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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.

In order to study the origin of late potentials, their distribution was analyzed in 16 patients who had undergone surgery for arrhythmia due to ventricular tachycardia following myocardial infarction. The potentials were measured in sinus rhythm using 63 unipolar leads placed on the chest before the operation, then on the epicardium and endocardium during the operation. Epicardial and/or endocardial activity extending beyond the QRS complex measured from unfiltered chest signals and characterized by slowed propagation at the edge or inside of necrotic regions, stable from one beat to the next, and showing simple (39 per cent), double (34 per cent) or fragmented (27 per cent) deflections on the electrocardiograms were observed in 5/6 patients without bundle-branch block and in 5/10 patients with block. Similar activity but which did not extend after the QRS was detected in the 6 other patients. For signals filtered at 55 Hz, a close correlation between the distribution of chest, epicardial and endocardial potentials was observed, thus allowing approximate location of the origin of late potentials from the chest. Anterior or apical sites corresponded to close extrema in the precordial region, whereas the other sites were associated with more distant extrema. An analysis of potential distribution thus gives a better understanding of the electrogenesis of late potentials as well as their detection on the chest.

Digitalis glycosides are used in the supraventricular arrhythmias either to slow the ventricular response or to restore or maintain sinus rhythm. The direct cellular effects of digitalis are probably not involved in its antiarrhythmic action. The indirect effects of digitalis through parasympathetic stimulation and adrenergic inhibition explain the results obtained when treating arrhythmias. At toxic doses, adrenergic stimulation may contribute to the arrhythmias of digitalis toxicity.