Effects of Beta Adrenergic Blockade on the Circulation, with Particular Reference to Observations in Patients with Hypertrophic Subaortic Stenosis

The circulatory effects of blocking the beta adrenergic receptors with Nethalide were studied in 10 patients with hypertrophic subaortic stenosis and in five postoperative subjects undergoing right heart catheterization. In the resting state, the heart rate and the rate of pressure development in the right ventricle diminished slightly, but cardiac index was not altered by the administration of Nethalide. These observations suggest that tonic sympathetic activity is not of major importance in basal subjects in the supine position. Nethalide attenuated the increase in heart rate and right ventricular dp/dt associated with exercise, and abolished the response of these two variables to the administration of isoproterenol. In the patients with hypertrophic subaortic stenosis Nethalide had little effect on the severity of the obstruction at rest, but reduced the intensification of the obstruction produced by exercise or isoproterenol. The possible clinical benefits of blocking the beta adrenergic receptors in these patients were discussed.