The Spatial Characteristics of Atrial Activation in Ventriculo-Atrial Excitation

¹ Director, Coronary Care Unit, and Assistant Physician-in-Chief, Sinai Hospital; Assistant Professor of Pediatrics, Johns Hopkins University School of Medicine
² Chief, Cardiology Division, Sinai Hospital, and Assistant Professor of Medicine, Johns Hopkins University School of Medicine

Spatial characteristics of atrial activation were analyzed in arrhythmias displaying a ventriculo-atrial sequence of excitation: junctional rhythm with preceding ventricular activation, "reciprocal" atrial beating, complete or high-grade A-V block with ventriculoatrial response and ventricular extrasystoles with ventriculoatrial response. It was found that the coupled P waves were markedly dissimilar with regard to their polarity and vectorial characteristics. Vectorial analysis suggested that the course of the anomalous atrial activation is consistent with an A-V nodal origin of impulses in a minority of cases only, while in the majority the depolarization process appeared to originate in various portions of both atria. This interpretation is in conflict with the theory postulating retrograde conduction of impulses through or from the A-V node as the basic mechanism of ventriculo-atrial excitation, and raises the possibility that the "retrograde" P waves are frequently due to stimuli originating in various automatic atrial centers induced, in some way, by the preceding ventricular activity.