Competitive anterograde and retrograde atrioventricular junctional activation in atrial fibrillation

Abstract

In eight medically-treated patients with chronic atrial fibrillation and a random ventricular rhythm, we studied the effect of single right ventricular stimuli delivered after each eighth spontaneous R wave during at least 1 hour. The coupling interval of the extrastimulus was fixed and differed marginally from the shortest spontaneous RR interval. The histograms of spontaneous RR intervals and of the "compensatory" pauses following the ventricular extrasystoles were calculated. Analysis of these histograms and simulation of the interaction between anterograde and retrograde impulses in a computer model suggests that in seven of the eight patients the compensatory pause may be caused by two distinctly different mechanisms: (1) reset of the timing cycle of atrioventricular nodal activation by relatively early retrograde impulses; and (2) interception of anterograde impulses by relatively late ventricular extrasystoles. The finding that early retrograde impulses are not blocked by concealed atrioventricular nodal conduction makes the existence of decremental conduction and extinction of atrial impulses at different levels within the node unlikely. The results of this study support the hypothesis that the distal side of a weakly coupled junctional area inside the AV node behaves as a pacemaker for the ventricular rhythm during atrial fibrillation.