Ectopic right atrial rhythms: Experimental and clinical data

In 18 out of 25 canine hearts studied with bipolar plunge electrodes, ectopic right atrial (RA) beats were observed occurring (1) spontaneously, (2) during vagal stimulation, (3) after destruction of the sinus node, and (4) during ventricular pacing. In these beats the RA appendage was activated first, followed by Bachmann's bundle, sinus node, left atrial appendage, posterior left atrium, and proximal coronary sinus. This sequence was consistently reproduced by pacing through the RA appendage recording electrode. In addition, 19 electrocardiograms exhibiting normal P waves in the extremity leads and inverted P waves in V₁ to V₄ were subjected to vectorial analysis which indicated the superoanterior RA as the pacemaker site. Conversion of these rhythms to sinus rhythm or vice versa was demonstrated. It is suggested that this human arrhythmia represents a counterpart of RA ectopic activity observed in the intact canine hearts.