The efficacy of intravenous
propranolol for suppression of inducibility of sustained
ventricular tachyarrhythmias (VT) was studied in 24 patients who had failed greater than or equal to 1 membrane-active
antiarrhythmic drug (mean 2.2 +/- 1.2 drugs/patient). The response to
propranolol was compared in 13 patients who had only stable monomorphic VTs inducible at baseline and another 11 patients who had greater than or equal to 1 episode of electrically unstable VTs (polymorphic VT,
ventricular flutter or
ventricular fibrillation) at baseline. Seven patients (29%) became noninducible (responders) and 17 patients (71%) remained inducible to sustained VT (nonresponders) after
propranolol. The basal heart rate was faster in responders than in nonresponders (101 +/- 14 vs 86 +/- 11 beats/min, p less than 0.01). The magnitude of heart rate reduction was also greater after
propranolol in responders (from 101 +/- 14 to 80 +/- 9 beats/min, p less than 0.001) than in nonresponders (from 86 +/- 11 to 74 +/- 9 beats/min, p less than 0.01) (p less than 0.05 between the groups), despite equal plasma
propranolol concentrations (84 +/- 50 vs 88 +/- 43 ng/ml, difference not significant). Seven of 11 patients (64%) who had greater than or equal to 1 episode of unstable VTs inducible at baseline responded to intravenous
propranolol, whereas none of the patients with only stable monomorphic VTs became noninducible after beta blockade (p less than 0.001). Responders had shorter cycle length of inducible VTs than nonresponders (225 +/- 38 vs 302 +/- 66 ms, p less than 0.001). Thus, intravenous
propranolol appears to be efficacious in suppressing fast, electrically unstable VTs, compared to monomorphic VTs with slower rates.