Atrioventricular Wenckebach periodicity in athletes: influence of increased vagal tone on the occurrence of atypical periods

In 37 athletes with atrioventricular (AV) Wenckebach periodicity, the relationship between PP and RR intervals was investigated. In most athletes, when PP intervals gradually lengthened, RR as well as PR intervals usually also gradually lengthened until a blocked P wave occurred, resulting in the occurrence of an atypical Wenckebach period with prolongation of the last RR interval (variant I). In 20 athletes, sudden marked prolongation of a PR interval occasionally occurred, which was usually followed by a blocked P wave (variant II). In five athletes, once sudden marked prolongation of a PR interval occurred, markedly long PR intervals were maintained for some time, and then a PR interval suddenly shortened without a blocked P wave (variant III). It appeared that the above findings were caused by spontaneous variations in vagal tone. It was suggested that longitudinal dissociation and concealed reentry in the AV node occurred in atypical Wenckebach periods of variants II and III, but not in the other periods.     

Electrocardiographic patterns during Holter monitoring in patients with first and second degree A-V block due to 'dual A-V nodal pathways'

The electrocardiographic patterns, observed during 24-h Holter monitoring, of 10 patients (mean age 35 +/- 22 years) with first and second degree A-V block due to dual A-V nodal pathways are reported. Recordings were selected according to the presence of: sudden and persistent prolongation of the PR interval: sudden normalization of the PR interval: 'atypical' Wenckebach sequences showing sudden and pronounced prolongation of any PR interval prior to the blocked P wave. Besides the already recognized pattern, new aspects were identified: (1) Wenckebach sequences in the slow and fast pathways characterized by a progressive increase in the PR interval until a blocked P wave occurred during long and short PR interval periods, respectively; (2) Wenckebach periods first in the slow and then in the fast pathway; (3) 2:1 A-V block with a normal PR interval in the conducted beat after a Wenckebach sequence in the slow pathway; (4) Wenckebach in the fast pathway and, subsequently, in the slow one characterized by a slight prolongation of the PR interval for some beats followed by a sudden and pronounced increase in the PR interval of one beat and a subsequent progressive slight PR prolongation until a blocked P wave occurred; (5) Wenckebach sequence in the fast pathway with subsequent conduction over the slow pathway without a blocked P wave; (6) blocked P waves during both long and short PR interval periods with slight prolongation of the preceding PR interval. The electrophysiological mechanisms involved in these electrocardiographic patterns together with the nature (anatomical or functional) of the intranodal pathways and the clinical significance of this type of block are discussed.     

Alternating Wenckebach periodicity: A common electrophysiologic response.

Alternating Wenckebach periods are defined as episodes of 2:1 atrioventricular (A-V) block in which conducted P-R intervals progressively prolong, terminating in two or three blocked P waves. In this study, His bundle recordings were obtained in 13 patients with pacing-induced alternating Wenckebach periods. Three patterns were noted: Pattern 1 (one patient with a narrow QRS complex) was characterized by 2:1 block distal to the H deflection (block in the His bundle) and Wenckebach periods proximal to the H deflection, terminating with two blocked P waves. Pattern 2 (four patients) was characterized by alternating Wenckebach periods proximal to the His bundle, terminating with three blocked P waves. Pattern 3 (eight patients) was characterized by alternating Wenckebach periods proximal to the His bundle, terminating with two blocked P waves. Alternating Wenckebach periods are best explained by postulating two levels of block. When alternating Wenckebach periods are terminated by three blocked P waves (pattern 2), the condition may be explained by postulating 2:1 block (proximal level) and type I block (distal level). When alternating Wenckebach periods are terminated by two blocked P waves (patterns 1 and 3), the condition may be explained by postulating type I block (proximal level) and 2:1 block (distal level). Pattern 1 reflects block at two levels, the A-V node and His bundle. Patterns 2 and 3 most likely reflect horizontal dissociation within the A-V node.     

Type A alternating Wenckebach periodicity in the reentrant pathway of interpolated ventricular extrasystoles

A 67-year-old man with interpolated ventricular extrasystoles is reported in whom alternate sinus QRS complexes were followed by interpolated ventricular extrasystoles with progressively lengthening coupling intervals until one of these alternate sinus complexes failed to be followed by an extrasystole. This is the first report to suggest the presence of type A alternating Wenckebach periodicity in the reentrant pathway of interpolated ventricular extrasystoles. It is suggested that 2:1 block occurred at a proximal level in the reentrant pathway, while Wenckebach block occurred at a distal level in the pathway.     

