Underappreciated occurrence of discrete subaortic membranes producing left ventricular outflow obstruction in hypertrophic cardiomyopathy.

Subaortic obstruction due to systolic anterior motion (SAM) of the mitral valve with ventricular septal contact is a major cause of progressive heart failure symptoms in patients with hypertrophic cardiomyopathy (HCM). However, we have recently observed a unique, but not uncommon subgroup of HCM patients with outflow tract obstruction due only to discrete subaortic membrane or who have a membrane in addition to SAM-septal contact. HCM patients with subaortic membranes may be at increased risk for developing progressive heart failure symptoms. Identification requires a high index of suspicion and raises important management considerations, including need for surgical myectomy for definitive relief of obstruction with associated excellent outcomes, as the alternative invasive treatment option with percutaneous alcohol septal ablation would be ineffective.