Mechanisms of concealed ventricular bigeminy: The concept of concealed conduction in the reentrant pathway

J. ELECTROCARDIOLOGY 19 (1), 1986, 67-76

Mechanisms of Concealed Ventricular Bigeminy: The Concept of Concealed Conduction in the Reentrant Pathway BY SII1NJI KINOSIIITA, M.D., KAOR1 TAKAIIASII1,M.D., KoJI NAKAGAWA,M.D., AKIRA SAGAWA,M.D., YOSIIINORI TANABE, M.D., AND TAKESIII KAWASAKI,M.D.

SUMMARY To clarify the presence of concealed conduction in the reentrant p a t h w a y of extrasystoles, 20 patients with ventricular extrasystoles were studied in whom two forms of interectopic periods were found in the same recording. One form is the XSIS,X period, in which two sinus QRS complexes (S l and S 2) intervene between an interpolated extrasystole (the first X) and the next extrasystole (the second X). The other is the XSzX or XSIX period, in which one sinus QRS complex intervenes between two extrasystoles. In all patients except one, the XX interval in the XSIS.>X period was longer than t h a t in the XSzX or XSIX period though shorter than twice the latter XX interval. This strongly suggests the presence of two-level block in the reentrant p a t h w a y of the extrasystoles. It appears t h a t the sinus impulse S 1 in the XSISz X period invaded a large portion of the reentrant p a t h w a y and then was blocked at a distal site of the pathway; namely, t h a t concealed conduction of the impulse S l occurred in the pathway. I t is suggested t h a t such concealed conduction prolonged the conduction time of the following sinus impulse, S 2, in the reentrant pathway, resulting in lengthening of the XX interval. The presence of three- or four-level block is also suggested. By the use of such multilevel block, mechanisms of concealed ventricular bigeminy are explained. vaded a considerably large portion of the pathway and prolonged the conduction time of the following sinus impulses in the pathway; namely, t h a t concealed conduction in the pathway favored the appearance of the next extrasystole. This s t u d y dealt with 20 patients with ventricular extrasystoles showing occasional interpolation. In these patients, in order to clarify the presence of concealed conduction in the reentrant pathway, influence of interpolation on the following extrasystolic r h y t h m was investigated.

In some cases of ventricular extrasystoles, the number of sinus QRS complexes intervening between two successive extrasystoles is always odd. This phenomenon was originally reported by Satoh et al. in 1960. I Thereafter, it was called "concealed ventricular bigeminy" by Schamroth and MarriottY .3 In concealed bigeminy, it has been suggested t h a t when manifest extrasystoles are not seen, alternate sinus impulses pass through the reentrant pathway of the extrasystoles, *Gbut they become "concealed extrasystoles" because of insufficient conduction delay in the pathway2 In two patients with concealed bigeminy, Kinoshita5 suggested t h a t although the other alternate sinus impulses were blocked within the pathway, they in-

MATERIALS A N D M E T H O D S The clinical material in this study was obtained from 20 patients with ventricular extrasystoles in whom two forms of interectopic periods were found in the same recording. One form is the XSIS2X period, in which two sinus QRS complexes (S l and S2) intervene between an interpolated extrasystole (the first X) and the next extrasystole (the second X). An example of such XSIS2X periods is shown in the bottom strip of Fig. 1. The other form is the XSIX or XS2X period, in which one supraventricular {usually sinus} QRS complex (Sl or S2) intervenes between two extrasystoles. The first extrasystole X in the XSlX period is interpolated, while the first one in the XS2X peried is non-interpolated. In the XS2X period, the first sinus impulse (Sl) after the

From the Department of Medicine, Health Administration Center, ttokkaido University; the Second Department of Medicineand the Departmentof CardiovascularMedicine,Hokkaido University School of Medicine; and the Department of Medicine, Sapporo Teishin ttospital; Sapporo, Japan. The costs of publicationof this article weredefrayedin part by the payment of page charges. This article must therefore be hereby marked "'advertisement" in accordance with 18 U.S.C. w solely to indicate this fact. Reprint requests to: Shinji Kinoshita,M.D.,the Department of Medicine, ttealth AdministrationCenter, ttokkaido University Sapporo 060, Japan.

