abnormal ecg in the absence of clinical diseases

8/7/2019 Abnormal Ecg in the Absence of Clinical Diseases

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Shahbudin H. Rahimtoola, MD, Section Coordinator

Abnormal ECG in ClinicallyNormal IndividualsCharles Fisch, MD

THE ECG is a record of the changingpotential of an electrical field gener-ated bythe heart and may not alwaysreflect accuratelythe electrical activ-ity of the heart per se. The clinicaldiagnosisextracted from the ECG isbased on studies correlating clinical,anatomical,pathological,and experi-mental findingscoupledwith careful,frequently purelydeductive,analysisof numerous records. In reality,therefore,the ECG reflects largelyanempiricalbody of information thatcan be used,within limits, to identifyanatomical,metabolic,ionic, and he-modynamicchanges.

Despitethis basic limitation, theECG is an extremelyuseful clinicaltool. It is the onlypractical method ofrecordingthe electrical behavior ofthe heart. It is often an independentmarker of myocardial disease and,occasionally,the only indication of apathologicalprocess. Since the ECGreflects an electrical phenomenon,itis not surprising that it may benormal in the presence of cardiacabnormality and abnormal in the

absence of cardiac disorder.This discussion deals largely with

the abnormal ECG in the absence ofcardiac disease or extracardiac disturbance known to affect the heartand the ECG.

The Normal ECG

Rangesof normalcyfor ECG components should be based on an analysis of randomlyselected,preferablyconsecutive,routine ECGs recorded inyoung persons without cardiovasculardisease. It is reasonable that onlyunequivocalECG changes should beconsidered. Consideration of minorchangessuch as, for example,QRSorT-wave amplitudeis often nonproductive. Admittedly, a statistical difference may exist between groups, butfor any one individual, the importance of an absolute amplitude or of aminor changefrom tracing to tracingmay

be difficult to assess. This is truebecause such variabilityoften reflectsa normal curve of distribution andbecause there is a lack of agreementas to when a given value becomesabnormal.

The prevalenceof abnormal ECGswas extremelylow in a studyof 776consecutive patients18 to 25 years ofage without cardiovascular disease.The patients were admitted becauseof acute psychiatric disorders. Left-axis deviation in excess of 30C,right-axis deviation greater than

+120, first-degreeatrioventricularblock,right bundle-branch block,nonspecific intraventricular conductiondefect, left ventricular hypertrophy,atrial premature complexesand ventricular premature complexesgreaterthan six complexesper minute, andWolff-Parkinson-White syndromewas noted in 1.4%,2.1%,0.3%, 0.3%,0.1%, 0.1%, 0.7%,0.8%, and 0.3%,respectively.'These findingsare inagreement with observations made ina group of 5,000male members of theCanadian Air Force.2In neither serieswere abnormalities of the ST segment, left bundle-branch block, oratrial fibrillation encountered.

An abnormal ECG in the absence ofheart disease may be the result offaulty techniqueof recording,extra-cardiac artifacts, or an abnormalityof the ECG per se.

Errors of Technique and ArtifactsErrors of Technique.Theseinclude

applicationof electrode paste over theprecordiumwithout ensuringdiscrete,isolated contact for each of the precordial electrodes, errors of leadplacement,failure to shift the switchfor aV to precordialV position,improperstandardization,excessivepaper speed,and incorrect mounting.

Poorly applied electrode paste"joins" the precordialelectrode sitesand may result in an abnormal recordreflectingthe net or "average"of a

This article is one of a series sponsored by theAmerican Heart Association.

From the Krannert Institute of Cardiology,Depart-ment of Medicine, Indiana University School ofMedicine, and the Veterans Administration MedicalCenter, Indianapolis.

Reprintrequests to Departmentof Medicine,Indiana University School of Medicine, Indianapolis,IN 46202 (Dr Fisch).

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number of otherwise normal precordial complexes.Two common errorsof electrode placement include reversal of the left- and right-arm connections and placementof the precordialelectrodes at the level of the second orthird rather than the appropriatefourth interspace. The reversal oflimb leads simulates mirror-imagedextrocardia. This error can be easilyrecognizedbecause the precordialcomplexes remain normal. Mirrordextrocardia, on the other hand,shows a gradual loss of precordialRamplitude from right to left, simulating clockwise rotation or, rarely, myo-cardial infarction. When all precordial complexesare identical to theaV the lead switch was not movedfrom the aVF to the precordialVposition.

