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.     

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.     

Second degree entrance block with supernormal conduction in intermittent ventricular parasystole

A patient with intermittent ventricular parasystole is reported in whom the presence of second degree entrance block with supernormal conduction was suggested for the first time. In this patient, ventricular extrasystoles with variable coupling frequently occurred. The QRS configuration of the extrasystoles was different from that of the parasystolic beats. When extrasystoles did not occur, the parasystolic beat was never seen because the conducted sinus impulse always reset the parasystolic rhythm. When an extrasystole occurred 0.52 sec or more after the preceding sinus beat, this extrasystolic impulse also reset the parasystolic rhythm. On the other hand, when an extrasystole occurred between 0.47 and 0.51 sec after the sinus beat, the parasystolic focus was protected from this extrasystolic impulse. When, however, an extrasystole occurred in a short terminal portion of the T wave of the preceding sinus beat, this extrasystolic impulse reset the parasystolic rhythm again, suggesting entrance block failure during the supernormal phase.     

Mechanism of bradycardia-dependent appearance of manifest extrasystoles in concealed bigeminy. A theoretical model derived from the concepts of longitudinal dissociation and multilevel block in the reentrant pathway of extrasystoles.

A case of bradycardia-dependent appearance of manifest extrasystoles in concealed bigeminy is presented. To explain the mechanism of such bradycardia-dependent appearance, a theoretical model is derived from the concepts of "longitudinal dissociation" and "multilevel block" in the reentrant pathway of extrasystoles. In the theoretical model, functional longitudinal dissociation divides the reentrant pathway into dual pathways F and S. When manifest extrasystoles are not found for a long time, alternate sinus impulses pass through both pathways F and S, but become concealed extrasystoles because of insufficient conduction delay in the pathways. The other alternate sinus impulses are blocked in the pathways; in pathway F, the impulses are blocked at the entrance, while in pathway S, the impulses are blocked at a more distal level. When sinus cycles gradually lengthen, one of such alternate sinus impulses passes through the entrance of pathway F and, traveling very slowly, is blocked at a more distal level. The next sinus impulse is blocked at the entrance of pathway F; namely, 3:2 Wenckebach block occurs at the entrance of pathway F. Thus this sinus impulse enters only pathway S and passes through pathway S with enough conduction delay to become a manifest reentrant extrasystole.     

Role of the compensatory pause in the production of concealed bigeminy

In experiments conducted on anesthetized dogs, a single prolonged cardiac cycle caused an increase in the duration of the refractory period of the ventricular myocardium. The refractory period remained prolonged for one or two additional cardiac cycles after the basic cycle length was resumed. In concealed bigeminy, a 2:1 block in a reentry path is postulated. The compensatory pause that follows a manifest extrasystole results in a prolongation of the refractory period. If the refractory period exceeds the propagation time of the next ectopic impulse conducted through the reentry path, that ectopic impulse will be concealed. However, if the refractory period does not exceed the propagation time, another extrasystole will occur, and a bigeminal sequence will ensue. Consecutive compensatory pauses appear to exert a cumulative effect on refractory period duration, so that for critical propagation times, the bigeminal pattern will be terminated briefly when an ectopic impulse becomes concealed. A quadrigeminal pattern occurs when the propagation time in the reentry loop lies between the refractory period durations of the beat terminating a compensatory pause and the beat that occurs two sinus cycles later. In concealed bigeminy where an odd number of conducted beats greater than five lies between extrasystoles, the propagation time in the reentry path is just less than the refractory period of the ventricular cells during normal sinus rhythm at the prevailing heart rate. Random increases in propagation time or decreases in refractory period result in manifest extrasystoles.     

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.     

Concealed (proximal) Wenckebach phenomenon with distal 2:1 exit block in the ectopic-ventricular junction.

The findings in two patients with interpolated ventricular extrasystoles showing 2:1 exit block are reported. In these patients the blocked impulses appear to penetrate into the ectopic-ventricular junction (or reentrant pathway) to a varying extent, and the coexistance of a distal 2:1 exit block and a proximal (concealed) Wenckebach phenomenon in the ectopic-ventricular junction is suggested.     

