atrial pacing at multiple in the wolff-parkinson-white syndrome1 · epicardial mappitng and2 with...

British Heart journal, 1977, 39, 506-514

Atrial pacing at multiple sites in theWolff-Parkinson-White syndrome1

P. DENES, C. R. WYNDHAM, F. AMAT-Y-LEON, D. WU, R. C. DHINGRA,R. H. MILLER, AND K. M. ROSEN

From the Section of Cardiology, Department of Medicine, Abraham Lincoln School of Medicine, Universityof Illinois College of Medicine, and the West Side Veterans Administration Hospital, Chicago,Illinois, U.S.A.

Atrial pacing at multiple sites was used in an attempt to predict the site of pre-excitation in 5 patients withWolff-Parkinson-White syndrome with 5 different anomalous pathway locations (right anterior, rightposterior, septal, left posterior, and left lateral). At least 3 atrial pacing sites were tested in each patient.Pacing sites tested included high right atrium, low lateral right atrium, low septal right atrium, proximalcoronary sinus, and distal coronary sinus. Atrial stimulation sites with shortest and longest stimulus-deltaintervals could be identified in each patient, the shortest stimulus-delta interval in each case ranging from60 to 80 ms. The difference between the shortest and longest stimulus-delta interval in each case rangedfrom60 to 110 ms. It was suggested that the site with the shortest stimulus-delta interval corresponded to a siteclose to the atrial insertion of the anomalous pathway. This hypothesis was confirmed in all cases (3 withepicardial mappitng and 2 with retrograde atrial activation data). In conclusion, atrial pacing at multiplesites is helpful in predicting the site of anterogradely conducting anomalous pathways, and appears parti-cularly useful for differentiation of right posterior, left posterior, and septal pre-excitation.

Cure of Wolff-Parkinson-White syndrome is nowpossible using epicardial mapping for delineatingthe site of pre-excitation, and surgical transection ofanomalous AV connections (Sealy and Wallace,1974; Gallagher et al., 1975). Anomalous pathwaylocation plays a role in determining the success ofoperation (Sealy and Wallace, 1974; Gallagher etal., 1975; Tonkin et al., 1975). Right anterior,lateral, and posterior as well as left lateral anoma-lous AV connections appear readily accessible tosurgical cure. Left posterior and septal anomalouspathways are less accessible to the surgeon. Since,therefore, the surgical cure of pre-excitation appearsto be partly related to anomalous pathway location,the accurate preoperative localisation of these path-ways has assumed considerable importance.The means of predicting anomalous pathway

locations include surface electrocardiography andvectorcardiography, as well as electrophysiologicalevaluation in the catheterisation laboratory (Wellens

'Supported in part by a USPHS Training Grant, and Basic Institu-tional Support of the West Side Veterans Administration Hospital,Chicago, Illinois.Received for publication 31 August 1976

et al., 1971; Touboul et al., 1972; Coumel andAttuel, 1974; Denes et al., 1974; Spurrell et al.,1974; Svenson et al., 1974, 1975; Wellens andDurrer, 1974, 1975; Wyndham et al., 1974; Zipeset al., 1974; Gallagher et al., 1975; Neuss et al.,1975; Denes et al., 1976a, b). Electrophysiologicaltechniques include lateralisation of the anomalouspathway by noting the effects of functional bundle-branch block on the cycle length of circus movementtachycardia or on retrograde anomalous pathwayconduction time (Coumel and Attuel, 1974; Spurrellet al., 1974; Zipes et al., 1974; Neuss et al., 1975;Wellens and Durrer, 1975); intracardiac catheterelectrode mapping of retrograde atrial activationduring circus movement tachycardia and/or withventricular pacing (Svenson et al., 1974, 1975;Wellens and Durrer, 1974, 1975; Zipes et al., 1974;Gallagher et al., 1975; Neuss et al., 1975; Deneset al., 1976a, b), and evaluation of atrial pacing atmultiple sites with observation of QRS morphologyand stimulus-delta intervals (Wellens et al., 1971;Touboul et al., 1972; Denes et al., 1974; Gallagheret al., 1975; Svenson et al., 1975; Denes et al.,1976a).

