Confidence in results of beta-blocker postinfarction trials.

Seventeen published trials of beta-blockers in myocardial infarction were scrutinised for the 95% confidence limits for the reported treatment effects. All the trials were prospective, randomised, and (except when treatment was given intravenously) placebo controlled. For analysis of pooled results the trials were divided arbitrarily according to whether treatment had been given "early" or "late" after the onset of pain. All trials were consistent with a treatment effect of just over 20%, but benefit was more apparent in trials using late intervention with beta-blockers. The pooled results of trials using early intervention showed a positive effect of 8%, whereas those using late intervention showed a 26% reduction in mortality and confidence limits of 17-35%. The results confirm that late intervention with beta-blockers after myocardial infarction reduces mortality but show that the effect of early intervention remains to be determined.