Facilitation of ventricular tachyarrhythmia induction by isoproterenol.

Ventricular tachyarrhythmia induction was facilitated during infusion of isoproterenol in 21 of 60 patients with ventricular tachycardia (VT) or ventricular fibrillation (VF) in whom programmed electrical stimulation alone failed to reproducibly induce sustained ventricular tachyarrhythmias. Of 44 patients with no ventricular tachyarrhythmias induced before isoproterenol infusion, 11 had a sustained ventricular tachyarrhythmia and 1 patient had unsustained VT induced by isoproterenol alone or by programmed stimulation during the infusion. In 9 of 16 patients in whom nonreproducible or unsustained ventricular tachyarrhythmias were induced before isoproterenol infusion, more reproducible or more sustained ventricular tachyarrhythmias were induced during the infusion. Tachyarrhythmia induction was facilitated by isoproterenol in 20 of 40 patients with sustained VT clinically, but in only 1 of 20 patients with unsustained VT or VF clinically. Among patients with sustained VT clinically, those with exercise-provoked VT and those who had not been tested with stimulation at a second right ventricular site or in the left ventricle were more likely to have induction facilitated by isoproterenol. Drugs effective against induction of isoproterenol-facilitated ventricular tachyarrhythmias were identified in 13 of 25 trials. These drugs were effective during a mean follow-up of 17 months in 7 of 9 long-term trials.