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

Abstract

The systemic and coronary hemodynamic effects of combined α- and β-adrenergic blockade produced by labetalol were assessed in 12 normotensive patients with angina pectoris and an ischemic electrocardiographic response to exercise stress. When given to the patient at rest, labetalol (0.5 mg/kg intravenously) produced systemic and coronary vasodilation (mean 16% and 13%, respectively, both p < 0.05); aortic pressure decreased, cardiac output increased and coronary flow and heart rate did not change. Before labetalol treatment, supine bicycle exercise produced angina in all patients. After treatment, exercise duration was prolonged in 8 patients (average 33%). At the same duration of exercise that led to angina during the control period, ST depression in lead V 5 was less after labetalol (from 1.2 to 0.4 mm, p < 0.5). During exercise, tachycardia was blunted (−12%, p < 0.05) as were the increases in aortic pressure (−12%, p < 0.05), left ventricular end-diastolic pressure (−7%, difference not significant) and coronary sinus flow (−16%, p < 0.05). Cardiac output and systemic and coronary vascular resistance were similar to values during control exercise. The hemodynamic effects of labetalol appeared to be beneficial and differed from those of classic β-adrenergic blocking agents.