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MYOCARDITIS

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.

General Considerations

Myocarditis is an inflammatory disease of the myocardium caused by a wide variety of both infectious and noninfectious agents (Table 25–1). Viruses are the most common etiology but other infectious agents including bacteria (such as Borrelia spp.), protozoa (such as Trypanosoma cruzi), and fungi can also lead to myocarditis. Myocarditis can also be induced by a variety of toxic substances, medications, and systemic immune-mediated diseases. The incidence of myocarditis has increased recently due to (1) reports of acute and chronic/recurrent myocarditis among severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infected and recovering individuals and (2) the widespread use of immune checkpoint inhibitors (ICIs) for first-line treatment of numerous cancers, which although effective, can lead to off-target immune-related adverse events including myocarditis. When cardiac dysfunction develops in the setting of myocarditis, the term inflammatory cardiomyopathy is often used. The formal diagnosis of myocarditis requires endomyocardial biopsy (EMB) demonstrating typical pathologic changes. However, in practice, the diagnosis is frequently made based on a combination of clinical features, laboratory testing, and imaging.

Table 25–1.Causes of Myocarditis
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Tschöpe  C, Ammirati  E, Bozkurt  B,  et al. Myocarditis and inflammatory cardiomyopathy: current evidence and future directions. Nat Rev Cardiol. 2021;18:169–193.
[PubMed: 33046850]  

Pathophysiology

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. ...

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