Introduction

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.

Epidemiology

  • Incidence: 30.00 cases per 100,000 person-years
  • Peak incidence: 20-30 years
  • Sex ratio: 1:1
Condition Relative
incidence
Aortic stenosis6.67
Hypertrophic obstructive cardiomyopathy1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Aetiology

Associations
  • Friedreich's ataxia
  • Wolff-Parkinson White

Pathophysiology

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

Clinical features

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
  • ejection systolic murmur
    • increases with Valsalva manoeuvre and decreases on squatting
    • hypertrophic cardiomyopathy may impair mitral valve closure, thus causing regurgitation

Investigations

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

ECG
  • left ventricular hypertrophy
  • non-specific ST segment and T-wave abnormalities, progressive T wave inversion may be seen
  • deep Q waves
  • atrial fibrillation may occasionally be seen

© Image used on license from Dr Smith, University of Minnesota
ECG showing typical changes of HOCM including LVH and T wave inversion

© Image used on license from Dr Smith, University of Minnesota
This young male patient was shown to have HOCM. Note the LVH and deep ST depression and T-wave inversions

Management

Management
  • Amiodarone
  • Beta-blockers or verapamil for symptoms
  • Cardioverter defibrillator
  • Dual chamber pacemaker
  • Endocarditis prophylaxis

Drugs to avoid
  • nitrates
  • ACE-inhibitors
  • inotropes

Prognosis

Poor prognostic factors
  • syncope
  • family history of sudden death
  • young age at presentation
  • non-sustained ventricular tachycardia on 24 or 48-hour Holter monitoring
  • abnormal blood pressure changes on exercise

An increased septal wall thickness is also associated with a poor prognosis.