimates were eH (ZWOHz) = 24.1, 14.7, 15.0. 18.6,22.9,13.9, 16.6,19.5,20.1 and 15.0 /rF. The mean capacitance values determined from accumulated s p e d @ averages of the same eleclrogram segments were C,, í 2 0 4 H z ) = 24.1. 18.3, 17.0, 17.4, 18.3, 17.4, 17.3, 17.5, 17.8 and 17.4pF. In this case it is seen that the mean tends lo stabilise after a few cycles. Ftde cycles were found to be a reasonable compromise between stability and computation time. The long-term stability of the electrogram was not evaluated, but one should try to have the unloaded and loaded electrogram records separated by as small time intervals as possible. In our investi- gation the two recordings were about a couple of minutes apart.

One may deduce that the presence of stationary noise n(r) in the recordings u ( I ) + R ( I ) - ~ u(r) will cause bias in the estimated parameter values unless the noise is generated over the same source impedance as the potential from the heart muscle fibres. Noise generated after the loading circuit, that is, in the amplifier, the tape recorder. and the a.d. convertor, will not be reduced by the load between the electrodes (Z, = O). This will yield too high E;- vaiues. From eqm. 33 and 35 in Appendix 3 it is possible to show that this tends to give foo low estimates for RT and too high estimates for C,,. By short-circuiting the input terminals of the amplifier it was found that this type of noise was minimal below 5 O H z but from that point on it was slowly increasing with increasing frequency. Due to this effect, y will be estimated too high (see below). These considerations also hold when ZN < Z. I f Z i 3 Z-thz converse will be true, R, will be too high and CH too low. in our experience it is reasonable to believe that Zw < 2, and that most of the noise is generated after the loading circuit. How RF and C, will be modified by this noise when using the more complex model in eqn. 31 is difficult to predict, hut a lower total electrode impe&nce value is to be expected. in the frequency range O-iOHz, where the contribution to the amplitude/frequency

implanted electrode pows a special problem with *:

,

,

. . . . . . - ................. .~ . .I . . . . . .

. .a1 .

C,.. - - Fi . fquivalenf block diagram for.^ the impeilance' .' "" . L - : Qh;enbyeqn. i2. C,in F&. 1 hasbeemreplaced Values obiaínea.fro~.analysis of long rnullicore wire

by a frequency de,nendent capaiirance C. electrodes according" (0 eqn. 35 (ApperiUix 3 ) in '. Famdav resisfance has been shunred'by a palien- after open- hean surgery. The superscripts

- ~ '

; . . ~~~

indicate number of days after operation . . , .~ . . , p:. Jogqncv-depeodent . . rerislanc,o .. .:: . ~

. . . . . . . . . . . . . . . . . . . . 1 Li_C_.i , I : . ,. - 229

i .,

i, Biological Engineering & Computing March 1980 j ; ,

. . . . . . . . 1 ' .

!

. . . . . . . . . . .- r<. YW?.

300 164 17-6 181 17.1 528 !3 9 200 177 19.0 196 18.1 561 9.9 100 165 19.9 269 25.3 - .- W7) (150) (190) (339)

The paired values k T. e,, were obtained according to eqn. A.3.1 (Appendix 3) in the frequency range above 15 HZ in patienis after open heart surgery (see iext lo Table 2). R'

Tabte 4. Dcpmdence of Faraday resistance f i r on the load resistance R L

= initial impedance during stimulation

RL

kSl 7 4 3 2 1

6.. C" .~,. ~ r .

AKS,:P EHJ' VS?' k < i pF k i l pF kR pF 3.5 27.3 3.6 3U.6 7.7 ' '15.0 3.7 20.9 5.6 27-5 7.6 13.1 4.2 21.2 3 . 3 . 19.1 6.7 '11.4 4.8 18.6 4.1 21.5 8.3 12.0 4.9 17.8 4-8 20.2 9.8 12.3

The paired values Rp and C n were obtained according io eqn. 31 (Appendix 2) over the frequency range [O, 101 Hz in patients after open heart surgery (see text to Table 2)

. .

mi' Ol//

10k 1Ok

Fig. 6 Comparison between electrograms of unloaded ' . ond resistir? loaded signals. Upper curve: uri-

haded; -niiddlE curve: loaded in vivo with IOkl? : lower ccvve; unloaded recorded signal fed through a 3-component in vitro network and

. loaded with lOkC3 (see text for further , explanation)

. . .. '., Medicel 8. Biological Engineering & Carnputing March 1980

" . ' 230 . .

. . . . . . , .

i

i

i i i !

1 I

I 1

i

i i

i

I

. .,

..

!

fact ti1;~1 !!:< ,:;!%icitrn<:l.iiccd in the ;ti t'riroiiiodciivai [,< 2.3 { ) I ' , i ~ ; ~ , m i i i c d in t!ic Errquency range

. IZO. 401 IIL. C-:,nx,,pwiitly the source im;ied;ince wi l l ,h highzr w irh thi\c;ip:icitatice below IO H<:hdiiiW1?cfi using <',, 1 0 - 10 H i ) . which is more-correct. for this freqiiency r x g c . I n the ac!uiI case Gi 10-10 Hz) uac estimatcd tr, he 3.1 F E . ' The to!al impedance between two elecir»de poles Z = I<, + / < , ; I I + jo,Cil It,) is strongly Srequeiicy

j dependcnt. i t may be useful t n separate this impe- ,ill source impedance during recording

load impedance during siimulaiion frcqucncy conrents of the electrograin

arid thc uimulation pulse are lying iri entirely different f'wqiicncy intervals. After passing the input : filter of ihc sensing circuit in most pacemakers. the , elec!roprarn signiil j t i l l will h3ve its maximiim energy wcil k l u i v 30-40 Hz. Llsing the parameter values for the Vitient T K (Table I ) , Z of this particular electrode ;I\ ' a y ?SHz will be 3419exp{.-I .33j!R. It is knoiin that the input iinpcdance of some pacemakers niay be of comparable mdngitude (.OHM el al., 19771. I t then becomes clcar ihnt \,oltage division betoeen the signal source impedtince of rhe electrode :ind the input impedance of the pulse generator niay cause significant reduction of the signal available for the sensing circuit, and demand failure may follow (see eqii. 2). Thib risk is enhanced with the use of electrodes of small areiis, such as ball-tip electrodes. The formation of low impedance current pathways in the sensing circuit by minute amounts of fliiid that may leak through the sealing of the pulse generator, may be another contributory factor (HUGHES vi al., 1976).

.

Ackkno~~kr@n~=nfs--The work was supported by grants from the Royal Norwegian Ccuncil for Scientific and Industrial Research. the Bergen Bank's Jutmilee Fund to The Chr. Michelren Inrtiiure, and tbe Norwi:gian Cuuncil on Cardiovascular Diseases.

Referemes BAKER. L. E. (1971) Biomedical application!; of electricai-

impedance measurements. in IEE .Medirol Electronics Momgraphs 1-6 (Cds. HILL, D. W, md WAT:?N, B. W.), Peter Peresrinus Ltd., London. 1-42,

~;.WLI>. 5. S. an4 \VivifR. I. A. (1976) Techniques nnd ,i~nifi,:unce "1 tlirL,huld inc:riircmrnt for z?cd¡?c

H h w . R. niid SPKH, M. S. (1977) Sampling rates rrquired for digital recording of inlracellslilr 3!id extracelluliir cardiac potentials. Circulariorr. 55. JOlh.

CASHM&S, P, M. M. (1977) The use of R'R irdcwal -and difference histograms in classifying dis0rdei.i of

pacing. (:I,~w. 7n. 760-766.

sinus rhyih:n. J. Md Eng. & Techno/.. I. 2e.28.

H. D.. KAENFL, R. A,, LASO, W. W., M ~ r i i ü , G. C.. NELSON, D. E.. Rmrn. C. M. and 'WELCH, P. D. (1967) What is !he fast Fourier lransiorm. IEEE Tram., AU-IS, 45-56.

COOLEY, J. W. and Ti:xru, J. W. (1965) An algorithm for the machine calculation of comnlex Fourier series.

COCHRAN, W. T., COOLEY, J. W., FAVIS, D. L t1EL'W

~~. .~~ ~ ~

Morlr. Coniprif.. 19, 297401. Dworo, A. M. (1976) Characteristics of the metal tissue

interface of stimulation electrodes. I E E E Trans.. BhlE-23, 274-180.

EPELBO~N, I. and KEUDAM. hl. (1970) faradaic impedances: diffusion impedance and reaction impeúance. J, Electrochem. Suc., 117, 1052-1056.

HUGHES. H. C. Jr., BROWSLEE, R. R. and TIERS. G. F. O. (1976) Failure of demand pacing with smali surface electrodes. Circr~lulim~, 54, 128-132.

Lnvrcii. W. (1976) Elektruierapi d<s H~i-:rnr-P/i).sio- logixhe und Bioicchnische Aspekfe. Fachierlag Schiele & Schon, Berlin, 28 and 93-96.

JAROX, D., BRILLER, S. A.. SCHWAN, U. P. r n d GESELOWTZ. D. B. (19691 Nonlinearity of cardiac pacemakerelectrodes. IEEE Trans., B31E-16, 13?-l38.

KurrEn, R. D. (1973) An cptimally energizcd cirdiac pacemaker. ¡EL€ Trans. BILE-IO, 350-356.

K L A n f R , R . D., KOLLER, U. K. and VAS Di.YsE. P. D. (1974) Determination of a cardiac pacem.iLer dectrode impedance using a time domain mcrhod. In the Proceedings of the 17th ACEMB. Philadelphia. u).

KREYSZ~G. E. (1967) Adronrrd engineering mwiwmtics. Kew York, John Wiley g; Soni lnc., 70 and 5-1

KROVETZ, L. J. and GOLOBLM~~ , S. 2. (19741 Frequency content of ir,!ravascuIar and intracardiac pwsurzs and their time deri\,ativer. IEEE Tr6.n~. BbIE-21, 49s-501.

MISDT, W. and SCR~LD*CH. M. 119751 Elecriochmical aspects of Fqcing electrodes. In E w i n ~ r r U i ~ in Mcdiciiie: i Adwnces iit pocenzuker technolog? E&. SCHALDACH. M. and F~RMAS, S.), Springer Veda% 297-305.

M u m , K., RICHTER, G.. WE~DL~CH, E., 1'0s Srcnrt. E and DAVID. E. (1976) Equivaleni circuit diazram arid power consump!ion of stimulating electrourr. Bio- elecmrhemisrry arid Bioenergefics. 3, '1:-?83.

