Prognostic significance of the number of induced ventricular complexes during assessment of therapy for ventricular tachyarrhythmias.

We analyzed 255 long-term trials of antiarrhythmic therapy, each of which had been evaluated at electrophysiologic study, to identify the maximum number of induced ventricular complexes consistent with the long-term efficacy of antiarrhythmic therapy. All patients had spontaneous and inducible sustained ventricular tachycardia or ventricular fibrillation. The incidence of therapeutic efficacy at 1 month and throughout follow-up was similar for trials in which zero, one, two, three, four, five, six to 10, and 11 to 15 complexes were induced, but significantly lower (p less than .001) for trials in which 16 or more complexes were induced. The cumulative incidence of efficacy at 1 year was 75 +/- 5% for 0 to 5 induced complexes, 72 +/- 11% for six to 10 complexes, 83 +/- 15% for 11 to 15 complexes, 42 +/- 10% for 16 complexes to 15 sec, and 48 +/- 6% for sustained ventricular tachycardia. At 1 year, the incidence of "sudden death-free" survival was higher for patients in trials that prevented initiation of sustained ventricular tachycardia than for those in trials that permitted initiation of sustained ventricular tachycardia (91 +/- 3% vs 75 +/- 6%; p = .01). The duration of the arrhythmia induced at therapy assessment was in the range of 11 to 20 complexes for only 4% of trials. Antiarrhythmic therapy is likely to be effective if as many as 15 complexes are induced at therapy assessment. The best cutoff, between 11 and 20 complexes, is difficult to identify because of the small fraction of trials in this range. Patients in whom initiation of sustained ventricular tachycardia is not prevented are at high risk for arrhythmia recurrence and sudden death.