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 (MYBPC3)
• 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

Associations

• Friedreich's ataxia
• Wolff-Parkinson White

PC

• often asymptomatic
• exertional dyspnoea
• angina
• syncope
  • typically following exercise
  • due to subaortic hypertrophy of the ventricular septum, resulting in functional aortic stenosis

Examination:

• jerky pulse, large 'a' waves, double apex beat
• ejection systolic murmur
  • increases with Valsalva manoeuvre and decreases on squatting
  • hypertrophic cardiomyopathy may impair mitral valve closure, thus causing regurgitation
• S4 heart sound