67

68

KINOSHITA ET AL

first extrasystole was non-conducted to the ventricles, or, before occurrence of the first sinus impulse, the sinus node was discharged by the retrogradely conducted impulse of the extrasystole. Examples of XS2X periods are shown in Fig. 1. The ages of the patients in this study (17 men and 3 women) ranged from 20 to 58 (mean 39.6) years old. None of the patients had organic heart disease, and no one was receiving antiarrhythmic therapy. In all the patients, coupling intervals of the extrasystoles and XX intervals of XSlS2X periods and XSIX or XS2X periods were measured. On the basis of these data, we attempted to clarify the presence of concealed conduction in the reentrant pathway of the extrasystoles, and the mechanisms of concealed ventricular bigeminy.

RESULTS Coupling intervals of ventricular extrasystoles, and interectopic intervals of XS~S2X periods and XS2X or XS~X periods in all the patients are shown in Table I. Relationship between XSISzX and XSzX periods In 17 of the 20 patients, XS~S2X and XS2X

periods were found in the same recording (Patients 1 to 17). Coupling intervals of the extrasystoles in these patients were considerably variable though they were usually much shorter than the sinus cycle length. In all these patients, except one (Patient 17), the XX interval in the XS~S,X period was longer that that in the XS2X period. Fig. 1 shows an example of such cases. In Fig. 1, when the X S 2 interval in the XS2X period lengthens, the following coupling interval, S2X, shortens nearly to the shortest one (the third strip). When the XS 2 interval lengthens further, the extrasystole X following the S 2 complex fails to become manifest (the fourth strip). This suggests that the coupling interval S.~X here is too short for the extrasystole X to become manifest; namely, that though the sinus impulse S 2 passes through the reentrant pathway, it becomes a "concealed extrasytole" because of insufficient conduction delay in the pathway. On the other hand, when the XS 2 interval in the XS2X period shortens, the coupling interval S2X lengthens nearly to the longest one

TABLE I Electrocardiographic data in patients with ventricular extrasystoles showing occasional interpolation (intervals in sec) Ranges of XX intervals Patient No.

Ranges of coupling intervals

in XS~S2X

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

0.47-0.66 0.61-0.84 0.48-0.65 0.46-0.67 0.39-0.46 0.39-0.49 0.46-0.53 0.48-0.78 0.53-0.72 0.43-0.67 0.42-0.56 0.50-0.61 0.42-0.50 0.41-0.44 0.49-0.57 0.48-0.54 0.50-0.90 0.53-0.70 0.38-0.44 0.52-0.63

1.77-1.78 2.39-2.46 1.80-1.90 2.06-2.29 1.80 1.62-1.68 1.94-2.04 2.18-2.21 2.30-2.45 1.55-1.56 2.14-2.34 1.66-1.77 1.78-1.88 1.78-1.96 2.26 2.11-2.20 2.01-2.04 2.18-2.24 1.60 2.24

in XS2X (or XS~X) 1.52-1.56 2.05-2.17 1.71-1.72 1.46-1.58 1.58-1.63 1.40 1.62-1.74 1.90-1.94 1.85-2.19 1.33 1.92-2.00 1.44-1.58 1.52-1.55 1.67-1.72 1.68-1.74 1.89-1.96 1.98-2.10 (1.22-1.27)* (0.95-0.97)* (1.34-1.41)*

*These numbers represent XX intervals in XS1X periods, while the other numbers in this column represent those in XS2X periods. S 1= sinus QRS complex following an interpolated extrasystole; S2 = supraventricular (usually sinus) QRS complex following $1 or a non-interpolated extrasystole; X = v e n t r i c u l a r extrasystole.

