Studies on Ventriculo-Atrial Conduction and the Reentry Phenomenon

Ventriculo-atrial conduction and the reentry phenomenon was studied during right ventricular and bundle of His pacing in the intact dog heart. Bipolar electrogram recordings were obtained from the sinus node, Bachman's bundle, the right and left atria, the bundle of His, and the ventricle. Retrograde conduction resulted in a specific change in the sequence of atrial activation. The recording of both antegrade and retrograde His deflections provided a more accurate means of comparing A-V and V-A conduction times. In all experiments retrograde conduction time exceeded antegrade conduction time. The A-V nodal region was found to be the zone of retrograde conduction delay and block. Increasing the driving rate of the heart, vagal stimulation, and isoproterenol, affected V-A conduction similar to the way in which these maneuvers affect A-V conduction. Reentry (ventricular echoes) commonly occurred when right ventricular or bundle of His pacing resulted in the reverse Wenckebach phenomenon.