Left Ventricular Outflow Tract Obstruction in Hypertrophic Cardiomyopathy: Do We Need to Stand to Be Counted

Abstract

Hypertrophic cardiomyopathy (HCM) is clinically defined by the presence of unexplained left ventricular (LV) hypertrophy in the absence of abnormal loading conditions. Although HCM was once considered a rare disorder associated with a poor prognosis, epidemiologic studies have detected HCM in around 1 in 500 individuals, most of whom have relatively good prognoses. Dynamic LV outflow tract (LVOT) obstruction (LVOTO) is an important and frequent manifestation of HCM and can be a major cause of symptoms such as dyspnea, chest pain, presyncope, and syncope. Symptoms in patients with HCM may be due to LVOTO but can also be caused by regional myocardial ischemia, diastolic dysfunction, arrhythmias, and systolic dysfunction. Dynamic LVOTO can often be controlled with medical therapy, and when necessary, interventional therapy with septal alcohol ablation or surgical myectomy can be performed with low patient risk at experienced centers. Echocardiography plays a critical role not only in the diagnosis of HCM but also in the follow-up and risk stratification of an affected individual. In addition, echocardiography has provided valuable insights into the mechanism of obstruction in HCM. The cause of LVOTO is multifactorial and includes not only vigorous LV ejection but also alterations in chamber geometry and morphology. LVOT cross-sectional area has been shown to be reduced because of a combination of septal hypertrophy and anterior displacement of the mitral valve apparatus and papillary muscles. Rapid LV ejection leads to a Venturi effect, which in the presence of elongated mitral leaflets and greater coaptation of the mitral leaflets at the leaflet body rather than tips, as well as drag forces, results in systolic anterior motion of the mitral valve. In a minority of patients, the dynamic obstruction is primarily at the midventricular level.