Re-entry near the site of the ventricular parasystolic focus: an ECG study of patients with artificial ventricular pacemakers.

Morphology of ventricular ectopic complexes was examined in 1,746 ECGs of 149 patients with permanent ventricular pacemakers. In 20 of 80 patients (25%) the morphology of ventricular ectopic complexes was similar to that of the paced complex. This resulted in a ventricular couplet where the spontaneous premature complex originated at the site of pacing, possibly due to local re-entry. Repeated re-entry (two ventricular ectopic complexes in a row) occurred only in one of these patients, and none had ventricular tachycardia. These observations 1) verify the existence of a mechanism which we have postulated in explaining the association between couplets and ventricular parasystole, and 2) confirm the rare occurrence of repeated reentry in such a setting. Other observations in this studyshow that premature stimulation during right ventricular pacing may alter morphology of the ventricular complex from a left to right bundle branch block pattern in some leads.