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Atrial pacing at multiple sites

Although all these techniques appear to be ofvalue in localisation of anomalous pathways, majoremphasis has been placed upon the use of retro-grade atrial activation sequences in the prediction ofanomalous pathway location (Zipes et al., 1974;Wellens and Durrer, 1974, 1975; Gallagher et al.,1975; Neuss et al., 1975; Svenson et al., 1975; Deneset al., 1976a). The use of atrial pacing at multiplesites has received less attention. In the present study,we describe the results of atrial pacing studies atmultiple sites in 5 patients with anterogradelyconducting anomalous pathways in different loca-tions. Our results confirm the value of multipleatrial pacing sites in anomalous pathway localisa-tion. In addition, criteria are developed for using theinformation obtained with this technique in pre-dicting the site of pre-excitation.

Methods

Five patients with pre-excitation were selected forpresentation in this report. All patients had typicalsurface electrocardiographic findings of Wolff-Parkinson-White syndrome including a short PRinterval (less than 0 12 s), wide QRS complexes(0.12 s or greater), delta waves, and documentedsupraventricular tachyarrhythmias. These 5 patientswere selected because: (1) technically adequatemultiple atrial pacing site data were obtained foranalysis, and (2) the anomalous pathway locationwas reasonably well documented, so that the pre-dictive value of multiple atrial pacing sites could beexamined. (3) The patients represented 5 differentanomalous pathway locations.

Electrophysiological studies were performed inthe supine, non-sedated state. Informed writtenconsent was obtained from all patients before thestudy. All cardioactive drugs were discontinued 48hours before the study. Catheter techniques forrecording and stimulation were similar to thosepreviously described (Wyndham et al., 1974;Denes et al., 1976a, b). Electrocardiographic leadsI, II, III, and VI, atrial and His bundle electro-grams were recorded using a paper speed of100 mm/s. Intervals were measured by averaging 10consecutive beats. Tripolar and quadripolarcatheters (with interelectrode distances of 1 cm)were placed under fluoroscopic control.The following atrial pacing sites were used: (1)

high right atrium, at the superior vena cava-rightatrial junction, (2) low lateral right atrium, at theinferior vena cava-right atrial junction, (3) lowseptal right atrium (using the His bundle recordingcatheter) at the most distal site on pull-back fromthe ventricle, where stable atrial capture with anatrial depolarisation preceding the QRS complex

could be obtained, (4) right atrial appendage, (5)proximal coronary sinus (just inside the os of thecoronary sinus), (6) distal coronary sinus (at themost distal site in the coronary sinus where atria]capture could be obtained, usually close to the leftheart border).The atria were stimulated from the tested sites at

rates slightly faster than sinus and then in 10 beats/minute increments until total pre-excitation wasachieved. The stimulus-delta remained constant atincreasing pacing rates. For purposes of comparisonresults in each case were compared at an identicalcycle length between 460 and 600 ms. Epicardialmapping techniques were similar to those pre-viously described by our laboratory (Wyndham etal., 1974; Denes et al., 1976a, b).

DEFINITIONSPre-excitation was classified electrocardiographic-ally during maximal pre-excitation. The electro-cardiographic classification of pre-excitation wasbased on the work of Boineau et al. (1973).

Anterior right ventricular pre-excitation (type B)was defined by the presence of a QS or rS in Vl andan R in I and III. Posterior right ventricular pre-excitation (type AB) was defined by the presence ofa QS or rS in Vl, an R in I, and a QS in III.Posterior left ventricular pre-excitation (type A)was defined by the presence of an R or RS in V1, anR in I, and a QS or rS in III. Lateral left ventricularpre-excitation (type C) was defined by the presenceof an R or RS in VI, a QS or rS in I, and an R in III.

Stimulus-delta intervals were measured from theonset of the stimulus artefact to the earliest onset ofthe delta wave on simultaneous surface electro-cardiographic leads. This interval represented theatrial and anomalous pathway conduction timesfrom the site of atrial stimulation.

Total or maximal pre-excitation referred to aQRS complex resulting from ventricular activationexclusively through the anomalous atrioventricularconnection.

Results

CASE 1The patient was a 25-year-old woman with sympto-matic recurrent paroxysmal supraventricular tachy-cardia and recurrent paroxysmal atrial fibrillationwith rapid ventricular response. Electrocardio-grams revealed type B pre-excitation (Fig. 1). Basicconduction intervals were recorded during sinusrhythm at a cycle length of 610 ms and revealed aPA interval of 30 ms. AH and HV intervals couldnot be measured since the His bundle electrogramswere buried within the ventricular electrogram. TheP delta interval was of 75 ms.

