Göteborg Metoprolol Trial: electrocardiographically estimated infarct size.

In 236 patients with anterior myocardial infarction (MI), infarct size was estimated by analyzing the R- and Q-wave amplitude in 24 precordial leads 4 days after randomization. In 254 patients with inferior MI, the final R- and Q-wave amplitude was evaluated in leads II, III and aVF. Electrocardiographic signs of a smaller MI were observed in anterior MI in the metoprolol group compared with the placebo group when treatment was started 12 hours or less after the onset of pain, but no difference was found when treatment was started later. There was no sign of an effect of metoprolol in inferior MI. An immediate reduction in ST-segment elevation was observed after metoprolol treatment regardless of infarct localization or delay between the onset of pain and treatment.