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.     

Hemodynamics and intracardiac conduction after operative repair of tetralogy of Fallot

Electrophysiologic studies were performed in 47 children aged 3 to 18 years, 15 of whom had cardiac arrhythmias 1 to 15 years after repair of tetralogy of Fallot. Six exhibited sinus or atrioventricular nodal dysfunction, 8 had ventricular extrasystoles, and 1 had supraventricular tachycardia. Hemodynamic and electrophysiologic data were obtained at postoperative catheterization. Although electrophysiologic responses were abnormal in a proportion of both the children with and those without arrhythmia, hemodynamic values were similar. Three of 6 children with impaired sinus impulse generation or atrioventricular nodal conduction had a prolonged A-H interval, and in 3 Wenckebach heart block developed at low pacing rates. Ventricular ectopic rhythm was not associated with any particular abnormality of basic intracardiac conduction intervals. Thus, arrhythmias and conduction abnormalities are not consistently related to residual right ventricular hypertension. Abnormalities in electrophysiologic function are common after repair of tetralogy of Fallot in patients with sinus rhythm and may have prognostic implications for these patients.     

2 or 3 level blocks in the Tawara node during atrial tachycardia]

In atrial flutter (or paroxysmal atrial tachycardia), the ventricular response is dependant on the passage through 3 superposed zones of conduction in the Tawara node, the zone of decremential conduction being the central zone N. When the ventricular response is between half and a quarter of the atrial rate there are two possible explanations: type B alternate Wenckebach period (mobitz I block in the central zone N, 2/1 block at the nodo-ventricular junction) or type A alternate Wenckebach period (Mobitz I block in the central zone N and 2/1 block at the atrio-nodal junction). These two responses may alternate in the same patient depending on the drug therapy or vagal activity due to a phenomenon similar to the "GAP" phenomenon. Inexactitudes in the working out of the arithmetic formulae may easily be explained by a certain degree of concealed conduction of blocked activation in one zone or more rarely by hisian extrasystoles. Type A alternate Wenckebach periods are always easier to construct than type B. Perfect 3/1 atrial flutter can only be explained by a type B alternate Wenckebach period with a 3/2 period with a 3/2 period in the N zone and a 2/1 block in the NH zone. When the ventricular rhythm is permanently very slow or when the RR intervals are greater than four times the atrial cycle, 3 zones of block are usually at issue (the third being located in the inferior part of the node or superior part of the bundle of His). Examples of 5/1, 6/1 flutter are thereby analysed. Rapid atrial pacing after termination of the atrial arrhythmia allows a better analysis of its mechanism and the successive reproduction of conduction defects in each zone of block.     

Extra AV nodal Wenckebach periodicity

Extra AV nodal Wenckebach periodicity was diagnosed in seven patients. The most frequent form of this conduction abnormality was an exit block. The underlying block was localized in the sinoatrial junction and in the atria in two patients; the AV junction and the ventricle were the site of the Wenckebach periodicity in one case each. In extra AV nodal exit block, the actual conduction delay is not seen on the ECG and the diagnosis is based on the progressive shortening of the P-P or R-R intervals followed by a pause which is less than twice the shortest P-P (R-R) interval depending on the level of the block. A Wenckebach periodicity in the bundle branches or within the reentry pathway each occurred in one patient. In these forms of Wenckebach periodicity, the diagnosis is established more readily because the conduction delay can be demonstrated on the surface ECG. The clinical significance of extra AV nodal Wenckebach periodicity is discussed.     

Adenosine's effectiveness in long RP' re-entrant tachycardia: additional evidence of the decremental qualities of the retrograde limb.

Adenosine's ability to terminate atrioventricular (AV) re-entrant supraventricular tachycardia is well documented. Typically, termination occurs as a consequence of transient conduction block in the atrioventricular node, a tissue with decremental qualities. However, the atrioventricular node is not always the site of action when adenosine is used on the re-entrant types of long RP' tachycardias. These tachycardias are, in part, characterized by the decremental qualities of the retrograde limb of the tachycardia circuit, which, in turn, are typically exemplified by retrograde Wenckebach during ventricular (VVI) pacing during intracardiac electrophysiology studies. This case report involves adenosine's ability to block conduction in the retrograde limb of the permanent form of junctional reciprocating tachycardia to provide further evidence as to the AV "nodelike" decremental qualities of this limb.     

