Potentiation of Coronary Vasoconstriction by Beta–adrenergic Blockade in Patients with Coronary Artery Disease

Although,β-adrenergic blocking agents reduce myocardial oxygen consumption and symptoms of myocardial ischemia in patients with coronary artery disease (CAD), propranolol has been reported to exacerbate coronary artery spasm in some patients with variant angina. To determine whether increased coronary vasomotor tone can be induced by β-adrenergic blockade, we measured the changes in coronary vascular resistance (CVR) during cold pressor testing (CPT) in 15 patients, nine with severe CAD and six with normal left coronary anatomy, before and after i.v. propranolol (0.1 mg/kg). Coronary blood flow was measured by coronary sinus thermodilution. CVR was calculated as mean arterial pressure divided by coronary sinus blood flow. Heart rate was maintained constant at a paced subanginal rate of 95 ± 5 beats/min.Before propranolol, CPT induced significant increases in coronary vascular resistance in patients with CAD (15.0 ± 2.2%, p < 0.02), but no increase in CVR in the normal patients. After propranolol, the CVR change during CPT was augmented for patients with CAD (29 ± 6%, p < 0.01) and for the normal population (9 ± 5%, NS). The potentiated increase in CVR occurred without significant changes in resting CVR or in the magnitude of the hypertensive response to CPT.We conclude that,β-adrenergic blockade with propranolol can potentiate coronary artery vasoconstriction in some patients with CAD, possibly mediated by unopposed α-adrenergic vasomotor tone. These changes may be important in patients in whom intense adrenergic stimulation may increase coronary artery tone and adversely influence the balance between myocardial oxygen supply and demand.