J. ELECTROCARDIOLOGY 19(1), 1986

CONCEALED VENTRICULAR BIGEMINY

(the second strip). When the XS 2 interval shortens further, the S 2 complex fails to be followed by an extrasystole again (the top strip). This suggests that the sinus impulse S2 here is blocked within the reentrant pathway. In Fig. 1, the XS 2 interval in the XS~S2X period of the bottom strip is almost equal to that in the XS2X period of the fourth strip; nevertheless, the complex S 2 in the bottom strip is followed by a manifest extrasystole. This indicates that the intervention of the sinus complex S I results in prolongation of the coupling interval S2X. Accordingly, the XX interval in the XS~S2X period is considerably longer than that in the XS2X period. Two-level block in the reentrant pathway The above relationship between the XS~S2X and XS2X periods strongly suggests that, except for one patient (Patient 17), concealed conduction of the sinus impulse S~ in the reentrant pathway prolonged the conduction time of the impulse S 2 in the pathway. The diagram below the upper strip in Fig. 2 shows such concealed conduction in the reentrant pathway. In the upper strip the X2X3 inter"val containing the $1 and S 2 complexes is considerably longer than the X~X2 interval containing only the S 2 complex. Shaded bars in the diagram represent markedly prolonged absolute refractory periods in the reentrant pathway. The longest absolute refractory period is found at a distal site of the pathway. The diagram shows that the supraventricular impulse S 2 following the extrasystole X~ falls shortly after the absolute refractory period of the distal site of the pathway, and that it passes through the pathway with a marked conduction delay, and becomes a manifest extrasystole, X 2. After that, the impulse X 2 reaches the entrance of the pathway again, but it is blocked without an appreciable invasion of the pathway. On the contrary, the impulse S~ following the extrasystole X 2 invades a considerably large portion of the pathway, and then it is blocked at a distal site of the pathway; namely, two-level block occurs in the pathway. Thus the next impulse, $2, falls shortly after the absolute refractory period of the proximal site of the pathway. As the result, this impulse S 2 passes through the pathway with a marked conduction delay. Thereafter, the impulse becomes a manifest extrasystole, X 3, despite the fact that it falls long after the absolute refractory period of the distal site. In the following part of the diagram, i.e. in the period between the extrasystoles X 3 and X 5, conduction of impulses in the reentrant pathway occurs in almost the same way as in the period be-

J. ELECTROCARDIOLOGY 19(1), 1986

69

tween the extrasystoles X, and X 3. However, the X3S2 interval is somewhat longer than the X~S2 interval. Thus the extrasystole X 4 becomes a concealed extrasystole because of insufficient conduction delay in the pathway. Quadrigeminy in concealed bigeminy, XS2(X)SaS4X rhythm When twice the sinus cycle length was about equal to the middle length between the XX intervals of the XS2X and the XS,S2X period, a r h y t h m due to the alternation of XS2X and XS,S2X periods was occasionally sustained, in the same way as in the X1-X3 period of Fig. 2. In three patients with such a rhythm (Patients 1, 6 and 7), most coupling intervals of i n t e r p o l a t e d extrasystoles in the rhythm were too short for the extrasystoles to become manifest. Thus these interpolated extrasystoles became concealed extrasystoles in the same way as in the X3-X5 period m-:..--::

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Fig. 1. Interectopic periods XS2X and XSIS2X (Patient 1). Strips are not continuous. The XX interval in the XSIS2X period is considerably longer than that in the XS2X period. X=ventricular extrasystole; S=sinus QRS complex; (S)=sinus impulse that is non-conducted to the ventricles.

70

K I N O S H I T A ET A L

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2. Two-level block in the reentrant pathway (Patient 2). Two strips are not eontinuous. The diagram below the upper strip represents the reentrant pathway of the extrasystules X. The diagram shows that unidirectional block occurs at the exit (the upper end) of the reentrant pathway; namely, that supraventricular impulses cannot enter the pathway through this site. Intraventricular conduction of supraventrieular or extrasystolic impulses leading to the entrance of the pathway is represented by dashed lines. Shaded bars in the diagram represent long absolute refractory periods at proximal and distal levels in the pathway. The QRS complex S2 before the extrasystole X 2 is an atrioventricular junctional escape beat. The lower strip shows that when temporary sinus arrest was caused by vagal stimulation due to pressure on the eyeball, no ventricular ectopic beat is found. This indicates the absence of ventricular parasystole, namely, that extrasystules X are not parasystolic beats. RP=reentrant pathway; S =supraventricular (usually sinus) QRS complex; (S)=sinus impulse that is non-conducted to the ventricles; V= ventricles; X = manifest ventricular extrasystole; (X)= concealed ventricular extrasystole due to insufficient eonduction delay in the reentrant pathway.

Fig.

