Mechanisms of Intermittent Ventricular Bigeminy

In order to analyze the cause for the appearance and disappearance of ventricular premature systoles giving rise to temporary bigeminal rhythm, the electrocardiographic material was divided into two major groups: group A, consisting of ectopic beats with fixed coupling occurring during grossly irregular dominant rhythms, and group B, consisting of ectopic beats with varying coupling occurring during regular dominant rhythms. Analysis of group A, the subject of the present report, shows a definite relationship between the duration of the ventricular cycle and the occurrence of ventricular premature systoles, in that long cycles favor their appearance whereas short cycles tend to preclude it. This "rule of bigeminy" is best explained on the basis of a re-entry mechanism of the ventricular premature systoles. Criteria are given for the differential diagnosis between ventricular premature systoles and aberrant ventricular conduction of supraventricular impulses which is prone to occur under similar circumstances. The analysis of group B is presented in a subsequent report.