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The myocardium can be affected by inflammatory (infectious or
immune-mediated), metabolic, infiltrative, ischemic, or primary disease
processes. These disorders may be inherited and may have significant
overlap (eTable 489.1). Myocardial diseases
may present acutely, with signs of congestive heart failure that
include tachypnea, often with rales; tachycardia; an enlarged but
quiet heart; soft heart sounds that may have a tic-tac rhythm; cardiac
gallops; and either no murmurs or systolic murmurs of mitral or
tricuspid regurgitation. Alternatively, they may present chronically
with failure to thrive, decreased exercise tolerance, and more subtle
findings of heart failure. Occasionally, the predominant process
may be an arrhythmia, either atrial or ventricular tachycardia/fibrillation,
or heart block. These present clinically with palpitations, syncope,
or sudden death. The electrocardiogram and chest x-ray are useful
in confirming the presence of heart disease, but are rarely diagnostic.
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In acute presentations, the chest x-ray usually shows diffuse
cardiac enlargement, passive pulmonary congestion, and interstitial
edema; the electrocardiogram shows normal or ...