ARRHYTHMIAS
AND CONDUCTION
DISTURBANCES
Comparison of a Vectorcardiographically Derived 12-Lead Electrocardiogram with the Conventional Electrocardiogram During Wide QRS Complex Tachycardia, and Its Potential Application for Continuous Bedside Monitoring Barbara J. Drew, RN, PhD, Melvin M. Scheinman, MD, and G. Thomas Evans, Jr., MD
Previous investigators published conflicting reports comparing a vectorcardiographically derived electrocardiogram (ECGo) with the conventional 12-lead one (ECG). Prior comparisons were obtained in adults during sinus rhythm, but never in patients with wide QRS complex tachycardia. The ECGD was evaluated during baseline rhythms in patients with varying cardiac diagnoses; and the diagnostic accuracy of the 2 methods was compared during 64 episodes of wide QRS complex tachycardia in 49 patients during cardiac electrophysiologic study. All leads of the 124ead ECGD closely resembled the conventional ECG in baseline and tachycardia tracings, except leads Vs and V4. QRS voltages were less in the ECGo, resulting in an inability to detect left ventricular hypertrophy in one third of patients with that diagnosis. There was excellent agreement between the ECGo and ECG in diagnosing prior myocardial infarction (92%), ventricular preexcitation patterns (loo%), bundle branch and fascicular blocks (lOO%), and axis deviation. The ECGo was equally as valuable as the ECG in the diagnosis of wide QRS complex tachycardia. There was perfect agreement between the 2 lead systems in application of the morphologic criteria differentiating supraventricular tachycardia with aberration from ventricular tachycardia in leads VI, Va and Vs, and for criteria requiring axis determination and measurement of RS intervals in the precordial leads. The ECGo tracings contained less muscle artifact during body movements (e.g., after direct-current defibrillation). In conclusion, the ECGo’s close correlation with the ECG, and its technical superiority and simple 5 torso-positioned electrode configuration make it worth pursuing as an option for continuous bedside monitoring. (Am J Cardiol 1992;69:612-618) From the Department of Physiological Nursing, and the Cardiovascular Research Institute and Department of Medicine, University of California, San Francisco, California. This study was supported by a National Research Service Award from the National Center for Nursing Research, the National Institutes of Health, Bethesda, Maryland. Manuscript received September 3, 1991; revised manuscript received November 11,1991, and accepted November 12. Address for reprints: Barbara J. Drew, RN, PhD, School of Nursing, N61 lY, University of California, San Francisco, California 941430610.
612
THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 69
urrent bedside electrocardiographic monitors have several significant limitations. First, a limited selectionof leadsis available. For example,no currently available monitoring system allows for the simultaneous recording of >l precordial lead. Thus, it is not possible to record lead VI, which is preferable for arrhythmia analysis,while also recording lead V2 or Vs, which is ideal for detecting anterior wall myocardial ischemia. Second, bedside leads are often significantly different from correspondingones from a standard 12lead electrocardiogram (ECG).1,2This difference is due in part to the bedsidemonitoring practice of positioning the arm and leg electrodeson the torso.1,2 Dower et al3 derived 12 electrocardiographic leads using a modified Frank vectorcardiographic lead configuration (Figure l), which they report to more approximate the conventional than the torso-positioned ECG used for exercisetesting or bedsidemonitoring. The coefficients of vector leads X, Y, and Z necessaryfor deriving the lead vectors for the 1Zlead ECG have been previously established.4The original reports of Dower et a15,6suggesteda good correlation betweenthe vectorcardiographically derived (ECGn) and conventional ECGs in the diagnosis of myocardial infarction, frontal plane QRS axis and intraventricular conduction delays; however, these findings were not corroborated by Wolfe et a1.7 Although the ECGo offers potentially significant improvementsfor continuous bedsidemonitoring, insufficient data is available regarding its diagnostic accuracy. Furthermore, all previous comparisonsof the ECGn with the ECG have beenperformed at rest during stable (generally, sinus) rhythms. The purpose of the present study was to compare the 2 lead systems in patients with varying cardiac diagnoses. In our investigation, clinical and echocardiographicdata were available to allow for an independent standard relative to a correct diagnosis. Prior studies compared the ECGo with the ECG, but left unclear which of the 2 reflected the true diagnosis. In addition, for the first time, we compared the 2 lead systemsduring wide QRS complex tachycardia using invasive electrophysiologic studies as the gold standard for correct diagnosis.
