Unifocal origin of multiform extrasystoles in concealed bigeminy

J. ELECTROCARDIOLOGY 13 (2), 1980, 199-203

Unifocal Origin of Multiform Extrasystoles in Concealed Bigeminy BY DEBRA ECHT, M.D.* SUDHAKER CHANDURKAR, M.D.,t LEONARD GOLDBERG, M.D. AND MATTHEW N . LEVY, M . D .

SUMMARY A case of concealed bigeminy is presented in which two forms of extrasystolic complexes were evident on the ECG. One form (type B) appeared after a single conducted sinus beat, in a pattern o f manifest bigeminy. The other form (type A) occurred after a sequence of more than one conducted sinus beat. The two configurations have previously been explained on the basis of different foci and mechanisms. Certain features of the ECG from our patient suggested that the two forms originated from a common site. An experimental model was developed in which the right ventricle o f a dog was stimulated at sub- or suprathreshold voltages on alternate sinus beats to simulate concealed bigeminy. The ECG obtained during stimulation of a single site was remarkably similar to that recorded from the patient. We have proposed that the extrasystoles that occur after a compensatory pause may spread in a manner different from those that follow a basic cardiac cycle length. The different pattern of propagation is probably ascribable to the lengthening of the refractory period of the cardiac tissues by the compensatory pause.

S c h a m r o t h and M a r r i o t t 1,2 deduced t h e presence of '~concealed extrasystoles" in certain patterns of ventricular extrasystoles t h a t occur in a non-random fashion. Those patterns in which there were an odd number of conducted sinus beats (S) between extrasystoles were termed "concealed bigeminy;" i.e., S = 2n - 1, where n = any positive integer. Schamroth also observed t h a t extrasystoles associated with concealed bigeminal r h y t h m s occasionally h a v e d i f f e r e n t electrocardiographic forms 3,4. He noted t h a t when the extrasystole was preceded by more t h a n one consecutive sinus beat, it m i g h t have one form, whereas when it followed a single sinus beat t h a t terminated a compensatory pause, it

m i g h t h a v e a d i f f e r e n t configuration. He termed the former " p r i m a r y extrasystoles" and labelled them type A. The latter were referred to as "secondary extrasystoles" and were labelled type B. He proposed t h a t the two different complexes were multifocal as well as multiform. He inferred t h a t the type B extrasystoles were somehow dependent upon type A, since they only occurred after the compensatory pause t h a t followed the type A extrasystoles. He further distinguished them on the basis that type B extrasystoles obey the "rule of bigeminy,''5 but type A extrasystoles do not. We have recently found an ECG which displayed concealed bigeminy with extrasystoles of two different configurations, similar to the pattern described by Schamroth. 3,t Certain features of the ECG suggested t h a t the two forms of extrasystoles originated from a common site; i.e., from the same automatic focus or from the same r e e n t r y loop. If this presumption were correct, then both extrasystolic forms would probably have originated on the basis of a common mechanism. Therefore, we conducted an e x p e r i m e n t on an anesthetized dog to determine if the two forms of extrasystoles could be generated from a single focus. An electrocardiographic pattern was obtained from the animal which closely resembled t h a t recorded in the patient.

From the Divisions of Investigative Medicine and Cardiology, Mt. Sinai Hospital, 1800 E. 105 Street, Cleveland, Ohio 44106. *Resident in Internal Medicine at University Hospitals, Cleveland, Ohio. tDepartment of Cardiology at Fairview General Hospital, Cleveland, Ohio. Supported by U.S. Public Health Service Grant HL 10951. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. w 1734 solely to indicate this fact. Reprint requests to: Matthew N. Levy, M.D., Chief, Investigative Medicine, Mt. Sinai Hospital, 1800 E. 105 Street, Cleveland, Ohio, 44106.

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Fig. 1. Standard lead II electrocardiographic rhythm strip from a patient with concealed bigeminy. The extrasystoles are of 2 forms, type A and type B, depending on the number of conducted sinus beats in the sequence that precedes the extrasystole. The two strips are continuous.

