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DILATED CARDIOMYOPATHY: DEFINITION
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Dilated cardiomyopathy (DCM) is a chronic heart muscle disease characterized by “the presence of dilatation and systolic impairment of the left or both ventricles unexplained by abnormal loading conditions or coronary artery disease sufficient to cause the observed myocardial dilation and dysfunction.”1 According to the American Heart Association (AHA) classification, “dilated forms of cardiomyopathy are characterized by ventricular chamber enlargement and systolic dysfunction with normal left ventricular (LV) wall thickness.”2
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In this chapter, DCM is intended as a primary disease of heart muscle. More than 60% of DCMs are proven to be familial diseases with identifiable genetic defects.3,4 Acquired disorders manifesting with the DCM phenotype, or DCM phenocopies (defined as environmentally induced phenotypes mimicking one usually produced by a specific genotype), are sporadic and are categorized as nongenetic DCM. This distinction is essential to separate genetic DCM from acquired, nongenetic, and potentially reversible phenotypes arising from protean causes. The therapeutic options for acquired DCM often differ from those for familial DCM (FDCM). Ischemic heart disease may manifest as, or evolve into, a DCM-like phenotype; it is discussed further in Chap. 43.
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In its descriptive definition, DCM represents the end phenotype of heart muscle damage induced by different causes; the disease mechanisms are increasingly being identified by the implementation of molecular and genetic assays for patients and families, high-resolution and functional imaging, and novel biomarkers. In this end stage, most DCMs look phenotypically alike (Fig. 58–1). Intermediate phenotypes are manifest by borderline, persistent LV dilation and/or dysfunction and may present with arrhythmias and/or conduction disease, now recognized as “early DCM.”5 In genotyped families, the preclinical phase of the disease can be diagnosed in phenotypically healthy, but genetically affected, relatives of probands with DCM. Therefore, DCM can be grouped mechanistically as genetic and nongenetic.
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