C
METHODS
We prospectively analyzed 64 wide (10.12 second) complex tachycardias recorded from 49 adults undergoing cardiac electrophysiologic study. Only monomorMARCH 1, 1992
phic tachycardias at a rate of 100 to 290 beats/mm were selected for analysis. Supraventricular tachycardias with anterograde conduction over an accessory atrioventricular. pathway were excluded from analysis. More than 1 tachycardia from the same patient was used in the analysis if the patient developed: (1) both supraventricular and ventricular tachycardias, (2) supraventricular tachycardia with both right and left bundle branch block-type aberrations, or (3) a second ventricular tachycardia with a clearly different QRS morphology. Ventricular tachycardias were defined as morphologically distinct if they exhibited different bundle branch block patterns or if they had a markedly different (>60”) frontal plane QRS axis. The diagnosis of tachycardia was verified by intracardiac recordings in all patients. Simultaneous recordings were obtained with the 2 lead systemsusing identical Marquette instruments during baseline rhythm before electrophysiologic study and during wide QRS complex tachycardia. Two investigators independently compared baseline ECGs with respect to frontal plane QRS axis, evidenceof infarction, bundle branch and fascicular block, and ventricular preexcitation and hypertrophy using standard criteria.* Similarly, 12-lead ECGs’ were compared during tachycardia. Each diagnosis of tachycardia was obtained without benefit of the patient’s baselineECG, or knowledge of the lead system, clinical information or electrophysiologic findings. Furthermore, each of the 12 leads of the ECGn was compared with its counterpart conventional ECG lead during baseline and tachycardia rhythms to determine the similarity of the 2 recording methods. The 2 leads being compared were considered identical if they had identical QRS patterns in terms of sequence,width and morphology of QRS waves, and similar voltages. We used a modification of the algorithm proposed by Brugada et a1,9in which a diagnosis of ventricular tachycardia was made if: no RS complex was present in any precordial lead, the interval from onset of the R to nadir of the S was >lOO ms, atrioventricular dissociation was present, or the frontal plane QRS axis was in the right superior quadrant (i.e., -90 to f 180’). If ventricular tachycardia could not be diagnosed on the basis of these criteria, QRS morphology was analyzed in leads Vi, Vl and Vs. The morphologic criteria used to diagnoseventricular tachycardia in those with a right bundle branch block pattern included a monophasic R, biphasic QR or RS, or M-shaped complex with a taller left peak in lead Vi. lo Ventricular tachycardia was diagnosed in those with a left bundle branch block pattern when the complex contained a prolonged R wave >30 ms, a slurred or notched S downstroke, or a delayed S nadir >60 ms in leads Vi or V2. l1 Lead Vs was also used to obtain the diagnosis of ventricular tachycardia if any of the following patterns were present: a monophasic QS, biphasic QR, late peaking of the QRS 170 ms,12 or RS configuration (R:S < 1) in tachycardias with a right bundle branch block pattern. lo A diagnosisof supraventricular tachycardia with aberrant conduction was obtained when criteria from the
first 4 steps were negative for ventricular tachycardia, and QRS morphology suggestedaberrancy, including: (1) a triphasic RSR’ configuration in lead Vi in tachycardias with a right bundle branch block pattern, (2) absentor tiny R wave followed by a steepS downstroke without slurring or notching in leads Vi and V2 in tachycardias with a left bundle branch block pattern, l l (3) early peaking of the QRS 150 ms in lead Vg,12or (4) a triphasic QRS configuration (R:S > 1) in lead V,j in tachycardias with a right bundle branch block pattern.‘O When the first 4 criteria yielded negative findings for ventricular tachycardia, and the morphologic criteria in lead Vi indicated a diagnosis contrary to that of Vg, an “indeterminate” diagnosis was obtained. RESULTS Sample characteristics: Patients comprising the sample were referred for cardiac electrophysiologic study to select antiarrhythmic drugs, catheter ablation or device therapy for symptomatic supraventricular or ventricular arrhythmias. Two thirds of the patients were men (mean age 56 years, range 19 to 86). Cardiac history of the 49 patients was as follows: previous myocardial infarction (28), coronary artery disease without myocardial infarction (l), dilated cardiomyopathy (4), valvular heart disease (l), accessory atrioventricular pathway (12) and absenceof heart diseasewith history of paroxysmal tachycardia or unexplained syncope(3). Eighteen patients had history of aborted suddencardiac death. At the time of electrophysiologic study, 27 patients (55%) were receiving no antiarrhythmic drugs; the remainder were treated with a variety of such agents. As indicated from intracardiac recordings, 22 tachycardias were supraventricular with aberrant ventricular
IA
FIGURE 1. A, in contrast with conventional 1%lead elecb-ocardiogram that needs 10 electrodes, vectorcardiographiiy derived electrocardiogram needs just 5 elecbodes on chest. When using standard Weadwire bedsii cable, chest (C) eiecbode is placed on lower sternum at level of fiRh intercostal spoco. Righl and iofl arm (RA and LA) ektrodes are placed in right and left axilla, respectively, at same horizontal level as chest electrode. Left leg (LL) electrode is placed on manubrium, and right leg (RL) ground electrode can be placed anywhere. B, ktrizontal plane diagram illustrates how posterior view of heart is derived without need of ektrode on patient’s back Anterior-posterior lead is derived by comparing midpoint of right and left axilla electrodes with lower sternal electrode. Vertical, right-left and anterior-posterior orthogonal leads resulting from these electrode positions produce approximations of vector leads X, Y and 2.
