Ventricular Extrasystoles with Interpolation or Postponed Compensatory Pause during Atrial Fibrillation: Fact or Fiction?

Abstract

A Holter recording obtained from a patient with atrial fibrillation showed ventricular extrasystoles often in bigeminal rhythm. Most extrasystoles were followed by a long return cycle, and only in a few instances the postextrasystolic interval was short. The latter phenomenon was interpreted as a manifestation of poor retrograde concealed penetration of the ventricular impulse into the atrioventricular (A‐V) junction: accordingly, an ensuing relatively early fibrillation impulse reached the ventricular chamber, since it did not find the A‐V node refractory. These events are similar to what happens in interpolated ventricular extrasystoles occurring during sinus rhythm, the absent or minimal concealed retrograde penetration of the ectopic impulse into the A‐V node being necessary to permit anterograde conduction of the ensuing sinus impulse.

Analysis of the recording also revealed that a very long (>2 second) interval between two consecutive narrow beats only occurred after an “interpolated” extrasystole. This was interpreted with the same mechanism underlying the “postponed compensatory pause” observed at times after interpolated ventricular extrasystoles during sinus rhythm: the minimal or nil penetration of the ventricular ectopic impulse into the A‐V junction, followed by conduction of an ensuing early atrial impulse, “shifts to the right” the A‐V nodal refractory period, preventing conduction of several further supraventricular impulses and generating a pause.

Both interpolated ventricular extrasystoles and the phenomenon of “postponed compensatory pause” are, thus, conceivable during atrial fibrillation, although no definite demonstration is possible.

Ventricular extrasystoles occurring during sinus rhythm are often followed by a fully compensatory pause, and infrequently by a less‐than‐compensatory pause. At times, ventricular extrasystoles are interpolated, i.e., not followed by any pause because the ensuing sinus impulse succeeds in reaching the ventricles and results in a QRS complex, so that the premature ventricular beat is “sandwiched” between two sinus beats. Very rarely, the extrasystole is interpolated but a pause occurs after the sinus beat closely following the premature one: this phenomenon has been termed as “postponed compensatory pause.”1, 2

During atrial fibrillation, ventricular extrasystoles are, in several cases, followed by an unexpectedly prolonged return cycle (a “pause”) that is due to the atrioventricular (A‐V) nodal refractoriness caused by concealed retrograde penetration of the ectopic ventricular impulse into the A‐V junction.3 To our knowledge, interpolation of ventricular extrasystoles, as well as “postponed compensatory pause,” have not been hitherto reported in atrial fibrillation. We describe a case of atrial fibrillation in which both of these phenomena can be hypothesized.

CASE STUDY

A 68‐year‐old male patient, affected by hypertensive heart disease and permanent atrial fibrillation, underwent 24‐hour Holter recording. He was on warfarin (INR target from 2.0 to 3.0), ramipril 5 mg, and hydroclorothiazide 25 mg. In the whole Holter tracing, 8,468 isolated monomorphic ventricular extrasystoles were observed. In the ensuing discussion, any ventricular extrasystole will be defined as V (ventricular) and any narrow beat, expressing conduction of an atrial impulse, as S (supraventricular); S1 is the first narrow beat following an extrasystole, S2 the second one, and so on.

A sample of 4 hours (the period showing the highest concentration of extrasystoles) was carefully analyzed, and for each extrasystole the following measurements were performed: (1) the coupling interval; (2) the return cycle, namely the interval between the extrasystole and the ensuing narrow beat (V‐S1); (3) the RR interval following the return cycle (S1‐S2), whenever S1 was not followed by an extrasystole. All time intervals will be hereunder expressed in hundredths of a second.

The coupling intervals of extrasystoles were slightly variable, ranging from 48 to 60. V‐S1 intervals have been divided in two classes on the basis of their duration (Table 1), and classified as short V‐S1 intervals (duration <120), and long V‐S1 intervals (duration >130). No V‐S1 intervals with a duration ranging from 120 to 130 were observed. S1‐S2 intervals, in turn, were classified as short (<175 hundredths of a second) or long (>200 hundredths of a second). Only two S1‐S2 intervals ranging from 175 to 200 were observed.

Table 1.

Analysis of V‐S1 and S1‐S2 Intervals

RR Intervals and Sequences	Duration	Mean ± SD	Number of Observations	%
V‐S1 (short)	<120	101 ± 15	147	3.7
V‐S1 (long)	>130	153 ± 22	3809	96.3
S1‐S2 (short)	<175	153 ± 22	152	78.4
S1‐S2 (long)	>200	215 ± 11	42	21.6
Short V‐S1/long S1‐S2			42
Short V‐S1/short S1‐S2			53
Short V‐S1 in bigeminal runs			52
Long V‐S1/short S1‐S2			3809
Long V‐S1/long S1‐S2			0

V = ventricular extrasystole; S = conducted beat of supraventricular origin; V‐S1 = interval between a ventricular extrasystole and the ensuing conducted beat; S1‐S2 = interval between two consecutive conducted beats. Time intervals are expressed in hundredths of a second.