CASE REPORT A 50 y e a r old black female was adm i t t e d to the coronary care uni t with a history of prolonged chest pain. The admission E C G revealed a normal sinus r h y t h m , r i ght bundle branch block, and other changes that suggested an inferior wall myocardial infarction. T h e p a t i e n t s u b s e q u e n t l y d e v e l o p e d serum enzyme elevations consistent with an acute myocardial infarction. Convalescence was complicated by an episode of left vent r i c ular failure and frequent p r e m a t u r e vent r i c ular contractions. A s e g m e n t from a long r h y t h m s t r i p is shown in Fig. 1. Ventricular extrasystoles are labelled A or B; "A" denotes those t h a t follow more t h a n one conducted sinus beat, and ~B" denotes those t h a t follow just one sinus beat; i.e., a manifest bigeminy. The coupling interval in all cases was 490 _ 10 msec (mean _+ range). The baseline R-R interval of the sinus r h y t h m was 860 _+ 30 msec. The immediate post-extrasystole cycle length (compensatory pause) was 1220 _+ 20 msec. This section (Fig. 1) of the cardiographic strip is consistent with concealed bigeminy, with interectopic intervals that contained e i t h er one or three sinus beats. A continuous strip with 59 interectopic intervals has been analyzed from this pat i ent and the results are shown in Table 1. The num ber s of conducted sinus beats (S) in the 58 interectopic intervals were all odd integers, i.e., t hey conformed to the formula S = 2n - 1. Based on the null hypothesis of an equal likelihood of odd and even values of S, the probability t h a t this

could represent a random occurrence is only 2 -Ss. E very extrasystole t h a t followed more t h a n one conducted sinus beat had a type A configuration. Almost every extrasystole t h a t followed just one sinus beat was of the B type, except for one sequence where the configuration gradually changed from the A to the B form over a sequence of four extrasystoles in a manifest bigeminal p a t t e r n (Fig. 2). The coupling intervals of all extrasystoles were constant, regardless of the type, and remained constant t h r o u g h o u t the entire r h y t h m strip. Certain critical features of the cardiogram s u g g e s t t h a t b o t h f o r m s of e x t r a s y s t o l e s originated from a common focus or common r e e n t r y circuit. First, the fact t h a t the coupling.intervals were the same for type A and B extrasystoles suggests a unifocal origin,6 even though the forms of the complexes were

TABLE 1 Distribution of the Numbers of Conducted Sinus Beats (S) in a Series of 58 Consecutive Interectopic Intervals. S Incidence 1 21 3 24 5 6 7 1 9 3 11 1 13 0 15 0 17 2 Total 58

J. ELECTROCARDIOLOGY, VOL 13, NO. 2, 1980

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Fig. 2. Another segment from the same rhythm strip as in Fig. 1. Note the gradual change in morphology of the extrasystoles during the bigeminal sequence. different. After reviewing the r h y t h m strips in earlier articles ~,4 on concealed bigeminy with multiform extrasystoles, we have found the coupling intervals to be constant, within the accepted limits of variation of .08 sec. 5 Second, the initial deflections of types A and B extrasystoles were similar to each other. With only one lead available, however, this tends to support, but does not establish, the same direction of the initial vector. Third, the sequence in Fig. 2 suggests a gradual transition of complex configurations, progressing from the type A configuration to the type B configuration. Although these changes could represent progressive fusion between extrasystoles originating from two separate sites, it seems much more likely t h a t there is a progressive change in the propagation of the excitation wave originating from a single focus. These suggestive features led us to the following experiment on a dog in an attempt to determine whether similar electrocardiographic changes could be elicited from a common focus in the heart.

ANIMAL EXPERIMENT Methods. An experiment was conducted on a m o n g r e l dog a n e s t h e t i z e d w i t h m o r p h i n e sulfate, 2 mg/kg im, followed 30 minutes later by chloralose, 75 mg/kg iv. A tracheal cannula was inserted and intermittent positive pressure respiration was instituted. A transverse thoracotomy was performed at the level of the fourth intercostal space. A bipolar electrode catheter was introduced into the right a t r i u m through the auricular appendage for recording of the atrial electrogram. Another bipolar electrode catheter was inserted into the right external jugular vein and advanced into the right ventricular cavity. It was wedged into the apex for stimulation of the right ventricular endocardium at a fixed site. The thorax was closed with sutures and the air was evacuated from the thoracic cavity. Blood pressure was recorded from the left femoral artery by means of a strain gauge J. ELECTROCARDIOLOGY,