VECTORCARDIOGRAPHICALLY
DERIVED ELECTROCARDIOGRAM
613
TABLE I Baseline Comparison of Derived and Conventional Electrocardiograms Patients RBBB
LBBB
IVCD
LAFB
LVH (n = 9)*
Preexcitation
MI (n = 28)*
3 3 100
1 1 100
6 6 100
2 2 100
6 % 66
6 6 100
24t 22 92
conduction, and 42 were ventricular. Supraventricular arrhythmia mechanismsincluded orthodromic atrioventricular reciprocating tachycardia in 12 patients with Wolff-Parkinson-White syndrome, atrioventricular nodal reentry in 5, atria1 tachycardia in 4, and sinus tachycardia in 1. Baseline conventional
vectorcardiographically electrocardiogram:
in 49
derived
versus
In all patients, the baseline ECGo closely resembled the ECG with 2 exceptions: (1) QRS morphology was dissimilar in lead V3 in 35% of patients, and in V4 in 51%. This disparity between the 2 lead systemswas typically an early transition of the “right ventricular” rS to the “left ventricular” qR pattern in the ECGo. Whereas the transitional zone generally appearedin lead Vs or V4 of the ECG, it frequently occurred between V2 and Vs in the ECGn. (2) QRS voltage tended to be less in the ECGn, especially in the precordial leads,which affected the diagnosis of left ventricular hypertrophy. A comparison of the diagnosesdetermined from the 2 recording methods is shown in Table I. There was complete agreement between the 2 lead systems in
all casesof the following diagnoses: (1) right bundle branch block, (2) left bundle branch block, (3) nonspecific intraventricular conduction delay, and (3) anterior fascicular block (no patients exhibited posterior fascicular block). Nine patients had echocardiographic evidence and voltage criteria for left ventricular hypertrophy in the ECG, however, only 6 of these had such evidence in the ECGn (Figure 2). An additional young patient with a normal echocardiogramand no history of hypertension had false positive voltage criteria for left ventricular hypertrophy in the ECG, but not in the ECGo. Six patients with Wolff-Parkinson-White syndrome had evidenceof ventricular preexcitation during sinus rhythm in the baseline ECG. All 6 patients also had evidenceof preexcitation in the ECGo, with deltawave morphology nearly identical between the 2 lead systems. There was agreement between the 2 methods in 45 patients (92%) in absenceor presenceof prior myocardial infarction and in the location of infarction. Of 28 patients with clinical history and echocardiographicevidence of prior myocardial infarction, 22 had such evi-
FIGURE 2. Simultaneous conventiinal and vectorcardiographically derived ektrocardiigraphic recordings illustrating voltage differences between the 2 lead systems in patient with severe mitral regurgitation. Diagnosis of left ventricular hypertrophy was obtained with conventional electrocardiogram (ECG) by noting S wave in lead V3 of 25 mm, P-terminal force in Vi >0.04, and typical ST-segment shifts. Left ventricular hypertrophy was not detected with vectorcardiographiilly derived electrocardiiram (ECGo) and QRS voltage was less than that of ECG in every lead except VI and V2.
