Comparison of the infusion of acetylcholine into the artery of the sinoatrial node with the electric stimulation of cardiac parasympathetic nerves

Atrial fibrillation occurring after open heart surgery largely depends on heterogeneous dispersion of refractoriness. To investigate the contribution of the autonomic nervous system in this phenomenon, we studied the regional distribution of neurally induced atrial electrophysiological events. Electrical stimulation of the right atrial fat pad, acetylcholine injection into the sinus node artery, and stimulation of the right and left vagosympathetic trunks were compared with respect to detailed atrial mapping. Unipolar electrograms were recorded from 127 atrial sites before and after neural stimulation or acetylcholine injection (10(-7) mol) in 8 anesthetized dogs. Regional changes in atrial repolarization were estimated by epicardial isointegral maps generated from computed values of the area under each electrogram and plotted on an atrial grid. The anatomical distribution of the sinus node artery was assessed by intra-arterial injection of microspheres. The effects of right and left vagal and right atrial fat pad stimulation extended contralaterally. Acetylcholine injected into the sinus node artery affected the lower left atrium whereas no microspheres could be found in this region upon microscopic examination. Therefore, this effect was possibly related to cholinergic activation of neuronal cell bodies located in the right atrial wall and projecting to the lower left atrium, supporting the hypothesis that local circuit neurons were involved in the activation of the intrinsic nervous system of the heart.