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ABSTRACT

  • Hypertrophic cardiomyopathy is a primary disorder of ventricular muscle characterized by myocardial and myocyte hypertrophy. Disease penetrance and clinical manifestations vary considerably; some affected individuals lack symptoms, but most develop angina, dyspnea, and exercise intolerance. Sudden death, heart failure, and thromboembolic events account for the significant morbidity and mortality of hypertrophic cardiomyopathy.

  • Clinical diagnosis is based on family history, physical exam, electrocardiogram, and two-dimensional echocardiography demonstrating unexplained ventricular hypertrophy (wall thickness >13 to 15 mm in the absence of confounding factors such valvular heart disease or hypertension).

  • Hypertrophic cardiomyopathy can occur as isolated (sporadic) disease, but most often is inherited as an autosomal dominant trait (termed familial hypertrophic cardiomyopathy).

  • Cardiac pathology demonstrates increases in myocardial mass, predominantly affecting the left ventricle. Although a variety of morphologic forms of hypertrophy are recognized, asymmetric involvement of the septum is most common. Histologic findings include enlarged disorganized myocytes (disarray) interspersed with connective tissue and fibrosis.

  • The pathophysiology of hypertrophic cardiomyopathy is characterized by normal or hyperdynamic systolic function and impaired diastolic performance. Subaortic outflow tract gradients, systolic motion of the anterior mitral valve leaflet, and mitral regurgitation occur in a subset of affected individuals.

  • Familial or sporadic hypertrophic cardiomyopathy is caused by mutations in one of eight different sarcomere protein genes: cardiac actin; β-cardiac myosin heavy chain; α-tropomyosin; cardiac troponin T; cardiac troponin I; essential myosin light chain; regulatory myosin light chain; and cardiac myosin-binding protein C. At least one other disease gene (mapped to chromosome 7) remains unknown.

  • Distinct genetic etiologies of hypertrophic cardiomyopathy account for some of the variable clinical findings of disease, including age of onset of hypertrophy and survival.

  • Hypertrophic cardiomyopathy mutations rarely produce null alleles, but rather encode mutant polypeptides that are likely to be incorporated into sarcomeres. The predominant mechanism by which disease alleles perturb cardiac function therefore appears to be through dominant negative actions by mutant polypeptides.

  • Hypertrophic cardiomyopathy mutations have been genetically engineered into animals to produce relevant models for exploring the mechanisms of disease and consequences of protein mutations on sarcomere structure and function.

OVERVIEW

Hypertrophic cardiomyopathy is a primary disorder of the myocardium characterized by an increase in heart mass (hypertrophy) that particularly affects the left ventricle (Fig. 257-1). This pathology was initially described more than 100 years ago,1 and since then a multiplicity of descriptive names have been appended to the disease, including idiopathic subaortic stenosis, asymmetric septal hypertrophy, and hypertrophic obstructive cardiomyopathy. A modern approach to hypertrophic cardiomyopathy began when the heritable nature of the disease was recognized2 and familial transmission defined as autosomal dominant. The development and widespread use of cardiac echocardiography over the past 25 years has, however, substantially increased clinical awareness of this disease. Current estimates indicate an incidence of hypertrophic heart disease in 1 per 500 individuals,3 but the fraction caused by heritable gene mutations is unknown. In addition to familial disease, isolated cases of hypertrophic cardiomyopathy ...

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