Usefulness of isoproterenol facilitation of ventricular tachycardia induction during extrastimulus testing in predicting effective chronic therapy with beta-adrenergic blockade.

ABSTRACT

Previous studies indicate that programmed extrastimulus testing (PES) during isoproterenol infusion facilitates induction of clinical ventricular tachycardia (VT) in some patients. This study attempts to determine if VT inducible only during isoproterenol infusion predicts suppression of VT with chronic oral beta-adrenergic blockade. Nine patients, aged 23 to 77 years, with symptomatic VT or syncope not necessarily provoked by exercise or stress were evaluated. Extrastimuli did not induce VT in any patient. However, during isoproterenol infusion (1 to 4 micrograms/min), all patients had reproducibly inducible VT corresponding to their spontaneously occurring VT (recordings available in 7 patients). Coupling intervals inducing tachycardia during isoproterenol were similar to intervals that did not induce VT without isoproterenol. No patient had VT with isoproterenol infusion alone (without extrastimuli). In only 4 of 8 patients who underwent exercise tests while not taking medications was VT provoked. With propranolol therapy (160 mg/day) or its equivalent, only 1 patient had recurrent symptoms during a mean follow-up of 39 months (range 23 to 52). VT inducible with extrastimuli only during isoproterenol infusion predicts that oral beta-adrenergic blockade will prevent spontaneous VT or syncope long term. These data suggest that occurrence of VT in some patients depends on premature depolarizations in the setting of beta-adrenergic influence.