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THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 69
MARCH 1, 1992
dence in the ECG compared with 24 in the ECGo. Discrepanciesbetweenthe 2 lead systemsincluded evidence of previous inferior wall myocardial infarction in 4 patients with the ECGo, but not with the ECG. Two of these patients were young (23 and 28 years, respectively) with no history of heart disease,and both had normal echocardiograms.Thus, the ECGo was assessedas showing false positive evidence of prior inferior infarction in these 2 cases.The other 2 patients had false negative findings of inferior infarction on the conventional tracings. Both of thesepatients had recurrent monomorphic ventricular tachycardia with clinical history and echocardiographic evidence of prior myocardial infarction; however, electrocardiographic evidence was present only in the ECGo. Thus, in summary, the ECG produced false negative findings in 6 patients with prior myocardial infarction, and the ECGo produced false positive findings in 2 and false negative findings in 4. There was a close correlation betweenQRS axis calculated with the ECGo and ECG. The averageaxis difference calculated independently from the’ 2 methods was 19”, with a 95% confidence interval of 14 to 24”. Tachycardia: sus conventional
vectorcardiographically ekctrocardiogram:
derived
ver-
The ECGo closely resembled the ECG during wide QRS complex tachycardia, except in voltage (ECGn tended to be less), and in QRS morphology in leads Vs and Vd. Thirty-nine percent of tachycardias had dissimilar QRS configurations between the 2 methods in lead Vs, and 55% had dissimilar patterns in V4. The average difference in QRS axis between the 2 methods during tachycardia was 17”, with a 95% confidence interval of 12 to 22’. The following 3 criteria were 100% specific for ventricular tachycardia and the ECGo was as sensitive as the ECG in recording them: absenceof precordial RS complex (11 of 41 ventricular tachycardias; sensitivity 27%), precordial RS interval > 100 ms (20 of 41 ventricular tachycardias; sensitivity 49%) and atrioventricu-
lar dissociation (7 of 42 ventricular tachycardias; sensitivity 17%). The fourth criterion, an axis in the right superior quadrant, was observedin 10 patients during tachycardia, 9 of which were ventricular tachycardia (sensitivity 22% and specificity 90%). Because of the close similarity of the ECGo to the ECG in leads VI, Vz and Vg, the morphologic criteria were present with equal frequency in the 2 lead systems(Figures 3 to 6). There was complete agreement between the 2 investigators in obtaining the diagnoses of tachycardia. An accurate diagnosis was obtained in 56 of the 64 (87.5%) tachycardias with both methods (Table II). The same indeterminate diagnoses and misdiagnoses occurred with both methods. One misdiagnosis occurred in a patient with a ventricular tachycardia due to bundle branch reentry, which was diagnosed as supraventricular tachycardia with left bundle branch block. A second misdiagnosis was an atrioventricular nodal reentrant tachycardia that was negative for all ventricular criteria except 1: the tachycardia had a left bundle branch block pattern with an R wave >30 ms in lead V2. Examination of the patient’s baseline tracings revealed R-wave prolongation in lead V2 during sinus rhythm also, with an intraventricular conduction delay pattern Thus, the misdiagnosismay not have occurred if the investigators had the benefit of the baselineECG. A third misdiagnosedtachycardia was supraventricular with an unusual pattern of aberrancy including a monaphasic R-wave pattern in lead VI, a nondiagnostic pattern in Vg, and a right superior axis. Five tachycardias (3 supraventricular and 2 ventricular) were labelled as indeterminate for both lead systems,because the first 4 criteria produced negative findings for ventricular tachycardia, and the morphologic criteria were contradictory in lead Vt versus Vg. An additional finding was that the ECGo was often technically superior to the ECG. Conventional tracing contained more artifact and baseline wandering, pre-
FIGURE 3. Simuitaneous resting (feffj and wide CLRS complex tachycardia (tigbf) tracings shown in this and subsequent figures are recorded during cardiac electrophysiologii study with conventional (fop) and vectorcardiographically derived (f~offom) electrocardiographic tracings. Pattern of ventricular preexcitation is identical in the 2 lead systems in 22.year-old man with WolffParkinson-White syndrome. Note early transition to upright complex between leads V2 and V3 in the vectorcardiographically derived electrocardiogram (ECGo). Atrioventricular ~orthodromic reciprocating tachycardia with aberrant conduction was induced during cardiac ekctrophysiologic study. Morphohgic criteria for abenancy (i.e., RSR’ conftguration in VI, and QRS pattern in Vs[R:S ratio >l]) are evident in both lead systems. ECG = electrocardiogram.
VECTORCARDIOGRAPHICALLY
DERIVED ELECTROCARDIOGRAM
615
sumably due to movement of the patients’ extremities, compared with that of the ECGb (Figure 7). This technical advantage of the ECGn was especially noticeable after direct-current defibrillation of patients in whom 21 of the 10 conventional electrodesfrequently pulled loose and caused major artifact or frank loss of the electrocardiographic signal.