OHM, 0.4.. HAMMER, E. and M ~ R K R ~ U . L. (10771 Dio- logical signals and their characteristics as a cause of pacemaker malfunction. in Cardiac paciiig (Ed. WATANABE. Y.), Excerpta Medica, Amsterdam. Oxford, 401404.

Apimdix elstrodeitissue interface 1 Resultan: impedance d a n electrode pair ; $ - Z , + Z , . . . . ' . . . . . . (16)

as shown in Fig. 7 yields the resulting imwdance of the Z , - R ~ / ( l - t j w R ~ C , ) i = 1 , 2 . . . (17)

M.dicel & Biological Engineering &. Computing March 1980 231

Seria coupling of the active and indiffeirnt elcetrodes where

Suh\iiri.ting

and

into cqn. 17 one has 2, . Rr\ ( L+ jwc , /q ) . . . . . . . . 124)

If th? two clectrodcs are vade of the s a m e malerial ana thc properties in the rnetal\ti5?ie interface ?rc equal, one shoiild expecl thdt

Eqn. I6 II then simplified

R, i : . . : i . . . . . . . . . . . (18)

C ! ~ ~ c,,4<. . . . . . . . . . (19)

< ! ; e , ii c2/*.2 . . . . . . . . . . (21)

.?,, R / ( l + j w R C ) . . . . . . . . . (22)

R ~= R,+R1 . . . . . . . . . (23)

~= c A , n , / ( A ! L A ? ) == C,C,/(C,~tC,). . (21)

~~

whwe '

and C = c/xíR, + R J - cK l lA1 + l /A,)

Eqns. ?3 and 21 imply that R and C a r e the direct reries couplmgs of R , . R , and C,. C2. In terms of electrode lengths one then has from the two preceding eqas. and eqns. 18 and 19

and

This shows that as far as the total impedance is concerned, it can be represented by the impedance of one electrode with lhe equivalent length given by

x ~ 1 7 ~ l / l , + l / / z ) / R / m = I/(Rlzqu m) . . . . (25)

e = ( l / / * + l / / 2 ) c / o = C,Y.<" 0) . . . . (26)

/... = I , / 2 / ( / ,+ . l? ) . . . . . . . . (27)

T h e e calculations are useful both when examining long multicore wire electrodes used in ionnoction with open hcan surgery nnd in studies of permúnent bipulir eiec- trodes. In the latter case, i: is more appr0p:iate to use areas in the place of lengths i~ eqn. 27. With unipolar. permanent pacemaker systems. uhere the pulse senerator acts as the indifereiir electrode, the impedance of this electrode is small enough to he neglec:rd in eqn 16. Buacise of the great difference in eleurode rea as. rhe active unipolar electrode is reswnribk for <nos? of the impedance in the interface between the electrode surface and the tissue. To get the total impedance of the

ac:ive leod

R2 c$ 1

___o

cz indifferent leod ' equivalen: diogrom

e~e:rai?:,'!i~suc iyr!en. t k impedanc: of I ~ C !:3& 3r.L ttw tis'i,,c~c!cCtrolytG must te included in ecn. !h. This additionat irni>cd;ince i5 usually though1 10 t*r ?Cre!S rc!,;&c ir, ihdracter, and w i l l be repre,rnicJ ;;r Rr.

2 Calculation of How) with resistive and capacitive load5

With the p r o p 0 4 electrode imvddnce model cui Loading the elecrrode with a rtsisior. Zr = RL.

Z = R r i - R , / ¡ l + j w C ~ R ~ ) . . . . . . (28)

eqn. 4 in the text yields

~tf(jw) - ( R ~ ( R ~ + R L + R F ) I x [(I t j w C , .?&(I - j d " R d l (29)

where Rp is the parallel coupling of (Rr--RL) and Rr

Eqn. 29 can also k written

R,=(RT+RL)Rr/(Rl+Rr-Rr) . . . . (30)

(b) Using a capacitor as load impedance, * ... I - l/ijuKd. Inxrtioii in eqn. 4 gives

3 Seieetion of spciHc loads and frequency intervals in the regression runs

(o) Delerminatjon of RT and Cx with resistive load. At frequencies f BJo = 1/(2aRI(;,i. the efect cf

omitting Rr from the electrode impedance ~ s k l should be negligible. Letting RF - I one has frmn eqn. 31

IH0'w)l x WCU RL,\ ( I ~ ( w C a .W) . ., . (3:) uhere Rs repments the series coupling of Rr :?nd Rr, Rr = R L I R r .

Fig. 8 Modulus of theoretical transfer funclions (bold trace) befween loaded and unloaded signals genereled over the 3-componen1 source irnpe- dance shown in Fig. /. (A) resistive load. I , = tii, (8) capacitive load, Z, = 1 '(j:'..;C,I.

~

Fig. 7 A paif of pacemaker electrodes represented by A&nptotic values. zeros and pales of the one equivalen1 electrode !with the sanie transfer functions are indicaled (thin lines,.

.. , impedance. R = R, +X2 and The bioken liner represenl the care "hen c = c, C2/(C, +Cd RF+OCi

. . . . . ', ,292 . , Madical & Biological Engineering & Computing Mnrch 1980

.. I I >

<..

* 3-

' b I

i,p>;* ;.:,/le-

IC' ,,

iiii

'. i . 2 -

t:nes). Wt^"

i IBiD

F~~ ~ r s q u c n c i c r / ~ ~ , I I ( Z ~ R , c,,) > tC, the t r m i c r funct ion in eqn, 33 hcconii5 lar,$y iiidiclicridenr <;(

insnsitivc: to change5 iii C,,, and its niWi;itOdc IS iH( jw)[ z C,,,'(C,+C~) . . . . . . . (16) iHO*,)l Rri f Ri ~ RT) . . . . . . . (34) Es!irnated wlues for f, were as a rule higher than 100 H Z

with the permanent electrodes but in many instances Note that .f, is identical to /> uhcn RF - 'xi. lower than !O0 Hz for the temporary multicore wires. i t is appropriafe to choori RI. in the vi::irii:y of and be used instead of the rimpier

somcwhar larger than R,. l h c condifion I 9 1 2 is Often relation 36 when calculating C,, from capacitive loaded difficult to sati\fy since I; in wnic iniranics may evin signals. The value R,. measured as voltage!current ratio

' exceed 100 ti?. Consequently eqn. 33 wa5 used and the at myh-ardial thresho]?, frWuency jntelYaI 115. loo] H L c h o m h : n estima% was u r d as input parameter. in this way. C,, %as eslt- .Q~ and c,, from reiistive haded signals. I t .hould be mated over two different frequency ranges; [2O.J01 and

[60. ,uF from the impedancc model. since /O 1, mal¡. In a series of 31 patiints with temporary pacemaker elecrr3di (c) Detcrmination of Rr and CH with resistive load. w i r ~ , 91 analyses performed preiiperatively and on different postoperacive days gar,: the follouing eitimites In this caw q n . 31 was used without any approni- for fo; l.97i0.68 Hr (rnenn!cu.d.), range 0.76-3.96Hz. mation in the frequency ranges up to 10 HZ. For Rr the Sitnilar values were found from 63 aiialyscr of different same parameter value was used as In the previous section. implanted permanent pacemaker electrodes: The resistive load ought to have the same ordcr of f. = 2.01 magnitude as RI, but was as a tule chosen somewhat

smaller than RI to enhance the stability of the estimates (6) Determination of C , with capacitive load. Rr and CH.

The essential features of IHUY)~ us a function of Letting .Rr + m as before, one gets from eqn. 32 frequency when using resistive and capacitive lu3ds i r e

IHíj4I cdcL!d(l~-('"c~ R#) ' ' ' . (35) depicted in Fig. 8. The effect of omitting Rr from itis where Cr is the series coupling of CS and ~ZL. electrode-impedance model is also illustrated.

iii :h¿ ..il ' ' ".- ,.., cy rmzc whcrr .f, <f< I, the t r m rulic;i~n i, ~aigcly independent of frequency and rathc

frequency This provj<Ics a :i(i.,,ii i s riittier k p . w i v e 10 c h w e s in RE and XT:

Thus cqn, 35 had

~s inti, the

fairly safe to use I5 HI as the iuw'er limit wilen uiliiitinE 32.

1.26 Hz (mean _+s.d.). rungc0.6'>-9.61 Hz.

Medical & Biological Engineering & Computing March lSS0

. .. 4 ' ~ , ,. . . .. . . , " , , ~ , , ,

', , .,'TI IN OF THE YJITABILIT'! OF AN ELECTIN ICARDIO~~IG!J . < I! 'i'1-E RIGHT VENrltICULPl( E!IIiOC,'LRDIUM TO C íINTROL

I \ i , X T !6CARDIOS1 I?lULAT[I(

A. . Sheremer'ev and S . S. Grigorov UDC f) , .12-l:F 3.2,:- !i : 62 I. . '~ 035. :> 1. I1 , .97

b r treatment o f a s r r i t i s of dis turban :es of cai-i: a c rhyt.1 1 bio io i i t r i i l cardi.o!j! imulüt: !

I , w I o s t physL,i:togic 111 . B i o c o n t r o l c.$rdiostimii:. t o r s o f he R-e:iclusion type i:"de- :. c t :y ;e) have h i d t h e crezitest d i s t r i b u t i o n . 'They r e contl l l e d b:r a n e l e c t r x . :diosi! . i [r i . i n g from . i l ~ e c t r o i e s whic.h a r e a l so si.multaneii s l y use( f o r s t :mulat ion. 1. the c i : : f c :.in; r i l y appli.ed monm~pol~ar endocardia l s t imulat i~ct , t h e a( i v e e l i ic trode concii,: ::s the 1, 2 , i r d : um o f t h e . r ight - rent : r i c le , and t h e large-artizi i n d i f f e i n t e l e c t r o d e i s loc.. red suk- I 3 ,iriu:ly on t h e c h e s t ,if t h e p a t i e n t .

:or r e l i a b l e i r i g g e r i n g o f the cardios : imulator t e amplit de o f the t r igger in i ; ?lec- -, : : ( l . icsignal mur t be not l e s s than 2 mV ind i t s r a t o f char e musf be not les.; irtim 9.5 'l .

:n t h e a r t i c l e a r e piresfnted the r e s u 1 : s o f measu ing e l e c rocardios ignal pairai

]:lec t rocardios , igna ls were recorded f ro i i 23 pat ien . s : i n 1 2 a c u t e (cases (eight: ii:n frori

' IC lie c~rrespondc 'nce o f t h e parameters ob:ained to t o s e reqc red i s evaluated.

