CLINICAL AND HEMODYNAMIC APPRAISAL OF BETA ADRENERGIC BLOCKING DRUGS

The recent availability for use in man of drugs which interfere with sympathetic stimuli to the myocardium has led to considerable interest in the clinical use of beta adrenergic blocking agents for conditions in which the intensity of the sympathetic drive to the heart might be excessive. These conditions have included angina pectoris, various atrial and ventricular arrhythmias, idiopathic hypertrophic subaortic stenosis, and pheochromocytoma. I t is the purpose of this report to review some of these early clinical trials in an attempt to appraise the clinical value of the beta adrenergic blocking drugs in the light of their hemodynamic effects. However, it must be appreciated that while these agents have been shown to be capable of producing blockade of beta adrenergic receptors, they also possess other actions which may modify their clinical effects. The contractility of the myocardium, i.e. the level of cardiac performance a t any given end-diastolic fiber length, is regulated to an important extent by the impulse traffic in the cardiac sympathetic nerves, which determines the rate a t which the neurotransmitter is released from the nerve terminals, and, therefore, the quantity of norepinephrine acting upon the myocardium. During muscular exercise or other conditions in which the requirements for cardiac performance are augmented, there is an increase in the activity of the cardiac sympathetic nerves. Accordingly, it might be anticipated that beta adrenergic blockade would limit the cardiac output during muscular exercise and, thereby, places a limit on exercise performance.