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Fig. 1 The effect of atrialpacing at multiple sites onstimulus-delta intervals in case1 with type B pre-excitation.Shown in each panel from topto bottom are surface electro-cardiographic leads I, II, III,and Vl. HRA represents highright atrial pacing; LLRA lowlateral right atrial pacing;LSRA low septal right atrialpacing; RAA right atrialappendage pacing.Cycle length was 500 ms.Stimulus-delta intervals arelisted and expressed in ms.Time lines are at 1 second andpaper speed is 100 mm/s in thisand subsequent illustrations.Note that the shortest stimulus-delta interval (60 ms) isobtained with right atrialappendage pacing (panel D).

Four atrial pacing sites were studied at a cyclelength of 500 ms. The stimulus-delta intervals andQRS durations from these sites were as follows:(1) high right atrium, with a stimulus-delta of100 ms and QRS duration of 180 ms (Fig. 1A);(2) low lateral right atrium, with a stimulus-delta of130 ms and a QRS duration of 150 ms (Fig. 1B);(3) low septal right atrium with a stimulus-delta ofllOms;and QRS duration of 130ms (Fig. 1C);(4) right atrial appendage, with a stimulus-delta of60 ms and QRS duration of 180 ms (Fig. 1D).

Curative surgery was attempted because of re-current tachyarrhythmias. Epicardial mappingrevealed earliest ventricular activation on theanterior right ventricle adjacent to the right atrialappendage (Fig. 2). The epicardial ventricularelectrograms preceded the onset of the delta waveby 38 ms. After epicardial mapping, the rightatrium was entered during cardiopulmonary bypass.A transmural atrial incision was made parallel to theAV ring and adjacent to the area of earliest ventri-cular activation. All subsequent electrograms haverevealed normal PR intervals without pre-excitation.Arrhythmias have not recurred (6-month follow-up).

CommentElectrocardiograms before surgery suggested a rightanterior anomalous pathway. Atrial pacing studiesat multiple sites provided strong evidence of ananterior right AV connection with demonstration ofthe shortest stimulus-delta interval (60 ms) and

maximum pre-excitation from the right atrialappendage pacing site. The predicted site of pre-excitation was confirmed at cardiac surgery.

CASE 2This was a 15-year-old youth with recurrentparoxysmal supreventricular tachycardia. Electro-cardiograms during total pre-excitation revealedtype AB pre-excitation. This case has been pre-viously reported because of bilateral anomalouspathways (a manifest right posterior anterogradepathway, and a left lateral concealed retrogradepathway), and will, therefore, be described onlybriefly here (Denes et al., 1976a).Three atrial pacing sites were studied at a cycle

length of 600 ms (Fig. 2 of Denes et al. (1976a)).The stimulus-delta intervals and QRS durationfrom these sites were as follows: (1) high rightatrium, with a stimulus-delta of 140 ms and QRSduration of 120 ms; (2) low lateral right atrium,with a stimulus-delta of 80 ms and QRS duration of180 ms; (3) proximal coronary sinus, with a stimu-lus-delta of 115 ms and QRS duration of 170 ms.Epicardial mapping revealed early activation of theposterior right ventricle contiguous to the intra-ventricular groove, with early activation coincidingwith the onset of the delta wave (Fig. 6 of Deneset al. (1976a)). A transmural right atrial incisionparallel to the AV ring adjacent to the site of earliestventricular activation resulted in cure of antero-grade pre-excitation.

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CommentIn this patient, the electrocardiogram during totalpre-excitation suggested a posterior right ventricularconnection. The atrial pacing site study showedthe shortest stimulus-delta and widest QRS com-plex from the low lateral right atrium suggesting alateral right atrial connection. The posterior rightatrium was not tested. Epicardial mapping studiesand surgery localised the anterogradely conductinganomalous connection to the right posteriorventricle.

CASE 3This was a 37-year-old man with recurrent paroxys-mal supraventricular tachycardia. Electrocardio-grams during total pre-excitation indicated typeAB pre-excitation (Fig. 3).