Table 1 demonstrates that the majority of V‐S1 intervals (96.3%) were long: only in a few instances a conducted beat followed an extrasystole with a relatively short interval. In addition, long S1‐S2 intervals were extremely rare (42 in a total of 3,956 occurrences) and only occurred following a very short V‐S1 interval.

The longest RR interval observed during the short periods without extrasystoles was 168.

Figure 1 shows: (1) several long V‐S1 intervals (in the middle strip all V‐S1 intervals are long); (2) many short V‐S1 intervals (e.g., those measuring 84 and 80 in the top strip); (3) some short V‐S1 intervals followed by a short S1‐S2 interval (e.g., the last V‐S1 interval in the top strip, that is short and is followed by an S1‐S2 interval measuring 80); (4) a short V‐S1 interval (90, bottom strip) followed by a very long S1‐S2 interval (208). Further examples of short V‐S1 intervals followed by very long S1‐S2 intervals are shown in Figure 2.

Figure 1.

Selected Holter strips (lead CM5, the two bottom strips are continuous). Numbers indicate RR intervals in hundredths of a second.

Figure 2.

Selected noncontinuous Holter strips (lead CM5). Numbers indicate RR intervals in hundredths of a second.

DISCUSSION

In the analyzed Holter recording, the majority of ventricular extrasystoles are followed by a long return cycle, a phenomenon that has been called as “attempt to compensatory pause,” and depends on concealed retrograde conduction of the ectopic ventricular impulse into the A‐V junction.3 It is worth noting that very long V‐S1 intervals often result in a further ventricular extrasystole following S1: a phenomenon defined as “rule of bigeminy.”4

Short V‐S1 intervals, in contrast, are likely to depend on failure of the ventricular impulse to penetrate retrogradely into the A‐V junction. As a consequence, an ensuing relatively early fibrillation impulse succeeds in reaching the ventricular chamber, since it does not find the A‐V node in a refractory state. This is quite similar to what happens in interpolated ventricular extrasystoles occurring during sinus rhythm: in this situation, the scarce or absent concealed retrograde penetration of the ectopic impulse into the A‐V node is a prerequisite to permit anterograde conduction of the ensuing sinus impulse, despite this is early, with respect to the extrasystole. During atrial fibrillation, it is conceivable that conducted beats closely following ventricular extrasystoles depend on the same mechanism producing interpolation of extrasystoles during sinus rhythm. In atrial fibrillation, however, additional phenomena, such as concealed anterograde conduction of atrial impulses, may play a role in determining the postextrasystolic cycle duration; in the reported case, the few ventricular extrasystoles not followed by a prolonged V‐S1 cycle could be defined as “interpolated” also for the reasons discussed below.

It is not devoid of significance that extremely long intervals between narrow beats (>200) are, without any exception, S1‐S2 intervals that follow a very short V‐S1 interval (<120). The close relationship between a short postextrasystolic cycle (V‐S1) and the ensuing unexpectedly long S1‐S2 interval suggests that only an “interpolated” ventricular extrasystole is able to determine a marked prolongation of the RR cycle following the postextrasystolic beat. The mechanism underlying this phenomenon is likely to be similar to that causing the “postponed compensatory pause” associated, during sinus rhythm, with some interpolated ventricular extrasystoles.

Figure 3 shows an example of postponed compensatory pause following an interpolated ventricular extrasystole during sinus rhythm. The ectopic premature impulse penetrates incompletely into the A‐V junction in retrograde direction and undergoes a block; the next sinus impulse, in turn, is conducted to the ventricles with a markedly prolonged PR interval, as a consequence of the partial A‐V nodal refractoriness caused by the extrasystole. The ensuing A‐V nodal refractory period is, therefore, “shifted to the right,” to the extent that the next sinus impulse is blocked, and a “postponed compensatory pause” occurs.

Figure 3.

A simultaneous recording of leads CM5 and CM1 with a ladder diagram explaining the phenomenon of “postponed compensatory pause” in interpolated ventricular extrasystoles during sinus rhythm.

Something very similar is represented in Figure 4 to explain the occurrence of a very prolonged S1‐S2 interval following an “interpolated” ventricular extrasystole during atrial fibrillation. The ectopic ventricular impulse partially penetrates into the A‐V junction, whose refractoriness is prolonged. The ensuing conducted fibrillation impulse encounters a partially refractory A‐V node and undergoes a very slow conduction; the A‐V junctional refractory period is thereby “shifted to the right,” in such a way that several subsequent fibrillation impulses do not succeed in reaching the ventricles, and a long RR interval (a “postponed compensatory pause”) ensues.

Figure 4.

Part of the bottom strip of Figure 2 is represented with a ladder diagram to explain the phenomenon of “postponed compensatory pause” in atrial fibrillation.

Although the above hypothesis cannot be proved, being impossible both to assess whether a defined fibrillation impulse is conducted or not, and to measure the inherent conduction time, the sequence of a very short V‐S1 cycle and a very long S1‐S2 cycle suggests the presence of an “interpolated” ventricular extrasystole followed by a “postponed compensatory pause.”