Concealed intraventricular conduction in the His bundle electrogram

Wenckebach's periods or alternating Wenckebach's periods during 4:1 atrioventricular block?

This article deals with the tracings of a patient having episodes of atrial flutter with 4:1 atrioventricular (AV) block increasing to 8:1 AV block. This phenomenon was attributed to the coexistence of 3-level block due to transverse dissociation with 2:1 AV block in the most proximal level, or first level as well as in the second level coexisting with a Wenckebach's period in the most distal, or third level. It is suggested that perhaps the term Wenckebach's periods during progression of 4:1 AV block best describes this arrhythmia so as to maintain the term alternating Wenckebach's periods only to those occurring when 2:1 block increases to higher degrees of AV block.

Electrophysiologic demonstration of concealed conduction in anomalous atrioventricular bypass tracts

To demonstrate the occurrence of concealed conduction in anomalous atrioventricular (AV) bypass tracts, 11 patients were selected for study. Two had a right-sided and nine had a left-sided bypass tract. Electrode catheters were placed in the right atrium, coronary sinus, AV junction and right ventricle. After every eighth atrial or ventricular driving beat (A1 or V1) at a constant cycle length, two successive atrial or ventricular premature beats (A2 and A3 or V2 and V3) were delivered. The A1A2 or V1V2 interval was fixed at 30 ms greater than the effective refractory period of the atrium or right ventricle, but less than the effective refractory period of the bypass tract in the anterograde or retrograde direction. This allows A2 or V2 to capture the atrium or ventricle, but not conduct in the bypass tract. The A3 or V3 was delivered from late diastole with a progressively shorter A2A3 or V2V3 interval until atrial or ventricular refractoriness was encountered. In the anterograde direction, the presence of A2 prevented A3 conduction in the bypass tract despite A1A3 intervals being longer than the anterograde effective refractory period of the bypass tract in 8 of the 11 patients. In the retrograde direction, the presence of V2 prevented V3 conduction in the bypass tract despite V1V3 intervals being longer than the retrograde effective refractory period of the bypass tract in 3 of the 11 patients. Thus, using the technique of programmed electrical stimulation, concealed conduction in anomalous AV bypass tracts can be demonstrated in both anterograde and retrograde directions.

Wenckebach phenomenon (W.P.) at sites other than A-V junctional area

W.P. occurring at sites other than A-V junctional area are reported. Some of the cases are rather rare. His bundle electrography may be the best method in discovering the site of block, but the using of conventional ECG is also able to detect a correct diagnosis. Clinical significance are discussed, some are innocent, some are related to serious heart disease. Thorough examination is necessary before arriving at any conclusion.

Transverse dissociation of the human His bundle

"Completed" and "abortive" alternating Wenckebach periods occurred in a symptomatic female with calcification of the mitral annulus. These arrhythmias were attributed to transverse dissociation of the His bundle into two horizontal levels "connected in series," with 2:1 block in the "distal" level and Wenckebach periods in the "proximal" level. Intra-Hisian alternating Wenckebach periods resembled those resulting from transverse dissociation of other infra-AV nodal structures in that they are rare, usually symptomatic and require pacemaker implantation. This contrasts with the variety of rhythms resulting from transverse dissociation of the AV node which occur frequently, are not always malignant, and generally are not treated with implanted pacemakers.

Rapid ventricular parasystole with possible multilevel exit block

A case of ventricular parasystole firing at the extremely rapid rate of 214 beats per minute in a 73 year old woman is described. Manifest cycle lengths of parasystolic complexes varied widely due to variable degrees of exit block, which could be best interpreted by the concept of multilevel block or alternating Wenckebach periodicity in the ventriculo-ectopic junction. Discontinuation of digoxin reduced the degree of exit block and unmasked parasystolic tachycardia.

His bundle recordings in atrioventricular nodal alternating Wenchebach periods ending in 5:1 atrioventricular block coexisting with paroxysmal atrioventricular nodal block

Atrioventricular nodal alternating Wenckebach periods ending in 5:1 atrioventricular block occurring during rapid atrial rhythms were explained by postulating the presence of block in three levels of the atrioventricular node. This pattern of conduction occurred in ten of 11 patients who either had received ouabain or verapamil (nine patients) or who had organic atrioventricular nodal disease (two patients). In contrast, this pattern of conduction occurred in only one of eight nonmedicated patients without organic atrioventricular nodal disease. The frequent association of this pattern with paroxysmal, tachycardia-dependent atrioventtricular nodal block suggested a similar, but not necessarily identical, mechanism. In conclusion, atrioventricular nodal alternating Wenckebach periods ending in 5:1 atrioventricular block, as well as paroxysmal atrioventricular nodal block, were only rarely the result of rapid atrial rates per se their occurrence indicating organic or pharmacologic effects on the atrioventricular node. Since both can be produced by carotid sinus pressure, further studies appear to be necessary to determine the role that vagal effects can have in their genesis.

Second degree His-Purkinje block during his bundle pacing

This report presents, for the first time, clear evidence supporting the occurrence of Wenckebach and 2:1 H-V block during His bundle pacing. The simultaneous recording of various intracardiac electrograms, as well as the comparison of the effects produced by selective His bundle pacing and high right atrial pacing at the same rates, permitted the identification of conduction disturbances located distal to the paced His bundle site. This could be done although one criterion usually required to diagnose selective His bundle pacing (namely, stimulus-V intervals of constant duration) was not present.

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.

Electrocardiographic manifestations and clinical significance of atrioventricular nodal alternating Wenckbach periods

Atrioventricular nodal alternating Wenckebach periods were defined as episodes of 2:1 atrioventricular block in which there was a gradual increase in transmission intervals of conducted beats ending in two or three consecutively blocked atrial impulses. This is one of the mechanisms whereby 2:1 atrioventricular block progresses into 3:1 or 4:1 atrioventricular block. Alternating Wenckebach periods appear during rapid atrial pac,ng (even in the absence of depressed atrioventricular nodal function), provided that the atria can be captured at a rate fast enough to allow for the occurrence of this phenomenon. Treatment of atrial flutter with digoxin and quinidine produces alternating Wenckebach's periods, with associated electrocardiographic changes specific for the type of drug given. In patients with "atrial tachycardia with atrioventricular block" due to digitalis intoxication or with primary disease of the conducting system or with acute myocardial infarction, there are coexisting severe arrhythmias and clinical symptoms requiring almost immediate pharmacologic or electrical therapy. We conclude that atrioventricular nodal alternating Wenckebach's periods are common and frequentyly transient and that they occur in a variety of clinical conditions, most of which are benign; however, contrary to what is commonly accepted, some episodes appear in clinical settings requiring prompt pharmacologic or electrical treatment.

Pseudo bundle branch block produced by premature impulses arising in the bundle branches

Pseudo bundle branch block, a previously unreported arrhythmia produced by concealed premature impulses arising in the bundle branches, was seen in two patients with sick sinus node syndrome. Although concealed conduction was not apparent in either the surface or intracardiac leads, the latter were essential in localizing the site of manifest impulse formation. Patient 1, with left bundle branch extrasystoles, had pseudo bundle branch block and pseudo atrioventricular block that depended on the timing and extent of concealment of premature depolarization. Because of the coexisting sinus bradycardia in this patient, electrical stimulation and the recording of the right ventricular apical electrograms gave additional information that helped corroborate the postulated mechanisms. Patient 2 had right bundle branch extrasystoles with sinus beats that showed a right bundle branch block pattern possibly caused by pseudo bundle branch block. In this case the possibility that both the automaticity and the conduction disturbance had a mechanical origin could not be excluded.