, . 'I 68 years o l d and four woman 63-66 yea:.b o l d ) and in 11 ch m i c rciises ( f i v e neri ages ' .!. 7 anc six women ages 44-82) . An a c u t e {irse was a . ' ase wher t h e i?.lectrode was :i:.tro- c I C ? for the f irst time or was e s t a b l i s h e d :not moire t : : m 5 day before t h e recordi i I i i 'I an 3T segment e1evat:ion c h a r a c t e r i s t l i : f o r an acxite c a s e 3s pri!:;ent on the Ei # 1 1 :mnic case was a c a s e where t h e e lec t roc la was i n t r o i u c e d no l e s s than 30 days l,!fiore I i t 5:coriing. I n a l l the c a s e s n a t u r a l c a i . 4 i a c c o n t r . i i t i o n s ( ithou:: s t imula t ion) cere ob- ! ! I I :. 111 t h e recordings were made u s i n g iinipolür r<':ording. As t'.ií! a c t i v e eltici: .ode i r . I r':, : t íc i t h t h e endocardium o f t h e r i g h t veiitricli? we ised n a t re (UZiSR) e lectrodes ; fVR-1 'i,! . a c i t e , seven chronic c a s e s ) , EKPZh-:L (one acute , two chr i i c c.iises), and fore. ~gn e l e !

I "c 1% ! o f t h e firm "Tesla" Czechoslovakia ( t h r e e acute and one ironic:: c a s e ) , the fi. :m "Cor.. : . : i " . ,SA :one chronic c a s e ) , and the f i r m "!imens-Íilemi# ' Sweden ( o n e acute c a s e ) . : . le lar! ' i ' i i I i i idi.iferent e l e c t r o d e was l o c a t e d e i t h c r in t h e io[ ? r a t i o n ' iund or subcutaneous y on t l : i

[he iight-chaniiel e lec t rocardiograph "YFngograf-:3,1 ' o f t h e i i r m 'IS Lmens-Élema" 1r.35 user 1 1: I ?<:or ling. On rlie f irst :s ix channels i7e recorded : 'ie EKG 1, ids I : 11, 111 , aVR, 3VL, a i ,

i I : . iiid In the seventh channel was recorded t h e e1ect : rocardios : p a l from t h e r i g h t 1 e n t r i c l t ! !d ( iirdi rm through a u n i v e r s a l d i f f e r e n t i a l a m p l i f i e r ':ype 854 m. !:1. The ac t iv !? e l e c t r o d o was swit thed h t o t h e iq . . ight ami . i f i e i ' input , and th,i indif. .

j 1:. I ': e l , , c t rode was switched i n t o t h e i n v e r t i n g input. , Thus, I

I ":ita d i o s i g n a l from t h e endocardium of t h e r i g h t v ! n t r i c l e -hich entered the b i c c o n t r o l - ! i h ; e : :ar i ' iost imularor input tías recorded, and not t h e I l e c t r o c z diosigr ia l obtained ' . s ing t l - t

#:)in. o f Wilson f o r t h e i n d i f f e r e n t e l Q - t r o d e , as ' ins done ' y Hurreler e t a l . (:l!275, rind Furman e t al. (1977;i [2-4]. S i n c e t h e v o l t a : ~ ~ ? rate €change! i n segment : iS was

1: L h , ' ewer o f 1 V/sec [Z, 311, recordings w?re made wj.ih a papf ' speed of 100 mmlsei: ( f i v e

: , > , . ;: i o f :he p a t i e n t .

part o:? the "Mingogi af-82"

the seventh channel t h e

. .

) * , i ,,'.tt i ardiac c y d e s ) and 1.000 mm/sec (on: t o two ?.y#: l e s ) .

11 a < u t e cases t.he negatl.ve monophasic Sorm o f t h e e l e c t r o c r d i o s i ~ p a l was recoi.:led l's'~ : \ i t e r (67% o f c a s e s ) . It: i s depic ted i . i F i g . la . ' i i t h a sn 11 R i k e , a l a r g e 3 s p i k e , '13 ai l RS segment wtii.ch i s a lr iost a s t r a i g h t l i n e . Les.! frequen l y (33 '2 o f cases) a 7íphasi.: : i ' 3 " t ~ ocai d i o s i g n a l from the r i g h t v e n t r i c u 1 , i r endocard lum was r corded w i t h roughly #?.qual L13 ' i ludes o f the I¿ and S s p i k e s depic ted 011 F i g . tb .

.-- - . . .- . -.

~~OSccw Engineering-Physics I n s t i t u t e . , i l l-Union C.irdiologi S c i e r i t i f i c Center , ,icademy ' I.te:::.cal Sc iences o f the USSR, Moscow. Tr;inslateri f r , !n Medits iskay,ii Tekhnika, No. 3 , pp. ' ' - I 6 , W - J u n e , 1980. O r i g i n a l a r t i c l e submitted May íi, 1979.

0006-3398/80/1403-0089$07.50 tC 1981 Ptenu-r Publ ish ng Corporation 89

TABLE . 1. S t a t i s t i c a l Data f o r Parameters of the Electrocar- diosignaf from the Rig t Ventricular Endocardium

Aci e alSr chlonic Cases

12 10.4 4.1 5.0-18.0 I 1 8.731.1 4.0-13.6 VRB. mV 77 I Z , ~ 5.5 2 ,036.4 56 10.5 4.8 i.z-z~..o S.S. v/ fcc 77

VST. mV 77 4.0 2.6 0.6-15.0 56 o o o

12 1 . 3 0.9 0 . w . o I I 0.5 0 . 3 0.16-1.0 2.9 1.5 0.84.2 56 1 . 7 0.86 0.4-4.2

I2 2.2 1.6 1.0-6,5 1 1 o o 0

a CJ) w m s e c

5 rnV&OO msec C

Fig . 1 Fig. 2

F ig . 1. Electrocardiosignal from the r i g h t ven- t r i cu la r endocardiud recotded i n an acute case. a ) Negative monophasic form; b) biphasic form.

Fig. 2 . Electrocard ios ignal from the r i gh t ven- t r i cu la r endocardium recorded i n a chronic case. a) Ne$ative monophasicforn; b) biphasic form; c) pos i t i v e monophasic form.

Inchroniccases, the ST segment e l eva t ion on the EKG disappears and a negat ive T wave i s observed. In 36% of ca$es a monophasic EKG of negat ive form was recorded, i n 36% o f cases, a biphasic EKG was recorded, and i n 28% of cases a monophasic EKG o f p o s i t i v e form was recorded (Fig. 2 ) .

EKG’s of the same morRhologica1 types were obtained a8 those Ci ted i n the work of iiur- z e l e r et a l . (1976) 131; however, the biphasic form was encountered less f requent ly both i n acute (33% according t o our data and 58% Bccord;ing t o the data o f Hurzeler et a l . ) and i n chronic cases (36 and67%. rCspec t i ve l y ) . observed, although i t was encountered i n 12% of the cases of Hutzeler et a l . [31. t h i s form was encountered iri our inves t i ga t ion i n 28% of chronic cases. ed i n the d is t r ibut ion fqequencies of EKG’s by morphologic type are poss ib ly explained by the smaller number of EKG‘s done i n OUK wcrk.

i n acute cases the monophasic pos i t i v e EKG was not However,

The d i f f e rences not-

From the e lectrocard iog ignal recordiags obtained we determined the fo l lowing: the peak- 1 to-peak amplitude of the RS segment Vas, the ST segment e l eva t ion VST, the amplitude o f the

T wave VT, the vo l tage ra t e of change on the ñS segment SRs (calculated as t h e r e l a t i on of the amplitude V the T wave ST (calculated as the re la t ionshtp of the ahplitude VT to hal f the duration of the T wave). Parameters VW, S 1000 mm/sec, and parametersv i , ST, were determined a t apaper speedof loom sec. S ta t i s t i - c a l da ta f o r acute and chronic cases are paesented in Table 1.

to the duration o f the vot tage change), and the r a t e o f vo l tage change f o r RS

and VST. ware determined from the EKG using a paper speed o f

An analysis of the date obtained revea ls the fo l lowing changes i n the e lec trocard ios ignal .

90

L A from t h e r i g h t v e n t r i c u l a r endocardium when going from an acuti? t o a chr0ni.c c a s e : M e amplitude decreases roughly by 17%, which, according t o a s tudent ' s t e s t , i s s i g n i f i c a n t with a p r o b a b i l i t y o f e r r o r of l e s s than 30%; the .rate o f w l t a g e c r e a s e s by more than two, w h i c h i s s t a t i s t i c a l l y s i g n i f c a n t w i i : h a p r o b a b i l i t y l e s s than 1%. ST segment e l e v a t i o n completely disappears .

These conc lus ions q u a l i t a t i v e l y co inc ide wit:h t h e d a t a of Hurzeler e t a l . and e t a l . [2-41. However, upon q u a n t i t a t i v e comparison o f our own data n i i t h t h a t o f

According t o our data, i n acute cases the a m p l i t u d e VRs on the average i s

e t a l . and Furman e t a l . [3, 4 1 , the fo1:lowing di . f ferences a r e noted.

r a t e SRs i s l e s s by 55%, and e l e v a t i o n VST i s less by roughly 50%. I n chronic tude VRs on the average i s 17% l e s s , and rate C

s i g n a l d i r e c t l y from t h e a c t i v e and i n d i f f e r e n t e l e c t r o d e completely agrees with the decrease of VRs by 20% c i t e d i n t h e work of Wurzel.er e t a l . [ 2 , 31 where the e l e c t r o c a r d i o s i t p a l i s taken o f f us ing Wilson's i n d i f f e r e n t zero e l e c t r o d e . change SRc obtained i n those works where t h e r e is t h a t k ind of change o f the lead :system can i n no way expla in t h e 2-3 t imes smal ler magnitude o f CRS recorded i n O U K investigai::.on w i t h a high degree o f confidence.

age i s roughly 3 t imes l e s s than the amplitude of t h e RS segment VRs, and t h e vo1tag;e rate change S T i s approximately 25 times l e s s than SRC. Not one EKG with VT l a r g e r than VRs ox with ST l a r g e r than 0 . 1 SRS ( i n the same p a t i e n t ) was observed. SRs exceeds t h e maximum o f C less than t h e rate change maximum f o r the T wave S T = 0 . 1 2 Vlsec c i t e d by Hurzeler e t a l . [ 2 , 31. Such r e l a t i o n s between amplitudes VRs and VT and rates S T completely confirm t:he p o s s i - b i l i t y o f i s o l a t i n g R s p i k e s i n the presence of T waves using a high pass f i l t e r (i.n t h e s imples t case of a d i f f e r e n t i a t i n g RC c i r c u i t ) and an amplitude d iscr iminator [ 2 ] which i s used i n input c i r c u i t s o f b i o c o n t r o l l e d cardios t imulators .

i s 70% less. RS

A d e c r e a s e o f t h e amplitude VRs on t:he average by 17-202 when taking t h e e l e c t r o c a r d i o -

B u t t h e 5% decrease o f v o l t a , g ! r a t e

S t a t i s t i c a l d a t a for t h e T wave i n chronic c a s e s show t h a t t h e amplitude VT o n t h e aver-

The minimum o f the r a t e roughly by a f a c t o r o f 3 . The l a t t e r i n t u r n i s almost 2 times T .

