Mechanism of alternating bundle branch aberrancy with atrial bigeminy: electrocardiographic-electrophysiologic correlates.

The mechanism of alternating bundle branch aberrancy in response to atrial bigeminy with fixed coupling intervals lacks adequate explanation. In this report, electrophysiologic studies on five patients with fixed coupled atrial bigeminy, identical impulse intervals arriving at the His bundle and alternating bundle branch aberrancy are presented. The mechanism of alternating bundle branch aberrancy in these patients appears to be alternating changes in the refractory periods of the bundle branches resulting from differences in the activation sequence of the distal bundle branches. These findings provide further insight into the mechanism of aberrant conduction.