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(Statham P23AA). The arterial blood pressure, right atrial electrogram, right ventricular pacing signal, and various electrographic leads were recorded on an eight channel oscillograph (Brush, Mark 200). The dog's right ventricle was stimulated electrically via the electrode catheter on alternate sinus beats. The stimuli consisted of 3 msec pulses with a constant suprathreshold voltage. The stimuli were programmed by an analog computer (EAI 580); the program was similar to t h a t used previously in a study of the role of the compensatory pause in the production of concealed bigeminy. ~ The coupling interval between the sinus R wave and the stimulus was preset initially to a value t h a t was just great enough to induce a premature contraction with each stimulus. The output of the circuit was controllable by a m a n u a l on-off switch. The stimulus was enabled when the switch was turned on, at which time a suprathreshold current was delivered after the appropriate coupling interval. This produced a b i g e m i n a l r h y t h m with a l t e r n a t e beat stimulation. When the switch was t u r n e d off, the extrasystoles were not produced, but the p a t t e r n of s t i m u l a t i o n was m a i n t a i n e d , because the triggering signal was delivered every other sinus beat regardless of whether the output switch was on or off. Periodically setting or resetting the output switch simulated the electrocardiographic pattern of concealed bigeminy. Results. Fig. 3 is a tracing (lead V4) from the dog experiment in which the right ventricle was stimulated on alternate sinus beats at a fixed apical site, in order to simulate concealed b i g e m i n y . The o u t p u t switch was turned on prior to each label "A" and turned off after "B". The coupling interval was set at 200 msec, and the basic cycle length was 400 msec. The immediate post-extrasystole cycle (the compensatory pause) was approximately 600 msec. The extrasystoles (A) t h a t followed more t h a n one consecutive sinus beat had configurations t h a t were distinctly different from those (B) t h a t followed a single sinus beat. When the coupling interval was increased to

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Fig. 3. Precordial lead Vt electrocardiographic strip from the dog experiment, demonstrating simulated concealed bigeminy. The right ventricle was stimulated on alternate sinus beats from a single endocardial pacing site. Note the 2 forms of extrasystoles, labelled A and B. 300 msec or more, the differences in configuration of the two types of extrasystoles were no longer discernible.

DISCUSSION The r h y t h m strip obtained from the dog was remarkably similar to t h a t recorded from the patient. In the experimental model, the paced extrasystoles were unifocal by design. The type B extrasystoles had deeper S waves with more prominent notches and the T waves were taller t h a n for the type A extrasystoles. These were also the most prominent distinguishing features in the patient's ECG (Fig. 1). This supports the hypothesis t h a t the extrasystoles in the patient were either unifocal in origin or were initiated by the same reentry circuit. Unifocal but multiform extrasystoles have been attributed to aberrant ventricular conduction by Schamroth s and others. Schamr o t h s s t a t e d t h a t an e x t r a s y s t o l e w i t h a g r a d u a l l y c h a n g i n g QRS morphology and constant coupling interval is highly suggestive of a unifocal origin. Fig. 2 t a k e n from our patient demonstrates just t h a t phenomenon. Concealed bigeminy has been explained on the basis of a 2:1 block in a reentry loop 9 or a 2:1 exit block from an ectopic focus2 ~ We propose the following mechanism to account for m u l t i f o r m e x t r a s y s t o l e s in concealed bigeminy. The type A and type B configurations might reflect different patterns of impulse spread through the ventricles from the same site of origin. The wavefront of the excitation wave might be slightly different due to localized conduction block in areas with part i a l l y or a b s o l u t e l y r e f r a c t o r y tissue. We

