Improvement of myocardial metabolism in coronary arterial disease by beta-blockade

Abstract

Twenty patients with angina pectoris associated with obstructive coronary arterial disease were investigated by stressing the heart by atrial pacing. Arterial and coronary sinus blood was sampled and the time taken to provoke angina (pacing time) measured. Nine of the patients acted as a control group and did not receive beta-blocking drugs. In this group both pacing time and myocardial lactate extraction were reproducible provided that 45 minutes rest was allowed between pacing tests: we have called this period the myocardial recovery time. The 11 remaining patients were paced before and after beta-blockade, the rate being kept constant for each patient. In contrast to the control group, beta-blockade improved myocardial metabolism as shown by increased myocardial lactate extraction (P<0.02) and decreased glucose extraction (P<0.01). The pacing time to angina was increased (P<0.01) and the degree of ST segment depression was decreased (P<0.05). There was no significant effect on systolic or diastolic blood pressure, myocardial oxygen extraction, or extraction of free fatty acids and potassium. Failure to allow adequate time for full myocardial recovery after pacing will invalidate assessment of antianginal drugs. When this precaution is taken beta-blocking drugs are seen to improve nyocardial metabolism independently of their effects on heart rate and blood pressure.