Basic conduction intervals were recorded duringsinus rhythm at a cycle length of 870 ms and wereas follows: P delta of 100 ms and PA of 30 ms. AHand HV intervals could not be measured since theH potential was buried within the ventricularelectrogram.Four atrial pacing sites were selected for pacing at

a cycle length of 460 ms. The stimulus-delta inter-vals and QRS duration from these sites were asfollows: (1) High right atrium, with a stimulus-delta of 110 ms and QRS duration of 170 ms (Fig.3A). (2) Low lateral right atrium, with a stimulus-delta of 110 ms and QRS duration of 170 ms (Fig.3B). (3) Low septal right atrium, with a stimulus-delta of 70 ms and QRS duration of 170 ms (Fig.3G). (4) Distal coronary sinus, with a stimulus-delta of 140 ms and QRS duration of 170 ms(Fig. 3D).

Retrograde atrial activation sequences weredetermined during right ventricular pacing. Lowright atrial septal electrograms preceded high rightatrial, lateral right atrial, and right atrial appendageelectrograms by 30, 40, and 50 ms, respectively.The retrograde conduction time measured from theonset of the QRS to the low septal right atrialelectrogram was 90ms and was constant at allventricular paced cycle lengths.

CommentThe electrocardiogram in this patient was similarto that of case 2 and suggested a posterior rightventricular connection. However, atrial pacing sitestudies strongly suggested a septal anomalous path-way, because of the very short stimulus-delta withlow right atrial septal pacing. Though this anoma-lous pathway location was not confirmed with epi-cardial mapping and surgery, the retrogradeactivation data provided strong confirmatoryevidence for this predicted site of pre-excitation

Inferior

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Fig. 2 Diagram of epicardial activation during pre-excitation in case 1. Isochronous lines are drawn at 10 to20 ms intervals with reference to the onset of delta wave.

Inferior (upper), anterior (lower left), and left lateral(lower right) views of the heart are shown. The earliestarea of epicardial activity is on the posterolateral leftventricle.

(Gallagher et al., 1975). These electrophysio-logical findings led to a decision not to attemptsurgical cure of the pre-excitation.

CASE 4

This was an 18-year-old youth with paroxysmalatrial fibrillation. Electrocardiograms revealed typeA pre-excitation (Fig. 4). Basic conduction intervalsat a cycle length of 765 ms revealed a P delta of 120

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ms, PA of 24 ms, AH of 53 ms, and an HV of 38 ms.Six atrial pacing sites were selected for pacing at a

cycle length of 460 ms. The stimulus-delta intervalsand the QRS duration from these sites were asfollows: (1) High right atrium, with a stimulus-delta of 130 ms and QRS duration of 120 ms(Fig. 4A). (2) Low lateral right atrium, with astimulus-delta of 140 ms and QRS duration of120 ms. (3) Low septal right atrium, with a stimu-lus-delta of 100 ms and QRS duration of 100 ms(Fig. 4C). (4) Proximal coronary sinus, with a

Fig. 3 The effect of atrialpacing at multiple sites onstimulus-delta intervals incase 3 with type AB pre-excitation. In each panelsurface electrocardiographiclead I, II, III, and Vl areshown. Abbreviations aresimilar to Fig. 1. DCSrepresents distal coronary sinuspacing. Note that the shorteststimulus-delta interval (70 ms)is obtained with low septalright atrial pacing.

stimulus-delta of 60 ms and QRS duration of 140 ms(Fig. 4D). (5) Midcoronary sinus, with a stimulus-delta of 80 ms and QRS duration of 140 ms (Fig.4E). (6) Distal coronary sinus with a stimulus-deltaof 100 ms and QRS duration of 130 ms (Fig. 4F).

Retrograde atrial activation sequences weredetermined during ventricular pacing. The proxi-mal coronary sinus atrial electrogram preceded thelow septal right atrial, high right atrial, low lateralright atrial, and distal coronary sinus activation by5, 20, 60, and 30 ms, respectively. The retrograde

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Fig. 4 The effect of atrialpacing at multiple sites onstimulus-delta intervals incase 4 with type A pre-excitation. In each panel,surface electrocardiographicleads I, II, III, and Vl areshown. Abbreviations aresimilar to Fig. 1 and 3.PCS and MCS representproximal and mid coronarysinus pacing. Note that theshortest stimulus-deltainterval (60 ms) is obtainedwith proximal coronarysinus pacing.

