MECHANISMS OF PACING INTERVENTIONS IN ATRIAL-FIBRILLATION

Pacing in Atrial Fibrillation, Atrial flutter is due to large single r eentrant loops, typically oriented around the caval veins and a line o f functional conduction block in between, These reentrant circuits can easily be terminated by properly timed extra beats colliding in the a ntidromic direction with the reentrant orthodromic wavefront and being blocked in the orthodromic direction within the area of slow conducti on. Due to the complex situation in atrial fibrillation with multiple, ever-changing wavelets and a marked functional inhomogeneity of the a trial tissue, these simple concepts do not apply. However, regional co ntrol of atrial tissue by rapid pacing is feasible during atrial fibri llation, and through a multisite approach, this pacing modality might lead to a situation where the remaining nonentrained atrial tissue is just no longer reaching the critical mass. Single-site, dual-site, and biatrial pacing seems to reduce the incidence of atrial fibrillation recurrences. Specific advantages and disadvantages of each approach st ill need to be elucidated. Apart from preventing bradycardia, preventi ve pacing modes reduce intra-atrial conduction times and might reduce intra-atrial dispersion of refractoriness, Still, the specific mechani sms relevant for their effectiveness need further clarification.