Characteristics of ventricular tachycardia in ambulatory patients

Characteristics of Ventricular Tachycardia in Ambulatory Patients

ROGER A. WINKLE, MD DAVID C. DERRINGTON JOHN S. SCHROEDER, MD, FACC

Stanford, Cafifornia

From The Cardiology Division, Stanford University School of Medicine, Stanford, California. This work was supported in part by Grant HL-5866 and Program Project Grant 1-P01-HL-15833 from the National Institutes of Health, Bethesda, Maryland. David Derrington was supported by the Research Associates Program of the California Heart Association, San Francisco, California. Manuscript received June 16, 1976; revised manuscript received October 18, 1976, accepted October 20, 1976. Address for reprints: Roger A. Winkle, MD, Cardiology Division, Stanford University School of Medicine, Stanford, California 94305.

This study analyzes 94 episodes of ventricular tachycardia recorded in the ambulatory electrocardiograms of 23 patients with stable cardiac disease. The episodes were asymptomaUc in 19 patients, and only one episode resulted in ventricular fibrillation. Eighty-five percent of the episodes occurred when the underlying heart rate was less than 100 beats/rain, and 17 percent occurred during sleep. The rate of the ventricular tachycardia was between 120 and 180 beats/min in 78 percent of the episodes and showed a modest correlation with the underlying heart rate (r = 0.59, P <0.001). Only 14 of the 94 episodes were initiated by R on T premature ventricular contractions, and the mean prematurity index (-4- standard deviation) (R-R'/Q-T) for all episodes was 1.31 4- 0.28. Episodes of ventricular tachycardia recorded during ambulatory electrocardiographic monitoring are usually self-limited and asymptomaUc. They occur during ordinary nonexertional activity and are frequently initiated by late coupled premature ventricular contractions.

Sudden cardiac death results largely from the consequences of ventricular fibrillation. 1 Because ventricular tachycardia is a cardiac rhythm capable of degenerating into ventricular fibrillation, its discovery in the electrocardiogram causes concern. Its life-threatening potential among patients with acute myocardial infarction is established. In that setting, it occurs more often among patients with frequent or paired premature ventricular contractions or with accelerated idioventricular rhythm. 2 Although many authors :~,4 believe that when ventricular tachycardia occurs during acute infarction it is associated with premature ventricular contractions that interrupt the T wave (R on T phenomenon), the recent study of DeSoyza et al. 2 does not confirm this association. The significance and electrocardiographic characteristics of ventricular tachycardia occurring in ambulatory patients with or without heart disease are less well described. Bleifer et al. '~ analyzed 783 ambulatory electrocardiographic tapes and found that episodes of ventricular tachycardia did not occur in tapes showing only the R on T phenomenon but occurred more often in tapes with frequent, paired or multifocal premature ventricular contractions than in tapes without such events. Except for the observation of Kleiger et al. ~ that only I of 19 episodes of ventricular tachycardia was initiated by the R on T phenomenon, there are no data on the electrocardiographic characteristics of yentricular tachycardia in the ambulatory patient. This study analyzes ventricular tachycardia occurring in ambulatory cardiac patients in relatively stable condition with regard to the patients' symptoms, prematurity of the initiating beat, heart rate and activity before the onset of the episode and the duration and rate of the ventricular tachycardia. April 1977 The American Journalof CARDIOLOGY Volume39

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VENTRICULAR TACHYCARDIA--WINKLE ET AL.

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FIGURE 1. Distribution of the number of beats in each episode of ventricular t a c h y c a r d i a (VT).

FIGURE 2. Typical three beat paroxysm of ventricular tachycardia beginning immediately after the T wave. More than half of the episodes of ventricular tachycardia were three beat paroxysms.