sttggest t h a t the compensatory pause t h a t follows an extrasystole is responsible for the change in the pattern of propagation of the ectopic excitation wave. The prolongation of the action potential and the refractory period of ventricular myocardial cells and conducting tissue when the duration of the preceding R-R i n t e r v a l has been i n c r e a s e d is well documented. 1H3 Our studies in the dog have shown t h a t when an extrasystole is produced electrically, the r e s u l t a n t compensatory pause is responsible for lengthening the refractory period of the beat t h a t terminates t h a t pause, v The existence of unifocal but multiform extrasystoles has been accepted, s,It,I5 However, the concept of unifocal ventricular extrasystoles with different configurations because of different patterns of propagation has not been well ss Singer et al. 1~ have documented t h a t the development of conduction abnormalities is often a rate-dependent phenomenon. Castellanos et al.17 reported a case in which a patient with complete A-V block was paced from a right ventricular site. The result a n t QRS complex had a left bundle branch block morphology. An indwelling d e m a n d pacemaker in the left ventricle had been set at a lower rate to serve as a monitor. The QRS complexes t h a t originated from the left ventricular site had a right bundle branch block pattern. W h e n the left v e n t r i c u l a r pacing stimulus fell in the relativerefractory period, there was a change in QRS configuration, with a loss of the classic right bundle branch block morphology. Multifocal v e n t r i c u l a r ectopy carries a more serious prognosis t h a n do unifocal extrasystoles25 A l t h o u g h unifocal but multiform extrasystoles do not yet constitute a J. ELECTROCARD~OLOGY, VOL 13, NO. 2, 1980

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c l e a r l y d e f i n e d entity, t h e i r p r o g n o s t i c significance is p r o b a b l y d i f f e r e n t f r o m t h a t of t h e multifocal variety. Therefore the understanding of t h i s a r r h y t h m i a is of clinical importance.

9. 10. 11.

REFERENCES 1. SCHAMROTH, L AND MARRIOTT, H J L: Intermittent ventricular parasystole with observations on its r e l a t i o n s h i p to e x t r a s y s t o l i c bigeminy. Am J Cardiol 7:799, 1961 2. SCHAMROTH, L AND MARRIOTT, H J L: Concealed ventricular extrasystoles. Circulation 27:1043, 1963 3. SCHAMROTH, L: Concealed extrasystoles and the rule of bigeminy. Cardiologia 46:51, 1965 4. SCHAMROTH,L: The physiological basis of ectopic ventricular rhythm: A unifying conept. S Afr Med J 45:(Suppl) 3, 1971 5. LANGENDORF,R, PICK, A AND WINTERNITZ,M: M e c h a n i s m s of i n t e r m i t t e n t v e n t r i c u l a r bigeminy. I. Appearance of ectopic beats dependent upon length of the ventricular cycle, the "Rule of Bigeminy." Circulation 11:422, 1951 6. COOKSEY,J D, DUNN, M AND MASSIE, E: Clinical Vectorcardiography and Electrocardiography. Year Book Medical Publishers, Inc, Chicago, 1977, pp 535-542 7. LEE, M H, LEVY, M N AND ZIESKE, H: Role of the compensatory pause in production of concealed bigeminy. Am J Cardiol 34:697, 1974 8. SCHAMROTH, L: The Disorders of Cardiac

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13.

14. 15. 16.

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Rhythm. Blackwell Scientific Publications, Oxford, 1971, pp 85-94 LEVY, M N, ADLER, D S AND LEVY, J R: Three variants of concealed bigeminy. Circulation 51:646, 1975 KINOSHITA,S: Concealed ventricular extrasystoles due to interference and due to exit block. Circulation 52:230, 1975 MENDEZ, C, GRUHZIT,C C AND MOE, G K: Influence of cycle length upon refractory period of auricles, ventricles, and A-V node in the dog. Am J Physiol 184:287, 1956 MOORE, E N, PRESTON, J B AND MOE, G K: Duration of transmembrane action potentials and functional refractory periods of canine false tendon and v e n t r i c u l a r myocardium: Comparisons in single fibers. Circ Res 17:259, 1965 JANSE, M N, VAN DER STEEN, A B M, VAN DAM, R T AND DURRER, D: Refractory period of the dog's ventricular myocardium following sudden changes in frequency. Circ Res 24:251, 1969 ROSENBAUM,M B, ELIZARI,M V AND LAZZARI,J O: The mechanism of bidirectional tachycardia. Am Heart J 78:4, 1969 FISCH, C AND BREST, A N: Complex Elect r o c a r d i o g r a p h y 2. F.A. Davis Company, Philadelphia, 1974. Vol. 6, No. 1, pp 281-282 SINGER, D H, LAZZARA,R AND HOFFMAN, B F: Interrelationships between automaticity and conduction in Purkinje fibers. Circ Res 21:537, 1967 CASTELLANOS,A, MAYTIN, O, LENBERG, L AND CASTILLO, C: Unusual QRS complexes produced by p a c e m a k e r stimuli. Am H e a r t J 77:732, 1969