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

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Abstract
Patients (20) with angina pectoris associated with obstructive coronary arterial disease were invesitgated by stressing the heart by atrial pacing. Arterial and coronary sinus blood was sampled and time taken to provoke angina (pacing time) measured. Of the patients, 9 acted as a control group and did not receive .beta.-blocking drugs [propranolol and tolamolol]. In this group both pacing time and myocardial lactate extraction were reproducible provided that 45 min rest was allowed between pacing tests: this period was called 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 O2 extraction or extraction of free fatty acids and K. 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 myocardial metabolism independently of their effects on heart rate and blood pressure.