Cellular mechanisms of vagally mediated XXXX in isolated arterially perfused @entity235 right atria.

@entity235 @entity4148 @entity955 @entity3451 @entity4710 @entity934
INTRODUCTION: Increased vagal tone significantly enhances susceptibility to @entity955 ( @entity955 ); however, the cellular mechanisms responsible for vagally mediated @entity955 are not completely understood. METHODS AND RESULTS: In 12 isolated arterially perfused @entity235 right atria, high-resolution optical mapping techniques were used to measure action potentials during control conditions, during @entity4148 ( @entity4148 ; 30 to 50 Hz) as a surrogate for vagal stimulation, and during @entity934 ( @entity3451 ) infusion (10 to 30 microM). During steady-state pacing, action potential duration was shorter during @entity3451 infusion (43 +/- 9 msec) than during @entity4148 (78 +/- 7 msec, P < 0.001) or control (129 +/- 5 msec, P < 0.001). In contrast, repolarization gradients were larger during @entity4148 (13 +/- 3 msec/mm) than during @entity3451 infusion (3 +/- 1 msec/mm, P < 0.01) or control (5 +/- 1 msec/mm, P < 0.01). Transmural repolarization gradients were relatively small for each intervention tested. During @entity3451 infusion, @entity4710 ( @entity4710 ) was easily initiated with a single premature stimulus and was associated with a focal pattern of activation (84%). @entity4710 also was easily initiated by a single premature stimulus during @entity4148 ; however, when repolarization gradients were large, patterns of conduction block and incomplete macroreentry were often observed (64%). Importantly, @entity4710 initiation during @entity4148 was associated with focal activity (36%) when repolarization gradients were small. CONCLUSION: In contrast to @entity3451 infusion, @entity4148 generally increased dispersion of repolarization and was often associated with patterns of conduction block and incomplete macroreentry, similar to that associated with in vivo cervical vagal stimulation. However, @entity4148 also was associated with a focal pattern of initiation that was independent of local repolarization gradients. These results suggest that during vagal stimulation, @entity4710 initiation does not always depend on repolarization gradients.