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RATE OF EACH EPISODE OF V T (BEATS/MIN) FIGURE 3. Distribution of the rates of ventricular tachycardia (VT) during each episode.

tricular tachycardia. The tapes were either 12 or 24 hour recordings, made using a single channel Avionics recorder and a modified Vl or V6 lead system. During each recording, the patients were ambulatory and carried out normal daily activities. These activities, as well as any medications taken and symptoms noted, were recorded in a patient diary. The tapes were analyzed using the Stanford ambulatory erectrocardiographic system described previously. 7,s

For each episode of ventricular tachycardia, the following measurements were made by manual analysis of the rhythm strips: heart rate before the onset of the episode, heart rate

Methods

Twenty-three patients, 16 men and 7 women, evaluated at Stanford University Medical Center were studied. Each patient had at least one ambulatory electrocardiographic recording containing an episode of ventricular tachycardia, defined as three or more consecutive beats of apparent ventricular origin. The underlying heart disease was coronary artery disease in eight patients, mitral valve prolapse and idiopathic hypertrophic subaortic stenosis in five patients each, cardiomyopathy and apparently normal heart in two patients each and rheumatic heart disease in one patient. The ambulatory electrocardiographic recordings were performed for a variety of research and clinical reasons, and some patients had several recordings demonstrating ven-

TABLE

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NUMBER OF BEATS PER EPISODE OF VT

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immediately after the episode, the R-R interval of the heartbeat immediately preceding the episode, the coupling interval (R-R') of the initial beat of the episode, the Q-T interval of the preceding sinus beat, and the number of beats and average heart rate of each episode. The prematurity index of the beat initiating each episode of ventricular tachycardia was defined as R-R'/Q-T, and the vulnerability index as (preceding R-R X Q-T)/R-R'. These data were analyzed for the group as a whole and for subgroups, classified according to antiarrhythmic therapy at the time of the recording. Statistical analysis of these subgroups was performed using a two-tailed t test. To evaluate the possibility that the patients with more episodes of ventricular tachycardia excessively weighted the

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Characteristics of Ventricular Tachycardia ( V T ) b y M e d i c a t i o n S u b g r o u p Medication

Averages Quinidine With

Episodes (no.) Patients (no.)* Heart rate before V T (beats/min)t Rate of V T (beats/min)t Prematurity index (R-R'/QT)t Vulnerability index ( R - R X Q-T~ ,, ~-R ~ i

None

Digitalis Preparation

Propranolol

Quinidine

20 6 87 +- 15 148 -+ 28 1.20 -+ 0.25 0.69 -+ 0.19

13 4 78 -+ 10 148 -+ 29 1.39 -+ 0.44 0.60 +- 0.16

29 7 77 +- 22 147 +- 34 1.41 +- 0.27 0.67 -+ 0.29

3 3 86 +- 25 125 -+ 27 1.27 +- 0.25 0.59 +- 0.15

Procainamide Propranolol Procainamide 12 3 83 -+ 7.3 152 -+ 13 1.38 +- 0.19 0.54 ,+ 0.11

15 1 85 -+ 11 151 +- 7.4 1.19 -+ 0.10 0.61 -+ 0.07

2 1 124 -+ 20 157 -+ 9.9 1.00 +0 0.48 -+ 0.08

Per Episode (no. = 9 4 )

Per Patient (no.=23)

83 -+ 17 148 -+ 26 1.31 +- 0.28 0.63 +- 0.21

80 +- 18 146 -+ 32 1.36 -+ 0.29 0.64 -+ 0.20

* Some patients had more than one recording demonstrating ventricular tachycardia and were taking different medications during each recordin~r'Mean + standard deviation.