Atrial tachycardia, 2:1 alternate Wenckebach periodicity, and atrial standstill

A case of atrial tachycardia, 2:1 alternate Wenckebach periodicity and atrial standstill is reported in an 80-year-old woman who complained of exertional dyspnea and occasional syncope for two years. Two blocked P' waves appeared after each Wenckebach period suggesting type B alternating Wenckebach phenomenon (Mobitz type II 2:1 A-V block distal, and Wenckebach conduction proximal).     

Atypical atrioventricular Wenckebach periodicity caused by conduction through triple atrioventricular junctional pathway as a probable mechanism

Electrocardiograms were taken from an 84-year-old man with right bundle branch block in whom atypical atrioventricular Wenckebach periodicity was frequently occurred. The electrocardiographic findings as mentioned below suggested that the atypical periodicity was caused by conduction through triple atrioventricular junctional pathways as a probable mechanism. When a P wave was blocked after a markedly prolonged PR interval of 0.64 s, the RP interval containing this blocked P wave ranged between 0.84 s and 0.86 s, and the next P wave was followed by a QRS complex of the same configuration, with the PR interval of 0.35 s. On the other hand, when a P wave was blocked after a PR interval of 0.49 s or 0.52 s, the RP interval containing this blocked P wave was comparatively long, ie, 0.95 s or 0.98 s, and the next P wave was followed by a QRS complex of somewhat different configuration showing borderline left axis deviation, with a shorter PR interval of 0.21 s or 0.23 s. These findings suggest that longitudinal dissociation occurred not only in the atrioventricular junction but also in the His bundle. This is the first report suggesting triple atrioventricular junctional pathways probably associated with longitudinal dissociation in the His bundle.     

Periodic variation in atrioventricular conduction time: Mechanisms of initiation,maintenance and termination of periods of long PR intervals

Five patients with periodic variation in atrioventricular (AV) conduction time are reported in whom periods of comparatively short PR intervals alternated with periods of comparatively long PR intervals. In all patients, the transition from a period of long PR intervals to a period of short PR intervals usually occurred without a blocked P wave. In 3 patients, however, the period of long PR intervals was occasionally terminated by a blocked P wave. The mechanisms of initiation, maintenance and termination of periods of long PR intervals are explained by the use of dual AV pathways consisting of fast and slow pathways. It is suggested that the effective refractory period of the fast pathway was abnormally prolonged by increased vagal tone and that, during the period of long P-R intervals, sinus impulses anterogradely passed only through the slow pathway and later retrogradely excited the fast pathway. Apparently, when vagal tone was decreased, the effective refractory period of the fast pathway was shortened, resulting in abrupt improvement in atrioventricular conduction without a blocked P wave.     

Permanent form of junctional reciprocating tachycardia with only even-numbered beats

An analysis of the electrocardiogram of a patient with the permanent form of junctional reciprocating tachycardia is presented. The patient demonstrated near-incessant tachycardia, with a 1:1 atrioventricular relationship and a retrograde P wave (P') occurring closer to the succeeding QRS complexes (ie, with a P'R interval that is shorter than the RP' interval). Each tachycardia episode was characterized by alternating short and long cardiac cycles due to alternation of retrograde conduction time (RP' interval), retrograde Wenckebach periodicity, and an even number of ectopic P' waves. The authors propose that there is an accessory AV connection with decremental functional properties that arborizes into two atrial branches with different conduction times. The fast branch initially exhibits a 3:2 retrograde conduction block followed by a cycle length-dependent 2:1 retrograde conduction block, thereby permitting alternate use of the slow branch, which is the weakest component of the reciprocating process.     