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d. ELECTROCARDIOLOGY 19(1), 1986

CONCEALED VENTRICULAR BIGEMINY extrasystole due to insufficient conduction delay in the reentrant pathway. An example of such concealed rhythm is shown in the third strip of Fig. 3. The diagram below the strip shows that the (X)SS(X) rhythm is sustained until an extrasystole becomes manifest. Thus the manifest extrasystole follows a sinus complex S~,, where n is an integer. In Fig. 3, every manifest extrasystole X follows a sinus complex S~. This indicates the presence of a "concealed bigeminal r h y t h m . " All strips in Fig. 3 are continuous. In eight patients (Patients 1, 2, 4, 5, 6, 8, 9, and 10), the presence of such concealed bigeminal r h y t h m was clearly shown. Three-level block in the reentrant pathway When twice the sinus cycle length was shorter than the XX interval of the XS~X period, the sinus complex S~ following a non-interpolated extrasystole X often failed to be followed by an extrasystole, suggesting that the sinus impulse S~ was blocked in the reentrant pathway. Examples are shown in the upper strip of Fig. 4. In the X~-X~ period of this strip, the sinus impulse S~ appears to be blocked in the pathway, but the next sinus complex, Sa, is followed by an extrasystole, X~, with a comparatively long coupling interval. As shown in the diagram below the strip, this suggests that the sinus impulse S~ is blocked after a considerable invasion of the pathway. In one patient (Patient 17), as mentioned above, the XX interval of the XSIS~X period was about I

Xl ,

equal to that of the XSeX period, suggesting the absence of concealed conduction of the impulse S~ in the pathway. However, in this patient too, the presence of concealed conduction of the impulse S~ in the XS~SaX period was suggested in the same way as in the X~-X~ period of Fig. 4. Thus, in all of the 17 patients with XS~S~X and XS~X periods, the presence of concealed conduction in the reentrant pathway was suggested. I n t h e XI-X ~ period of Fig. 4, the sinus impulse S~ also appears to be blocked within the pathway, but the S~Sa interval here is comparatively short, and the complex Sa fails to be followed by an extrasystole. As shown in the diagram below the strip, this suggests that the sinus impulse Sa is also blocked in the pathway as a result of concealed conduction of the preceding impulse, S~. However, the next sinus impulse, S~, is followed by a manifest extrasystole. Thus it appears that although the sinus impulse Sa is blocked in the pathway, this impulse also invades some portion of the pathway before block. In other words, the presence of threelevel block is suggested as shown in the diagram. On the other hand, when twice the sinus cycle length was shorter than the XX interval of the XS~S~X period, the sinus complex S~ after an interpolated extrasystole X often failed to be followed by an extrasystole. An example is shown in the X~-X~ period of the lower strip of Fig. 4. As shown in the diagram below the strip, the presence of

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J. ELECTROCARDIOLOGY19(1), 1986

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72

KINOSHITA

three-level block in the r e e n t r a n t pathway is also suggested here. In previous pa t i e nt s reported by Kinoshita et al. 9.~~and Bissett et al., H it was also suggested t h a t two successive sinus impulses were blocked in the r e e n t r a n t pathway because of concealed c o n d u c t i o n of t he first impulse in t he pathway.] 2 Four-level block in the r e e n t r a n t p a t h w a y In the X~-X 2 period of the b o t t o m strip of Fig. 5, the S~S 2 interval is comparatively short. Thus, in the same way as in the Xs-X 6 period of Fig. 4, the sinus impulse S 2 appears to be blocked in the r e e n t r a n t p a t h w a y af t e r some invasion of the pathway. In the bot t om strip of Fig. 5, however, the sinus complex S 3 fails to be followed by an ex-

ET AL

trasystole, and the n e x t sinus complex, S 4, is followed by a manifest extrasystole, X.,. This suggests t h a t the sinus impulse S 3 is also blocked in the pathway after some invasion of the pathway, as shown in the diagram below the strip. The diagram shows the presence of four-level block in the reentrant pathway. Relationship between XSISzX and XSzX periods. In t h r e e p a t i e n t s ( P a t i e n t s 18 to 20), t h e XS,S2X and the XS~X period were seen in the same recording. In these patients, the XX interval in the XS~S2X period was much longer t h a n t h a t in the XS~X period, t h o u g h the former XX interval was shorter than twice the l at t er XX interval. These findings are the same as in the patients with

