Hypertrophic obstructive cardiomyopathy (HOCM) is an autosomal dominant disorder of muscle tissue caused by defects in the genes encoding contractile proteins. The estimated prevalence is 1 in 500. HOCM is important as it is the most common cause of sudden cardiac death in the young.

Pathophysiology

• the most common defects involve a mutation in the gene encoding β-myosin heavy chain protein or myosin-binding protein C
• results in predominantly diastolic dysfunction
  • left ventricle hypertrophy → decreased compliance → decreased cardiac output
• characterized by myofibrillar hypertrophy with chaotic and disorganized fashion myocytes ('disarray') and fibrosis on biopsy

Features

• often asymptomatic
• exertional dyspnoea
• angina
• syncope
  • typically following exercise
  • due to subaortic hypertrophy of the ventricular septum, resulting in functional aortic stenosis
• sudden death (most commonly due to ventricular arrhythmias), arrhythmias, heart failure
• jerky pulse, large 'a' waves, double apex beat
• systolic murmurs
  • ejection systolic murmur: due to left ventricular outflow tract obstruction. Increases with Valsalva manoeuvre and decreases on squatting
  • pansystolic murmur: due to systolic anterior motion of the mitral valve → mitral regurgitation

Associations

• Friedreich's ataxia
• Wolff-Parkinson White

Echo findings - mnemonic - MR SAM ASH

• mitral regurgitation (MR)
• systolic anterior motion (SAM) of the anterior mitral valve leaflet
• asymmetric hypertrophy (ASH)