Availabilityof

the standardizationsignalis important for proper ECGinterpretation. Incorrect standardization may result in either abnormallylow or highvoltage.Similarly, inspection of the standard signal wouldalert the reader to the presence ofexcessive stylus inertia, which mayprove a source of serious errors ofinterpretation. Stylus "drag" mayobscure low-amplitudewaves such asthe Q waves, simulate intraventricu-lar conduction delay or ST-segmentdepression,and negate minor butimportant ST-segmentelevation. Excessive (50 mm/s) paper speedmaylead to an erroneous diagnosisofintra-atrial, atrioventricular, and in-traventricular conduction delaysandQTprolongation. Recognitionof inappropriate paper speedshould be simplebecause of a uniform prolongationof all the ECG components. Incorrectmounting, particularly of the precordial leads, may result in an "abnormal" R-wave progressionwith anerroneous diagnosisof myocardialdisease.Artifacts.As a rule, artifacts simulate atrial arrhythmias. Muscletremor may suggest atrial fibrillationor flutter; infusion pumps, atrialtachycardiawith block or atrial flutter. Hiccoughhas been mistaken foratrial parasystoleand intra-atrialdissociation. The artifacts simulatingarrhythmias can be recognizedbythepresence of a normal sinus rhythm insome leads with an RR interval identical to that in the leads with thesuspectedartifacts.

The Abnormal ECGCentral to any discussion of an

abnormal ECG in a normal heart isacceptanceof the fact that anatomical and functional disorders areexcluded on the basis of clinical andlaboratory evaluation. It is probable,however,that occasionallythe ECG isa more sensitive marker of myocar-dial abnormality than either the clinical or laboratory evaluation. Forexample,right bundle-branch block isalmost always an acquiredlesion andindicative of anatomical abnormality,despite the fact that it is oftenrecorded in the absence of clinicallyevident heart disease and is frequently associated with a favorable long-term prognosis.Despitethe latter,right bundle-branch block is rarely afalse-positivefinding. The absence ofclinical evidence of

organicheart dis

ease and a favorable prognosisarenot necessarilyassurances of a normal heart. Despitethese reservationsregardingour abilityto exclude heartdisease, abnormal tracings may berecorded in patientswith unequivocally normal hearts and in theabsence of extracardiac disorders capableof affecting the heart.

The ECG abnormality in the presence of a normal heart may be that ofthe P wave, QRScomplex,ST segment, or T wave.

The P Wave.The occasional highamplitudeof P waves in leads II, III,and aVF, the so-called P pulmonale,may be recorded in the absence ofcardiac abnormality.3AbnormallytallP waves may be seen during sinustachycardia or can be recorded in tallasthnie individuals with a low diaphragmand a vertical positionof theheart. Similarly, the specificityof anabnormal left atrial P wave, "Pmitrale," for heart disease is relatively low. A falselyabnormal P wave

shouldbe

suspectedin the absence of

other ECG changes indicative ofright- or left-sided heart involvement.

QRS Complex.Abnormalitiesofthe QRScomplexinclude abnormal Qwaves, usually in leads aV,, III, andaV,; QScomplexin leads V V2,and,rarely, V3;tall R wave in leads V, andV2;abnormal voltagein "left ventricular" leads I, aV,, V, V5, and V6;intraventricular conduction delays;and an altered sequence of ventricular activation.

The most common cause of anabnormal Q wave is an unusual position of the heart in the thorax. An"abnormal" Q wave in leads III andaV, is frequently observed in obeseindividuals with high diaphragms.Similarly, a Q wave can be observedin leads II, III, and aV, in associationwith tall R waves, both the result of avertical positionseen in asthnie individuals with a low diaphragm.The QScomplexin leads VV2,and V3can bedue to a low-lyingdiaphragm with arelatively high position of the electrodes in relation to the heart, andplacementof electrodes one or twointerspaceslower will display an Rwave. Failure to registeran R wavesuggests an organic cause for itsabsence.

Presence of a tall R wave in V

althoughsuggestiveof

rightventricu

lar hypertrophy or posterior myocar-dial infarction, may be seen in theabsence of heart disease and is mostlikelypositional in origin. The latteris suggestedbyabsence of other signsof right ventricular hypertrophy ormyocardialinfarction. Although abnormallyhighvoltageregisteredoverthe left ventricle may indicate leftventricular hypertrophy,the sensitivity and specificityof voltagealone forsuch a diagnosisare relatively low.The criteria are not applicable,forexample,to individuals younger thanage 25 or to patients in other agegroups with thin chest walls.

Although the acceptedupper limitof QRScomplexduration is 0.10 s,QRScomplexduration between 0.10and 0.12 s may be seen in the absenceof heart disease,particularly in well-developedathletic individuals.

