Hypertrophic Cardiomyopathy



  • Hypertrophic cardiomyopathy (HCM) is a form of primary myocardial hypertrophy, with or without presence of left ventricular outflow tract (LVOT) obstruction; it is characterized by four cardinal features:
    • Idiopathic LV hypertrophy (LVH) in absence of other cardiac or systemic disease causing hypertrophy of such magnitude
    • Cardiac myocyte and myofibrillar disarray
    • Familial occurrence
    • Associated sudden cardiac death (SCD)
  • System(s) affected: cardiovascular
  • Synonym(s): hypertrophic obstructive cardiomyopathy (HOCM); muscular subaortic stenosis (MSS); idiopathic hypertrophic subaortic stenosis (IHSS)


  • The disorder may present at any age.
  • It is seen in equal frequency in both sexes, although it is often underrecognized in females and African Americans.
  • Apical HCM is a variant seen more often in China and Japan (Yamaguchi apical variant).

~1% of patients with HCM die annually, but this is no different from the overall population.

Prevalence of HCM (positive phenotype or gene carrier) in the adult general population is 1:200 (1).

Etiology and Pathophysiology

  • LVH
    • ≥1 region of LV wall are thickened: classically at the basal anterior septum but may involve posterior septum or LV free wall and apex
    • Hypertrophy develops usually in adolescence, with an average 100% increase in LV mass.
  • Systolic anterior motion (SAM) of the mitral valve
    • Mitral valve abnormalities are primary manifestations of HCM: One or both leaflets may be elongated.
    • SAM is the abrupt motion of the mitral valve leaflet toward the septum, which creates dynamic LVOT obstruction in contact with the septum.
    • Caused by drag effect of the high-velocity jet caused by ejection through a narrowed LVOT and/or a Venturi phenomenon
  • Disorganized myocardial architecture
    • Myocytes and myofilaments are laid down in disorganized pattern, with increased matrix components causing myocyte disarray.
    • Microvascular disease leads to ischemia and replacement fibrosis.
  • Diastolic dysfunction
    • Result of reduced ventricular compliance; contributes predominantly to the symptoms of heart failure, such as dyspnea


  • Inherited as a mendelian autosomal dominant trait with >50% penetrance and variable expressivity
  • 11 sarcomeric gene mutations are known, including, among others, β-myosin heavy chain, myosin-binding protein C, and troponins I and T.

Risk Factors

Risk factors for SCD in patients with IHSS include the following (2):

  • A prior history of cardiac arrest or spontaneous sustained ventricular tachycardia (VT)
  • Family history of premature SCD (especially in first-degree relative[s])
  • Unexplained syncope
  • Extreme LVH measuring >30 mm
  • Hypotensive response to exercise: inability to increase by at least 20 mm Hg or a drop of at least 20 mm Hg
  • Nonsustained VT during Holter monitoring
  • Other factors that may indicate increased risk are LVOT obstruction (resting gradient >30 mm Hg), LV apical aneurysm, high-risk mutation, delayed enhancement on cardiac MRI.
  • A predicted risk ≥6% using a novel risk prediction model is classified as high risk by European Society of Cardiology (3).

General Prevention

  • Avoid strenuous exercise (particularly involving burst exertion) and heavy lifting (induces Valsalva maneuver).
  • Maintain hydration to avoid volume depletion.
  • Avoid alcohol.
  • Certain drugs, such as nitrates, digoxin, β-agonists, vasodilators, and diuretics, are best avoided, particularly in the presence of increased LVOT gradient.
  • Implantable cardioverter-defibrillator (ICD) is recommended for patients at high risk for SCD (3)[B],(4)[C].

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