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Fig. 5. Four-level block in the reentrant pathway (Patient 8). The first two strips are continuous, in these two strips, it appears that the sinus impulse S 2 following the extrasystole X 2 passes through the reentrant pathway and becomes a concealed extrasystole, (X:~),whereas the sinus impulse S 2 following the extrasystole X 7 is blocked within the pathway. In the XT-X~ period, 3-level block in the pathway appears to occur in the same way as in the XvX 2 period of Fig. 4. The diagram below the bottom strip shows that 4-level block in the pathway occurs in the XvX =period. In this figure, irrespective of whether the sinus impulse S,~passes through the reentrant pathway or it is blocked within the pathway, every manifest extrasystole follows an S.~, complex, where n is an integer. This indicates the presence of a classical form of concealed bigeminy. Abbreviations are the same as in Fig. 2.

J. E L E C T R O C A R D I O L O G Y

19(1), 1 9 8 6

CONCEALED V E N T R I C U L A R B I G E M I N Y

XS~S2X periods. Thus, in these three patients, it is also suggested t h a t the sinus impulse S~ in the XS~S2X period was blocked in the r e e n t r a n t pathway after a considerable invasion of the pathway. Fig. 6 shows an example of such coexistent XS,S2X and XS,X periods.

DISCUSSION M e c h a n i s m of c o n c e a l e d c o n d u c t i o n in the reentrant pathway

The term "concealed conduction" was first introduced by Langendorf in 1948. ~ Since then, concealed A-V conduction has been extensively studied in clinical electrocardiology by Pick and Langendorf. '4 In this study, the presence of concealed conduction in the reentrant pathway of extrasystoles was suggested in all the patients. In a recent study by the use of a theoretical model, Kinoshita ~5 postulated that there are many inexcitable gaps at different levels of the reentrant pathway. In Kinoshita's model, impulse transmission across the inexcitable gaps occurs by electrotonical mediation, but the effective refractory periods for transmission across the gaps are markedly prolonged, and their lengths are variable from gap to gap. When a sinus impulse falls shortly after such a long effective refractory period, impulse transmission occurs with a considerable delay. Thus it is possible that the sinus impulse invades a large portion of the pathway with a marked delay, and then is blocked at a distal level of the pathway. The observations in this study reinforce the above concept of concealed conduction in the reentrant pathway. On t h e o t h e r hand, in t h e biological or mathematical model of Jalife, Moe, Antzelevitch et al.,,62, there was only one inexcitable gap in the pathway. In their model, ectopic QRS complexes originated in the region distal to the gap. When a supraventricular QRS complex, S l, occurred comparatively early after the occurrence of an ectopic complex, X,, the supraventricular impulse conducted to the region proximal to the gap produced only a subthreshold electrotonic depolarization in t h e d i s t a l region. T h o u g h this e l e c t r o t o n i c depolarization failed to excite the distal region, it prolonged the effective refractory period for transmission of the next supraventricular impulse, S., across the gap, and, accordingly, the occurence of the next response, X,, in the distal region was delayed by some amount. In their model, however, this amount never exceeded the X~S, interval, i.e. the interval between the response X, in the distal region and the response S, in the proximal region. J. ELECTROCARDIOLOGY 19(1), 1986

73

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Fig. 6. Coexistent XSIS2X and XSIX period (Patient 18). The two strips are continuous. In the X4-Xs period, it appears that four-level block in the reentrant pathway occurs in the same way as in the bottom strip of Fig. 5. Abbreviations are the same as in Fig. 2. In Fig. 6, on the contrary, the difference between the X,-X 2 and Xs-X 6 intervals is much greater than the XsS ~interval. This does not indicate that the sinus impulse S~ in the Xs-X 6 interval produces only a subthreshold electrotonic depolarization in the reentrant pathway without exciting any portion of the pathway. Thus it is strongly suggested that the sinus impulse S~ excites a large portion of the pathway with a marked conduction delay, and then it is blocked at a distal level of the pathway. Fig. 7 summarizes various forms of concealed conduction in the reentrant pathway, and various forms of (manifest and concealed) interectopic periods. Mechanisms of "concealed bigeminy" The observations in this s t u d y suggest t h a t in patients with "concealed bigeminy," concealed trigeminy with interpolation, i.e. (X)SS(X) r h y t h m was sustained in the long period between 2 successive manifest extrasystoles, as shown in Fig. 3. Here, (X) represents a concealed extrasystole due to insufficient conduction delay in the reentrant pathway, while S represents a sinus QRS complex. In the usual classical form of concealed bigeminy, it appears that the (X)SS(X) r h y t h m is initiated by an XS2(X) or XS~S2(X) period when the sinus cycle length is comparatively long. After that, the (X)SS(X) r h y t h m appears to be termJnated by an (X)S=,.~S,~ X period when the sinus cycle length is comparatively short. Accordingly, in such a period between manifest extrasystoles, the last sinus complex is always an $2, complex, where n is an integer. Even when the (X)SS(X) r h y t h m here is initiated by an XS2S3S4(X) period with three-level block in the p a t h w a y or by an XS,S2S3S4(X) period with four-level block, the last sinus complex in a period between manifest extrasystole will be an $2,' complex, i n d i c a t i n g the p r e s e n c e of a classical form of concealed bigeminy. In patients with atrial extrasystoles reported by Levy et al. "2 and by Kinoshita et al., "3 the presence of the classical form of concealed bigeminy was also

