STUDY OF TRIGGERING EVENTS FOR VAGALLY-IN DUCED ATRIAL-FIBRILLATION IN DOG HEART IN-SITU

Enhanced vagal tone can be associated with atrial fibrillation in man. previously we studied acetylcholine Induced atrial fibrillation in is olated canine atrial preparations. The arrhythmia started as a multifo cal ectopic activity following acetylcholine Induced asystole which tr iggered reentry. These early polytopic Impulses were ascribed to async hronous Firing of multiple atrial pacemakers, Searching for more physi ologic model we used vagal stimulation (10-50 Hr, 1 ms, 10-17 V, 5 sec trains) instead of acetylcholine in open-chested dogs (n=6). This Int ervention induced premature atrial beats (single or multiple) and atri al fibrillation in 5 of 6 dogs. Occurence of atrial fibrillation incre ased with increase in vagal stimulation Intensity. Epicardial mapping (254 unipolar electrodes) of both atria revealed uni- or multifocal ac tivation patterns during first two beats (A1 and A2) st each tachyarrh ythmia. In some cases clear right atrial reentrant circuits which star ted during A2 were mapped. The A2 beat (potential or actual trigger fo r atrial fibrillation), usually emerged outside of the area of the ear liest activation during normal rhythm (caval region), most often from the right atrial appendage. Our data suggest that the sources of prima ry atrial premature beats Induced by vagal stimulation are widely disp ersed over both atria. This means that either vagally Induced atrial p remature beats are not the unique property of pacemaker cells or the l atter are widely distributed over the atria.