Metoprolol in acute myocardial infarction. Arrhythmias. The MIAMI Trial Research Group.

Forty-five patients in the placebo (1.5%) and 29 in the metoprolol (1%) groups, respectively, were receiving antiarrhythmic drugs on a long-term basis before entry into the trial. Before randomization, 2.2% (n = 64) of the placebo and 1.7% (n = 50) of the metoprolol patients developed ventricular fibrillation (VF) in the hospital. The corresponding figures for atrial fibrillation or flutter were 3% (n = 87) and 3.3% (n = 94). After randomization, there was no significant difference in the number of patients who developed VF in the placebo (n = 52) and the metoprolol (n = 48) groups. The total number of episodes of VF tended to be fewer in the metoprolol group (n = 67) compared with the placebo group (n = 96). The tendency was, however, not apparent until after 5 days. When the occurrence of VF was related to high- and low-mortality risk groups, any beneficial effect of metoprolol was confined mainly to the high-risk group. A similar proportion of patients underwent electric conversion for ventricular tachyarrhythmia in the 2 groups. Although antiarrhythmic drugs were intended to be given only for major ventricular tachyarrhythmias a large proportion of patients received such treatment. Significantly more patients were treated with antiarrhythmics in the placebo (21.5%) than in the metoprolol group (19.2%, p = 0.03) during the study period, but predominantly during the first 5 days. Atrial fibrillation or flutter and other supraventricular tachyarrhythmias were significantly less frequent in the metoprolol than in the placebo group, as was the use of cardiac glycosides.(ABSTRACT TRUNCATED AT 250 WORDS)