74

K I N O S H I T A ET A L

cealed a t r i ~ bigeminyJ 3 it was suggested t h a t the atrial (X)SS(X) r h y t h m was i n i t i a t e d by an XS2S3(X) period, and t e r m i n a t e d by an (X}S2,S2,+IX period. In the XS2S3(X) period here, the sinus node was discharged by the atrial extrasystolic impulse X before the occurence of the first sinus impulse (S,), and the sinus impulse S 2 appeared to be blocked in the reentrant pathway. The classical and variant forms of concealed trigeminy also have been reported in patients with ventricular extrasystoles,'.3.-~4 and in a patient with atrial extrasystoles. '~2 Kinoshita ~s suggested the p o s s i b i l i t y t h a t in concealed trigeminy, t h e (X)SSS(X) r h y t h m with three-level block might be s u s t a i n e d in t h e p e r i o d b e t w e e n m a n i f e s t extrasystoles.

demonstrated. This suggested that the mechanism for concealed atrial bigeminy was similar to t h a t for concealed ventricular bigeminy. The "even n u m b e r " v a r i a n t of c o n c e a l e d bigeminy has been reported in patients with ventricular extrasystoles,4.s and in patients with atrial extrasystolesY 2.~3In the even number variant, the number of conducted sinus beats intervening bet w e e n two s u c c e s s i v e n o n - i n t e r p o l a t e d extrasystoles is always even; namely, the last sinus beat in the interectopic period is always an S~,+,. In two patients with the even number variant of concealed ventricular bigeminy, KinoshitM suggested t h a t the (X)SS(X) r h y t h m was terminated by an (X}S2,+~X period when the sinus cycle length was comparatively long. On the other hand, in a patient with the even number variant of con-

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Fig. 7. Diagrams to show various forms of multilevel block in the reentrant pathway. In the left column, the first X in each diagram represents an extrasystole without interpolation, while, in the right column, the first X represents an extrasystole with interpolation. The extrasystoles without interpolation are always manifest, but the other extrasystoles in this figure sometimes become manifest and, at other times, become concealed because of insufficient conduction delay in the reentrant pathway. When an interpolated extrasystole in the right column becomes manifest, the extrasystolic impulse reaches the entrance of the reentrant pathway again, and then it is blocked without an appreciable invasion of the pathway, in the same way as in the non-interpolated extrasystolic impulse in the left column. The presence of the XS2S3S4SsX period with four-level block in the pathway was not shown in this study, but the presence of a similar period was suggested in a previous patient reported by Kinoshita et al. l~ Abbreviations are the same as in Fig. 2.