Paroxysmal tachycardia with atrioventricular dissociation in a patient with a variant of pre-excitation syndrome

We report a patient with a variant of the pre-excitation syndrome who has paroxysmal tachycardia with a pattern of left bundle branch block and ventriculo-atrial dissociation. The tachycardia is precipitated by exercise, reproduced by atrial pacing and terminated with lidocaine. Between attacks the electrocardiogram revealed prominent R waves in right precordial leads and the vectorcardiogram displayed anterior displacement of the mean QRS vector, but neither was diagnostic of pre-excitation. The resting P-R interval (140 msec) and A-H interval (60 msec) were within normal limits, but the H-V interval (30 msec) was at or slightly below normal limits. Increasing heart rate from 80 to 150/min with atrial pacing increased A-H from 70 to 160 msec, but did not change the H-V interval. With pacing at 160/min, A-H lengthened progressively from 160 to 190 msec, but A-V remained constant at the critical limit of 190 msec. Accordingly, the H-V interval decreased until the His spike disappeared into the QRS or did not occur because of A-V block. At this point, the QRS complex changed to that seen during spontaneous tachycardia. Pacing was stopped, but tachycardia continued at 160/min and ventriculoatrial dissociation appeared. Lidocaine promptly restored sinus rhythm. We speculate that the patient has anomalous conduction between the lower segment of the A-V node and the ventricular septum (Mahaim fibers) and a reciprocating tachycardia which results from antegrade conduction down the anomalous pathway and retrograde conduction up the His-Purkinje system and lower A-V node. Ventriculo-atrial Wenckebach during the tachycardia excludes participation of atria and upper part of the A-V node in the re-entrant tachycardia. This variant of pre-excitation syndrome could easily be mistaken for “true ventricular tachycardia” and serious heart disease.     

Microelectrode study of Wenckebach periodicity in canine Purkinje fibers

Electrophysiologic mechanisms responsible for Wenckebach periodicity produced experimentally in a segment of blocked canine Purkinje fibers were investigated with multiple microelectrode recordings. Transmission through the zone of block was electrotonic. The Wenckebach mechanism was related to a progressive decrease in the efficacy of the transmitted electrotonic potential as a stimulus for the regenerative response at the distal block boundary with successive impulses of the cycle. This was manifested in the transmembrane potentials as a progressive decrease in upstroke velocity and a voltage change that caused the electrotonic potential to become progressively removed from the threshold for stimulation. The immediate cause of this phenomenon was a progressive increase in the voltage level (more negative) from which the electrotonic potential originated and a resulting change in voltage-dependent membrane resistance that further attenuated the signal with successive impulses of the cycle.Two main mechanisms appeared to be responsible for these phenomena: (1) a progressive increase in maximal repolarization voltage (more negative) of the transmembrane potential, and (2) a progressive decrease in the diastolic interval that, in the presence of enhanced phase 4 diastolic depolarization, caused the voltage level from which the electrotonic potential originated to become further removed from the stimulation threshold with successive impulses of the cycle.     

Ventricular quadrigeminy as a manifestation of concealed bigeminy.

Long rhythm strips were analyzed from five patients with frequent ventricular extrasystoles. The predominant pattern was quadrigeminal; i.e., three sinus beats between extrasystoles. However, about 20% of the interectopic intervals contained numbers of sinus beats (S) greater than three. Analysis of the distribution of such values of S greater than 3 revealed that there were many more odd than even values (P less than 0.001). Also, carotid sinus pressure yielded only odd values of S greater than 3. This predominance of odd values strongly suggested the existence of concealed extrasystoles. Therefore, all odd values of S greater than 3 were analyzed to determine whether they satisfied the criterion for concealed bigeminy (S = 2n - 1) or for concealed quadrigeminy (S = 4n - 1). The distribution was found to satisfy the criterion for concealed bigeminy, suggesting that the quadrigeminal pattern was a manifestation of a 2:1 rather than a 4:1 block in a re-entry loop. Stable quadrigeminy occurs often in concealed bigeminy, because the re-entrant impulse finds the myocardium excitable after a normal R-R interval but refractory after a compensatory pause.     