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conduction time to the proximal coronary sinus sitewas 60 ms with ventricular pacing at all tested cyclelengths.

CommentIn this patient, the electrocardiogram suggested aleft posterior connection. The atrial pacing sitestudy revealed the shortest stimulus-delta andwidest QRS complex from the proximal coronarysinus, suggesting a posterior left atrial connection.Though this anomalous pathway location was notconfirmed with epicardial mapping and surgery,retrograde activation data provided strong con-firmatory evidence for the predicted site of pre-excitation (Gallagher et al., 1975).

CASE 5This was a 53-year-old man with primary myo-cardial disease, subacute pericarditis, and recurrentparoxysmal atrial flutter with 1:1 anomalous path-way conduction. Electrocardiogram revealed type Cpre-excitation (Fig. 5). Basic conduction intervalswere recorded during sinus rhythm at a cyclelength of 980 ms and revealed a P delta interval of130 ms, and a PA of 25 ms. AH and HV intervalscould not be measured since the H potential wasburied within the ventricular electrogram.

Five stimulation sites were selected for pacing ata cycle length of 460 ms. The stimulus-delta

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intervals and QRS duration from these sites were asfollows: (1) High right atrium, with a stimulus-delta of 170 ms and QRS duration of 180 ms (Fig.5A). (2) Low lateral right atrium, with a stimulus-delta of 180 ms and QRS duration of 180 ms (Fig.5B). (3) Low septal right atrium, with a stimulus-delta of 140 ms and a QRS duration of 140 ms(Fig. 5C). (4) Proximal coronary sinus, with astimulus-delta of 80 ms and QRS duration of190 ms (Fig. 5D). (5) Distal coronary sinus, with astimulus-delta of 70 ms and QRS duration of 190ms (Fig. 5E).

Because of pericarditis and medically intractablerecurrent atrial flutter with hypotension necessitat-ing frequent cardioversions, surgical ablation ofthe anomalous connection was attempted. Afterpericardectomy, the ventricular epicardium wasmapped. The earliest area of ventricular activationwas on the posterolateral left ventricle adjacentto the AV ring, preceding the onset of the deltawave by 25 ms (Fig. 6). After epicardial mapping,the left atrium was entered during cardiopul-monary bypass. A transmural atrial incision wasmade parallel to the AV ring and adjacent to theearliest site of ventricular activation, which resultedin normalisation of the electrocardiogram with lossof the delta wave. During surgical repair, the leftcircumflex artery was damaged with development ofintraoperative myocardial infarction. The patientexpired with postoperative cardiogenic shock.

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Fig. 5 The effect of atrialpacing site on stimulus-deltaintervals in case 5 with type Cpre-excitation. In each panel,

Dms surface electrocardiographicvt/~ / leads I, II, III, and Vl are

shown. Abbreviations aresimilar to Fig. 1 and 4. Note

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Fig. 6 Diagram of epicardial activation in case 1 during pre-excitation. Isochronous lines are drawn at 10 to 20 msintervals with reference to the earliest onset of delta wave on multiple surface electrocardiographic leads. Anterior(upper), left lateral (lower left), and inferior (lower right) views of the heart are shown. The earliest area ofepicardial activity is on the anterior right ventricle preceding the onset of the delta wave by 38 ms.

CommentThe electrocardiogram during total pre-excitationsuggested a left lateral anomalous connection.Multiple pacing site study strongly suggested a leftlateral bypass, because of the shortest stimulus-delta (70ms) with distal coronary sinus pacing.Epicardial mapping and surgery confirmed thepresence of a left lateral anomalous connection.

Discussion

The success of surgery in the Wolff-Parkinson-White syndrome is partially determined by ano-malous pathway location. In a recent report byTonkin et al. (1975) cure of pre-excitation wasachieved in 91 per cent of patients with anomalouspathways located in the free wall of the mitral ortricuspid annulus. In contrast, cure of pre-excita-tion was achieved in only 36 per cent of cases withseptal anomalous pathways (Tonkin et al., 1975).Thus, the ability to predict the site of anomalous

pathway before operation is of major importance inthe presurgical evaluation of patients with pre-excitation.

