Improvement of myocardial oxygenation is a major goal in the treatment of ischaemic
heart disease.
Propranolol, 0-1 mg/kg intravenously, was administered to 20 patients with acute
myocardial infarction without clinical evidence of left ventricular failure. The most important haemodynamic response was a substantial decrease in myocardial contractility. This was reflected by a fall in cardiac index (average of 0-4 l/min/M2, P less than 0-001) and of arterial mean pressure (average of 16 mmHg, P less than 0-001) with little change in systemic vascular resistance. Heart rate, not strikingly increased at the control state in the majority of patients, decreased an average of 7 beats/minute (P less than 0-001). Pulmonary wedge pressure varied; it decreased in 6 patients with high values (greater than 15 mmHg) prior to
propranolol. These changes in wedge pressure in the presence of decreased contractility are probably related to improved left ventricular compliance, produced by
propranolol.
Propranolol markedly improved myocardial metabolism. Arterial-coronary sinus
oxygen difference decreased an average of 0-72 ml/100 ml (P less than 0-001). Myocardial
lactate production shifted to extraction (average of -8% to 14%) or the rate of
lactate extraction increased (average of 20% to 29%). Coronary blood flow decreased an average of 13 ml/100 g/min (P less than 0-001). The finding, that myocardial metabolism improved, suggests that decrease in coronary blood flow was mediated by reduced myocardial
oxygen requirements. None of the 20 patients developed left ventricular failure or other complications related to beta-
adrenergic blockade. Severe
chest pain, unresponsive to conventional
therapy in four patients, was relieved by
propranolol. These findings demonstrate that acutely administered
propranolol improves myocardila oxygenation in patients with uncomplicated acute
infarction without endangering perfusion of other vital organs.