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.     

Alternating Wenckebach periods occurring in the atria, His-Purkinje system, ventricles and kent bundle

Alternating Wenckebach periods were defined as episodes of 2:1 block during which there was a gradual prolongation of the transmission intervals preceding the appearance of 3:1 or 4:1 block. Alternating Wenckebach periods occurring within the His-Purkinje system in symptomatic patients with right bundle branch block could have resulted from involvement of the His bundle only, the left bundle branch only or both structures simultaneously. Alternating Wenckebach patterns presumably occurring in the reentry pathway of ventricular extrasystoles and in the tissues surrounding an ectopic atrial focus or bipolar pacing electrodes were manifested in the coupling intervals of the premature beats; in the P-P intervals of atrial tachycardia with atrioventricular (A-V) block due to digitalis; and in the stimulus (St)-A intervals following electrical stimuli delivered to the atria at fast rates. Alternating Wenckebach periods of St-H and St-delta wave intervals in patients with the Wolff-Parkinson-White syndrome resulted from involvement of the Kent bundle itself, or of the atria as a proximal level common to distal longitudinally dissociated structures (Kent bundle and A-V node).

It is concluded that contrary to what is commonly believed alternating Wenckebach periods may be a tachycardia-dependent phenomenon occurring above, below or outside the A-V node and explaining a variety of spontaneous or electrically induced arrhythmias whose significance depends on the clinical setting in which they occur.     

Concealed intraventricular conduction in the His bundle electrogram.

Multiple areas of concealed intraventricular conduction are deduced on the basis of aftereffects observed in His bundle recordings. Electrocardiograms and His bundle recordings are presented from two patients with unstable bilateral bundle branch block, the instability of which depended on the interval at which ventricular depolarization was initiated by sinus or paced impulses. This circumstance allows postulation of 1) concealed transseptal retrograde penetration of the left bundle branch system; 2) concealed transseptal retrograde penetration of the right bundle branch system; 3) alternate beat Wenckebach phenomenon with two areas of block in the bundle branch system with concealed penetration of the proximal area; 4) concealed re-entry in the right bundle branch system during an H-V Wenckebach cycle with resetting of the sequence of 2:1 H-V block and return of the re-entry wave to the A-V node causing subsequent A-H block; 5) proximal 2:1 block and distal Wenckebach block producing only two consecutively blocked beats; and 6) infrahisian Wenckebach block with changes both in A-V conduction and QRS contour.     

Atrioventricular alternating Wenckebach periodicity: conduction patterns in multilevel block

Atrioventricular (A-V) conduction patterns were analyzed in three patients with atrial pacing-induced alternating Wenckebach periodicity. These cases were unique because in each (1) separate levels of block responsible for the conduction disturbance were located above and below the His bundle recording site, and (2) there were several departures from the simple alternating Wenckebach pattern. Apparent supernormal conduction, temporary 1:1 conduction and a specific form of gap in A-V conduction resulted from the interplay of many factors including a simple mathematic relation of the blocking ratio at the two levels, the characteristics of the Wenckebach cycles, and the cycle length-dependent features of refractory periods at the different sites. The findings indicate that (1) delay in proximal impulse transmission is usually the critical factor in overcoming prolonged distal refractoriness and producing variable conduction patterns during the course of alternating Wenckebach periodicity; (2) many irregularities in alternating Wenckebach periodicity can be explained by known electrophysiologic mechanisms; and (3) simple mathematic equations alone are too rigid to reflect properly the dynamic process underlying this conduction disturbance.     

His bundle electrocardiography in digitalis-induced "atrioventricular junctional" Wenckebach periods with irregular H-H intervals.

