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Hypertrophic cardiomyopathy (HCM) is characterised by idiopathic hypertrophy of the left ventricle (LV), sometimes accompanied by hypertrophy of the right ventricle. HCM is estimated to occur in 1:500 subjects in the general population.1 The disease is inherited as an autosomal dominant trait, but about 50% of the patients do not have relatives with HCM, suggesting sporadic mutations, unidentified genes or more complex patterns of heredity. The presentation of the disease is diverse with on the one hand asymptomatic subjects diagnosed through family screening or routine clinical examination, and on the other hand severely symptomatic subjects with impaired LV systolic function. Patients may also present with sudden cardiac death (SCD). The distribution of hypertrophy is also variable; the most common pattern is asymmetrical septal hypertrophy, but other LV morphologies are seen including concentric hypertrophy, apical hypertrophy, and hypertrophy of the LV free wall. About one quarter of patients have obstruction of the left ventricular outflow tract (LVOT); less commonly, dynamic obstruction may occur in the mid LV cavity or at the right ventricular (RV) outflow tract.2 3
Microscopy, macroscopy, and pathophysiology
Microscopy demonstrates a variety of abnormalities, including myocyte hypertrophy, myocardial fibre disarray (myocytes are not in parallel but lay chaotically intersected), interstitial and perivascular fibrosis, and intimal and medial hypertrophy in intramural arteries leading to narrowing of the microcirculation. These abnormalities are thought to contribute to LV diastolic dysfunction by impairing relaxation and reducing compliance as well as to scarring of the myocardium. Fibrosis and scarring may predispose to ventricular and atrial arrhythmias. Elevated left atrial and LV end diastolic pressures lead to reduced stroke volume, reduced cardiac output, and pulmonary congestion. The cardiomyopathic abnormalities are not confined to the (mostly septal) hypertrophic ventricular segments, and can be demonstrated in non-hypertrophied myocardium. Many patients show diffuse hypertrophy of the LV; in about …
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