LITERATURE CITED

1 . I. A.' Dubrovski i , S. S. Grigorov, V. A. Bezzubchikov, et a l . , Ked. Tekh., No. 6 , 25-30

2 . P. Hurzeler , V. De Caprio, and S. Furman, i n : Advances i n Pacemaker Technology, M.

3. P. Hurzeler , V. De Caprio, and S. Furman, Med. Instrum. , 0, 178-182 (1976). 4 . S. Furman, P. Hurzeler , and V. De Caprio, J. Thorac. Cardiovasc. Surg., z, 258-266

5. L. Zaks, S t a t i s t i c a l Evaluation [ i n Russ ian] , Moscow (1976) .

(1976).

Schaldach and S. Furman, e d s . , New York (1975) , pp. 307-316.

(1977) .

9 1

. : .. u ,. , .. . . - -

'! " . ;. . ., Anafysis of' the coupling of electromagnetic - - : . . interference to unipiar cardiac pacemakers

:,,. , .. . .-&I. .. . , , . . ~

,. ,

. .. ...

" . ., .. . ., Anafysis of'the coupling of electromagnetic interference to unipiar cardiac pacemakers .

.

, .. . .. . . - - . .-,I.

. ,

.I

. . -5 !.I!z)

. , . .

i

1

.- , ,, . , , : / abstract-A tkorclicai an'alvsis is developed la determine lhe behawiwr of the unfpolar pacemaker

calheler as a :ecawJng aeiul. The lheory is used lo predicl lhe effecl of pdfdmetars such as l ie i rewncy a m lne length of the catheter on lhe couplmg o i elecrromagnelic meriersnce

' : 16 fhepacemaker. itre resuhs are presented in lerms of an equivalent cifcuil which is ussfu, for developing simple e*perimenlal tests la evaluale lhe susceplibilitv oi pacemakers to elecrro..

: ' m~nelicinfwfeferice ... T ~ e rheorelical resuhs are shown lo be in good apreemenl wilh measure- mmts made on an amat catíxheier.

.Y .,,. , . .. , . .

'

tic interference. Sus~ptibffjry

. ' . , . .. . .

. . . .

be reduced by providing a better metallic shield over the pacemaker generator. while the second inechan- ism can only be controlled by introducing nrwcircu- ¡try info the pacemaker. Expcriríients hdve shown that pacemakers equipped with a unipdar catketer. as shown in Fig. 1. are the most sensitive to elect:o- magnetic interference when coupling IS through the catheter (Roy. 1975). Frequencies in the \.h.f. and u.h.f. bands are usually the most erfecrivs for coip!irig energy via the catheter. while niicrowa\e ircqueiiciel are the most eíf.ective for directly coupling to thc pacemaker generator.

The susceptibility of pacemakers io intederencs from high-frequency electromagnetic radiation is

'. .. riidio or micrOwave frequencies wli,,amplitude mod- usually evaluated using an enpcr:m:nta! t ist - procedure similar , to that recommendd in ths Pacemaker Standard (1975)ofthe .issocia:;on lor the

; ~ ( L I C I I I E K ~ ~ u!.. 1965; YATTEAU. 1970: BOSXEY Ct d.. .4dvancemeni of híedical Iiistrumentation. The schematic in Fig. 2 shows the arrangement of the equipment for this test. The pacemaker is S U -

spended in a rectangular plastic tank containing a saline solution. The size of the tank is chosen iargs

:A - :. ficemaker gcneratOr by directly i:oupiing un. enough tosimulatean infinite half-space oithesaline. The catheter is PSitiOned parallel t« and a; a disi- ance d from one side of the tank. Elxiromapneric

the-pJ++;iker radiation from an aerial is incident on this side o i i h p which tank with its electric-field vector parail:! to the side.

If the distance between the aerial aa.1 t h ? tank is . siifficient. the radiation impinging on :he tank is a

good approximation to a iiormally incident pidne wave. To minimise the reflcciions iron1 ntarby obiectr. the test is performed in an anect!oic cnamóer.

37

kt?-may (zsynch. Icctnc3!

i t is also sensitive io externally generatzii interfering signals which mimic cardiac elixtrii:al ac:i:ity. It i s wcll.documented that an electromisnetic sipnal a ,

uiation Can enter the pacemaker and kdemndolated hy the cirwitry tÓ produce this type of interference

1973: yAx wiia vAs ~ n n R v i h c H . ~ * c ~ , , , i?j4: .~*L . ..-~ S<.)II.ENTZ. 1975; M ~ ~ ~ ~ ~ ~ - ~ ~ ~ [ . , 197h;;&ssy

l !

... -

, .. ' - 4 &::.1977). ~k 4 i, ~l~~ ~ e c t r o m g n e t i c niay en!er-. the

. - 4iiclded electronic components or by . .

1

- A L L ' rliro~Fh+a?y j p i r f ~ i e g rn tiit m e t i a n i c c a s ~ ~ ~ ~ t e l e c - s/8i/0100s7+i3 SOt~5010 - , ' . . ' IFMBE: 1981

L

. <

. .

i\ne,jic.l! e. lR>G!3~,c.,l r;..~. .~ Medical & Biologicai Engineering &' C o m p u t i n g ' jan"ary 1981

. . 17;)

? .i

1 .' Electrodes in the saline solution arc used to rnoiiitor the pcrf.irmanci olthc pxcrxh:r and to L!c::rm:i:> the threshold lor interfcrcncc from the radiation.

An alternative test procedure to llle above is to inject the high-frequency interference sigrd into the pacemaker generator directly at ihe tcrininüls ?or thc catheter (output terniinals). This procedure I\ simpler

and much less errpnsivc than the one dcrcribed above, sinci it climinstcs the iie.-d for ~nlilier,ioil fir thc unit and replaces the high-power r.i, so~i?ce. arria! and anechoic chamb:r with a low-power signal generator. For this alternate procedure IO be succes~. ful. the relation (transfer function) between the 117ci. dent electromagnetic field and the voltage produced

i' : Q-

i

i . - . . - i ." ._ y. . , .

. .. , .. / I

.r

. .

. . ~. , .

. .

, .

. F\ helically COlled

r --------- I I I I I

I

1 ' ~ aerial I , .: . . , . .

I Cardiac piremuher w r h unipolar corhrrei

anechoic chamber ..

Medical & Biolcgical Engineering .3 Computing Januaw 1981 . . . . . . 98

. . ,, .:&.e..&-

.. .; dcscribcd 1 .: .!r:mer\ion of ,.!, source. aerial .., lwer signal , I , , i x 5uccess- . . i : i \ i ~ e ~ ~ the inci- ii~i:~!~i produced

thc terminalsolthcc;iiheterIiar;io hckii:wn.T!-.ii aIlows the signal inJC!ClCd at tht: tcrmindc o1 :he pirccmaker to be equated to an incident clectric field 01: power density.

I n this paper, a theoretical analysis is presented which determines'the relation hctueen the volt;i@r produced ai the terminals o1 the cathetcr i c d the

. : .I .. . . : incident electric field. The geometry for the model i s tlic" same as the ideal geometry which the test

. 1. ! . . ,. procedure in Fig. 2 simulates. ¡.e. a. plane electromag- P netic wave normally incident on a plan; interrace i , . . . '' . hi(w¿%n two semi-infinite regions. The results of the

theorf are presented in terms of a simple equivalent circuit (the Thivenin or horton equivalent circuit for a receiving aerial) and are 5hOWn to bc in good agreement with measurcnients made on aii actual catheter. The theory can be used as the basis for the aforementioned simple test procedure for susceptibi-

. lity. The theoretical model also gii:es insight into the . .ellcct changing parameters, such as the frequency.

length ofihe catheter. impekdnce ,at the terminals o í the pacemaker. etc., ha\.e on the c,oupling o( I L -1 ectro- magnetic interlerence into the paccmaker.

< .

.

. .

'

Iiclically coiled wire oí coil radius LI covered with a concentric cylindrical insulating sheath 01 radius h. At thedistal end, the catheter is terminated by a bare metallic electrode and. at the proximal end it is attached to the pacemaker generator. Both the catheter electrode and the metallic cose over the pacemaker generator are in .electrical contact with the surrounding saline solution.

In the theoretlcal model shown in Fig: 4. thc electrical contacts with the highly conducting saline solution at the electrode and nieiallic case are replaced by parallel perlectlv conducting image planes. The image planes are espected I O be a good approximation to the actual geometry when the electrode behaves as a short circuit irom the catheter to the highly conducting saline solution and the dimensions of the mctallic case of the pacemaker are much greater than the radius of the catheter. h. Each 01 the material regions in the model is described in terms 01 the efiectivc electrical constitutive parameters. viz~ the effective electrical conductivity o,. the eliectibe permittivity E. or relative eliective permittivity &*, = E. E,,. and the perrneabilit) ) I which is assumed lo be that lor lree space 61 = vu iur ail the materials since thev arc nonmametic. The subscrims

r .3

E~~ ~~~~ ~~~~, i = O, 2. 3 are used to denote the parameters Tor the air. insulation on the catheter and salme solution. r e s p ~ t i v e l y . * The air is assumed to have t h e param. eters af free space G , ~ =O. E& =E. aiid the sylastic insulation to be a good dielectric G',2 = o. F~~ a

harmonic tirne dependence e ,(, the wave-

2 Theoretical analysis The theoretical analysis developed in this section is

based on the experimental arrangement in Fie. 2 lor determining the susceptibility of pacemakers to elec- iromagneiic interlerence. The experimeiital arrange- men1 is an approximation to th8c ideal zeometrv ii,imhi.r in i is ... . ._ shown in Fig. 3: Here, the unipolar pacemaker cath-

~~ = B . - j,, = ,~T.------ I eter is lacated parallel to and at a distanced from the L 8 \,&~l<l<a(l -)Fec)

interlace between the saline solution and air. The where f electromagnetic radiation is a normally incident 0.. = u.;. W..i

air E saline solution

distal electrode

incident plane wave

\ sviastic j 1 4 , x

insulation

J<iiiuarv i s m I Medical & Biological Engineermg E Comput ing Januc-y 1981 I a-

i

99 .

