Non-surgical septal reduction therapy in hypertrophic cardiomyopathy

### Learning objectives Hypertrophic cardiomyopathy (HCM) is an inherited disease characterised by otherwise unexplained hypertrophy of the myocardium. It is transmitted in an autosomal dominant pattern with variable penetrance, with an estimated phenotypic prevalence of up to 1 in 500.1 HCM is a highly heterogeneous disease with varied patterns of hypertrophy. The prevalence of left ventricular outflow tract (LVOT) obstruction in HCM is 20%–30% at rest2 and up to 70% with provocation.3 ### LVOT pathophysiology Basal septal hypertrophy and systolic anterior motion (SAM) of the mitral valve (MV) are the key components to LVOT obstruction in HCM. The septal hypertrophy causes abnormal posteriorly directed flow through the left ventricle (LV).4 5 This flow circulates around the MV and back towards the LVOT, dragging the MV apparatus towards the septum. The MV is proposed to be abnormal as part of the HCM phenotype, with a variety of changes such as longer leaflets, abnormal papillary muscle architecture and anterior displacement of the apparatus. This anatomic predisposition means that the valve is more easily pushed towards the septum by the aberrant flow in the LV. Increased velocity through the LVOT also causes some drag effect pulling the MV towards the septum (the Venturi effect); however, SAM starts before velocities are notably elevated during systole, so this cannot be the sole cause of the anterior movement of the leaflets. The MV moves towards, and in severe cases contacts, the hypertrophied septum. Once mitral–septal contact occurs, the LVOT orifice is narrowed further and greater obstruction to flow develops, resulting in a higher pressure difference. This pressure difference …