J. ELECTROCARDIOLOGY 19(1), 1986

CONCEALED VENTRICULAR BIGEMINY

REFERENCES I. SATOII, T, KINOSlII'rA,S, TANABE, Y, KAWASAKI, T, KATOU, K, ODA, ~|, YAMAMOTO, K, KAMADA, H AND YOSmDA, T. Impulse conductivity in the region surrounding the extrasystolic focus: Wenckebach phenomenon of the coupling intervals,and the '~rule of multiples" {in Japanese). Saishin-Igaku 15:1865, 1960 2. SCIIAMROTII,L AND MARRIOTT,H J L: Intermittent ventricular parasystole with observations on its relationship to extrasystolic bigeminy. Am J Cardiol 7:799, 1961 3. SCIIAMROTII,L ANDMARRIOTT,H J L: Concealed ventricular extrasystoles. Circulation 27:1043, 1963 4. LEVY, M N, ADLER, D A AND LEVY, J R: Three variants of concealed bigeminy. Circulation 51:646, 1975 5. KINOSlIITA, S: Concealed ventricular extrasystoles due to interference and due to exit block. Circulation 52:230, 1975 6. EL'SIIERIF, N, LAZZARA, R, HOPE, R R AND SCHERLAG, B J: Re-entrant ventriculararrhythmias in the late myocardial infarctionperiod. 3. Manifest and concealed extrasystolic grouping. Circulation 56:225, 1977 9 7. KINOSmTA, S: Quadrigeminy in concealed bigeminy {letter).Circulation 54:523, 1976 8. KERIN, N, MORI, I AND LEVY, M N: Ventricular quadrigeminy as a manifestation of concealed bigeminy. Circulation 52:1023, 1975 9. KINOSIIITA,S. FUJITA,K, KAWAGUCHI,H, KANDA,K nED TANAUE, Y: Concealed (proximal) Wenckebach phenomenon with distal 2:1 exit block in the ectopicventricular junction. Chest 73:198, 1978 I0. KINOSIIITA,S, KUROKAWA, S, OnNISlll,S AND OYAMA, Y: rlypeA alternatingWenckebach periodicityin the re-entrantpath of ventricularextrasystoles.J Electrocardiol 13:285, 1980 11. BmSETT, J Ki I,VATSON,"J W, WANTA-MATTIIEWS, M AND OZEMAK, H: Rate dependent variation in concealed bigeminy. J Electrocardiol 15:295, 1982 12. KINOSHITA, S: Three-level block in concealed bigeminy {letter}.J Electrocardiol 16:221, 1983

J. ELECTROCARDIOLOGY 19(1), 1986.

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13. LANGENDORI-;R: Concealed A-V conduction: The effect of blocked impulses on the formation and conduction of subsequent impulses. Am Heart J 35:542, 1948 14. PICK,A ANDLANGENDORF,R: Interpretation of Complex Arrhythmias. Lea & Febiger, Philadelphia, 1979 15. KINOSHITA, S: M e c h a n i s m s of v e n t r i c u l a r arrhythmias: A theoretical model derived from the c o n c e p t s of "electrotonic i n t e r a c t i o n " and "longitudinal dissociation." Am J Cardiol 52:1350, 1983 16. JAI.IFE, J ANDMOE, G K: Effect ofelectrotonicpotentials on pacemaker activity of canine Purkinje fibers in relation to parasystole. Circ Res 39:801, 1976 17. MOE, G K, JALIFE, J, MUEI.LER, W J AN~ MOE, B: A mathematical model of parasystole and its application to clinical arrhythmias. Circulation 56:968, 1977 18. JALIFE, J AND MOE, G K: A biological model of parasystole. Am J Cardiol 43:761, 1979 19. ANTZELEVITCII, C, JALIFE, J AND MOE, G K: Characteristicsof reflectionas a mechanism of reentrant arrhythmias and its relationship to parasystole. Circulation 61:181, 1980 20. JALIFE, J AND MOE, G K: Excitation,conduction, and reflectionof impulses in isolatedbovine and canine cardiac Purkinje fibers.Circ Res 49:233, 1981 21. ANTZELEVITCH,C, JALIFE, J AND MOE, G K: Electrotonic modulation of pacemaker activity: Further biological and mathematical observations on the behavior of modulated parasystole. Circulation 66:1225, 1982 22. LEVY,M N, KERIN, N AND RUBENFIRE,M: Concealed atrial bigeminy and trigeminy. J Electrocardiol 11:185, 1978 23. KINOSHITA, S, KATO, Y, NAKAGAWA, K AND YASUKOUCHI, ~ Concealed atrial bigeminy: Mechanisms of disappearance and reappearance of manifest extrasystoles. Am Heart J 107:919, 1984 24. LEvy, M N, MORI, I AND KERIN, N: Two variants of concealed trigeminy. Am Heart J 93:183, 1977 25. KINOSHITA,S: Mechanisms of concealed trigeminy {letter}. Am Heart J 95:410, 1978