Role of intraventricular conduction disturbances in ventricular premature systoles

Ten thousand electrocardiograms were reviewed with reference to intraventricular conduction and ventricular premature systoles. Ventricular premature systoles were found in 444 electrocardiograms, an overall incidence of 4.44 percent. The incidence was small in the presence of normal intraventricular conduction (3.73 percent) and greater in the groups with abnormal intraventricular conduction (9.80 percent), increasing in parallel with the degree of conduction delay. The coupling interval was significantly longer in tracings revealing intraventricular conduction disturbances than in normal tracings. Studies of QRS configuration and mean frontal QRS axis of the dominant and ectopic beats disclosed: (1) a positive correlation between the QRS duration of sinus and premature beats; (2) a significantly greater angle between the QRS axes of sinus and ectopic beats in the presence of abnormal intraventricular conduction; and (3) in groups with intraventricular conduction delay, a QRS axis of premature systoles commonly either directed away from the region of the blocked bundle or suggesting an additional delay in the remaining nonblocked fascicles. From these data we conclude that (1) ventricular premature systoles are more likely to originate from the area of intraventricular conduction delay, and (2) the ectopic impulse seems to invade and at least partially utilize the other fascicles of the Purkinje system for ventricular excitation. The clinical significance of more frequent ventricular premature systoles in patients with cardiac disorders than in normal subjects should be reemphasized.