Evaluation of phentolamine as a provocative test for idiopathic hypertrophic subaortic stenosis.

Intravenous injection of phentolamine potentially offers a better provocative test for aortic left ventricular outflow tract obstruction than do Valsalva's maneuver, inhalation of isoproterenol, or of amyl nitrite. In hemodynamic studies, phentolamine enhanced myocardial contractility, and decreased afterload with only induction of slight tachycardia. Phentolamine (5 mg.) was administered intravenously to five patients who had idiopathic hypertrophic subaortic stenosis, and 35 patients who had valvular dysfunctions, after which echocardiographic and phonocardiographic recordings were performed. Recordings were of high quality despite changing hemodynamics. Systolic pressures fell an average of 20 mm. Hg; no pressure fell below 90 mm. Hg; there was no notable increase in heart rate. In the five patients with typical idiopathic hypertrophic subaortic stenosis, the amyl nitrite increased the obstructive index from 39.6 +/- 12 to 51 +/- 18.9 (P less than 0.05); whereas, phentolamine increased the obstructive index to 69.8 +/- 25.6 (P less than 0.015). After a 2 week course of oral administration of 80 mg. of propranolol daily, and then either inhalation of amyl nitrite or injection of phentolamine, there was no change from the mean resting obstructive index. Phentolamine appears to be a safe, simple and specific diagnostic agent, and more potent than amyl nitrite in eliciting dynamic obstruction in IHSS; phentolamine and amyl nitrite do not affect the obstructive index in patients with beta blockade.