Clinical Spectrum and Management Implications of Left Ventricular Outflow Obstruction With Mild Ventricular Septal Thickness in Hypertrophic Cardiomyopathy.

Hypertrophic cardiomyopathy (HC) has historically been characterized as a disease of substantial left ventricular hypertrophy, often associated with dynamic left ventricular outflow tract obstruction. However, we have recently encountered patients with subaortic obstruction and only minimal basal septal thickness, raising important management implications. Thereby, we sought to characterize the natural history and treatment strategies for this under-recognized subgroup of HC patients with dynamic obstruction. Of 1,591 consecutive patients with a HC diagnosis, 113 (7%) were identified with outflow obstruction due to elongated mitral valve leaflets producing systolic anterior motion and septal contact typical of HC (gradient, 84 ± 29 mm Hg at rest or with exercise), with maximal ventricular septal thickness ≤15 mm, including 14 patients with only 10 to 12 mm. In addition to the mechanism of outflow obstruction, other evidence supporting a HC diagnosis prominently included: positive HC family history and/or pathogenic sarcomere mutation, arrhythmic sudden death event, typical histopathology of septal muscle, and characteristic mitral valve and papillary muscle anomalies. Over 3.8 ± 3.5 years, 41 patients (36%) developed severe heart failure including 36 who have undergone myectomy associated with reconstruction of the outflow tract and mitral valve apparatus, resulting in relief of gradient without iatrogenic ventricular septal defect or mitral valve replacement. Postoperatively, all 36 patients have survived with symptom relief to New York Heart Association classes I/II. In conclusion, these observations expand the HC clinical profile and phenotype to include an under-appreciated subgroup in which disease expression includes outflow obstruction due primarily to an elongated mitral valve, associated with only minimal (or normal) ventricular septal thickness. Such HC patients can develop marked functional limitation amenable to an operative strategy that effectively relieved symptoms due to outflow obstruction, but without mitral valve replacement.

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.