Hypertrophic cardiomyopathy (HCM) is an inherited heart muscle disease in which the cardiac muscle becomes abnormally thick (hypertrophied), most commonly affecting the interventricular septum (the wall between the ventricles). The thickened muscle stiffens the heart, may obstruct blood flow leaving the left ventricle, and creates a substrate for life-threatening arrhythmias.
HCM is the most common cause of sudden cardiac arrest in young people and athletes, and is present in around 1 in 500 individuals. It is usually caused by mutations in genes encoding sarcomere proteins. Inheritance is autosomal dominant, meaning each child of an affected parent has approximately a 50% chance of inheriting the condition. Family screening is essential following any diagnosis.
Symptoms vary widely. Many people with HCM are asymptomatic and diagnosed incidentally on ECG or [echocardiogram](/glossary/echocardiogram/). Others experience breathlessness, chest pain, [palpitations](/glossary/palpitations/), pre-syncope, or syncope, particularly on exertion. High-risk features associated with greater sudden cardiac arrest risk include a family history of SCA, unexplained syncope, non-sustained [ventricular tachycardia](/glossary/ventricular-tachycardia/), extreme wall thickness, and abnormal blood pressure response during exercise.
Management includes beta-blockers or calcium channel blockers for symptoms, [ICD](/glossary/icd/) implantation for high-risk individuals, and septal reduction therapy (surgical myectomy or alcohol septal ablation) for symptomatic outflow obstruction. Exercise restrictions and regular specialist review are required. Mavacamten, a cardiac myosin inhibitor, is a newer treatment option for obstructive HCM.
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