A generalized description of Wenckebach behavior with analysis of determinants of ventricular cycle-length variation during ambulatory electrocardiography

Although variation in ventricular cycle length during Wenckebach-type second-degree atrioventricular block traditionally has been explained by the direction of incremental change in PR lengthening preceding the blocked complex, changing PP intervals can also affect Wenckebach periodicity. A generalized algebraic solution was derived to define changing ventricular cycle length as a function of both changing PP and changing incremental PR interval behavior in Wenckebach block. Based on this solution, the determinants of cycle-length variation were examined for 65 episodes of Wenckebach block detected by ambulatory electrocardiography in 51 patients. As previously demonstrated, only 20% (13 of 65) of Wenckebach episodes were characterized by the "classic" shortening of RR intervals; in contrast, ventricular cycle length increased in 57% (37 of 65) and remained constant in 23% (15 of 65) of cases. Algebraic analysis of these episodes revealed that the direction of ventricular cycle-length change preceding the blocked complex was primarily determined by the direction of change of incremental PR intervals in only 35% (23 of 65) of Wenckebach episodes; RR change was governed by the direction of change of preceding PP intervals in 34% (22 of 65) and by equal change of PP and incremental PR intervals in 31% (20 of 65) of these episodes. Both inverse and concordant relationships between changing RP and PR intervals were primarily determined by the direction of PP variation during in vivo Wenckebach block. These data confirm that classic Wenckebach block is less common than "atypical" Wenckebach periodicity and demonstrate that RR variation in Wenckebach block is governed by the changing PP interval as often as by the changing incremental PR interval.     

Apparent bradycardia-dependent right bundle branch block associated with atypical atrioventricular Wenckebach periodicity as a possible mechanism

The Holter monitor electrocardiogram was taken from a 15-year-old male athlete. Intermittent right bundle branch block frequently occurred at rest. When sinus cycles gradually lengthened, sinus impulses were conducted to the ventricles with right bundle branch block (RBBB) in succession. When, thereafter, sinus cycles gradually shortened, sinus impulses were conducted without RBBB. However, it seems that these findings do not show true bradycardia-dependent RBBB. Atypical atrioventricular Wenckebach periodicity was occasionally found in which sudden shift from the period of comparatively short PR intervals to the period of long PR intervals occurred. In the Wenckebach periodicity, when a QRS complex occurs after a much longer pause, RBBB was not found, while when it occurs after a much shorter period, RBBB was found. This suggests that this case may be apparent bradycardia-dependent RBBB, namely, a form of tachycardia-dependent RBBB. This is the first report suggesting apparent bradycardia-dependent bundle branch block associated with gradual lengthening of sinus cycles, as a possible mechanism.     

Atypical Wenckebach periodicity simulating Mobitz II AV block.

Eleven patients were studied and a total of 144 Wenckebach cycles in the AV node and 118 Wenckebach cycles in the His-Purkinje system were analysed to determine the incidence of typical and atypical Wenckebach periodicity, with particular emphasis on one variant of atypical Wenckebach that may simulate a Mobitz type II block. This pseudo-Mobitz II pattern was defined as a long Wenckebach cycle in which, at least, the last three beats of the cycle show relatively constant PR intervals (variation of no more than 0.02 s in surface leads and no more than 10 ms in His bundle electrograms) and in which the PR interval immediately following the blocked beat is shorter than the PR interval before the block by 0.04 s or more. Atypical Wenckebach cycles were found to be more common than the typical variety at both the AV node (67%) and His-Purkinje system (69%). The pseudo-Mobitz II pattern was seen in 19 per cent of atypical AV nodal Wenckebach periods and in 17 per cent of atypical His-Purkinje system Wenckebach cycles. The need to discern a ''classical'' Mobitz II block from a pseudo-Mobitz II pattern, especially in the setting of an acute inferior myocardial infarction, is emphasised.     

Reverse alternating Wenckebach periodicity

An atrial pacing-induced reverse conduction pattern of the alternating Wenckebach periodicity was observed in 5 of 42 children (12%) during electrophysiologic study. This conduction pattern is a reverse of the usual alternating Wenckebach periodicity: During an underlying 2:1 atrioventricular conduction block there is progressive shortening of the conduction time of the conducted impulses with termination in a lower degree of block. This reverse alternating Wenckebach periodicity may be caused by a mechanism similar to that in other Wenckebach phenomena.     

