II. Parasystole, and Parasystole or Re-entry with Conduction Disturbance

In a previous report dealing with intermittent ventricular bigeminy due to ventricular prema-ture 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 pre-mature systoles with varying coupling in the presence of a regular dominant rhythm, the mecha-nism of ectopic impulse formation is shown to be either parasystole or re-entry, and the intermit-tence 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. IN a preceding report, ' a group (A) of cases of intermittent ventricular bigeminy was analyzed in which the latter was caused by the occurrence of ventricular pre-mature systoles with fixed coupling during a grossly irregular dominant rhythm. Under such circumstances, intermittence and recur-rence of bigeminy were shown to depend largely on the duration of the ventricular cycle. In the course of the study, another group (B) of intermittent bigeminy was identi-fied in cases with a regular dominant rhythm and marked variability of the coupling of the ectopic beats. This group, too, was submitted to extensive analysis and, as in group A, certain conclusions were reached regarding the mech-anism involved in the intermittence and re-appearance of ventricular premature systoles. The results of this study, and their implica-tions pertaining to the genesis of ventricular premature systoles, are presented in this report. MATERIAL AND METHODS The material comprises 14 records from 12 pa-tients with a regular dominant rhythm and inter