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data, an average value for rate of ventricular tachycardia, underlying heart rate before ventricular tachycardia, coupling interval and vulnerability index was obtained for each patient. From these data, an average value per patient for each variable was computed. Results

The 23 patients had 94 episodes of ventricular tachycardia recorded during a total of 482 hours of ambulatory electrocardiographic monitoring. The number of episodes of ventricular tachycardia per patient ranged from 1 to 35. Duration and rate of the ventricular tachycardia: Figure I summarizes the number of beats of each episode of ventricular tachycardia. The arrhythmia terminated spontaneously in 93 of 94 instances, and 46 of the episodes were of only 3 beats' duration (Fig. 2). Only two episodes were relatively sustained, one lasting for 2,400 beats and the other degenerating into ventricular fibrillation. The rate of the ventricular tachycardia averaged 148 4- 26 beats (standard deviation)/min {range 81 to 222); in 73 of the 94 episodes (78 percent) it ranged between 120 and 180 beats/min (Fig. 3). The rate of the tachycardia showed a modest correlation with the underlying heart rate, faster rates of tachycardia occurring at faster underlying sinus rates (Fig. 4) (r = 0.59, P <0.001). The rate of the tachycardia was not affected by cardiac medication (Table I).

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Relation of ventricular tachycardia to symptoms and activity: Only four patients were symptomatic at the time of occurrence of the ventricular tachycardia. One patient with coronary artery disease experienced palpitation with several brief runs of ventricular tachycardia and had angina pectoris during a 2,400 beat episode. Another patient with coronary disease had a three beat paroxysm recorded during an episode of angina, and a patient with an apparently normal heart experienced presyncope during a five beat paroxysm of ventricular tachycardia. The patient whose episode terminated in ventricular fibrillation and sudden death had severe coronary artery disease and had had a myocardial infarction 1 month earlier. Analysis of the heart rate at the time of occurrence of ventricular tachycardia indicates that the majority of episodes occurred at a normal heart rate. The average heart rate before the onset of ventricular tachycardia was 83 4- 17 beats/min (range 47 to 133), and 80 of the 94 episodes (85 percent) occurred while the heart rate was less than 100 beats/min (Fig. 5). Only three episodes occurred at a sinus rate of less than 60 beats/min. When the episodes were analyzed according to the cardiac medication taken, the patients taking digitalis preparations and propranolol had a slower heart rate before the onset of ventricular tachycardia (78 4- 10 [P <0.07] and 77 4- 22 [P <0.08], respectively) than patients taking other preparations or no medication. There was usually no change in heart rate after the episode of ventricular tachycardia. The majority of the episodes of ventricular tachycardia occurred while the patient was going about everyday activities such as sitting or eating. Sixteen (17 percent) of the episodes occurred during sleep. The

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FIGURE 4. Relation of the rate of each episode of ventricular tachycardia (VT) to the underlying heart rate before the episode.

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HEART RATE PRIOR TO EPISODE OF VT (BEATS/MIN) FIGURE 5. Oisb'ibution of heart rates before each episode of ventricular tachycardia (VT).

April 1 9 7 7

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single fatal episode of ventricular tachycardia was preceded by a supraventricular tachycardia at a rate of 133 beats/min that occurred while the patient was having a bowel movement. Onset of v e n t r i e u l a r t a c h y e a r d i a : The average prematurity index for all episodes of ventricular tachycardia was 1.31 -I- 0.28 (range 0.8 to 2.1); 80 of the 94 episodes (85 percent) were associated with values greater than 1.0 (Fig. 6). These data indicate that the majority of episodes of ventricular tachycardia in the ambulatory patient are not initiated by the R on T phenomenon (Fig. 7 and 8). Analysis according to medication subgroup (Table I) indicated that the prematurity index tended to be longer for patients taking digitalis, procainamide and propranolol than for patients receiving no medication; however, this trend achieved statistical significance only for propranolol (P <0.01). The vulnerability index, which takes into account the R-R interval of the beat preceding the onset of the ventricular tachycardia, was 0.63 -I- 0.21 for the group as a whole (range 0.29 to 1.82) and was not significantly different when analyzed according to medication subgroup (Table I). Ninety-two of the 94 episodes were

