The Mechanism of the Wenckebach Type of a-v Block

Abstract

The Wenckebach type of auriculo-ventricular block is characterized by a progressive lengthening of the A-V conduction time, ending in a completely blocked auricular complexthe Wenckebach period. These periodically recurring dropped beats were first recognized clinically by Wenckebach in 1899 from a careful analysis of radial arteriograms; Engelmann (1896) had noted the same phenomenon in the frog's heart a few years earlier. Changing conduction times, due to varying degrees of recovery of the A-V junction, were postulated by them to account for the dropped beats. A typical feature of the progressive prolongation of the P-R interval is that the most marked increase in the conduction time is seen in the second complex of the group. Later ones show only slightly greater prolongation. The shortest A-V conduction time is seen in the first complex after the dropped beat; i.e. following the longest pause or the longest R-P interval.Clinically, the Wenckebach type of A-V block is seen especially in digitalis poisoning, in infective myocarditis, due particularly to rheumatic fever and diphtheria, in myocardial fibrosis or infarction due to coronary artery disease, and occasionally in other lesions of the conduction system. It occurs at low auricular rates, most often under the influence of digitalis, or at the high auricular rates of paroxysmal tachycardia (Wenckebach and Winterberg, 1927;Decherd, et al., 1943). A-V block, often of the Wenckebach type, has been produced experimentally by increasing the auricular rate

A Mathematical Model of Human Atrioventricular Nodal Function Incorporating Concealed Conduction

“…Lewis and Master (1925) showed that the conduction time of a single premature stimulus through the AV node decreased as the time interval since the last passage of a previous impulse through the AV node increased. The function describing this relationship, the AV nodal recovery curve, can be used to predict the rhythms that arise during atrial stimulation at a rate faster than the intrinsic rate (Decherd and Ruskin, 1946;Shrier et al, 1987). Further work has developed models of AV nodal function describing the response to both periodic and irregular inputs (Heethaar et al, 1973a,b;Cohen et al, 1983;Talajic et al, 1991;Meijler et al, 1996;Zeng and Glass, 1996).…”

A unified model of atrioventricular nodal conduction predicts dynamic changes in Wenckebach periodicity.

“…These include conduction slowing of single premature atrial impulses,1 variable conduction responses to accelerations in rate,23 and different patterns of conduction block seen during Wenckebach periodicity. [4][5][6][7] Several mathematical models of AV nodal conduction have been described. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] However, no single model has yet satisfactorily explained the wide variety of possible AV nodal behavior.…”

“…[4][5][6][7] Several mathematical models of AV nodal conduction have been described. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] However, no single model has yet satisfactorily explained the wide variety of possible AV nodal behavior. For example, the assumptions used to explain one type of behavior such as Wenckebach-type AV block may not correctly account for normal patterns of anterograde conduction of premature atrial impulses13 or may fail to explain time-dependent changes in the pattern of second-degree AV block6,7,14-20 that are observed with prolonged atrial stimulation in humans.7 Moreover, experimental confirmation of theoretical predictions is often lacking13-15 '19 or based on stimulation sequences that are closely related to the original manner in which the model was constructed.…”

Characterization and Modeling of Atrioventricular Conduction during Atrial Fibrillation

“…While Wenckebach periodicity could develop theoretically in a single-pathway model, it is the specific interaction between the two pathways in the intact heart that produces rich variability of Wenckebach patterns. These findings can help to explain some of the paradigmatic mechanisms underlying the atrioventricular conduction [61,141,142,143].…”

“…One of the first attempts to model the atrioventicular conduction time was done by Decherd et al [61]. In that work, Decherd attempted to unmask the role of the AV node in the Wenckebach periodicity.…”