Phasic coronary arterial flow velocity during arrhythmias in man

The influence of cardiac arrhythmias on coronary arterial flow velocity studied by means of a Doppler catheter flowmeter system is described in 47 patients. The arrhythmias examined included atrial and ventricular extrasystoles, atrial fibrillation, pacemaker-induced atrial tachycardia, paroxysmal atrial tachycardia, ventricular tachycardia, Wenckebach second degree atrioventricular block and complete heart block.     

Electrocardiographic changes in thyrotoxic periodic paralysis.

The electrocardiograms (ECGs) of 30 patients with hypokalaemic thyrotoxic periodic paralysis during and after paralysis were studied. During paralysis, typical features of hypokalaemia were seen in all patients with serum potassium levels of 2.8 mmol/l or less; above this level, the ECGs varied from non-diagnostic to those showing typical features of hypokalaemia. It was not possible to accurately predict the serum potassium level from the ECG except when either sinus arrest or heart block was present. Although extrasystoles have been reported to be common in hypokalaemia, none of the patients in this study had extrasystoles. Sinus arrest occurred in two patients and second degree atrio-ventricular block occurred in three patients, a finding which has not been reported in hypokalaemia.     

Permanent right bundle-branch block heralded by intermittent block and ventricular extrasystoles. A 13-year observation

A patient is described in whom the occurrence of frequent ventricular extrasystoles of right ventricular origin and intermittent right bundle-branch block caused by interpolation of these extrasystoles heralded the slow development of permanent right bundle-branch block over a period of observation of 13 years. Such a clinical course suggested gradual progression of an organic lesion in the intraventricular conducting system. The differential diagnosis of intermittent bundle-branch block and aberrant intraventricular conduction, and possible mechanisms of ectopic impulse formation in the presence of bundle-branch block are discussed.     

Electrophysiologic studies on atrioventricular nodal Wenckebach cycles

Wenckebach cycles with a 4:3 ratio, produced by rapid atrial pacing, were studied in 27 anesthetized denervated dogs using programmed stimulation. A test stimulus (S') could be inserted after any preselected beat of the Wenckebach cycle. An on-line computer measured the atrial (A) to His bundle (H) intervals. In all dogs a progressive increase in atrioventricular (A-V) nodal refractoriness was seen in the effective refractory period for each beat and a rightward shift of the A'-H' relative to the A-A' refractory curves. Atypical Wenckebach cycles could be produced by small changes in the basic cycle length. No evidence for reentry was found from the refractory curves of Wenckebach cycles and by interruption of stimulation after the third stimulus of a 4:3 Wenckebach cycle. Analysis of the A'-H' relative to the H-A' refractory curves did not confirm a positive feedback mechanism. In order to mimic a Wenckebach cycle, a blocked premature beat was inserted during stressed 1:1 conduction. The changes in the refractory curves for successive beats after the premature beat were rate-dependent and similar to those in Wenckebach cycles but smaller in magnitude. In Wenckebach cycles there is a progressive increase in refractoriness, caused by cumulative effect similar to that seen after a blocked beat during stressed 1:1 conduction, until block occurs and the cycle resets.     

Permanent right bundle-branch block heralded by intermittent block and ventricular extrasystoles. A 13-year observation.

A patient is described in whom the occurrence of frequent ventricular extrasystoles of right ventricular origin and intermittent right bundle-branch block caused by interpolation of these extrasystoles heralded the slow development of permanent right bundle-branch block over a period of observation of 13 years. Such a clinical course suggested gradual progression of an organic lesion in the intraventricular conducting system. The differential diagnosis of intermittent bundle-branch block and aberrant intraventricular conduction, and possible mechanisms of ectopic impulse formation in the presence of bundle-branch block are discussed.