DISCUSSION
This is the first study to assessthe value of the ECGu in the diagnosisof wide QRS complex tachycardia. We found the ECGu equally as valuable as the ECG in distinguishing ventricular from supraventricular tachycardia with aberrant conduction. There was perfect agreementbetween the 2 lead systemsfor mor-
FIGURE 4. Gther than early transition between leads Vs and Vs in vectorcardiographically derived electrocardiogram (ECGo), baseline tracings in the 2 lead systems are identiil, indicating left ventricular hypertrophy and prior inferior wall myocardial infarction. Cardiac electrophysiologic study revealed easity inducible monomorphic ventricular tachycardia with right bundle branch block pattern. Multiple criteria indicate correct diagnosis in both lead systems including: (1) precordial RS complexes >lOO ms, (2) axis in right Euperior quadrant, (3) late S nadir 170 ms in Vs, (4) taller left peak QRS configuration in VI, and (5) RS pattern in Vs (R:S ratio
AND CONDUCTION
DISTURBANCES
Comparison of a Vectorcardiographically Derived 12-Lead Electrocardiogram with the Conventional Electrocardiogram During Wide QRS Complex Tachycardia, and Its Potential Application for Continuous Bedside Monitoring Barbara J. Drew, RN, PhD, Melvin M. Scheinman, MD, and G. Thomas Evans, Jr., MD
Previous investigators published conflicting reports comparing a vectorcardiographically derived electrocardiogram (ECGo) with the conventional 12-lead one (ECG). Prior comparisons were obtained in adults during sinus rhythm, but never in patients with wide QRS complex tachycardia. The ECGD was evaluated during baseline rhythms in patients with varying cardiac diagnoses; and the diagnostic accuracy of the 2 methods was compared during 64 episodes of wide QRS complex tachycardia in 49 patients during cardiac electrophysiologic study. All leads of the 124ead ECGD closely resembled the conventional ECG in baseline and tachycardia tracings, except leads Vs and V4. QRS voltages were less in the ECGo, resulting in an inability to detect left ventricular hypertrophy in one third of patients with that diagnosis. There was excellent agreement between the ECGo and ECG in diagnosing prior myocardial infarction (92%), ventricular preexcitation patterns (loo%), bundle branch and fascicular blocks (lOO%), and axis deviation. The ECGo was equally as valuable as the ECG in the diagnosis of wide QRS complex tachycardia. There was perfect agreement between the 2 lead systems in application of the morphologic criteria differentiating supraventricular tachycardia with aberration from ventricular tachycardia in leads VI, Va and Vs, and for criteria requiring axis determination and measurement of RS intervals in the precordial leads. The ECGo tracings contained less muscle artifact during body movements (e.g., after direct-current defibrillation). In conclusion, the ECGo’s close correlation with the ECG, and its technical superiority and simple 5 torso-positioned electrode configuration make it worth pursuing as an option for continuous bedside monitoring. (Am J Cardiol 1992;69:612-618) From the Department of Physiological Nursing, and the Cardiovascular Research Institute and Department of Medicine, University of California, San Francisco, California. This study was supported by a National Research Service Award from the National Center for Nursing Research, the National Institutes of Health, Bethesda, Maryland. Manuscript received September 3, 1991; revised manuscript received November 11,1991, and accepted November 12. Address for reprints: Barbara J. Drew, RN, PhD, School of Nursing, N61 lY, University of California, San Francisco, California 941430610.
612
THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 69
urrent bedside electrocardiographic monitors have several significant limitations. First, a limited selectionof leadsis available. For example,no currently available monitoring system allows for the simultaneous recording of >l precordial lead. Thus, it is not possible to record lead VI, which is preferable for arrhythmia analysis,while also recording lead V2 or Vs, which is ideal for detecting anterior wall myocardial ischemia. Second, bedside leads are often significantly different from correspondingones from a standard 12lead electrocardiogram (ECG).1,2This difference is due in part to the bedsidemonitoring practice of positioning the arm and leg electrodeson the torso.1,2 Dower et al3 derived 12 electrocardiographic leads using a modified Frank vectorcardiographic lead configuration (Figure l), which they report to more approximate the conventional than the torso-positioned ECG used for exercisetesting or bedsidemonitoring. The coefficients of vector leads X, Y, and Z necessaryfor deriving the lead vectors for the 1Zlead ECG have been previously established.4The original reports of Dower et a15,6suggesteda good correlation betweenthe vectorcardiographically derived (ECGn) and conventional ECGs in the diagnosis of myocardial infarction, frontal plane QRS axis and intraventricular conduction delays; however, these findings were not corroborated by Wolfe et a1.7 Although the ECGo offers potentially significant improvementsfor continuous bedsidemonitoring, insufficient data is available regarding its diagnostic accuracy. Furthermore, all previous comparisonsof the ECGn with the ECG have beenperformed at rest during stable (generally, sinus) rhythms. The purpose of the present study was to compare the 2 lead systems in patients with varying cardiac diagnoses. In our investigation, clinical and echocardiographicdata were available to allow for an independent standard relative to a correct diagnosis. Prior studies compared the ECGo with the ECG, but left unclear which of the 2 reflected the true diagnosis. In addition, for the first time, we compared the 2 lead systemsduring wide QRS complex tachycardia using invasive electrophysiologic studies as the gold standard for correct diagnosis.