Electrophysiological studies in the catheterisa-tion laboratory may allow localisation of anomalouspathway location. The means for achieving thislocalisation are as follows: (1) Recording of retro-grade atrial activation sequences from multiplesites during AV re-entrant tachycardia or ventri-cular pacing, (2) observations of changes in retro-grade atrial activation time during the occurrence offunctional bundle-branch block, allowing latera-lisation of the anomalous pathway, and (3) measure-ment of stimulus-delta intervals and QRS durationfrom multiple atrial stimulation sites.The use of retrograde atrial sequence and of

functional bundle-branch block has been describedin detail in recent publications (Coumel and Attuel,1974; Spurrell et al., 1974; Zipes et al., 1974;Svenson et al., 1974; Wellens and Durrer, 1974;Gallagher et al., 1975; Neuss et al., 1975; Tonkin

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Atrial pacitng at multiple sites

et al., 1975). The use of atrial stimulation at multiplesites has received less attention. Wellens et al.(1971) noted that left atrial pacing produced morepre-excitation than right atrial pacing in one patientwith type A pre-excitation. Touboul et al. (1972)made similar observations in 2 patients with type AWolff - Parkinson - White syndrome. Recently,Svenson et al. (1975) reported on the electrophysio-logical evaluation of 25 patients with Wolff-Parkin-son-White syndrome and commented that thedegree of ventricular pre-excitation was greatestand the stimulus-delta interval was shortest whenatrial pacing was performed from the site at whichearliest atrial activation was recorded during AVre-entrant tachycardia. However, the atrial sitestested and their stimulus-delta intervals were notreported.The present study systematically presents mul-

tiple site data in 5 patients with the Wolff-Parkinson-White syndrome. In each of our cases, an atrialstimulation site with shortest stimulus-delta intervalcould be identified, as could a site with longeststimulus-delta. Several assumptions were made inevaluating our data. First, it was assumed that ano-malous pathway conduction time was constant andindependent of atrial stimulation during pre-excitation. Secondly, it was assumed that atrialconduction velocity was constant and independentof the site of atrial pacing. We did recognise that theanomalous pathway may respond in an all-or-nonefashion depending upon the site of stimulation(Svenson et al., 1975). Accepting these assumptions,differences in stimulus-delta intervals betweendifferent stimulation sites should reflect varyingdistances between atrial stimulation site and theatrial insertion of the anomalous pathway. Theatrial pacing site with the shortest stimulus-deltainterval should correspond to a location closest tothe atrial insertion of the anomalous pathway. Con-versely, the longest stimulus-delta interval shouldbe obtained from the most distant atrial pacing site.

In the present study, the shortest observedstimulus-delta interval in each of the patients wasbetween 60 and 80 ms. In all patients, the differencebetween shortest and longest stimulus-delta intervalwas always between 60 and 110 ms. The hypothesisthat the site with shortest stimulus delta reflectedthe atrial insertion of the anomalous pathway ap-peared to be confirmed. In 3 of our patients, oneeach with right anterior, right posterior, and leftlateral anomalous pathway locations, this confirma-tion was obtained by epicardial mapping andanomalous pathway surgery. In 2 of our patients,though epicardial maps were not obtained (surgerybeing avoided in these patients because of theresults of pacing site studies), strong supportive

evidence for the predicted site of pre-excitation wasobtained by use of retrograde activation data. Thelatter technique has been previously confirmed to beof value in predicting anomalous pathway locationwith epicardial mapping (Svenson et al., 1974,1975; Gallagher et al., 1975). It should also bepointed out that multiple stimulation site studiesallowed differentiation of the site of anomalouspathways in patients with similar electrocardio-graphic findings.

