Hypertrophic Carodiomyopathy (HCM)
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Hypertrophic Cardiomyopathy
Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy, also known as Hypertrophic Obstructive Cardiomyopathy (HOCM), is an autosomal dominant disorder, where there is thickening (hypertrophy) of the myocardium, particularly of the left ventricle, without an underlying cause.

It is the most common cause of sudden cardiac death in young adults.

It is one of several types of cardiomyopathy. All cardiomyopathies involve structural and functional abnormality of the myocardium, without an identifiable cause.

Epidemiology and Aetiology

  • Autosomal dominant, with variable penetrance. No one gene mutation is accountable, over 150 mutations have been identified.
  • Affects 1 in 500 people. More common in men and black people
  • Of those affected, annual mortality is approx 1-2%
  • Some cases do not have a family history
  • Most commonly presents in the second and third decades
  • Patients who have a Troponin T mutation are at greatest risk of sudden cardiac death



  • Hypertrophy of the myocardium, can occur anywhere, but particularly affects the left ventricle
  • Variable progression between individuals. Some have only mild hypertrophy (around 15mm) whilst other can have severe thickening, up to 60mm.
  • Most commonly, the septum becomes asymmetrically thickened.
    • In 25% of affected individuals, this leads to outflow tract obstruction secondary to systolic anterior motion (SAM) of the mitral valve.
    • The name HOCM has fallen out of use, as only 25% of cases are ‘obstructive’
  • There is also impaired diastolic filing as the ventricle becomes stiff and thickened
  • There is abnormal left ventricle structure (myocardial disarray), which can also alter the way electrical impulses travel through the ventricle



  • Patients who present younger are more likely to have severe disease
  • Course very variable between patients. Many patients are asymptomatic
  • May be picked up incidentally, e.g. on ECG
  • Symptoms may mimic those seen in congestive cardiac failure, although with very different pathology. For example, giving diuretics in HCM will actually worsen symptoms as it will reduce preload and increase LVOT resistance.
  • Symptoms may include:
  • Exertional chest pain
  • Palpitations
  • Exertional dyspnoea
  • Fatigue
  • Exertional syncope (worrying sign – suggest left ventricle outflow tract obstruction – LVOT). These patients are most at risk of sudden cardiac death


Examination Findings

Often normal. Classically, but not commonly:

  • Strong, palpable apex beat. May be able to feel a ‘double impulse’ if there is LVOT obstruction
  • Ejection systolic murmur, best heard at left sterna edge, worse on standing or with valsalva manoeuvre
  • Atrial fibrillation occurrs in about 20% of patients, and is associated with an increased risk of death



Many patients will have an abnormal ECG, although the changes are often non-specific. It is sometimes used as a screening tool. Changes may include:

  • Signs of left ventricular hypertrophy – e.g. increased voltages
  • Be wary, that in many normal fit healthy young people, sign of ‘LVH’ are seen on ECG, and this is normal. HCM should not be suspected on this alone.
  • P mitrale (bifid, often wide, p waves –  due to left atrial enlargement)
  • Non-specific ST and T wave changes, often T wave inversion
  • In asymmetrical septal hypertrophy, there may be sharp, deep Q waves, called dagger Q waves,  particularly in lateral (V5-6, I, aVL) and inferior (II, III aVF) leads.
  • Similar pathologic Q waves are seen in ECGs of patient with old MIs, but the dagger waves  of HCM tend to be >40ms duration, and pathologic q waves are <40ms.
  • Atrial fibrillation
  • SVT
  • VT – may lead to sudden cardiac death
  • Signs of Wolff-Parkinson-White syndrome (WPW) – there is a crossover of the two diseases, which may be related to the genetics of the two disorders. Sign of WPW can be seen in the ECGs of up to 30% of HCM patients
  • ECG changes are not correlated to the severity of the disease


Echocardiogram  is the diagnostic investigation of choice. It has about 80% sensitivity. Findings include:

  • Assymetric septal hypertrophy
  • Increased myocardium thickness
  • Left-ventricle is non-dilated
  • Absence of underlying cardiac disease

Chest X-ray is not all that useful. It may show normal are enlarged heart


Often difficult, due to the wide variability of the disease. There are very few trials on which to base management

  • Asymptomatic patients – can generally be left alone. They should be assessed for risk of sudden cardiac death, and ICD considered.
  • Control arrhythmias – amiodarone is useful to suppress both atrial and ventricular arrhythmias. If there is a particular arrhythmias persistently present it should be treated as per standard management – e.g. medication for AF, ablation for WPW features. Remember to consider anticoagulation in patients with AF
  • Control Left Ventricle function – beta blockers and verapamil are useful for reducing LVOT obstruction. In cases where drug treatment is insufficient, surgical myectomy may be used to reduce LVOT obstruction and septal asymmetry
  • Consider ICD – implantable cardioverter defibrillator should be consider in high-risk patients
  • Heart Transplant – may be considered in patients with severe disease who develop heart failure


Sudden Cardiac Death

Risk Factors

  • Young and asymptomatic  (age <30)
  • Family history of sudden cardiac death
  • History of arrhythmias
  • Unexplained syncopal episodes
  • Playing competitive sports

High risk patients should be considered for ICD. ICD prevents sudden cardiac death.


  • Very variable course, so hard to predict
  • Many patients who have sudden cardiac death, would not have been considered ‘high risk’
  • LV wall thickening of <20mm is associated with essentially normal life expectancy


  • Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
  • Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F
  • Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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