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The term cardiomyopathy is used to indicate myocardial dysfunction
in the absence of an obstructive lesion or sustained hypertension.
Cardiomyopathy is either an isolated abnormality (ie, confined to
the heart) or is associated with a multisystem disorder. Neonates
who have an unrecognized underlying cardiomyopathy may come to medical
attention with a life-threatening response to an otherwise minor
illness. Alternatively, evidence of cardiomyopathy may be noted on
an echocardiogram performed for evaluation of an unrelated problem.
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Mutations in genes encoding multiple proteins of the sarcomere,
cytoskeleton, sarcoplasmic reticulum, nucleus, and cell membrane
of the myocardial cell are now known to cause cardiomyopathy (Figure
9-1). More information regarding the structure and function of these
proteins is available in Chapter 2.
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Classification of cardiomyopathies is problematic and has evolved
as new information has become available regarding causation. Classification
based on phenotype (ventricular morphology and physiology) is practical
in that this information is what is most readily available after
initial evaluation of the patient (Table 9-1). Phenotypic groups
can be subdivided based on etiology (Tables 9-2, 9-3, 9-4). Some
congenital heart defects or systemic hypertension can cause phenotypes
that mimic various forms of cardiomyopathy and are included in text
and tables as they need to be included in the differential diagnosis
when evaluating patients. Phenotypic classification is certainly
not perfect as it does not define causation; moreover, it may be
misleading because some myopathic processes may be classified as
more than one type or may change from one type to another during
the course of the disease.
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