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- 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
- ≥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 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).
- 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].