Hypertrophic Cardiomyopathy (HCM)

• previously termed hypertrophic obstructive cardiomyopathy (HOCM) or idiopathic hypertrophic subaortic stenosis (IHSS), is one of the most common inherited cardiac disorders:
  • Prevalence ~1 in 500 people
  • Annual mortality ~1-2%
  • Number one cause of sudden cardiac death in young people
• It is a heterogenous disorder produced by mutations in multiple genes coding for sarcomeric proteins (e.g. beta-myosin heavy chain, troponin T). 
• Inheritance is primarily autosomal dominant, with variable penetrance. 
• Over 150 mutations have been identified, explaining the variability in the clinical phenotype.

Structural changes

• The chief abnormality associated with HCM is left ventricular hypertrophy (LVH), occurring in the absence of any inciting stimulus such as hypertension or aortic stenosis
• The degree and distribution of LVH is variable:
  • mild hypertrophy (13-15 mm) or extreme myocardial thickening (30-60 mm) may be seen.
• The most commonly observed pattern is:
  • Asymmetrical thickening of the anterior interventricular septum (= asymmetrical septal hypertrophy). 
    • This pattern has been classically associated with systolic anterior motion (SAM) of the mitral valve and dynamic left ventricular outflow tract (LVOT) obstruction

• However, in the majority of cases (75%), HCM is NOT associated with LVOT obstruction, hence the name change from HOCM to HCM
• Other less common patterns of LVH include
  • Concentric hypertrophy (20% of cases)
  • Apical hypertrophy (10%)

Processes responsible for clinical manifestations of HCM:

• Dynamic obstruction of the LVOT
• Left ventricular diastolic dysfunction, resulting from impaired relaxation and filling of the stiff and hypertrophied left ventricle (often associated with increased filling pressures)
• Abnormal intramural coronary arteries with thickened walls and narrowed lumens
• Chaotic, disorganised left ventricular architecture (“cellular disarray”) predisposing to abnormal transmission of electrical impulses, thus serving as a substrate for arrhythmogenesis

Clinical features

1. Exertional syncope or pre-syncope — this is the most worrying symptom, suggesting dynamic LVOT obstruction ± ventricular dysrhythmia, with the potential for sudden cardiac death
2. Symptoms of pulmonary congestion (e.g. exertional dyspnoea, fatigue, orthopnoea, paroxysmal nocturnal dyspnoea) due to left ventricular dysfunction
3. Chest pain — may be typical anginal pain due to increased demand (thicker myocardial walls) and reduced supply (aberrant coronary arteries)
4. Palpitations due to supraventricular or ventricular arrhythmias

Apical HCM

1. This relatively uncommon form of HCM is seen most frequently in Japanese patients (13-25% of all HCM cases in Japan)
2. There is localised hypertrophy of LV apex, causing a “spade-shaped” configuration of the LV cavity on ventriculography
3. The classic ECG finding in apical HCM is giant T-wave inversion in the precordial leads

Narrow, “dagger-like” Q waves in inferior and lateral leads

ECG finding in apical HCM is giant T-wave inversion in the precordial leads

Dilated Cardiomyopathy (DCM)

• Dilated cardiomyopathy (DCM) is a myocardial disease characterised by ventricular dilatation and global myocardial dysfunction (ejection fraction < 40%).
• Patients usually present with symptoms of biventricular failure, e.g. fatigue, dyspnoea, orthopnoea, ankle oedema
• Associated with a high mortality (2-year survival = 50%) due to progressive cardiogenic shock or ventricular dysrhythmias (sudden cardiac death)

• Causes of Dilated Cardiomyopathy
  • Ischaemic
    • Dilated cardiomyopathy commonly occurs following massive anterior STEMI due to extensive myocardial necrosis and loss of contractility
  • Non-ischaemic
    • Most cases are idiopathic
    • Up to 25% are familial (primarily autosomal dominant, some types are X-linked)
    • A very small proportion may occur with:
      • Viral myocarditis (coxsackie B / adenovirus)
      • Alcoholism
      • Toxins (e.g. doxorubicin)
      • Autoimmune disease
      • Pregnancy (peripartum cardiomyopathy)

Common ECG associations with DCM

• Left atrial enlargement (may progress to atrial fibrillation)
• Biatrial enlargement
• Left ventricular hypertrophy or biventricular enlargement
• Left bundle branch block (RBBB can also occur)
• Left axis deviation
• Poor R-wave progression with QS complexes in V1-4 (“pseudo-infarction” pattern)
• Frequent ventricular ectopics and ventricular bigeminy (seen with severe DCM)
• Ventricular dysrhythmias (VT/VF)

Ischaemic dilated cardiomyopathy:

• There is marked LVH (S wave in V2 > 35 mm) with dominant S waves in V1-4
• Right axis deviation suggests associated right ventricular hypertrophy (i.e. biventricular enlargement)
• There is evidence of left atrial enlargement (deep, wide terminal portion of the P wave in V1)
• There are peaked P waves in lead II suggestive of right atrial hypertrophy (not quite 2.5mm in height)

    Atrial fibrillation with LBBB is another ECG pattern commonly seen in DCM