Hypertrophic obstructive cardiomyopathy: mechanism of obstruction and response to therapy.

Hypertrophic cardiomyopathy is a primary, usually familial, disorder of heart muscle whose primary feature is muscular hypertrophy without recognized cause that encroaches on the ventricular chamber, reducing chamber area and volume. In roughly 25% of cases, there is associated obstruction to left ventricular outflow (hypertrophic obstructive cardiomyopathy [HOCM]). This article details the mechanism of obstruction in HOCM, focusing on obstruction at the mitral valve level, and reviews the pharmacologic and surgical therapies currently available. Mainstays of pharmacologic therapy include b-blockers, calcium channel blockers (verapamil in particular), and/or disopyramide. Surgical therapies include septal myotomy/myectomy, which has become the gold standard to which other therapies are compared, and mitral valve replacement. During the past 10 years, atrio-ventricular sequential pacing and alcohol septal ablation have been proposed as less invasive alternatives to surgery. A single, optimal therapy for patients with HOCM and refractory symptoms has not been established, and decisions regarding surgical versus noninvasive therapies need to be individualized based on functional status, comorbidities, local expertise in the surgical and nonsurgical techniques, and patient preference.