CLINICAL IMPLICATIONSThe present study suggests that atrial pacing atmultiple stimulation sites provides useful informa-tion in the electrophysiological assessment ofpatients with Wolff-Parkinson-White syndromewho are being considered for pre-excitation surgery.The demonstration of a stimulation site withshortest stimulus-delta interval, particularly if thatinterval is less than 80 ms, is strong evidence forthat site being close to the atrial insertion of theanomalous pathway. The simultaneous demon-stration of maximum pre-excitation at a relativelyslow-paced rate from the same site provides addi-tional supportive evidence. However, if normalpathway time is rapid from the site of the shortstimulus delta, then maximum pre-excitationmight not be noted (Amat-y-Leon et al., 1975).The use of multiple pacing site data appears to

be particularly useful in detecting patients withseptal anomalous pathways. In this group ofpatients, electrocardiograms do not reveal patho-gnomonic findings of septal pre-excitation, butusually suggest either left or right posterior pre-excitation (Tonkin et al., 1975). Studies of retro-grade conduction in these patients (either withventricular pacing, or during paroxysmal tachy-cardia) show early activation of the low septal rightatrium (Svenson et al., 1975). Previous studies haveshown that the normal sequence of retrogradeatrial activation in patients without pre-excitation ischaracterised by earliest activation of the low rightatrial septum (Amat-y-Leon et al., 1976). This isalso true in patients with AV nodal re-entrantparoxysmal tachycardia, when examining theactivation sequence of AV nodal re-entrant atrialecho beats (Amat-y-Leon et al., 1976). On theo-retical grounds, one would also expect a similar re-trograde activation pattern from a retrogradely con-ducting James tract (atrionodal connection) or atrio-fascicular tract (Anderson et al., 1975). Thus,demonstration of early retrograde activation of lowseptal right atrium would not be pathognomonic ofseptal pre-excitation. Demonstration of the shorteststimulus-delta interval with low right atrial septalpacing would provide strong evidence for the

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presence of an anterogradely conducting septalanomalous pathway bypassing the AV node.The present study thus indicates that atrial

pacing at multiple sites is useful in the evaluation ofpatients with Wolff-Parkinson-White syndrome,and supplements the other methods used for pre-diction of site of pre-excitation. The use of atrialsites provides relatively direct information concern-ing the location of anterogradely conducting ano-malous pathways.

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Amat-y-Leon, F., Dhingra, R. C., Wu, D., Denes, P.,Wyndham, C., and Rosen, K. M. (1976). Catheter mappingof retrograde atrial activation. Observations during ven-tricular pacing and AV nodal reentrant paroxysmal tachy-cardia. British Heart Journal, 38, 355-362.

Anderson, R. H., Becker, A. E., Brechenmacher, C., Davies,M. J., and Rossi, L. (1975). Ventricular preexcitation: aproposed nomenclature for its substrates. European J7ournalof Cardiology, 3, 27-36.

Boineau, J. P., Moore, E. N., Spear, J. F., and Sealy, W. C.(1973). Basis of static and dynamic electrocardiographicvariations in Wolff-Parkinson-White syndrome. AmericanJrournal of Cardiology, 32, 32-45.

Coumel, P. H., and Attuel, P. (1974). Reciprocating tachy-cardia in overt and latent preexcitation. Influence offunctional bundle branch block on the rate of the tachy-cardia. European Journal of Cardiology, 1, 423-436.

Denes, P., Wyndham, C., Dhingra, R., Wu, D., Amat-y-Leon, F., Levitsky, S., and Rosen, K. M. (1974). Predictionof anomalous pathway location in patients with Wolff-Parkinson-White syndrome using atrial pacing at multiplesites. Circulation, 49-50, Suppl. III, 222.

Denes, P., Amat-y-Leon, F., Wyndham, C., Wu, D., Levitsky,S., and Rosen, K. M. (1976a). Electrophysiologic demon-stration of bilateral anomalous pathways in a patient withWolff-Parkinson-White syndrome (type B preexcitation).American Journal of Cardiology, 37, 93-101.

Denes, P., Wyndham, C., and Rosen, K. M. (1976b). In-tractable paroxysmal tachycardia caused by a concealedretrogradely conducting Kent bundle. Demonstration byepicardial mapping and cure of tachycardias by surgicalinterruption of the His bundle. British Heart J'ournal, 38,758-763.

Gallagher, J. J., Gilbert, M., Svenson, R. H., Sealy, W. C.,Kasell, J., and Wallace, A. G. (1975). Wolff-Parkinson-

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Neuss, H., Schlepper, M., and Thormann, J. (1975).Analysis of reentry mechanisms in those patients with con-cealed Wolff-Parkinson-White syndrome. Circulation, 51,75-81.

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Requests for reprints to Dr. Pablo Denes, Sectionof Cardiology, University of Illinois Hospital,P.O. Box 6998, Chicago, Illinois 60680, USA.

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