Hypertrophic obstructive cardiomyopathy (HOCM) is the obstructive form of hypertrophic cardiomyopathy (HCM), in which abnormal thickening of the upper interventricular septum narrows the pathway through which blood is ejected from the left ventricle into the aorta. This narrowing produces a dynamic obstruction in the left ventricular outflow tract (LVOT), meaning the obstruction varies in severity depending on heart rate, filling, and contractile state.
In HOCM, as the left ventricle contracts, the thickened septum bulges towards the outflow tract, and the anterior leaflet of the mitral valve is drawn towards the septum (systolic anterior motion, SAM), further obstructing outflow. This produces a characteristic systolic ejection murmur that worsens when standing or performing a Valsalva manoeuvre (which reduces cardiac filling), and improves when squatting.
HOCM is a recognised cause of sudden cardiac arrest, particularly in young people and athletes. Symptoms may include breathlessness on exertion, chest pain, palpitations, and syncope (blackouts). Diagnosis is confirmed by echocardiography, which measures the outflow tract gradient and degree of septal hypertrophy.
Management depends on symptom severity and gradient. Beta-blockers, calcium channel blockers, and disopyramide reduce obstruction and control symptoms. For severe obstruction unresponsive to medication, surgical myectomy (removing part of the thickened septum) or alcohol septal ablation are effective interventional options. ICD implantation is recommended for those at high risk of sudden cardiac death.
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