His bundle electrograms were recorded during catheter insertion for prophylactic demand pacing in two patients with accelerated or nonaccelerated "atrioventricular (A-V) junctional" rhythms associated with A-V junctional Wenckebach periods. This appears to be the first published report of so-called A-V junctional Wenckebach periods in which the characteristic irregularities of the H-H intervals were recorded. Patient 1 had an additional area of "complete" anterograde A-V nodal (A-H) block. In Patient 2 the rate of impulse formation was consistent with nonparoxysmal A-V junctional tachycardia. The His bundle recordings were obtained in patients with digitalis toxicity and should be interpreted in the context. The integration of clinical and intracardiac findings with extrapolations from microelectrode and pharmacolic studies and with deductions from the clinical electrocardiograms suggests that the conduction disturbances probably occurred within the A-V node itself (in its AN region). This hypothesis implies that automaticity also originated in the A-V node because the site of impulse formation must have been proximal to the site of the Wenckebach periods. However, conclusive proof of of these postulates will require further studies with refined techniques.     

Wenckebach periods with repetitive block: evaluation with His bundle recording

Two patients are reported in whom repetitive block of two consecutive P waves occurred during Wenckebach beating induced by atrial pacing. His bundle recordings revealed block proximal to H in the first case, suggesting inhomogeneous conduction in the A-V node. In the second case, long cycle lengths were produced in the His-Purkinje system due to A-V nodal Wenckebach periods. The long cycles prolonged refractory periods in the His Purkinje system so that subsequent beats (short cycles) were blocked distal to H.The repetitive block of consecutive multiple atrial impulses could result in unexpected degrees of ventricular asystole during usually benign Type I second-degree A-V block.     

Coexisting intra- and subnodal block: an unusual abnormality of atrioventricular conduction

The presence of A-V block occurring at two levels of the conducting system was demonstrated in an asymptomatic patient by means of the His bundle recordings. During sinus rhythm, first degree A-V block with complete left bundle branch block was noted, suggesting the presence of bilateral bundle branch block. His bundle recordings demonstrated the coexistence of intranodal (Wenckebach periods, Mobitz Type I) and subnodal (Mobitz Type II) block. The evidence of block below the proximal His bundle offered confirmatory evidence of bilateral bundle branch block. In spite of the abnormal antegrade conduction, there was 1:1 V-A conduction during right ventricular pacing at 110 per minute. With more rapid (130 per minute) ventricular pacing, retrograde Wenckebach periods were observed, suggesting that there was, in addition, possible impairment in retrograde conduction. This report serves to demonstrate (1) the limitations of the body surface ECG in the assessment of A-V conduction and (2) that His bundle electrograms make it possible to detect the presence of coincidental lesions at two levels of the A-V conducting system.     

Wenckebach periods associated with high grade second degree (2 : 1 and 3 : 1) A-V block.

An electrocardiogram (ECG) of bilateral bundle branch block (BBBB) which may be attributable to a mixture of 2 : 1 and 3 : 1 atrioventricular (A-V) block is described. The irregularity of QRS complexes with left bundle branch block (LBBB) pattern during 2 : 1 A-V block may be ascribable to "Wenckebach periods", which might be due either to A-V nodal or His bundle or bundle branch delay. However, it was impossible to distinguish between them precisely because appropriate His bundle studies were not performed during the active arrhythmic phase. Although the exact mechanism involved were not established with certainty, different rates of recovery in conduction in the bundle branches in association with a marked prolongation of the refractoriness would seem to be the unique feature of this complex arrhythmia. An ECG tracing of BBBB indicating high grade second degree (2 : 1 and 3 : 1) A-V block, in which "spontaneous" occurrence of "Wenckebach periods" with 2 consecutive blocked P waves can be observed during 2 : 1 A-V block, has never been reported previously as far as can be ascertained from published records.     

Electrophysiological and clinical observations in patients with alternating bundle branch block.

Electrophysiological studies (His bundle recordings and atrial stimulation) were performed in nine patients who manifested periods of both right and left bundle branch block (RBBB and LBBB). In seven of the patients, alternating bundle branch block appeared to reflect intermittent or chronic bundle branch block superimposed on incomplete (but electrocardiographically complete) block of the contralateral bundle branch. In three of these seven, shift from one bundle branch block pattern to the other was associated with reproducible change in H-V (mean change 30 msec), and could be induced by alteration of cardiac rate with carotid massage, coupled atrial stimulation, and rapid atrial pacing. In one of the seven, RBBB with a P-R of 0.20 seconds preceded chronic LBBB with a P-R of 0.24 seconds, implying that RBBB had been incomplete. In three of the seven, although a definite mechanism of alternation could not be demonstrated, transient contralateral bundle branch block occurred superimposed on chronic ipsilateral bundle branch block, implying that the ipsilateral block was incomplete. Two patients manifested periods of narrow QRS, LBBB, RBBB, and paroxysmal A-V block. Based upon pathological data (one case), this pattern appeared to reflect a lesion involving the distal His bundle and proximal bundle branches. In the total group of patients, clinical course was primarily determined by the severity of heart disease and not by occurrence of A-V block. The conduction defect in the majority of patients was surprisingly benign.     

