Spatial distribution and frequency dependence of arrhythmogenic vagal effects in canine atria

Arrhythmogenic Vagal Effects in Dog Atria. Introduction: Prior studies in i solated canine atria demonstrated that acetylcholine-induced reentrant atri al fibrillation (AF) was triggered by multifocal activity in the area of no rmal impulse origin (sinus node-crista terminalis). The aim of this study w as to investigate the activation sequence in AF induced by vagal stimulatio n (VS) in intact dog hearts. Methods and Results: VS (10 to 50 Hz, 1 msec, 15 V, 5-sec trains) induced s ingle or multiple atrial premature depolarizations (APDs), and/or AF in 8 o f 10 open chest dogs. Occurrence of APDs and AF increased with increasing V S intensity. Epicardial mapping (254 unipolar electrodes) of both atria sho wed that APDs as a rule emerged from ectopic sites, often from the right at rial appendage. Activation mapping of the first 10 cycles of AF showed that only a small number (<3 to 4) of unstable reentrant circuits were possible at the same moment. Moreover, most sustained VS-induced AFs were accounted for by a single leading stable reentrant circuit that activated the remain der of the atria. Conclusion: (1) Occurrence of vagally induced APDs and AF increases with in creasing frequency of VS, (2) VS-induced focal ectopic APDs are widely dist ributed over the atria, (3) A single APD can be sufficient for initiation o f reentrant AF. (4) Despite its high rate of sustained AF, it may be mainta ined by single stable reentrant circuit. (5) The atrial septum can play an important role in both the initiation and the maintenance of VS-induced AF.