Infarct size limitation after early intervention with metoprolol in the MIAMI Trial

One of the secondary objectives of the MIAMI Trial which evaluated the role of the beta-1-selective blocker metoprolol in suspected acute myocardial infarction was to further assess whether early intervention with beta-blockade can limit infarct size. A total of 5,778 patients from 104 worldwide centres were randomized into the trial. Various enzymes such as aspartate aminotransferase (ASAT), creatine kinase (CK), CK MB, CK B, lactate dehydrogenase (LD) and LD isoenzyme I were analysed. All enzymes were used according to the clinical routine of the respective hospital, except ASAT which was analysed once daily for 3 days in the majority of cases and LD I which was analysed every 12 h for 72 h in a subsample. A consistent observation was the lower serum enzyme activity among patients receiving metoprolol and randomized early after onset of symptoms, whereas no difference between metoprolol and placebo was observed in patients treated later in the course. The results of the MIAMI Trial support previous observations that early institution of metoprolol therapy limits infarct size, as indicated by the maximum serum enzyme activity.