I .... "

" is the eñectivc loss tangent.. I,. = - ró,,'(z + Z,.)

= ISC Yl.!( Y + Y,.) ic 4

The unipolar pacemaker catheter acts as ap. :-- sulated linear aerial when receiving electromae::tt,r signals. The insulatedaerialis peculiar 10 the siiud:.':- where an aerial is immersed in a material med.-- I t is formed by placing a dielectric sheath o¡ I,.:%

j

I : ,'

.The ohjrct or the theoretica! anaipis is to derirc Art expression lor the voltage V, across. oí currcnt I , .

-through, u load impedance Z,. connected :o (he. terminals of the catheter when a plan<: wavc with electric field strength E' = E'(r)i = EOCJ'* , ' ! is

t .. incidcnt. see Fig. 4. I n the analysis, thNe catheter is 1 treated 'as a receiving aerial and is represzntrd.

+d -f image plane \\\\\,\\\\-

saline solution

0*3. c.3.flll

L - incident plane :,\,,\,hi I h. [\,,;,\;\, imase olane

by the Thevenin and Norlon equiralent circuits shown in Fig. 5. The elements in the equivalen! circuits are the input impedance Z = ,R + jX or the input admittance Y = G + jB of the catheter when i t is driven at its terminals. the voltage receiied at the terminals of the catheter when they are open circuited and thecurrent lsc received al the lerminals of the catheter when they are short circuited. Th.: elements in the two equivalent circuits are simply related by

Y = IjZ (3) Isc = - V",/Z (4)

Once the elements in the equivalimt circuit 2. V,,(U. f sc) are determined. the signals at the load impedance Z,. = R,, + jX,. (admittance Y,. = G,. + jB,. = i/Z,.) are easily computed.

VL = VorZL/G' + Z J

= -fsr/(Y -I. Y,) (5 )

4

"0, -

Fig. 4 Geometry for rkorrticul o ~ l y s i s

1

Y+

/- *L Y

lo0 Medical & Biological Engineerin: & Computing January 1981

1

i :-, 1981

y1 = jruc, = jw2nr:,~iln(h~u'j (:)&where the cliaracteristic impedance Z , and complex - Piavenumbrr k,. can be expressed in terms o1 the ?*::!es pnpedance and shunt admittance per-unit length

,:,.a.+.-, ,e....,,>?, nce,per-unit !cngtli due io tke sxternalr;:

. itiductaiice . '. .

',' i

ere .H!,'!(;) is th&&seLtunction of the iliird kind = - jc tan(k, / ) :Z, (17 h the thebretical model of Fig. 4. the distal end of

:.. is ;hort-circuited the imaee planE .. :... . . . , .. . . I . . . at z - I. When the terminals at the oroximal end o i

snkel lotqion)oí Prder VI. and ilic~impedaiice.pe~ ..: :. gth [oi~lh5-<e!icarcoil that iorins ihc catheter.

F."=,=&-+T&--- I . . , _ , I . . , . . .

' . (fqo-"the catheter are 'short ciicuited to' determine t i e

i ~" *:, ~1 .current I,,.. the termination is identical to that at the ' - : disial~end. The catheter. interlace and incider.: fieid

are then bounded hy infinite parallel image p!aiies ríectly conducting planes) at 2 = O and : = /. B\~ lying the method of images, this geometry can be

lo be electrically equivalent in ihe repior. 1 10 one where the catheter. interface and ail infinite ii? the : direction. ¡.e. extend to

k, The electromagnetic analysis lor this new ,I + . geoqetry is fairly simple. After transmission through ,: .. the air saline interface the iticident Field at the

A catheter (1 = d) is .~

.. (15) E'(d) ~ tE,e-",*'")' ,

Fjg. 6 Eyuiiulrnf cirmii lor !mif fr,itgfh i>l:I.~~,n.ssiisU,>,i i i w L - - p ~ v " i ~ < ~ f h < y - -- - - - .. . .. _....-...I c.= &lib + k,).~

Medical & Biological Engine

wher-the iraiismission coefficient T is i

1 (19)

101

I .' '

. , - .~ . .., .~ . . .. . .. ,.. , .., ,. .

This field produces a current

' Is= 5 E'(d)/:, (29 in the fatheter lead (iniicr conductor of the transmission line).

Eqns. 17 and 20 for the input admittarice and thc short-circuit current with the Norton equivalent

j circuit (Fig. Sh) completely determine thi: operation of the unipolar catheter as a receiving aerial. The , elements in the Thevenin equivalent circuit (Fig. 5a)

, and the voltage and current in any load impedance I (admittance) connected to the termin:als of the

catheter are simply determined from eqns. 17 and 20 I wing eqns. 3 -6. ! Note that the scattering of electrornagne!ic energy ~ between the catheter and the airisaline interface has

not been included in the present analysis. This approximation is equivalent to assuming the catheter is in an infinite saline solution when determining the input admittance and neglecting multiple reflections ofthe incident field between the cdthster and ifiter- face when determining the short-circuit current. This approximation improves as the attenuaiion in the salinebetween thecatheterand the interfac. -increases. ¡.e. as the frequency. distance d, or conductivity nc3 is increased.

, .'

. .

3 Daenninntion of parametem for catheter

Physical pxameters for the saline solution and the catheter appear in the theoretical exp:essicins descrih- ing the operation of the catheter as a receiving aerial. For the catheter, the parameters whic'h must be determined from experimental measurement are the electrical properties of the sylastic insulat,ion orl and E,*' and the resistance and inductance per-unit length of the catheter lead. ri and I,.

The electrical parameters ola cylindricti1 sample of the sylastic were meastired over the frequency range 60 MHz < .f < 500 MHz using a standari! capacitive test cell (BUSSCY, 1967). The measured relative enec- tive permittivity E-,~ of the sylastic is shown as a function ofthe frequency in Fig. 7 (open circles), and

is seen to he constant. I : , . ,~ : 3-0. The etTective con- dtictivit) nez dthe sample was very small and no; rneasurahle with the instrumentatiori used. The sample of sylastic was immersed in a saliiis solution of eíiective conductivity 0- 2 1.9 %m and measured periodically to see if the solution had permeated the material to chsnge its electrical propertier. No significant change in the permittivity or measurable increase in the conductivity was observed over a six-month period. Measured values oí the permittivity sRer six months immersion are in Fig. 7 (fui1 circles). The measurements show that a reasonable choice for the electrical parameters Sor the sylastic insulation on the catheter is <i.> : O. : 3.0. even when the catheter is immersed in a salinr solution.

The tightly wound helicai coil that iorms the catheter lead behaves as a lossy inductor with an ini- pedance per-unit length &. The inductive part (c of this impedance isexpected to be lairly independem o¡ the írequency and the resistance part re to be propor- tional to the square root of the frequency as a result of the skin eíiect loss:

:< = r, + jaiC = cI ;5 + j o C , ,421) The constants C, and C1 in eqn. 21 are not ersily computed theoretically owing to the proximity cíiect between the turns ofthe coil (SMITH. 152). To measure C, and Cz. a length I = 320 mm of a standard unipolar catheter with its distal end stripped of the insulation and a connector (SMA ;ype) attached IO

its proximal end was cast into a block of nietai. see Fig. 8.. 'The metal used had a low melting tsmpera- ture. SO the casting was accomplished without dam- aging the sylastic insulation. The catheter with its distal end in contact with the metal forms a section of transmission line terminated by a short circuit. 'The input admittance Y at the connmtor is given by eqn. 17:

Y = G + j B = -i ctan(k,l)iZo (22)

' l h a ~ n m ~ ~ r c.lh=te, b d I> Iormd horn w m w m radius of O i Z mm wound rmo coi< o1 radws # ~ 0.33 mm with npmoxrmnnv 35 twns, crn lhe radius d h a I Y b S t x msulatmn Y b - I Z ? mm

2-1 Fig. 1 Rehriw psrmirririry (di!ielecrnc con-

sranrl d sdasric os n lunciioii 0 1 I O before being placed in saline . , . Jrequency

aher six months in saline

. . . O

O 100 200 300 400 500

frquency, MHz

' I . , , , , ,

., 1 o2 Medical & Biological Engineering & Computing January 19üí

i

.my.- <---..*

.!¡ve con- ,,!,:til anil 1101

,. .-cd~ Th? .,: : solution .<> ,niasured

,,:rnicated the ' ' !.tics. No I 8 *::isurnhie s.;. 4 over a i I I K permiiti-

, .- ;on:il>lc :i ..c sylastic i , ,2 t- 3.0. even ! , . c!ution. . . fhecath- , ..., :, al! im- :tive pan I, of :I<', <dent of , 2 , <propar- u.; .s ;1 rcsult

1' ' 'Y:. 7 (lull

31: ,101 easily rnsimity eífect ,;'i. To meas- t31 siandard 'ra;.;rd of the

:+!ached to I ,' :ictal, see i!; tempera- wi.iioui dam- iliefer with its .., rcctionoí ':I 'cuit. The 'i~ ... $¡ven by

_ I

'uiih the characteristic imprdancc 2,) acd waKoum- hrk,,determined bycqnr. 14:ind 1 5 . The impcdnnce

line are . .

and admittance per-uhit lcngth lor ih.: trünimiision .:L = 2= + r; +IC ~.

(23)

i SL = Y2 (24)

Fix. 8 Detail ojcmhmr c a t in met41

. .

16

1 UleOr"~

l. : ' 12 . . 'B experiment . . . . .

. . . . . .

1 . , I ? 8 0 - .

. .

, , - 4

1 I ' O --

303 400 Fig.9 Comparison ofme4wed mi iheor. erica1 inpur odtlirranrr Y = G + for carherer c m in m m i . I = 320 mm

frequency, MHz i

. . . .

. . . . 103 i

Medical & Biological Engineering & Computing Januav 1981 . . . . . . i , .