C
METHODS
We prospectively analyzed 64 wide (10.12 second) complex tachycardias recorded from 49 adults undergoing cardiac electrophysiologic study. Only monomorMARCH 1, 1992
phic tachycardias at a rate of 100 to 290 beats/mm were selected for analysis. Supraventricular tachycardias with anterograde conduction over an accessory atrioventricular. pathway were excluded from analysis. More than 1 tachycardia from the same patient was used in the analysis if the patient developed: (1) both supraventricular and ventricular tachycardias, (2) supraventricular tachycardia with both right and left bundle branch block-type aberrations, or (3) a second ventricular tachycardia with a clearly different QRS morphology. Ventricular tachycardias were defined as morphologically distinct if they exhibited different bundle branch block patterns or if they had a markedly different (>60”) frontal plane QRS axis. The diagnosis of tachycardia was verified by intracardiac recordings in all patients. Simultaneous recordings were obtained with the 2 lead systemsusing identical Marquette instruments during baseline rhythm before electrophysiologic study and during wide QRS complex tachycardia. Two investigators independently compared baseline ECGs with respect to frontal plane QRS axis, evidenceof infarction, bundle branch and fascicular block, and ventricular preexcitation and hypertrophy using standard criteria.* Similarly, 12-lead ECGs’ were compared during tachycardia. Each diagnosis of tachycardia was obtained without benefit of the patient’s baselineECG, or knowledge of the lead system, clinical information or electrophysiologic findings. Furthermore, each of the 12 leads of the ECGn was compared with its counterpart conventional ECG lead during baseline and tachycardia rhythms to determine the similarity of the 2 recording methods. The 2 leads being compared were considered identical if they had identical QRS patterns in terms of sequence,width and morphology of QRS waves, and similar voltages. We used a modification of the algorithm proposed by Brugada et a1,9in which a diagnosis of ventricular tachycardia was made if: no RS complex was present in any precordial lead, the interval from onset of the R to nadir of the S was >lOO ms, atrioventricular dissociation was present, or the frontal plane QRS axis was in the right superior quadrant (i.e., -90 to f 180’). If ventricular tachycardia could not be diagnosed on the basis of these criteria, QRS morphology was analyzed in leads Vi, Vl and Vs. The morphologic criteria used to diagnoseventricular tachycardia in those with a right bundle branch block pattern included a monophasic R, biphasic QR or RS, or M-shaped complex with a taller left peak in lead Vi. lo Ventricular tachycardia was diagnosed in those with a left bundle branch block pattern when the complex contained a prolonged R wave >30 ms, a slurred or notched S downstroke, or a delayed S nadir >60 ms in leads Vi or V2. l1 Lead Vs was also used to obtain the diagnosis of ventricular tachycardia if any of the following patterns were present: a monophasic QS, biphasic QR, late peaking of the QRS 170 ms,12 or RS configuration (R:S < 1) in tachycardias with a right bundle branch block pattern. lo A diagnosisof supraventricular tachycardia with aberrant conduction was obtained when criteria from the
first 4 steps were negative for ventricular tachycardia, and QRS morphology suggestedaberrancy, including: (1) a triphasic RSR’ configuration in lead Vi in tachycardias with a right bundle branch block pattern, (2) absentor tiny R wave followed by a steepS downstroke without slurring or notching in leads Vi and V2 in tachycardias with a left bundle branch block pattern, l l (3) early peaking of the QRS 150 ms in lead Vg,12or (4) a triphasic QRS configuration (R:S > 1) in lead V,j in tachycardias with a right bundle branch block pattern.‘O When the first 4 criteria yielded negative findings for ventricular tachycardia, and the morphologic criteria in lead Vi indicated a diagnosis contrary to that of Vg, an “indeterminate” diagnosis was obtained. RESULTS Sample characteristics: Patients comprising the sample were referred for cardiac electrophysiologic study to select antiarrhythmic drugs, catheter ablation or device therapy for symptomatic supraventricular or ventricular arrhythmias. Two thirds of the patients were men (mean age 56 years, range 19 to 86). Cardiac history of the 49 patients was as follows: previous myocardial infarction (28), coronary artery disease without myocardial infarction (l), dilated cardiomyopathy (4), valvular heart disease (l), accessory atrioventricular pathway (12) and absenceof heart diseasewith history of paroxysmal tachycardia or unexplained syncope(3). Eighteen patients had history of aborted suddencardiac death. At the time of electrophysiologic study, 27 patients (55%) were receiving no antiarrhythmic drugs; the remainder were treated with a variety of such agents. As indicated from intracardiac recordings, 22 tachycardias were supraventricular with aberrant ventricular
IA
FIGURE 1. A, in contrast with conventional 1%lead elecb-ocardiogram that needs 10 electrodes, vectorcardiographiiy derived electrocardiogram needs just 5 elecbodes on chest. When using standard Weadwire bedsii cable, chest (C) eiecbode is placed on lower sternum at level of fiRh intercostal spoco. Righl and iofl arm (RA and LA) ektrodes are placed in right and left axilla, respectively, at same horizontal level as chest electrode. Left leg (LL) electrode is placed on manubrium, and right leg (RL) ground electrode can be placed anywhere. B, ktrizontal plane diagram illustrates how posterior view of heart is derived without need of ektrode on patient’s back Anterior-posterior lead is derived by comparing midpoint of right and left axilla electrodes with lower sternal electrode. Vertical, right-left and anterior-posterior orthogonal leads resulting from these electrode positions produce approximations of vector leads X, Y and 2.
