Treatment of acute myocardial infarction with propranolol. Further studies on enzyme appearance and subsequent left ventricular function in treated and control patients with developing infarcts.

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Abstract
The effect of propranolol 0.1 mg/kg i.v. followed by 320 mg in divided doses given over 27 h orally was further evaluated in a randomized trial involving 62 patients up to 65 yr old who were seen within 4 h of onset of uncomplicated myocardial infarction. Patients (33) were given propranolol and 29 served as controls. Two indices of infarct size were used: total creatine kinase appearance and peak activity levels measured during the acute stage of infarction; and subjective analysis of biplane left ventriculograms performed 1 mo. later in a subgroup of these patients. Total enzyme appearance was reduced by 25% and peak levels were reduced by 23% in treated patients compared with controls. The subgroup subsequently studied by angiocardiography did not show the reduction in enzyme levels shown by the whole group; quantitative subjective analysis of the left ventriculograms did not show any significant difference between the 2 groups. This radiological method did not confirm that reduction in enzyme appearance by .beta.-adrenoceptor blockade was associated with restriction in infarct size but this seems the most likely cause for the lower enzyme levels. The safety of i.v. .beta.-blockade when used in carefully selected patients suggests that large-scale clinical trials can be recommended in which measurements of infarct size, morbidity and mortality can be used as end-points.