Mechanisms of atypical atrioventricular Wenckebach periodicity. A theoretical model derived from the concepts of inhomogeneous excitability and electrotonically mediated conduction

To explain the mechanisms of atypical atrioventricular (AV) Wenckebach periodicity, a model of the AV node was theoretically derived from the concepts of "inhomogeneous excitability" and "electrotonically mediated conduction." The theoretical model of the AV node has the following characteristics: (1) increased vagal tone depresses excitability in the AV node, (2) depressed excitability in the AV node is inhomogeneous in both transverse and longitudinal directions, and (3) electrotonically mediated conduction occurs across inexcitable gaps in the AV node. Many features in atypical AV Wenckebach periodicity are explained by the use of this model. Delayed AV conduction is caused mostly by electrotonically mediated conduction across a much-depressed region in the AV node, and thereafter AV conduction is blocked at the same region, resulting in the occurrence of an AV Wenckebach period with gradual lengthening of PR intervals. Occasionally, longitudinal dissociaton and concealed reentry in the AV node occur in the part below (distal to) the above depressed region, resulting in the occurrence of an AV Wenckebach period with sudden marked lengthening of a PR interval. The sinus impulse following such suddenly delayed AV conduction is usually blocked in the AV node as the result of concealed reentry of the preceding impulse.     

Atrial pacing-induced alternating Wenckebach periodicity and multilevel conduction block in children

Multilevel block within the atrioventricular (AV) node has not been previously described in children. Six children with atrial pacing-induced repetitive block are presented. The conduction patterns satisfy the requisites for alternating Wenckebach periodicity or multilevel AV block. In 2 patients the block is documented in the AV node and infra-His region. In 4 patients multilevel block within the AV node is postulated by deductive reasoning. In this study, 2 patterns of alternating Wenckebach periodicity are reported for the first time: sequences of 3:1 block with progressive prolongation of the conducted impulses terminating in 4:1 block; and sequences of 2:1 block with progressive prolongation of the conducted impulses terminating in 2 series of 3:1 block, in which the first conducted impulse following the first 2 blocked beats is not the shortest one, whereas that following the second 2 blocked beats is the shortest.     

Alternating Wenckebach periods with acute myocardial infarction. Report of two cases.

This report describes two patients with the spontaneous occurrence of alternating Wenckebach periods during the course of acute myocardial infarction. Both patients demonstrated alternating Wenckebach periods which terminated in a sequence of two blocked P waves. In one patient, His bundle electrocardiographic study documented the site of block to be proximal to the His bundle. Alternating Wenckebach periods with the block proximal to the His bundle may be compatible with a benign prognosis.     

Electrophysiologic observations in a patient with bradycardia-dependent atrioventricular block

In a patient with atrioventricular (A-V) block distal to the His bundle (H), 1:1 A-V conduction with right bundle branch block and an H-V interval of 70 msec was established with atrial pacing at rates of 120 to 150/min, suggesting that the A-V block was bradycardia-dependent. Advanced second degree A-V block distal to the H deflection occurred with atrial pacing at 160/min after completion of A-V nodal Wenckebach periodicity proximal to the H deflection because of the long H-H encompassing the blocked P wave. Atrial extrastimulus testing coupled with sinus rhythm (with A-V block) demonstrated that critical H₁-H₂ intervals of less than 545 msec allowed conduction to the ventricles. The H₂-V₂ interval shortened progressively from 290 to 70 msec with shortening of these critical H₁-H₂ intervals. Atrial extrastimulus testing coupled with an atrial driven cycle length of 500 msec (with intact A-V conduction) revealed block of the H₂ deflection with an H₁-H₂ interval longer than 540 msec.In conclusion, at critical diastolic intervals, impulses were blocked, creating a state of decreased responsiveness. If a cycle length of subsequent impulses was shorter than the critical diastolic blocking interval, membrane responsiveness gradually improved and conduction resumed. If a cycle length of subsequent impulses was longer than the critical blocking diastolic interval, A-V block was sustained. Blocked impulses continually penetrated to the site of block and reset the state of membrane responsiveness.     

Evaluation of five computer programs in the diagnosis of second-degree AV block.

Five electrocardiogram (ECG) analyzing systems were tested with a microcomputer-based ECG signal generator to assess the accuracy of the systems in interpreting Wenckebach periodicity. Although normal sinus rhythm with normal PR intervals and sinus rhythms with first-degree atrioventricular (AV) block were diagnosed by all five systems, second-degree AV block with classic Wenckebach periodicity was routinely misdiagnosed by four of the five systems. No system recognized the atypical Wenckebach periods in a total of 200 trials, misinterpreting the phenomenon as atrial fibrillation, supraventricular rhythm, sinoatrial block, and other rhythm disturbances. In advanced AV block and a variety of ventricular arrhythmias, none of the five systems diagnosed second-degree AV block with Wenckebach periods. Marked unsatisfactory performance with regard to the diagnosis of Wenckebach periodicity indicates the urgent need for accelerated and comprehensive testing of ECG diagnostic equipment. The present generating device was seen as an effective troubleshooter in optimizing the diagnostic competency of computerized ECG systems.     