VECTORCARDIOGRAPHICALLY
DERIVED ELECTROCARDIOGRAM
613
TABLE I Baseline Comparison of Derived and Conventional Electrocardiograms Patients RBBB
LBBB
IVCD
LAFB
LVH (n = 9)*
Preexcitation
MI (n = 28)*
3 3 100
1 1 100
6 6 100
2 2 100
6 % 66
6 6 100
24t 22 92
conduction, and 42 were ventricular. Supraventricular arrhythmia mechanismsincluded orthodromic atrioventricular reciprocating tachycardia in 12 patients with Wolff-Parkinson-White syndrome, atrioventricular nodal reentry in 5, atria1 tachycardia in 4, and sinus tachycardia in 1. Baseline conventional
vectorcardiographically electrocardiogram:
in 49
derived
versus
In all patients, the baseline ECGo closely resembled the ECG with 2 exceptions: (1) QRS morphology was dissimilar in lead V3 in 35% of patients, and in V4 in 51%. This disparity between the 2 lead systemswas typically an early transition of the “right ventricular” rS to the “left ventricular” qR pattern in the ECGo. Whereas the transitional zone generally appearedin lead Vs or V4 of the ECG, it frequently occurred between V2 and Vs in the ECGn. (2) QRS voltage tended to be less in the ECGn, especially in the precordial leads,which affected the diagnosis of left ventricular hypertrophy. A comparison of the diagnosesdetermined from the 2 recording methods is shown in Table I. There was complete agreement between the 2 lead systems in
all casesof the following diagnoses: (1) right bundle branch block, (2) left bundle branch block, (3) nonspecific intraventricular conduction delay, and (3) anterior fascicular block (no patients exhibited posterior fascicular block). Nine patients had echocardiographic evidence and voltage criteria for left ventricular hypertrophy in the ECG, however, only 6 of these had such evidence in the ECGn (Figure 2). An additional young patient with a normal echocardiogramand no history of hypertension had false positive voltage criteria for left ventricular hypertrophy in the ECG, but not in the ECGo. Six patients with Wolff-Parkinson-White syndrome had evidenceof ventricular preexcitation during sinus rhythm in the baseline ECG. All 6 patients also had evidenceof preexcitation in the ECGo, with deltawave morphology nearly identical between the 2 lead systems. There was agreement between the 2 methods in 45 patients (92%) in absenceor presenceof prior myocardial infarction and in the location of infarction. Of 28 patients with clinical history and echocardiographicevidence of prior myocardial infarction, 22 had such evi-
FIGURE 2. Simultaneous conventiinal and vectorcardiographically derived ektrocardiigraphic recordings illustrating voltage differences between the 2 lead systems in patient with severe mitral regurgitation. Diagnosis of left ventricular hypertrophy was obtained with conventional electrocardiogram (ECG) by noting S wave in lead V3 of 25 mm, P-terminal force in Vi >0.04, and typical ST-segment shifts. Left ventricular hypertrophy was not detected with vectorcardiographiilly derived electrocardiiram (ECGo) and QRS voltage was less than that of ECG in every lead except VI and V2.