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associated with a vulnerability index of less than 1.1 (Fig. 9). Data analysis by patient: The average values of heart rate before ventricular tachycardia, rate of ventricular tachycardia, prematurity index and vulnerability index are summarized in Table II as averages per episode and averages per patient. The values for each are similar, suggesting that those patients with the largest number of episodes of ventricular tachycardia are not excessively weighting the data when the findings are averaged per episode. This lack of influence probably results from the wide range of intrasubject variability observed for these variables among the patients with multiple episodes of ventricular tachycardia. O t h e r arrhythmias: Table II lists other arrhythmias recorded in the ambulatory electrocardiograms in these patients. Generally, these tapes contained frequent multiform ventricular ectopic beats manifested as bigeminy and pairs. Six patients (23 percent) had only

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T A B L E II

Arrhythmias Other Than Ventricular Tachycardia R e c o r d e d in t h e A m b u l a t o r y E l e c t r o c a r d i o g r a m s Patients

(no.)

FIGURE 7. Electrocardiogram showing two episodes of ventricular tachycardia in the same patient. The tipper strip demonstrates a seven beat paroxysm initiated by a late coupled premature ventricular contraction resulting in a fusion beat. Alternatively, but less likely, this episode could represent the R on T phenomenon. The lower strip, recorded later in the same tape, shows a similar episode initiated by a premature beat falling well away from the T wave.

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Bigeminy Paired PVCs Multiform PVCs PVC frequency (peak number in any 15 minute period): 0-1 >1-10 >10-100 >100--1000 PVCs = premature ventricular contractions.

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VENTRICULAR TACHYCARDIA--WlNKLE ET AL,

infrequent premature ventricular beats (less than 10 peak/15 min). Follow-up: Three patients died during an average 9.5 month (1 day to 19 months) follow-up period. One died suddenly during the recording, one died suddenly 19 months after the ventricular tachycardia was recorded and one died of a noncardiac cause. Two patients with cardiomyopathy underwent cardiac transplantation for severe heart failure. Discussion

Our study documents that the majority of episodes of ventricular tachycardia in ambulatory patients are not initiated by the R on T phenomenon. Only 14 of 94 episodes (15 percent) were associated with a prematurity index of less than 1.0, the value indicating R on T. Our data do not permit conclusions about the relative likelihood of early and late coupled ventricular ectopic beats initiating ventricular tachycardia because the total number of early and late coupled premature ventricular beats in these tapes is unknown. Perhaps pertinent to this point is the finding of Bleifer et al. 5 that the R on T phenomenon by itself in an ambulatory electrocardiogram is not associated with the occurrence of ventricular tachycardia, suggesting that the prematurity of ventricular ectopic beats in ambulatory patients may be less important than previously assumed. 9:° These observations do not preclude the possibility that in ambulatory patients fatal, and hence usually unrecorded, episodes of ventricular tachycardia or fibrillation are initiated primarily by the R on T phenomenon. E a r l y v e r s u s late v e n t r i c u l a r ectopic b e a t s and v e n t r i c u l a r t a c h y c a r d i a : The mean prematurity index of 1.31 + 0.28 for episodes of ventricular tachycardia in our ambulatory patients with cardiac disease is slightly less than the value of 1.52 found by DeSoyza et al. ~-after myocardial infarction. In that study, only 12 percent of the episodes were initiated by the R on T phenomenon. Lie et al. lJ found that many episodes of primary ventricular fibrillation after myocardial infarction were initiated by late coupled premature ventricular contractions. An association between relatively long coupling intervals and the onset of ventricular tachycardia was reported by Kleiger et al. ~ on the basis of ambulatory electrocardiographic monitoring in postinfarction patients. Williams et al. 1'~evaluated the initiation of ventricular tachycardia and fibrillation by ectopic beats in anesthetized open chest dogs with myocardial ischemia. They concluded that the malignancy of the ventricular ectopic beat is primarily related not to the portion of the cardiac cycle in which it falls, but to underlying alterations of activation in the ischemic epicardium. They observed that premature beats falling late in diastole were consistently able to initiate ventricular tachycardia and that ventricular tachycardia was more likely to progress to ventricular fibrillation when there was increasing ventricular activation time of successive beats of ventricular tachycardia. These studies all suggest that a large number of potentially serious ventricular arrhythmias are initiated by pre-

