Effect of alpha 1-adrenoceptor blockade on ventricular ectopic beats inacute myocardial infarction

Experimental studies have shown that alpha1-adrenoceptor blockade can reduce ventricular arrhythmia associated with myocardial ischaemia. To examine the efficacy of prazosin in clinical acute infarction 38 patients were randomized, on presentation, to prazosin or placebo. Oral therapy was commenced at 0.5 mg, incremented and continued for seven days, Holter recordings being obtained for the first 48 hours and on day 7. The final dose of prazosin was 2.5 +/- 1.7 (SD) mg and placebo, 3.1 +/- 2.0 mg. During dose titration in the first 24 hours, and on day 7, there was no difference in ventricular ectopic beats. In the second 24 hours, ventricular ectopic beats averaged two per hour in the prazosin group (n = 9) and 60 per hour in placebo (n = 15) (P = 0.05, Mann-Whitney rank testing). The results indicate that alpha1-adrenoceptor blockade may reduce ventricular arrhythmia in clinical acute myocardial infarction. While early and adequate therapy is currently limited by vasodilation, this small study suggests that more extensive clinical trials will be warranted as relatively cardio-selective alpha1-adrenoceptor blocking drugs are developed.