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THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 69
MARCH 1, 1992
dence in the ECG compared with 24 in the ECGo. Discrepanciesbetweenthe 2 lead systemsincluded evidence of previous inferior wall myocardial infarction in 4 patients with the ECGo, but not with the ECG. Two of these patients were young (23 and 28 years, respectively) with no history of heart disease,and both had normal echocardiograms.Thus, the ECGo was assessedas showing false positive evidence of prior inferior infarction in these 2 cases.The other 2 patients had false negative findings of inferior infarction on the conventional tracings. Both of thesepatients had recurrent monomorphic ventricular tachycardia with clinical history and echocardiographic evidence of prior myocardial infarction; however, electrocardiographic evidence was present only in the ECGo. Thus, in summary, the ECG produced false negative findings in 6 patients with prior myocardial infarction, and the ECGo produced false positive findings in 2 and false negative findings in 4. There was a close correlation betweenQRS axis calculated with the ECGo and ECG. The averageaxis difference calculated independently from the’ 2 methods was 19”, with a 95% confidence interval of 14 to 24”. Tachycardia: sus conventional
vectorcardiographically ekctrocardiogram:
derived
ver-
The ECGo closely resembled the ECG during wide QRS complex tachycardia, except in voltage (ECGn tended to be less), and in QRS morphology in leads Vs and Vd. Thirty-nine percent of tachycardias had dissimilar QRS configurations between the 2 methods in lead Vs, and 55% had dissimilar patterns in V4. The average difference in QRS axis between the 2 methods during tachycardia was 17”, with a 95% confidence interval of 12 to 22’. The following 3 criteria were 100% specific for ventricular tachycardia and the ECGo was as sensitive as the ECG in recording them: absenceof precordial RS complex (11 of 41 ventricular tachycardias; sensitivity 27%), precordial RS interval > 100 ms (20 of 41 ventricular tachycardias; sensitivity 49%) and atrioventricu-
lar dissociation (7 of 42 ventricular tachycardias; sensitivity 17%). The fourth criterion, an axis in the right superior quadrant, was observedin 10 patients during tachycardia, 9 of which were ventricular tachycardia (sensitivity 22% and specificity 90%). Because of the close similarity of the ECGo to the ECG in leads VI, Vz and Vg, the morphologic criteria were present with equal frequency in the 2 lead systems(Figures 3 to 6). There was complete agreement between the 2 investigators in obtaining the diagnoses of tachycardia. An accurate diagnosis was obtained in 56 of the 64 (87.5%) tachycardias with both methods (Table II). The same indeterminate diagnoses and misdiagnoses occurred with both methods. One misdiagnosis occurred in a patient with a ventricular tachycardia due to bundle branch reentry, which was diagnosed as supraventricular tachycardia with left bundle branch block. A second misdiagnosis was an atrioventricular nodal reentrant tachycardia that was negative for all ventricular criteria except 1: the tachycardia had a left bundle branch block pattern with an R wave >30 ms in lead V2. Examination of the patient’s baseline tracings revealed R-wave prolongation in lead V2 during sinus rhythm also, with an intraventricular conduction delay pattern Thus, the misdiagnosismay not have occurred if the investigators had the benefit of the baselineECG. A third misdiagnosedtachycardia was supraventricular with an unusual pattern of aberrancy including a monaphasic R-wave pattern in lead VI, a nondiagnostic pattern in Vg, and a right superior axis. Five tachycardias (3 supraventricular and 2 ventricular) were labelled as indeterminate for both lead systems,because the first 4 criteria produced negative findings for ventricular tachycardia, and the morphologic criteria were contradictory in lead Vt versus Vg. An additional finding was that the ECGo was often technically superior to the ECG. Conventional tracing contained more artifact and baseline wandering, pre-
FIGURE 3. Simuitaneous resting (feffj and wide CLRS complex tachycardia (tigbf) tracings shown in this and subsequent figures are recorded during cardiac electrophysiologii study with conventional (fop) and vectorcardiographically derived (f~offom) electrocardiographic tracings. Pattern of ventricular preexcitation is identical in the 2 lead systems in 22.year-old man with WolffParkinson-White syndrome. Note early transition to upright complex between leads V2 and V3 in the vectorcardiographically derived electrocardiogram (ECGo). Atrioventricular ~orthodromic reciprocating tachycardia with aberrant conduction was induced during cardiac ekctrophysiologic study. Morphohgic criteria for abenancy (i.e., RSR’ conftguration in VI, and QRS pattern in Vs[R:S ratio >l]) are evident in both lead systems. ECG = electrocardiogram.
VECTORCARDIOGRAPHICALLY
DERIVED ELECTROCARDIOGRAM
615
sumably due to movement of the patients’ extremities, compared with that of the ECGb (Figure 7). This technical advantage of the ECGn was especially noticeable after direct-current defibrillation of patients in whom 21 of the 10 conventional electrodesfrequently pulled loose and caused major artifact or frank loss of the electrocardiographic signal.
DISCUSSION
This is the first study to assessthe value of the ECGu in the diagnosisof wide QRS complex tachycardia. We found the ECGu equally as valuable as the ECG in distinguishing ventricular from supraventricular tachycardia with aberrant conduction. There was perfect agreementbetween the 2 lead systemsfor mor-
FIGURE 4. Gther than early transition between leads Vs and Vs in vectorcardiographically derived electrocardiogram (ECGo), baseline tracings in the 2 lead systems are identiil, indicating left ventricular hypertrophy and prior inferior wall myocardial infarction. Cardiac electrophysiologic study revealed easity inducible monomorphic ventricular tachycardia with right bundle branch block pattern. Multiple criteria indicate correct diagnosis in both lead systems including: (1) precordial RS complexes >lOO ms, (2) axis in right Euperior quadrant, (3) late S nadir 170 ms in Vs, (4) taller left peak QRS configuration in VI, and (5) RS pattern in Vs (R:S ratio