mature ventricular contractions that do not interrupt the T wave. V u l n e r a b i l i t y index: Han and Goel 4 proposed the vulnerability index because of an observed relation between a long preceding cycle and the likelihood of ventricular tachycardia induced by a ventricular ectopic beat. This index is expressed as the ratio of the product of the basic Q-T interval and preceding cycle length to the coupling interval. In their experience, ventricular tachycardia was likely at a vulnerability index of 1.1 to 1.4, and ventricular fibrillation at values over 1.4. In our study, most episodes of ventricular tachycardia occurred when the vulnerability index was less than 0.9, and only two episodes were associated with a value greater than 1.1. Thus, in ambulatory Patients most episodes of ventricular tachycardia are not associated with a high vulnerability index. As with the coupling interval, our data do not permit conclusions concerning the relative likelihood of premature ventricular beats with a vulnerability index above or below 1.1 in initiating ventricular tachycardia, because we do not know the vulnerability index of all such beats on these tapes. R e l a t i o n to patient's activity: The occurrence of most episodes of ventricular tachycardia at a time when the heart rate and the patient's diary suggested only a modest level of exercise suggests that ventricular tachycardia in ambulatory patients is generally not precipitated by exercise. This may explain why so few of these episodes terminate in ventricular fibrillation. Our data suggest that episodes occurring when the underlying heart rate is increased, as during exercise, may be associated with more rapid ventricular tachycardia. This faster ventricular rate may result in less efficient pump activity during the episode. Episodes that occur during exercise may also be more likely to degenerate into ventricular fibrillation because of the simultaneous occurrence of ischemia and increased levels of circulating catecholamines. Our data support the finding of Bleifer et al. r~that tapes that recorded tachycardia showed a large incidence of frequent, multiform and paired premature ventricular beats. The asymptomatic status of 19 of our 23 patients is also similar to the status of patients in their study, in which only 5 of 58 patients noted symptoms at the time of their ventricular tachycardia. I n c i d e n c e d u r i n g sleep: In our study, 16 (17 percent) of the episodes occurred during sleep. The true incidence of ventricular tachycardia during sleep may be somewhat greater than our study suggests because many of our recordings were only 12 hours in duration and did not include periods of sleep. Lown and Wolf l:~ initially suggested that many malignant arrhythmias occur during sleep but subsequently concluded 14 that such arrhythmias disappear during sleep because they recorded only two episodes of ventricular tachycardia during sleep in 69 24 hour recordings containing ventricular arrhythmias. Our overall experience with ambulatory electrocardiographic monitoring is that sleep suppresses ventricular arrhythmias in many patients, but that some patients manifest marked ectopic activity and ventricular tachycardia during sleep.

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Effect of antiarrhythmic medication: The variety of cardiac diagnoses and administration of antiarrhythmic drugs may limit the interpretation of our data. However, more than one third of the episodes of ventricular tachycardia occurred while patients were taking no medication or digitalis alone. Additionally, there were no major differences in the characteristics of the episodes of ventricular tachycardia when analyzed according to antiarrhythmic medication subgroup. Our clinical experience indicates that brief self-limited episodes of ventricular tachycardia not initiated by the R on T phenomenon are occasionally encountered in ambulatory electrocardiograms, primarily in patients with frequent premature ventricular contractions, regardless of cardiac diagnosis or medication taken. The fact that approximately 50 percent of these episodes are of only three beats' duration may suggest that this current definition of ventricular tachycardia is too liberal ancl that the term should be reserved only for those episodes persisting beyond three beats. Prognosis: The prognostic significance of ventricular tachycardia in the ambulatory electrocardiogram is uncertain. Hinkle et al. 15 found no deaths over a 5 year period among nine patients with ventricular tachycardia recorded in an ambulatory electrocardiogram; however, eight of the nine had no evidence of heart disease. Hinkle et al. postulated that many patients must experience thousands of episodes of nonfatal ventricular tachycardia over the course of several years. Most

