Early intravenous beta blockade in acute myocardial infarction.
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In the critical period during which ischemia progresses to infarction, beta-blocking drugs are known to reduce oxygen demand and prevalence of arrhythmia. To investigate whether this treatment confers clinical benefits, 28 trials have been conducted involving some 27,500 patients during the early hours after onset of symptoms suggesting acute myocardial infarction (MI). Patients were randomized to receive either initial intravenous beta blocker plus oral maintenance or standard therapy. In toto, these trials indicated that early-intervention short-term beta-blocker treatment reduces: (1) the risk for early death, reinfarction, and ventricular fibrillation by about 15%; (2) enzymatic indices of infarct size; (3) the number of patients with threatened MI in whom a confirmed MI develops; and (4) the frequency of repetitive and nonrepetitive ventricular arrhythmias. Overall, the treated group had few major side effects other than a small excess of reversible and nonfatal heart block and hypotension. Retrospective analyses suggest (but do not prove) that the reduction in mortality is greatest for those treated within two hours of pain and during the first two days. These results indicate that early initial administration of intravenous beta blocker plus one week's oral beta-blocker treatment produces modest benefits that would presumably be of major public health importance if such treatment were widely used.
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