,*bni z+, ,and . yz,-arc its in cqr:c. 7 .::d ri ~ ! , l ! stants: C , = 2.4 x 10.' Rim(Hz)l yrr-unit

. h g i h of (he mctii,putcr condi~tor 5 LIli: oleal "is a good conductor with conduciiiity 6". ri, and i:.

and C : = flm.+& iS.,(hC, intcrnaI irnl-c,( 4-5 x 10 ~' H m írc = 2-4 x 10-','0 n m and 1, =

J.5 x io.-" H-m). It,.is interesting to note that thesimple formulas Sor

the ~' inductance and skin-effect resistance per-unit ite coil give rc : 0.81 x

3 x 10.' H m. These ured ones primarily be-

s are not included in :he simple

are simply

. ...,

detefminld by fitting eqn. 22 to a. set ni mcarnred values fot th,e admittance Y o x r tkc Ircqucncy. range

i f % easy to use the theoretical analysis Sor the catheter to study how changes in various Darameters.

f s-4ou: .M&. lhc, T C I L I I ~ S cPdik ' l ike the frequency. afíect the electromqneric interfer-

pacemaker. The corresponding eaper~mental inresti- shown in Fig. 9. wliere tnr measured ence (voltage VI.) produced iif the leniinals of the

line) computed usini the con- gation is much more difficult to perform. In this M wL-.S-a<-e compaxd wirh#hior-

'"1 .- . .- -

ea

I 4 1

T1

cuihctcr is shown as a function ol the frequency (?O MI-lz ? f .5 500 MHz) for two lengths o¡ catheter, t - 3Ml nim and 6(K) mm. B o t h components o l the admittance C and B are oscillatoq iunstions ol the frequency ai the lower frequencies and bccoms fairly constant at the higher frequencies. Ths oscilldttons are a result of the currenl in the driven catheter being a standing wave. The standing wave is evident in Fig. I 1 where the magnitude o l the normalised current l It V, [ is graphed lor the 600 mm catheter at a frequency oí,2@ MHz (dashed line). The standing

-wave U produced when energy travelling down the catheter is reflected at the electrode (short circuit). At the high frequencies, the attenuation constant I , . is large a d only a small amount of the energy travelling down the catheter reaches the elec!rode. TI:? current decays exponentially along the catheter and only a small standing wave exists near the electrode:

f = 20 MHr .---- - f - 500MHz

U t s .<--.: .-: ,i.óo -..

...,, 200 300 4w 500 frequqw. MHr

Medical , & Biological Engineering & Computing January 1981

1.0 * r; x

1 O5

. ., . ,< . , . . ,. I

I .

, . . ig. 11 lor ~ b c úoo rnm cdihiicr at

.i&cquswy u1 500 M t k (solid line!. The rxponciiiial decay..cauas thc current lo he locaiised near !he proxinul &;(driven end) of the cai:heter at high úequsocies A inoderate change i n the length oí ihe catheier,:herdore. does not change the current or the 'inau:iU(mrttilii~~..This is why G and for the 300 mni and NKI tnm, catheters approach the same limiting .valueaT tbcfrcyiieiicy is increaced. sec'Fi.g. 10. Al the hipher írcqucricics, thc qiiaiit i t? *!.I is large SQ thai the trigonornctric iuiictior! ctan:k, i) : ji arid ike i n i C i admittarice (eqni 17) is Y,,, : I Z,;. The iinfkdaricr .per-unit lcngth is approximatelv í,. ::jodr making iihe high-frequency raliie for the inpiit admittance

. .. .~ . .

, ., :..-. (24)

aiues used in the examples. G,,FFLI mS (R,,p = I /G , ,F : 190 0 ) whic!i is in good agi&ment with the value computed from the full theoiv ?d hieh freouencies. see Fie. 13.

- ~ . ,

/c3g/i. of lead (7 = 300 mm. W) mm) as a resuit of both Y arid being ind'ependeni, of the lengtk, (11; ~ = I!?, 1.1 i ; ~ + G,;J). The deca! of the voirage ivilh iiicredsing frequency shown in Fig. 13 estrnds 02 into t h e riiicrowaue-ranpr.. In this range. the ioliage imduced hy the catheter at the terminals r f the gexr i tor can-k'so's!iiall that i t 15 insignificant compared to electromagnetic signals coupied dtrecily ii, tlic iiircuitry ofthegenerator. This is u h'the 1311er mechanicm For mi!?ting electromagnetic. interferencc !O ;'nor!y shicldGd paceixakeis is the most important at~miciowaw íirqucnOSs; ~ - '

A n -important c6nclusion that can LY drawn from the rew!!s in this Section is that for nigh frequencies (.f?;W WHr) and a t h e t e n of madirate k n g h 0.1- 3&3Tiiiri). the e1miienti-m the Xonm cquivaieni &cüit for the mthetr . Fig. Sh. are v u ? simple. The ~-~ i rku í t . ca*mt is girenbyeqn. 2 0 m d the input admittance is simply a conductance G,:: given hy sqn. 26. If the Thevenin equivalent is desird. the elements can e2sJybe eomputed from eqns. 3 and 4. _-

> T#e4~&n'itude of (he shon circuircurrent 4 I., c r I . 5 .E, & v c l o d at the terminals of tlie catheter bv the 'perrmentP' verification Of Y

hcident-;plane &e is shown as a function.'6rtKe ' ' tn order 10 provide experimental verification for - frequency (n Fig. 12'The current is sox to decrease the theory Qexelopedj?'the previous Sections. a series i.Dn>Jorlically with increasing frequency. This de- Xñi&ureménts'weri performed on a standard uni-

$$ai(c is a result- pf the iiicrease in the attenuation in polar calhete!. The cr!$eter selected \vas of tlie same B e saline. ¡.e. an iiicrease in z3. Note ):hat the short- fyj j j i 'Sdescrihtd7n Ssction 3. had a length I = 571

cilrrcnt (eqn. 20) d o n not depend on mm, and radii for the lead and insulation o l u = t)33 r m and h = 1.27 mm. respectively. Ta measure the

agnitude of the voltage 11; 1 dhepd - - i r i p i adniiffame of the catheter. a connsi'tor iSS1.A C l i o ~ ~ - ~ e s i s t a n c e R,. connected to the' ty&kas..auackd Mthe proximal end a d this was he catheter is shown as a ~ u n c t i r r n . o l t h r _ . i n o . ~ ~ ~ . ~ f ~ p l a t e . The catheter was then

frequenci in Fig. 13. Note that at the lower Irquen-. suspended elow the pl+ejnto a saline soitition K i t h

cies the voltage produced a: the pacemaker terminals an eiTrcliie conductivity a<, 2 1.9 S m. The c x p r - t Eo f =-?75 'h c m he its large tmrr!!nt-mníigtration resembled tr,a shorw in Fis. S

At the higher frcqwxies .*¡ti: the tasi metal replaced by !he salinc solution. the voltage is approximately the same b r . both The input admittance I = G i jB mcasurs3 at ttir

. -._._ . <.. .- - ,,,, . . * . i r . . . .i I . . ~ . . ,

,!,I. J I.C\Ult of ,i..m 01 t i x 1C:ligth ' ' . d ilir voltage

, , ::x terminals of . ' i, iii,ignificant

,., ouplcd directly .4.. $s why ilic latter .::.XI~C iiitcrkrence

.,,' 'iiov impurtant

he drawn from ,_ r i,igli frcqucncies .>: ' 'Idcrate length , .ion cquivalent ..c.,cíy sirnpie. The

20aiid the input :.' i;?;, given by

. ...

." :IS oithe same

ir *:$ measure the .a mector ISMA . , I i r d ihii was k . ~ 4 ~ i u e r was then .iii;ic solution with :i. The cxper-

'i:, $own in Fig. 8 ; K saline solution. b 7ipsured et the

1 ,

.\:wary 1981

I:illlli~illc of thc ~arhcrcr (zGni;xiar) i, ~ I O U I ~ ni t i [i,r,~~im or the frequcricy over tlic r.inoc 25 MHz, c

.IO(J M t i L ill Fig. I4 (circic';). Thc th:iire!ical re- ..UII\ (solid line) are seen IO bc in :ocd agreement .y,itt ilic measured vaiucs 'Thc 'iieht difii,rcncc be. tWLl;ti thc tbeoretical and exp?rimen!;i! v : i I u ~ s o iG at thc liiylicr frcqucnciei is thou!i.ht t o hc :I junction itf~ct. i.c. a rL%uIt ofthe gcometry ofthc rci:\on where tk catheter and connector are joincu (:.;I,.G ri ul..

''

""79fT). Ahitn&i<innsfexpcrimmrai check

ihc vullagc at the terminals oí tl7.c citilieter was m&rxurcd when i t was irradiated in a nianncr similar tu t l iat shown in Fig. 2. I n designing this ex;>criment. the components and their arranpnent ~ c r e careíu!ly CII<IICI~ so as lo model t he ideal geonetrj or Fig. >as wiU.as possible. The thin-wailed polyeth>iene tank rliown in Fig. 15 was used to hobd the saline solution which had an ellective conductivity of * 1.9 S/m.

... rtie catheter wi!h the connector and mal¡ metal plate attached lo the proximal end 'was attached I O a very thin nylon cord (radius 0.25 mm). The cord was stretched parallel lo and at a distanced = 50 mm ( 2 2 in) From the wall of the tank This arrangement held the catheter in a fixed position without prturb- ing the electromagnetic fieid. A vector voltmeter probe measured the voltage produced at the ter- minab ofthe catheter (connector). The probe and its lead were contained iii a watertight plartic tube rhat extended from the wail of the tank to the connector on the catheter.

At a frequency O F 450 MHz the incident field mea .tired in the anechoic chamber at the locaticm of the tank (tank absent) had a componenr parallel to the catheter of lEoJ = 3.15 V m. The voltage measured across thevector voltmeter prohe (2,. 5 - j140 R at 450 MHz) was V, = 0-580 mV (0.184 mV for a I V8 m incident field). This is to be compared

11

O I 1 1

frequency. MHr ZOO 300 400 100

14 Contpoñ.wn olnworured and rlieorurirul i n p r ad- rniltcnce i' = C + j B @ vniplar mrhn.r. I = 572 rnm

1 I 1 200 300 400 100

frequency, MHz

Medical & Biological Engineering & Computing January 1981 107

. . . . ~ . .- . A

Technícaf note

.' ' ..Pacemaker vectorcardiograph .. ~ . . .

. . . Keywords--€.C. G.. Frequency moduls!ion. lsolaiion ~mpiifier. Pacemaker. vector cardiograph

~. . . . . .. .

. . . <* 1 IntrVdUction

-. . . Tm'pacemaker vcctor cardiograph ha, betn devclowrl . Io c~niplcment the equipment already in UIC a t the pact- &lg clinic of the Kent and Canterbury Cardiac

. ~. . The.pactmak& veetor cardiograph provides a visual ._'-.-4isplay of the magnitude and direction of each pacing

. . - - pulse on tlie screen o f a storage scope. whereas the equip-

. . ., , mat. already in use provides B digital display o f the . . average magnitude and rate of sevemi pacinr: p u i s . The

. main application. !herefore. of the ?xeniakrr wctor ' ' 'cardiograph will be in checking for iiiicrmitteni faults in

the pacing circuit. as a fault that mcurs for ii single pulse - . . . ' siwuld..be readily observable on the display of the storage %o'&. This'facilit), for example, wi:l be useful in looking

. 'for thc type of'laulr that cauces the patient IO mmrt the loss of pacing or ihc presence of pulsed pain when

, . '. The vector cardiograph facility has beeii included in ordSr that investigations may be made inlo The effect of

. . exercise oh the heart vector, as i t i s hoped that this will . , . . . . . gi? further information o! the way in which tne damaged heart functions under load.

