Comparison of immediate versus day to day variability of ventricular tachycardia induction by programmed stimulation

The use of programmed stimulation to assess long-term oral antiarrhythmic drug efficacy for ventricular tachycardia is complicated by the fact that mode of ventricular tachycardia induction varies from day to day in the absence of drug therapy. The purpose of this prospective study was to assess whether mode of ventricular tachycardia induction is more reproducible within one study than from day to day. Thirty-nine consecutive patients with documented sustained ventricular tachyarrhythmias secondary to coronary artery disease underwent three inductions of ventricular tachycardia at 15 min intervals in the absence of drug therapy. A stimulation protocol in which the only major variable was the number of extrastimuli required for tachycardia induction was used. Subsequent day to day variability in mode of tachycardia induction was also assessed in the same patients at two further drug-free inductions at intervals of 5 ± 2 days. The number of extrastimuli required for tachycardia induction was significantly more reproducible at the immediate repeat studies than from day to day (69% of patients versus 31 %, p < 0.01). From these data, probability tables were derived that show the likelihood that changes in inducibility at subsequent tachycardia inductions are due to chance. The QRS configuration of induced ventricular tachycardia was also more reproducible at the immediate studies (64% versus 26%, p < 0.01). Basic electrophysiologic and stimulation variables differed over a significantly wider range from day to day than at the immediate studies. These findings suggest that short-term intravenous antiarrhythmic drug testing at electrophysiologic study should be more accurate than testing of oral drug therapy when drugs with similar pharmacodynamic effects by either route are used. The probability tables constructed from these data should permit drug-related changes in inducibility to be identified with a 95% accuracy for antiarrhythmic effects and a ?90% accuracy for proarrhythmic effects.