Hypertrophic cardiomyopathy (HCM) is known by other terms, including idiopathic hypertrophic subaortic stenosis and asymmetrical septal hypertrophy. This disorder is best described as hypertrophic cardiomyopathy and is defined by a hypertrophied, nondilated left ventricle. In 95 percent of cases, the septum is asymmetrically enlarged, but the free wall of the ventricle is also hypertrophied. The atrium is typically enlarged, and the mitral valve is thickened. Only one-fourth of patients with this disorder have a ventricular outflow obstruction sufficient to cause symptoms; therefore, idiopathic hypertrophic subaortic stenosis incompletely describes this disorder. This disease is discussed in Chapter51, "Cardiomyopathies, Myocarditis, and Pericardial Disease," and is mentioned here only to aid in its differentiation from valvular aortic stenosis.
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