hypertrophic cardiomyopathy

Picture a muscle that bulks up far beyond what the workload requires — like an arm that keeps thickening even though it is only lifting light weights. In hypertrophic cardiomyopathy the heart muscle, especially the wall between the two ventricles, grows abnormally thick without any pressure overload to explain it. The thick walls leave less room inside the chamber and become stiff, so the heart fills poorly.

Most cases are caused by inherited mutations in genes that build the heart-muscle contractile machinery (the sarcomere), and it runs in families in a dominant pattern. In some people the thickened septum bulges into the path of blood leaving the ventricle, causing left ventricular outflow tract obstruction; in others there is no obstruction. The disorganised, thickened muscle also predisposes to abnormal rhythms.

Hypertrophic cardiomyopathy is a leading cause of sudden cardiac death in young athletes, though many people live normal lifespans and some never have symptoms. Care includes assessing the risk of dangerous arrhythmias, sometimes placing a defibrillator, using medications to ease obstruction, and screening close relatives. It is not the same as the wall thickening (left ventricular hypertrophy) that hypertension causes — that has an obvious pressure driver.