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.

Abstract

The effect of propranolol 0.1 mg/kg intravenously followed by 320 mg in divided doses given over 27 hours orally was further evaluated in a randomised trial involving 62 patients up to 65 years of age who were seen within four hours of onset of uncomplicated myocardial infarction. Thirty-three patients were given propranolol and 29 served as controls. Two indices of infarct size were used: (a) total creatine kinase appearance and peak activity levels measured during the acute stage of infarction, and (b) subjective analysis of biplane left ventriculograms performed one month later in a subgroup of these patients. Total enzyme appearance was reduced by 25 per cent and peak levels were reduced by 23 per cent 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; likewise, quantitative subjective analysis of the left ventriculograms did not show any significant difference between the two groups. Though it could not be confirmed by this radiological method that reduction in enzyme appearance by beta adrenoceptor blockade was associated with restriction in infarct size, this seems the most likely cause for the lower enzyme levels. The safety of intravenous beta blockade when used in carefully selected patients suggests that large-scale clinical trials can be recommended in which measurements of infarct size as well as morbidity and mortality can be used as end-points.