Systemic and coronary hemodynamic effects of combined oral alpha- and beta-adrenergic blockade (labetalol) in normotensive patients with stable angina pectoris and positive exercise stress tests

Abstract

The systemic and coronary hemodynamic effects of combined alpha- and beta-adrenergic blockade produced by oral labetalol were assessed in 12 normotensive patients with angina pectoris and an ischemic electrocardiographic response to exercise stress. At rest, labetalol (200 mg, orally) produced systemic vasodilation (systemic vascular resistance -9%, p less than .01) as aortic pressure fell and cardiac output was unchanged. Left ventricular (LV) end-diastolic pressure also fell slightly (17%, p = .05). Systemic vasodilation was not accompanied by reflexly mediated increases in heart rate. Coronary flow and resistance and myocardial oxygen uptake were unchanged. Before labetalol, supine bicycle exercise produced angina in 10 patients. After labetalol, exercise duration was prolonged in 6 of these 10 (average 56%). During exercise, tachycardia was blunted (-7%, p less than .05) as were increases in aortic pressure (-12%, p less than .01) and coronary sinus flow (-25%, p = .03). Cardiac output and LV end-diastolic pressure were similar to control period values. These hemodynamic effects of oral labetalol appeared beneficial, differed from those expected of classic beta-adrenergic blocking agents, and were, in general, similar to those we have observed after intravenous labetalol. The clinical response was good and the drug safe. Labetalol should undergo further evaluation in normotensive as well as hypertensive patients with ischemic heart disease.