Effects of proximal intra-atrial Wenckebach on distal atrioventricular nodal, and His-Purkinje, block with special reference to the theory of alternating Wenckebach periods

Intra-atrial Wenckebach patterns of stimulus-to-response intervals coexisting with distal, A-V nodal, and His-Purkinje, blocks occurred in eight patients during high right atrial stimulation at rapid rates. In two patients with 2:1 St-H block and in two patients with 4:1 St-V block, an increase in the degree of block occurred when the proximal intra-atrial Wenckebach cycle was completed with the stimulus which otherwise would have been propagated to the distal levels. However, the degree of block did not increase when the intra-atrial Wenckebach terminated in distally blocked stimuli. In one patient progression of 4:1 into 5:1 St-V block was due to the association of intra-atrial Wenckebach with alternating 2:1 block at the A-V nodal, and His-Purkinje, levels. Contrasting with most reports dealing with the mechanisms of alternating Wenckebach in a single structure, this study permitted the determination of the boundaries between proximal and more distal levels. It also showed that alternating Wenckebach cycles (of St-H intervals) ending with two consecutively blocked stimuli could result from the association of proximal intra-atrial Wenckebach with distal, A-V nodal Wenckebach, or abortive AW, cycles. The electrophysiology of documented two, or three, level block in different structures has validated previously made assumptions regarding multilevel block in a single structure.     

AV nodal dual pathway electrophysiology and Wenckebach periodicity

Dual Pathways and Wenckebach Periodicity. Introduction: The precise mechanism(s) governing the phenomenon of AV nodal Wenckebach periodicity is not fully elucidated. Currently 2 hypotheses, the decremental conduction and the Rosenbluethian step‐delay, are most frequently used. We have provided new evidence that, in addition, dual pathway (DPW) electrophysiology is directly involved in the manifestation of AV nodal Wenckebach phenomenon. Methods and Results: AV nodal cellular action potentials (APs) were recorded from 6 rabbit AV node preparations during standard A1A2 and incremental pacing protocols. His electrogram alternans, a validated index of DPW electrophysiology, was used to monitor fast (FP) and slow (SP) pathway conduction. The data were collected in intact AV nodes, as well as after SP ablation. In all studied hearts the Wenckebach cycle started with FP propagation, followed by transition to SP until its ultimate block. During this process complex cellular APs were observed, with decremental foot formations reflecting the fading FP and second depolarizations produced by the SP. In addition, the AV node cells exhibited a progressive loss in maximal diastolic membrane potential (MDP) due to incomplete repolarization. The pause created with the blocked Wenckebach beat was associated with restoration of MDP and reinitiation of the conduction cycle via the FP wavefront. Conclusion: DPW electrophysiology is dynamically involved in the development of AV nodal Wenckebach periodicity. In the intact AV node, the cycle starts with FP that is progressively weakened and then replaced by SP propagation, until block occurs. AV nodal SP modification did not eliminate Wenckebach periodicity but strongly affected its paradigm. (J Cardiovasc Electrophysiol, Vol. pp.1‐7)     

Influence of pacemaker-induced tachycardia with A-V block on left ventricular blood velocity in man.

Phasic instantaneous left ventricular blood velocity was measured by radiotelemetry in 28 subjects with a Doppler ultrasonic flowmeter catheter during atrial pacing and induced A-V block Type I Wenckebach A-V block with conduction ratios of 9:8 or lower generally produced a stepwise reduction of peak left ventricular blood velocity in relation to shortened R-R intervals. Longer Wenckebach periods resulted in little or no blood velocity alteration during 1:1 A-V conduction. Those beats following a blocked atrial depolarization were associated with augmented blood velocities. In three subjects, bigeminal periods of 3:2 A-V block resulted in larger left ventricular blood velocities when compared with 2:1 A-V block, despite identical R-R intervals following the blocked P wave. This latter phenomenon was attributed to diastolic augmentation of left ventricular contraction following the second and hemodynamically ineffective beat during 3:2 A-V block. Three patients manifested true blood velocity alternation during second-degree A-V block and changing R-R intervals. The variations in peak left ventricular blood velocity observed during atrial pacing and A-V block are related to changing inotropic state and cycle length dependent alterations of left ventricular diastolic filling.