studies correlating ventricular arrhythmias in ambulatory electrocardiograms with sudden death in the postmyocardial infarction period have had too few patients with ventricular tachycardia to reach any statistical conclusions. 16 Our data are presented to provide insights into the characteristics of ventricular tachycardia occurring in ambulatory patients and do not indicate the long-term prognostic significance of this rhythm disturbance. However, the vast majority of these episodes are self-limited, and the spontaneous cessation of most of the episodes in our patients may be related to several factors. These include (1) use of antiarrhythmic medications; (2) more homogeneous temporal dispersion of the impulse in the absence of acute ischemia; (3) relatively little effect of the arrhythmia on coronary perfusion, in view of lack of symptoms and lack of increase in heart rate after the episode; (4) absence of coronary disease in many patients; (5) the natural preselection process, permitting ambulatory electrocardiographic recording only in those patients with nonfatal episodes; or, perhaps, (6) the fact that this rhythm, when detected in the ambulatory electrocardiogram not in the acute setting, may not always be as malignant as is generally assumed.

Acknowledgment We thank Patricia Bell for technical assistance and Dorothy McCain for manuscript preparation.

References 1. Liberthson RR, Nagel EL, Hirschman JC, et ah Pathophysiologic observations in prehospital ventricular fibrillation and sudden cardiac death. Circulation 49:790-798, 1974 2. DeSoyza N, Bissett JK, Kane JJ, et ah Ectopic ventricular prematurity and its relationship to ventricular tachycardia in acute myocardial infarction in man. Circulation 50:529-533, 1974 3. Lown B, Klein MD, Hershberg Ph Coronary and precoronary care. Am J Med 46:705-724, 1969 4. Han J, Goel BR: Electrophysiologic precursors of ventricular tachyarrhythmias. Arch Intern Med 129:749-755, 1972 5. Bleifer SB, Karpman HL, Sheppard JJ, et ah Relation between premature ventricular complexes and development of ventricular tachycardia. Am J Cardiol 31:400-403, 1973 6. Kleiger RE, Martin TF, Miller JP, et al: Ventricular tachycardia and ventricular extrasystoles during the late recovery phase of myocardial infarction (abstr). Am J Cardiol 33:149, 1974 7. Fitzgerald JM, Clappler RR, Harrison DC: Small computer processing of ambulatory electrocardiograms. IEEE Proceedings, Bethesda, 1974, p 31-36 8. Lopes MG, Fitzgerald JW, Harrison DC, et ah Diagnosis and quantification of arrhythmias in ambulatory patients using an improved R-R interval plotting system. Am J Cardiol 35:816-823, 1975

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9. Smirk RH: R waves interrupting T waves. Br Heart J 11:23-36, 1949 10. Smirk FH, Palmer DG: A myocardial syndrome. With particular reference to the occurrence of sudden death and of premature systoles interrupting antecedent "Pwaves. Am J Cardiol 6:620-629, 1960 11. Lie KI, Wellens HJJ, Downar E, el ah Observations on patients with primary ventricular fibrillation complicating acute myocardial infarction. Circulation 52:755-759, 1975 12. Williams DO, Scherlag BJ, Hope RR, et ah The pathophysiology of malignant ventricular arrhythmias during acute myocardial infarction. Circulation 50:1163-1172, 1974 13. Lown B, Wolf M: Approaches to sudden death from coronary heart disease. Circulation 44:130-142, 1971 14. Lown B, Tykocinski M, Garfeln A, e! ah Sleep and ventricular premature beats. Circulation 48:691-701, 1973 15. Hinkle LE, Carver ST, Stevens M: The frequency of asymptomatic disturbances of cardiac rhythm and conduction in middle-aged men. Am J Cardiol 24:629-650, 1969 16. KoUer MN, Tabatznlk B, Mower MM, et al: Prognostic significance of ventricular ectopic beats with respect to sudden death in the late postinfarction period. Circulation 47:959-966, 1973