Wenckebach phenomenon occurring in the distal conducting system in a young adult.

This report describes the case of a young man who presented with right bundle-branch block and second degree atrioventricular block; intermittent episodes of Wenckebach periods were recorded. His bundle electrograms demonstrated progressive prolongation of the HV interval followed by block occurring distal to His. This report emphasizes the fact that the Wenckebach phenomenon as a manifestation of the distal conducting system disease can occur in young adults. The observations lend credence to the concept that Lenègre's disease can occur in young people.     

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.     

Wenckebach phenomenon occurring in the distal conducting system in a young adult.

This report describes the case of a young man who presented with right bundle-branch block and second degree atrioventricular block; intermittent episodes of Wenckebach periods were recorded. His bundle electrograms demonstrated progressive prolongation of the HV interval followed by block occurring distal to His. This report emphasizes the fact that the Wenckebach phenomenon as a manifestation of the distal conducting system disease can occur in young adults. The observations lend credence to the concept that Lenègre's disease can occur in young people.     

Asynchronous conduction in the human His bundle.

2 patients with symptoms of paroxysmal AV block showed widening, splitting, slurring and decreasing amplitude of the His potential. Concomitantly, this was followed by different patterns of bundle branch block. In one of the patients it was obvious that a left bundle branch block was related to a Wenckebach phenomenon in the His bundle, and in the other patient different bundle branch block patterns were related to the occurrence of the intra-His bundle conduction delay. It is suggested that the present electrophysiological findings reflect asynchronous conduction in the His bundle causing a critical conduction delay in parts of the bundle branches leading to bundle branch block.     

Significance of A-H interval in patients with chronic bundle branch block. Clinical, electrophysiologic and follow-up observations.

His bundle electrograms were recorded in 308 adults with chronic bundle branch block. The A-H interval was normal in 249 patients and prolonged in 59. Comparison of patients with normal and prolonged A-H intervals revealed a greater incidence of demonstrable organic heart disease in the latter (P less than 0.01). Dyspnea, cardiomegaly and congestive heart failure were more frequent in patients with A-H prolongation. These patients also had longer P-R intervals and atrioventricular (A-V) nodal effective refractory periods, lower paced rates producing second degree A-V block proximal to the His bundle and a greater frequency of H-V prolongation. All patients were prospectively followed up in a conduction disease clinic with mean follow-up periods (+/- standard error of the mean) of 523 +/- 23 and 588 +/- 47 days in the patients with normal and prolonged A-H intervals, respectively. Seven (3 percent) of the patients with a normal A-H interval had A-V block with probable or definite site of block proximal to the His bundle in three and distal to the His bundle in four. In five of the six patients with a prolonged A-H interval who experienced A-V block (10 percent), the probable or definite site of block was proximal to the His bundle. Mortality (both sudden and nonsudden) was not significantly different in the patients with normal and prolonged A-H intervals. In summary, A-H prolongation was associated with increased incidence of organic heart disease and myocardial dysfunction. The risk of development of A-V nodal block was greater in patients with a prolonged A-H interval but appeared to be of minimal clinical significance.     

Disappearing His deflection. Electrophysiological evidence for conduction defect within the His bundle.

