Discrete membranous subaortic stenosis. Report of 31 patients, review of the literature, and delineation of management.

The presentation, management, and follow-up of 31 patients with discrete membranous subaortic stenosis (DMSS) is presented. DMSS comprised 16% of 185 patients with congenital left ventricular (LV) obstruction. Only one patient was older than 40 years. The rarity of DMSS in older patients in both our population and in the literature is noted, and possible explanations are discussed. One-quarter of these patients had dyspnea, chest pain, or syncope combined with electrocardiographic left ventricular hypertrophy (LVH) and strain, and these all had peak LV outflow gradients (PSG) greater than 85 mm Hg. One-quarter had neither symptoms nor electrocardiographic abnormalities and all had PSG less than 90 mm Hg. Bacterial endocarditis was found in 13%, and in 13% an immediate family member also had congenital LV obstruction. Following surgical resection (25 patients), 18 were asymptomatic, two had residual fibromuscular obstruction, and four developed new fibromuscular obstruction after from one to six years (leading in one to late sudden death). Thus, even after resection, these patients require continued re-evaluation for residual or new LV obstruction.