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Cardiomyopathy is generally defined as a “disease of the myocardium associated with cardiac dysfunction.”1 Primary cardiomyopathies are divided into four major classifications: (a) dilated cardiomyopathy (DCM), (b) hypertrophic cardiomyopathy (HCM), (c) restrictive (or infiltrative) cardiomyopathy (RICM), and (d) miscellaneous group including left ventricular non-compaction (LVNC), arrhythmogenic right ventricular dysplasia (AVRD), and Tako-tsubo cardiomyopathy. Each of the primary cardiomyopathies has distinctive morphological and functional characteristics even though they may present clinically in a similar fashion. The etiology of primary or idiopathic cardiomyopathies is not attributable to another systemic disease process. Alternatively, primary cardiomyopathies refer to primary diseases of the heart muscle (Table 14–1).
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The incidence of cardiomyopathy is less than 1% in the general population, with DCM representing the vast majority of cases.2 Hypertrophic cardiomyopathy is less prevalent, while RICM, LVNC, and AVRD are the least common. The incidence of cardiomyopathy varies depending on a number of factors including diagnostic testing, the type of institution reporting the data, and the referral patterns. When all cardiomyopathies are considered, the incidence varies depending on the prevalence of cardiac pathology associated with coronary artery disease, valvular pathology, systemic hypertension, and a host of other systemic pathophysiologic conditions. Accurate diagnostic assessment of patients suspected of having a cardiomyopathy is important to establish prognosis and to institute appropriate treatment. This chapter focuses on salient echocardiographic features of primary cardiomyopathies, but also includes discussion and description of non-primary cardiomyopathies for completeness.
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Etiology and Clinical Presentation
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Dilated cardiomyopathy (DCM) accounts for 60% of all cardiomyopathies and is defined as an intrinsic myocardial disease process characterized by progressive myocyte hypertrophy, dilation, and contractile dysfunction of one or both ventricles.1,3,4 Although ventricular wall thickness can be increased, the degree of hypertrophy is proportionally less compared to the amount of dilatation.5 The development of left ventricular (LV) hypertrophy is initially beneficial in reducing systolic wall stress, a major determinant of myocardial oxygen consumption. However, wall stress is never fully normalized and eventually stimulates LV remodeling, resulting in a reduced ejection fraction (EF) as the ventricle continues to dilate and assume a spherical shape.6 The combination of apoptotic and necrotic cell death, myocardial fibrosis, and cytoskeletal uncoupling contributes to eventual myocardial mechanical failure. In contrast to hypertrophic and restrictive cardiomyopathies, which often present with normal end-diastolic volumes and preserved or increased EF, DCM is defined by ...