Mechanisms of Intermittent Ventricular Bigeminy

In a previous report dealing with intermittent ventricular bigeminy due to ventricular premature systoles with fixed coupling in the presence of a grossly irregular dominant pacemaker, it was shown that the appearance and disappearance of the ectopic beats were dependent upon the length of the ventricular cycle ("rule of bigeminy"). In the present report, dealing with ventricular premature systoles with varying coupling in the presence of a regular dominant rhythm, the mechanism of ectopic impulse formation is shown to be either parasystole or re-entry, and the intermittence of bigeminy is due to simple interference or to a disturbance in conduction of a parasystolic or of a re-entrant impulse. Intermittent parasystole is illustrated and presented as a possible link between the two fundamental mechanisms of parasystole and re-entry.