The effects of metoprolol given early in acute myocardial infarction on ventricular arrhythmias.

The effects of metoprolol, administered in the early stages of acute myocardial infarction was studied in 126 patients. Patients were treated in a double-blind randomized fashion, with metoprolol -15 mg, intravenously followed by 100 mg twice daily for 15 days or placebo, with a mean delay of 8.1 hours from onset of symptoms. All patients underwent 24 hour Holter monitoring on days 1, 5 and 15 after randomization. Although there was no antiarrhythmic effect on day 1, metoprolol reduced the number of hours with warning arrhythmias (greater than 30 ventricular ectopics/hour, any R/T ectopics or ventricular tachycardia) on both days 5 (35 +/- 16% vs 8 +/- 11%; P less than 0.05) and day 15 (13 +/- 37% vs 4 +/- 13%; P less than 0.05). Metoprolol also reduced the incidence of ventricular fibrillation and ventricular tachycardia requiring cardioversion -6% vs 0%; P = 0.058. Metoprolol, administered in the early stages of acute myocardial infarction, had an antiarrhythmic effect which was evident only in the later phase of the study.