: . . Dcp;lrIment fFrTZIrRALt>. 1977).

. . .. . . . .

... . . .

. . . .

..

' ' moving through Certain postures.

. . . .. .

. . . . . . .

IlievLrtorco-ordinatesuudarethoreoftheEiniho\eii lcfd Cystem ¡THOMAS, 1974) so that

1 X I = B [ L A - R A ] . .. . . . . . . (1

Y , ; - [ ( L L - R A ) + ( L L - L A ) . . . (2)

whrie LA ir left arm, RA is right arm. L L is left leg and Bis the gain ofthe system ( 2 10 for unipolar pacernakcn, 100 for bipoiar pacemakers and approximately loo0 for the e.c.:.)

in order to reduce the number of iiecessary inrut amplifiers (THOMAS. 1974). eqn. 2 is rearranged as follows:

Y ~ - - [ Z í L L - R A ) - ( L . . I - R A ) I . . . (3)

.Thus. only two differential inputs are needed (Fig. i j so that

channel 1 - ' R A - L A . . . . . . . (4)

E ' \ 3

'9 \ 3

and . .

channel 2 = LL - L A . . . . . . . 0)

? $

..

channel 2 isolalmn stage

roput 2

Y.C.O. p.1.t. modulator

ra

- I1 3140

A1 .. .

J .

...

aiid thus co-ordinatc X,. can be obtained Iroiii ci~aiinci 1 and co-ordinate Y , from a combinaiion o1 chnrmels I and 2 (the Einthovcn co-ordinate Y , ih rclatrd io Íhe Caytcsian co-ordinate Y, by the expression Y, ~ ~-Yvi.

2 Apparatis A block diagram of the circuit is given in Fig. 1

2.1 'Isolafion rmxc (Fig. 2)

Thejsolation~ stages for channel t and channel 2 are identical and thus only one channel.will, be described..

(8). Ampltfimiiw~: High-impedance diKerentiai-input amplifiers with the necessary slew rate and frequency response are ohtnined by using m.o.s.f.e.1. omrational amplifiers. CA3110. In order to reduce the number of devices nececsary in the isolation stage, and thus mininime the power required from the isolated power supply. the gain configuration uiih feedback applied to one of the offset nulls (pin if rather than to the inverting input. was implemented ( S T ~ I T . 197ú). This configuration has ihc advantage over the traditional instrumentation amplifier form of retaining hoth a high input impedance and common-mode rejection ratio while using one amplifier rather than three. The main disadvantage of this system is that the maximum input signal at low gains is limited by the point at which the offset nulllbiasing network becomes saturated due to excessive feedback. The device CA3140 was chosen as it permits the largest input signal without distortion ( i 4 0 0 m V ) ofthe f.e.1. and rn.o.s.f,e.t. operational amplifiers readily available. The voltage gain was set IO be approximately 20. The inputs of the amplifier were protected from inputs greater than +450mV by use of the silicon diodes, as shown.

The second amplifier, A:, is also a CA3140. chosen so that the necessary 3s time constant ( 7 ~ RC) could be obtained using a large resistance and small capacitance between AI and A2. as shown in Fig. 2. The voltage g;iin of A2 can be changed by switch SI from one for unipolar inputs to I I for bipolar inputs and 100 for e.c.g. inputs. Shielded cables are used lo and from the switch in order to reduce pickup of any radiated noise from the pacing signals, the d.c.-d.c. convertor ( ~ 2 0 0 kHz) or from ithe voltage controlled oscillator (v.c.o.) of the frequericy

I '

1.h) Frr<luenc.v modularion: The alienuatcd signa! fro?? A2 is passed into the V.C.O. of a CD4046R phase-lockcd loop ;uid thus frequency rnodulaler the carrier signal. A, this dsvice op-rates from a - 12V supply, a.c. coupl~ng. with a time constant greater than 3 s. is necessary. Dio& protection, as shown. is also provided in order to prexrnr thc input signal rising above 12 V or falling below 0 V. The COW65 mas chosen as it is inexpensive, reasonably . ' linear (=I"<) and can operate at the high carriei'. ,

freoiicncies (21 MHz) necessarv for modulation t.v rtc pacing pulse (maximum frequency component z IW kHz) In order to obtain reasonable immunity to noise it c in

be shown that the modulation index B for ihe f.m. s iva l should otcy the following relationship (SL'HWARTZ. 1970):

wherc 1 f is the maximum frequency deviation of the carrier and i B is the bandwidth of the modulating s ipa l .

The transmission bandwidth Br of the modulated carrier is given by

u B T = 2 1 B [ 1 ~ ~ ] = 2 [ A B I - A f ] . . . . (7)

Therefore, the deviation of the modulated carrier must be greater than + A B about the centre freouencv. For the - - CA% of a p a w s p ~ l x khcre Irequenc) componeni> dp to 100 hbb arc de%ired. ihcn R , > ?O0 LHI

To obtain the necessary deviation and IO enabie the carrier to be readily filtered from the demodulated sienal. the centre frequency was chosen to be about 900 kHr ana the deviation I200 kHz (RCA, 1973).

(c) Isolation fmnsformer: In order to main:ain suitable isolation between the patient input and the signal output IO the oscilloscope, a Radio Spares pulse transformer (R.S.1976-369) was used. This device is rated as being proof to 2 kV between the primary and secondary wind-

gain seiect switch 5 1 . .

input protectim AI 470kO -I $adulator transformer

12kO 15k0-

Fig. 2 Isolation stage

110 Medical EL Biological Engineering & Computing January 1980

i

I .

. ~ . ., . . . . - . . ? . .

I

ings and to have a frqu:nc) is,poiii.i k r w . ~ ~ 3 LIUL arid 1 MHz.

( d ) Isolorrdpuwr supply: I t i s also iiecesiary to provide ,a isolat.ed power supply for thc i n y t s1agi:c and chi- uili .obtained by using a Gardeners Diicon 5il2D d.c.-i!.c. convertor. This device operates from a 5 V supply and provides t I2 V at 40 mA per rail.

sonriaiir T ai iiirdeniodulattng niter was adjiistea so t n n t

7 2 - . . . . . . , . . . . (8)

whsref, ic the maximum irequcncy component desired in the demodulated signal (,E 160 kHrl. the nacin? pu!cc. The demodulated output is, for channel I. r RA ~-LR.

I 2 T J <

470kfl

Fig, 3 Output stage: dtmodulation ana' summing network

2.2 ourpur stage (o) Frequency demodularion (Fig. 3): 'The frequency

modulated signal from the isolation transformer is demodulated by the CD40.168 phase-idcd loop. Phax comparator 2 was used. as the carrier remaining on the demodulated signal was then at twice the ioriginal carrier frequency and therefore easier to filter out (RCA. 1973). 1nordertoensurethatthep.l.l. wasalways inlockwith the incoming signal, even in the presence of noise, its lock range was made a few tens of kilohertz greater than any possible deviation o f the niodulated frequency. The time

and for channel 2, a LL -RA. The prformance of the modulatirg V.C.O. and the

demodulating p.l.1, i s given in Table 2, (b) Summing ncrwork: The amplifier A 3 of Fig. 3 sums

the signals from channels 1 and 2 in order to give the Cartesian Y vector

-B fZ(LL-- RA)--(L A- RA): Y, = - % 3

(9) = AY Einthoven . . . . . .

Table 1. Circuit parameters

Maximum Rise Input input Voltage Gain Frequency response time to Noise a t se!ect voltage' X Y (8V ,& out) +8V outputt

mV PS mV Unipolar t 4 0 0 156 180 0.08 Hr-150 kHz 5 40

Bipolar ? 40 170 195 0.08 Hz-145 kHz 5 40

E.C.G. t 5 1440 1660 0.08 Hz-220 Hz - 20

' . 1

3c.

~ ~ ~~~~~~~~~~~~ I

',Maximum output 513 V on Y and r7 V on X. The unipolar maximum input is limited by saturation of the first gain stage. the bipolar and e.c.g. maximum are limited by saturation of the input to the V.C.O.

t Noire for unipolarand bipolar modes is mainly caused by the V.C.O. and d.c.4.c. convertor carrier signals. That o he e c g mode includes a large amount of low frequency noise (flicker) from the first gain stage AI. UL ,:, ' ' .

Medical & Bio log ica l Enginearing & Comput ing January 1980 111

, . . .

Amplifier A4 gives the necerrary gain to channel I so that Lhe o u t ~ u r IS equivalent to the X Finrho\.i~i? .iec!cí cwordinate .

, (10) P.M.O.S. input amplifiers CA3140 are used for A 3 and A4 50 that the high input impedances, neessary to prevent lodding of the ouiput buffer stage of the p.l.1.. can be obtamcd. Tliere amplifier3 are also liequency compensated. as shown. in order lo reduce thcir band-

. width to 200 ktlz and thus litter out some more of the catricr ripple.

tc) T>vo-pole lowpors Bessel filtcr.~: To further reduce the carrier ripple. but with minimum distortion IO the

Table 2. Modulation and demodulerion parameters

Maximum Minimum Stage frequency frequency

MHz MHz

1 .O6 0.71

0.69

,,,. X - B ( L A - R A ) . . . .. . . .

-.

, . 8

. . i

' .

Modulation (v.c.o.)

Demodulation (p.I.1.) 1 .o7

pacing r ' i k e . the signal is passed through the two-pole L,..,..LA I L r s l filter ( w n , u n t rinx-delay film) ,.<i;t, 2 cutoR frequency of about 140 kHz (HiLsLns. 1973). The output o í the filter i s passed to the switch SI. which also conl ru l~ the gain of the amplifier A2, s u that ¡ne output signal for display may either come directly from the filter fur unipolar and bipolar pacing signals or after it har passed the 50 Hz and lowpasr filter for the e.c.g. signal (see Section 2).