A change in the voltage and character of the His bundle deflection following premature atrial stimuli was observed and analysed in 5 of 95 patients having intracardiac conduction studies because of AV conduction disturbances. Of these 5 patients, 3 had spontaneous block within the His bundle, 2 of them showing block in other segments of the conduction system. With increasing prematurity of programmed atrial stimuli, there was a progressive decrease in the voltage of the His deflection, followed by a split His deflection, and finally disappearance of the His deflection. The voltage of the His deflection was also reduced in sinus beats following spontaneous His bundle premature beats. Similarly, during atrial stimulation at increasing rates, the His deflection decreased in voltage, split, and finally disappeared, but when Wenckebach periods appeared the His deflection reappeared in the first paced beat after the dropped beat. The preceding H-H interval was the only electrophysiological variable consistently related to the changes in the His deflection. These changes in His deflection can be explained electrophysiologically as the result of a conduction disturbance within the His bundle. The clinical significance of the phenomenon is discussed. The occurrence of this phenomenon during a conduction study makes it difficult or even impossible to localise the AV block precisely.     

Mobitz II AV block within the His bundle, with progression to complete heart block.

A case of a 48-year-old woman with frequent syncopal episodes is reported. The electrocardiogram showed high degree AV block with narrow QRS complexes. The His bundle electrogram displayed a split His deflection indicating impairment of conduction within the His bundle of the Mobitz II type. The AH interval was prolonged and Wenckebach phenomenon occurred at the same atrial pacing rate before and after atropine administration. During spontaneous or induced high grade AV block an escape rhythm originating in the distal His bundle was observed. A secondary study performed one year later showed progression to complete AV block. Both His potentials were present, one following the atrial and the other preceding the ventricular deflection. The H'V interval was prolonged and a further lengthening was seen after ajmaline. All these findings indicated proximal, mid, and distal disease of the His trunk.     

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.     

Atrioventricular block in the atypical form of junctional reciprocating tachycardia: evidence supporting the atrioventricular node as the site of reentry

Serial electrophysiologic studies were performed in 19 patients with the atypical form of supraventricular tachycardia having a long RP and short PR interval. In all 19 patients, supraventricular tachycardia was found to have a 1:1 P-QRS relation during initial control electrophysiologic studies, and in all 19 patients, electrophysiologic studies suggested that junctional reentry was the mechanism of supraventricular tachycardia. Seven of the 19 patients developed atrioventricular (AV) block during initiation of supraventricular tachycardia or after induction of supraventricular tachycardia following various drug administrations in subsequent studies. In three patients, second degree block within the His bundle or block distal to the His bundle recording site occurred after administration of quinidine. In one patient it occurred after procainamide, and in another patient it occurred after atropine. In one patient, 2:1 block proximal to the His deflection occurred after verapamil. In the remaining patient, a transient Wenckebach block proximal to the His deflection was noted after adenosine triphosphate. In this latter patient, 2:1 AV block was also noted after propranolol and digoxin. The site of reentry in these seven patients with AV block during supraventricular tachycardia was confined to the AV node area. Their supraventricular tachycardia did not involve a slowly conducting paraseptal accessory pathway because the distal AV node, His bundle and ventricle were not found to be necessary links in the tachycardia circuit.     

房室结折返性心动过速伴2:1房室阻滞的机制初探

目的 本研究探讨电生理检查时诱发的房室结折返性心动过速（AVNRT）伴2:1AVB的机制和阻滞部位。方法 回顾分析电生理检查中遇到的9例AVNRT伴2:1AVB患者的资料。结果4例希氏束记录不全的不作分析,其余5例患者中,3例在阻滞的激动上见到H波,在发生AVNRT伴2:1AVB起始阶段出现H-V文氏传导阻滞伴LBBB或RBBB,另外2例在阻滞的激动上未见H波,但有一例2:1AVB过程中突然出现一次H-V3:1文氏传导阻滞。结论 电生理检查诱发的AVNRT伴2:1AVB可能是功能性的希-浦系统阻滞。     

Double Wenckebach phenomenon in atrioventricular node and His bundle. Electrophysiological demonstration in a case of atrial flutter.

In a case of atrial flutter with a 9:2 atrioventricular response, the only possible way to explain the conduction pattern was 3:1 block in the atrioventicular node (which is 3:2 Wenckebach sequence in the N zone and a 2:1 block at the junction of the node with the bundle of His) plus 3:2 Wenckebach sequence distal to the H deflection. The recording of the His bundle deflection confirmed this analysis.