Role of extrastimulus prematurity and intraventricular conduction time in inducing ventricular tachycardia or ventricular fibrillation secondary to coronary artery disease.

The influence of extrastimulus prematurity and changes in intraventricular conduction time on ventricular tachycardia (VT) inducibility were evaluated in 78 patients with coronary artery disease undergoing electrophysiologic study. In a retrospective portion, the effect of adding ventricular extrastimuli vs shortening the ventricular drive cycle length on extrastimulus prematurity and VT inducibility was evaluated in 59 consecutive patients with inducible ventricular arrhythmias (group I). In a prospective component, changes in intraventricular conduction of the last ventricular extrastimulus and the relation to initiation of VT were evaluated in 19 consecutive patients undergoing programmed electrical stimulation (group II). Single (V2), double (V3) and triple (V4) ventricular extrastimuli were introduced during ventricular drive pacing (V1) at multiple cycle lengths. Although reduction of drive cycle length facilitated arrhythmia induction in 25% of patients, addition of an extrastimulus was a more potent method in group I patients. However, the mechanism of arrhythmia induction is not dependent on attainment of shorter coupling intervals with either method. In group II patients QRS duration and intraventricular conduction time of the extrastimuli increased as the coupling interval was reduced. Significant changes in QRS duration and intraventricular conduction time of the extrastimuli that initiated VT were not observed.