Ventricular arrhythmias during the first year after acute myocardial infarction: influence of long-term treatment with metoprolol.

Three hundred and one patients who had been hospitalized for acute myocardial infarction, were less than 70 years old, were in sinus rhythm, and did not have complete bundle branch block were stratified before discharge according to age, size of infarction, and type of ventricular arrhythmias as determined on a 6 hr electrocardiogram (ECG). They were thereafter randomly assigned to double-blind treatment with 100 mg bid metoprolol or placebo. Repeat 6 hr ECGs were recorded 3 days and 1, 6, and 12 months after treatment had begun. In the placebo group there was a significant increase in the proportion of patients with complex premature ventricular complexes (PVCs) (i.e., multiform, paired and R-on-T PVCs, or ventricular tachycardia) as well as increased numbers of PVCs in the patients during the follow-up. In contrast, an initial decrease in the number of PVCs (p less than .001) was found in the metoprolol group, whereas the complexity of PVCs was constant in those patients who continued on metoprolol therapy throughout the follow-up period. We conclude that the increase in complexity and number of PVCs that is part of the natural clinical course after myocardial infarction is counteracted by long-term treatment with metoprolol.