Alternate patterns of ventricular activation during supraventricular bigeminy

Several investigators have previously noted that in the presence of bigeminal atrial extrasystoles, the premature beats may exhibit an alternate pattern of ventricular excitation either in the form of alternating left and right bundle-branch block, or alternating right bundle-branch block and normal intraventricular conduction. However, the association of alternating intraventricular conduction with other types of supraventricular bigeminy has rarely been documented. In this report we present five diverse forms of supraventricular bigeminy exhibiting the phenomenon of alternating ventricular excitation on the early beats. Our findings suggest that the exact mechanism of supraventricular bigeminy is irrelevant in terms of subsequent ventricular events. Practically any type of supraventricular bigeminy may result in an alternate pattern of ventricular activation.