Eleven patients with muscular subaortic stenosis were studied by use of combined right and transatrial septal left heart catheterization. A variety of stimulating maneuvers were performed to induce or increase the functional outflow tract obstruction; 150 pug/kg of propranolol was administered intravenously, and the stimulating maneuvers were repeated. Outflow obstruction was latent (present only with stimulation) in four patients, labile (present intermittently at rest) in five patients, and persistent and severe in two patients. Propranolol abolished or significantly decreased the spontaneous variations in outflow obstruction occurring at rest, during the enhanced gradient in the post-exercise state, and during variations induced by isoproterenol infusion. The outflow obstruction induced by inhalation of amyl nitrite, the Valsalva maneuver, and premature ventricular contractions was only inconsistently prevented. Long-term oral propranolol therapy has been of significant symptomatic benefit in all the patients with latent or labile outflow obstruction and is considered the treatment of choice in these groups. In one patient with persistent outflow obstruction, an increase in symptoms occurred when oral propranolol was administered, and the drug was discontinued. Evidence is presented to support the concept of a cycle of obstruction and hypertrophy in the natural history of this disease. This vicious cycle might be prevented by propranolol. Additional Indexing Words: Amyl nitrite Isoproterenol

SUMMARY

Twenty patients with mitral insufficiency (MI) due to ruptured chordae tendineae, papillary muscle infarction, or left ventricular enlargement with no organic disease of the mitral valve have been studied during the past 3 years. Nineteen had valve replacement, and one had plastic repair of ruptured chordae tendineae; all have been followed from 6 months to 3 years. Preoperative data were different in those who were improved by surgery (13 patients) and those who were not (seven patients). The group in which good results were obtained had a short history of heart failure, little or no evidence of left atrial (LA) enlargement in the electrocardiograms and x-rays, and striking LA v waves at catheterization. In the group demonstrating poor results, heart failure was of longer duration, gross four-chamber cardiomegaly was present, and LA v waves were only moderate. Thus, patients with nonrheumatic mitral insufficiency with high-pressure LA regurgitant waves and only moderate LA enlargement are likely to benefit from mitral valve surgery, even when the primary cardiovascular disease is hypertension, arteriosclerosis, or a cardiomyopathy. These patients generally have ruptured chordae tendineae.