The pattern of RR' can be recordedin many young individuals from theV, position and in most, if not all,from positionsto the right of V,. TheR' is a normal reflection of lateactivation of the posteriorseptum. Itcan be differentiated from incompleteright bundle-branch block by the R'amplitudebeing lower than that ofthe R and especiallyif the R' is ofbrief duration, the wave beingsimplya "spike."

Abnormal left axis or axis in excessof 30,also referred to as left anterior divisional block or left anteriorfascicular block,is found in 1.4% ofindividuals younger than 25 yearswithout heart disease and in a signifi-



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cantly higher proportion of individuals older than 70 years.14Whether inthe young without heart disease or inthe agedreflectingan acquiredanatomical disorder,abnormal left axis isfrequently registered in the absenceof clinicallyevident heart disease andis often associated with a good long-term prognosis.In essence, the prognosis of abnormal left-axis deviationis that of the underlying heart disease.

Atrioventricular Conduction.The acceptedupper limit of 0.22 s for thePR interval may be exceeded in theabsence of heart disease. Occasionally, especiallyin the asthnie orathletic vagotonicindividual with aslow resting heart rate, second-degreeatrioventricular block or Wencke-bach's type 1 block may be present.The block usuallydisappears withexercise

or

after administration ofatropine.ST Segmentand T Wave.A com

monly encountered deviation of theST segment in the absence of heartinvolvement is an elevation,so-calledearly repolarization.56The elevatedST segment is usuallyconcave, mostoften present in leads II, III, and aVless commonlyin lateral leads V4,V5,and V6,and least commonlyin leadsV V2, and V3. Elevation in right

ventricular leads is frequently associated with an RR' pattern in the sameleads. The diagnosisof "early repolar-ization" is fairly secure in the youngand especiallywhen accompanied byslow heart rates. In the presence ofsymptoms or in older age groups,serial tracings and clinical correlation may be essential to rule out an

organic cause for the ST-segmentelevation.

Of all the ECG abnormalities, failure to appreciatethe fact that theT-wave inversion is not necessarilyamarker of disease is the most common and most serious form of iatro-genicECG form of "heart disease."

Normal juvenile, symmetrically inverted T waves in leads VV2, V3,andoccasionallyVmay persist into theteens and occasionallyinto the 20sand rarely into the 30s.' On the basis

of morphologicconditions alone,suchT waves cannot be differentiated fromT-wave inversion due to organicheartdisease. A correlation with availablelaboratory and clinical findingsmaybe essential to establish the benignnature of such T-wave changes.

In the young, usually younger than20 years, one can record an elevatedST segment probablydue to "earlyrepolarization" with a terminal T-wave inversion. The combination may

givethe appearance of a saddle. It ismost often recorded in leads V, V5,and V6and less commonlyin leads Iand aV,.

Occasionally,an isolated precordialT-wave negativity may be a normalvariant. It may manifest, for example,byupright T waves in leads V,,V2,V5,and V and inverted T waves inleads V3and V4.7

Frequently, abnormal T waves areregisteredin leads V,, V2,and V, inmiddle-agedwomen in the absence ofheart disease. The genesis of suchT-wave inversion is obscure. The Twave is usually"shallow" and itslimbs asymetrical,in contrast to thesymetrical inversion of the T wavewhen caused by ischmie heart disease.

Conclusion

These ECG abnormalitiesmay

berecorded in the presence of a clinically normal heart. Since the prevalence of such abnormalities is relatively rare, it is prudent that theseshould be viewed with suspicionandcorrelated with the available clinicaland other laboratory data.

This investigation was supportedin part bythe Herman C. Krannert Fund, grants HL-06308and HL-07182 from the National Heart, Lung,and Blood Institute, and the American HeartAssociation, Indiana Affiliate,Inc.

References

1. Fisch C: The electrocardiogramin the aged.Cardiovasc Clin 1981;12:65-74.

2. ManningGW: Electrocardiographyin selec-tion of RoyalCanadian Air Force crew. Circula-tion 1954;10:401-412.

3. Chou T-C,Helm RA: The pseudoP pulmo-nale. Circulation 1965;32:96-105.

4. Fisch C: The electrocardiogramin the aged:An independentmarker of heart disease? Am JMed 1981;70:4-6.

5. Parisi AF, Beckman CH, Lancaster MC:The spectrum of ST-segmentelevation in theelectrocardiogramsof healthy adult men. JElectrocardiol 1971;4:137-144.

6. SpodickDH: Differential characteristics ofthe electrocardiogramin early repolarizationand acute pericarditis. N Engl J Med 1976;295:523-526.

7. Grant RP: Clinical Electrocardiography:The Spatial Vector Approach.New York,McGraw-Hill Book Co,1957,p 47.


abnormal ecg in the absence of clinical diseases

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