Atrionodal rhythm with ventricular bigeminy: Report of a case with unusual mechanism

Abstract

1. 1. A case of atrionodal rhythm with ventricular bigeminy of unusual mechanism is presented. 2. 2. The sequence of events was probably as follows: Periodically there occurred marked depression of the sinus nodal pacemaker accompanied by depression of the lower automatic centers as well. As a result, sinus pauses occurred, with either the A-V node or the ventricle taking command of the heart, either as a series of escape beats or as a dominant atrionodal or idioventricular rhythm. The dominant beats were followed at a fixed interval by abnormal auricular complexes which originated either in the S-A node, outside of the normal pacemaker, or in the auricle. The auricular beats were followed in turn by ventricular responses which were normal or aberrant in contour. Apparently the second ventricular systole led to further depression of the dominant pacemaker so that the rate was unusually slow. 3. 3. The possible mechanisms which might account for this unusual bigeminy were reviewed but none was found applicable to this case.