Rate stabilization by right ventricular apex or His bundle pacing in patients with atrial fibrillation

AIMS: In patients with atrial fibrillation right ventricular pacing can block antegrade conduction at pacing intervals longer than the shortest spontaneous R-R interval, causing the stabilization of ventricular rhythm. In this study the effects of pacing at two sites were compared in order to evaluate the role of conduction times in determining the stabilization of ventricular rhythm. METHODS: In eight patients with permanent atrial fibrillation, the ventricular rate was recorded before and during pacing at the right ventricular apex and the His bundle with different cycle lengths. RESULTS: In all patients, we obtained a reduction in spontaneous QRS complexes with respect to those anticipated at pacing rates slightly above the spontaneous mean rate, and the ventricular rhythm stabilized at pacing intervals longer than the spontaneous shortest R-R intervals. Between pacing sites we did not observe any difference in the reduction in spontaneous beats and the cycle stabilizing the rhythm. Moreover, simulation of the interaction between antegrade and retrograde impulses in a computer model confirmed that results obtained by pacing at the His bundle cannot be readily explained as a consequence of conduction delays. CONCLUSION: This study suggests that the lag introduced by the His-Purkinje conduction cannot explain, as proposed, the stabilization of ventricular rhythm observed in patients with atrial fibrillation and right ventricular pacing.