Abstract 14342: The Underappreciated Occurrence of Discrete Subaortic Membranes Producing LV Outflow Obstruction in Patients With Hypertrophic Cardiomyopathy
Background: Subaortic obstruction due to systolic anterior motion (SAM) of the mitral valve with ventricular septal contact is a major cause of progressive heart failure (HF) symptoms in hypertrophic cardiomyopathy (HCM). However, we have recently observed a unique 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.
Methods and Results: Of 1412 HCM patients, 15 (1.1%) were identified with a subaortic membrane at a wide range of ages (24 to 74 years), with a maximal LV wall thickness of 18 ± 3 mm. Membranes were identified 1.5 ± 0.2 cm below normal aortic valve by transthoracic echocardiography in 13 patients (87%), but in 2 patients only by cardiovascular magnetic resonance or transesophageal echocardiogram. In 7 of the 15 patients (47%) outflow obstruction was attributed to only the subaortic membrane (gradient, 59±11 mmHg) in the absence of SAM, while in 8 (47%) subaortic membrane and SAM-septal contact resulted in two discrete levels of obstruction (gradient, 56 ± 20 mmHg and 100 ± 25 mmHg, respectively). Over 4.6 ± 2.9 years of follow up, 9 of the 15 patients (60%) experienced progressive and advanced HF symptoms (NYHA class III/IV), despite treatment with AV nodal blocking agents. Surgical resection of the subaortic membrane with extended septal myectomy was performed in 8 of the 9, including 4 with obstruction secondary only to the membrane. Histopathologic examination of the resected septum demonstrated myocyte disarray and hypertrophy, with replacement and interstitial fibrosis. At most recent evaluation, 4.0 ± 3.0 years post-operatively, all patients had a significant improvement in limiting HF symptoms, to class I (n=7) or II (n=1) without recurrence of the membrane.
Conclusions: Subaortic membrane represents an under-appreciated mechanism of obstruction in patients with HCM, requiring a high index of suspicion for diagnosis. Membranes in HCM patients are associated with increased risk for progressive HF symptoms and raise important management considerations including need for surgical myectomy for definitive relief of obstruction, since the alternative invasive treatment option with percutaneous alcohol ablation would be ineffective.
Author Disclosures: M. Kannappan: None. B.J. Maron: None. H. Rastegar: None. N.G. Pandian: None. M.S. Maron: None. E.J. Rowin: None.
- © 2016 by American Heart Association, Inc.