Table 3. Safety da;#

Test Result

Earth rbsistance. n 0.15

Insulation resistance, Mi2 (a) mains input t o earth ' >loo, lb) patient input to earth >lo0

(a) mains to eanh 16 . (b) patient input to eanh 5

Leakage current, p.4

- 8 .

to SI and e.c.9. amplifier

OASI -

100 pulse)

iokn

two pole ücsael t i l ler

Fig. 4 Lowpass Bessel filter and trace blanking amplifier

tam

II . 0.IpF 12kn

.l I ' ~

. lOkO

~~ id . , ,

:

50Hz filter - t inverter

: F13.5 ECG 50H2 filter and Inverting amplifier

> 112 r .M.dicSl 81 Bio log ica l Engineering 8 Comput ing January 1980

, . i -.-

1.

i.Sli.11

I I

(4 Oscillowopr rruw hlanki~r<irnpliii?r f Q 4) : A. the pacing sisnd Is dirphyed on :? 'ilm?: VmW iinG !is mark-space ralio i s small (1 : 10001 i t I S neceswy to prevent wturation of the screen ccntrc by blanking oll:he

poin: 10 2 ü I i z . The 50 l i z f i l trrs are bypa*wi ahrn :IlnL:$~}h& tlic pactrig pulses in order to avoid the ringing :hat occurs a t 50 HZ when impulses are parwd ihrough circuits with a Q of greater than one.

-.

fig. 6 Pacemaker-vector cardiograph

electron beam between pulses. The blanking signal i s provided by amplifier A5 of Fig. 4. This configuration permits triggering from signals o f either polarity and of any level. The triggering level being set b y the potentio- meters as shown. For the oscil lowqx being used. a positive output blanks off the electron beam. The blanking signal is disconnected by switch S I when the e.c.g. mode is being used.

(e) E.C.C. 50 Hi filter nnd iriorrrer (Fig,, 5): When the c.c.g. mode is being used, che outpuis from the 50 Hz filters (HILBURN and JOHNSON, 1973) and subsequent inverters are selected via switch SI as mentioned in section 2 . 2 ~ . The capacitor C restricts the upper 3 dB

..<!

, . .- ...... .....

. . . L ..

... .. ~

, , .

, ' , .:'

1 , J

. . . . . . . -- . . , . . ,

! : .

Arknow/edgimnr.7-1 wish to thank D. J. Taylor of the Cardiac Department for his initiation of and continued interest in this project; J. Scurr of the Cardiac Depart- ment for his assistance with clinical trials and J. Coirfirid. Principal Physicist. for the UK of the Medical Physics facilities at the Kent and Canterbury Hospital.

M. G. PEPPER ihe Eleciroonirs Laboratones

ihe Uniwrsiiy of Kent a? Canrr,Sur~ Cnnierbwy, Kent 0 2 7h'T Ensland

Rtfereiha

FITZGEULD. M. (1977) A s)stem fm the assemeni of implanted cardiac paceiiiaken J Wed Eng. & Technolopi.. 1. 350-352. I . . I

HILBUNX. J. L. and JOHNSON, D. E. (1973) .wanu0i o/

RCA (1973) Application Note 637 and 1.C.A.N.-6101. SCHWANTZ. M. (1970) Information. :ranrnii;rion. nti>dula-

lion and noise, McCraw-Hill, 2nd edn., chap. 1, 234-250.

octicefilrer design. McGraw-Hill.

STOTT. F. D. and WELLEN. C . (1976) Riomedical amplifiers usinu integrated circuits. Med. d Bioi. Eny.. 14, 684-687.

THOMAS, D. L. and CREES, G. D. (1974) A vector cardiograph foi assessing implanted cardiac pacrnakers. Med. & Riol. Eng., 12, 593-598.

- ...........

. .

-

. , , .

. . . . . . . . . . . _.

Medica l E Biological Engineering & Comput ing January 1980 113

<,..<.

Such a system would probably not be used at all for most normothermal perfusions. so it would appear desirable to design two types of thermalstabilizationsystems (with heat exchangers and thermal regulators).

The first type would be intended for normothermai perfusion and with stepwise cooling and heating in moderate hypothermal perfusion of the whole body. o r else deep organ hypothermic perfusion. The heat ex- changer and the thermal regulator should handle heat flows in the extracorporeal loop up to 1 kW.

The second type of equipment would be intended to cool the body rapidly in a short time, with the temperature difierence between the ingoing and outgoing blood flows of up to 10-15'C and a useful handling capacity of 4-5 kW.

The firat type of device would provide very precire control of temperature Lletting and maintenance; the device &odd be reasonably simple, convenient to use, and in fact a basic part of any extracorporeal-circulation system.

The second type would provide coarser control of temperature but would be a more powerful specialized device. The need for this must be determined on the basis of the need for hypotbermal perrüsion with high cooling rates.

L I T E R A T U RE C I T E D

1. 2. 3. 4. 5.

6.

V. P. Osipov, Principles of Altificial Circulation Maintenance [in Russian], ~ o s c o w (1976). V. V. Khaskin, Energy Aspects of Heat Production and Adaptation to Cold [in Russian], Novosibirsk (1975). Biomedical Data on Man [in Russian], Moscow (1977). S. M. Gorodinskii et al., Calorimetry of Human Protective Clothing [in Russian], Moscow (1976). P. M. Galletti and G. A. Brecher, Heart-Lung Bypass: Principles and Techniques of Extracorporeal CirCUhtiOn Fussian translation], Moscow (1968). N. A. Super-Fainshtein, Experimental Basis for Equipment for Auxiliary Regional Perfusion [in Russian], Candidate's Dissertation. Moscow (1965).

I N C R E A S I N G I N T E R F E R E N C E I M M U N I T Y O F

A S Y N C H R O N O U S C A R D I O S T I M U L A T O R S

G. V. Zusman UDC 615.472:616.12-085.844-78

In their daily lives the patients who have implanted cardiostimulators (Cs) are not infrequently subjected to the effect of electromagnetic interference sources that may lead to precarious disturhances in the normal Operation of the normal Operation of the CS [l. 21. For asynchronous CSs such a disturbance is primarily a change in its rhythm. If the rhythm is increaLled.tacky0ardiaandevenflbrillstionof the heart may develop while if it is decreased, bradycardia may occur. Al l these conditions, as is well know, are extremely hazard- ous for the patient.

frequency and amplitude of the interference as the interference-immunity characteristics of asynchronous CSs. The first relationship gives the frequency range of the interference to which a certain type of CS is most sensitive. The second relationship permits the rate of change of the CS rhythm to be determined as a function of the interference amplitude, i.e., to form an interference-immunity (or safety) criterion for a CS according to the variation of its rhythm.

Laboratory tests were conducted in the eleotronici department of the Moscow Institute of Physical Engi- neering to determine the interference immunity of the types EKS-2, EKS-4, and EKS-8 CSs. A block diagram of the interference-immunity measurements on a CS 1.8 shown in Fig. 1. The interfering voltage was produced by a type G4-102 sinusoidal-oscillation generator, it was amplified by the amplifier of a type 51-15 oscillograph. and wa8 measured by a type VK7-9 voltmeter. The CS pilses were filtered from the high-frequency interfer-

In testing CSs it is convenient to utilize the dependence of the pulse repetition period (or rhythm) on the

MOSCOW Institute of Physical Engineering. Translated Meditsinskaya Tekhnika, No. 4. pp. 4 2 4 4 , July- August, 1978. Original article submitted June 8. 1977.

206 0006-3398/78/1204-0206 S07.50 O 1979 Plenum Publishing Corporation

-36

Fig. 1. Block diagram of measurements on the interference immunity of asynchronous cardiostimulators.

I I I I I

Fig. 2. Normalized pulse-repetition period Ti as a function of the frequency f i and the amplitude Ui of the Interference at the distal ends of electrodes connected to type EKS-2 apparatus (a) and to types EKS-4 and EKS-ü apparatuses @). (1) Ui = 2 V i (2) Ui = 4Vi

I

(3) ui = 3 v. , h, .-, erice voltage by means of a n optoelectronic low-pass filter. The frequency and amplitude of the CS were

measured with a type ChZ-36 frequency meter and a type S1-19B oscillograph.

Shown in Fig. 2 are the average characteristics (solid lines) of the normalized pulse-repetition period as functions of the frequency and amplitude of the interference at the distal ends of the electrodes (which are sewn to the tissue) connected to the type EKS-2 apparatus (a) and the types EKS-4 and EKS-8 apparatuses (b). It is evident from these curves that with an interference amplitude of 6 V on a type EKS-2 apparatus in the frequency

', . ,

. ' p

I I I 207 !

I- ,. .

,!

I

, ". ~

range from 16 to 24 MHz, and with an amplitude of 4 V in the frequency range from 28 to 30 MHz on the types EKS-4 and EKS-8 apparatuses the rhythm of a C!; io nearly doubled,

From a comparison of the relationships in Fig. 2 it is seen that the type EKS-2 has a somewhat greater interference immunity than the types EKS-4 and EKS-8.

In order to improve the interference immunity it is necessary to reduce the high-friquency interference voltage at the proximal ends of the electrodes (which are connected to the apparatus). This can he achieved by connecting a capacitor C in parallel with the output terminals of the CS, as shown in Fig. 1 by the dotted line, The capacity of the capacitor is chosen on the basis that the front of the pulse from the CS is not distorted for a standard load of 500 0 , and it amounts to 10 nF. The average characteristics of the normalized pulse-repetition Nr i od when a 10 nF capacitor is connected to the output terminals of a CS is shown in Fig. 2 (dotted lines) as a function of the interference frequency and amplitude.

When comparing the relationships in Fig. 2 at an'iakrference voltage of 6 V on the distal ends of the electrodes (for types EKS-4 and EKS-8 without the Capacitor at an even lower 4 V) it is evident that over a frequency range from 1 to 50 MHz the interference immunity of a CS with a capacitor is substantially improved

ditions tests were made on five type EKS-2 apparatuses with a 500 0 load connected to the electrode in air when exposed to UHF therapeutia apparatus (at a frequewy of 40.68 MHz). The tests showed that when the rhythm of CSs without the capacitor C was increased, on the average, by 1.7 times, with the capacitor connected the rhythm was increased but 4%.

Thus the connection of an additional 10 nF capacitor between the output terminals of a CS will substantial- l y improve the interference immunity of the types EKS-2, EKS-4, and EKS-8 apparatuses while retaining their normal functioning so that patients having these types of CSs in practice can feel more confident when in the fields from sources of industrial and home electromagnetic interference.

In order to compare the interference immunity of CSs with and without the capacitor under working con-

LITE.13.A T U R E C I T E D

A. R Livenson, Med. Te!& No. 5,, 6-9 (1973). G. V. Zusman and N. V. Luzhina. Ekspress Informatsiya. All-Union Scientific Research Institute of Medical and Medicotechnical Information VNiIMI Nos. 7-8,'34-43 (1975).

1. 2.

+ . d

2 O8 ..

c tdad au ora me trop ol i na - 148.206.53.231

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