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Myocarditis

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ESSENTIALS OF DIAGNOSIS

  • Heterogenous clinical presentation including chest pain, heart failure, arrhythmias, or cardiogenic shock

  • A viral prodrome may precede the onset of symptoms

  • Elevated cardiac biomarkers

  • Electrocardiogram may be normal or show nonspecific ST changes, atrial or ventricular arrhythmias.

  • Echocardiography demonstrates left ventricular dilation and systolic dysfunction

  • Endomyocardial biopsy reveals cellular infiltrates with associated myocyte damage

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General Considerations

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Myocarditis is an inflammatory disease of the myocardium caused by a wide variety of both infectious and noninfectious agents (Table 25-1). In the developed world, viral infection is thought to be the most common etiology, whereas in developing countries, other etiologies including Chagas disease and rheumatic carditis are also important causes. When cardiac dysfunction develops in the setting of myocarditis, the term inflammatory cardiomyopathy is often used. The formal diagnosis of myocarditis requires endomyocardial biopsy demonstrating typical pathologic changes. However, in practice, the diagnosis is frequently made based on a combination of clinical features, laboratory testing, and imaging.

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Table Graphic Jump Location
Table 25–1.Causes of Myocarditis
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Kindermann  I, Barth  C, Mahfoud  F  et al. Update on myocarditis. J Am Coll Cardiol. 2012;59(9):779–792.
[PubMed: 22361396]  

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Pathophysiology

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The pathophysiology of myocarditis is not fully understood. Animal models of viral myocarditis suggest a three-phase response based on both the initial viral infection and subsequent maladaptive immune-mediated response. During the acute phase, virus enters the myocyte via a specific receptor. Once inside the myocyte, viral replication leads to injury and eventual myocyte necrosis. Myocyte necrosis causes exposure of cellular antigens that activate the host immune system. The initial response is composed of natural killer cells and macrophages, followed by T lymphocytes. This acute phase generally lasts several days and is followed by a subacute phase lasting weeks to months, where host immune reactions predominate. The subacute phase is characterized ...

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