Myocarditis

DEFINITION
Inflammation of the heart muscle, often caused by infectious agents affecting the myocytes, interstitium, vascular elements, or pericardium.
Viral, bacterial, rickettsial, fungal, and protozoal diseases are all associated with myocardial inflammation (i.e., myocarditis).
Pharmacologic agents (e.g., doxorubicin) can also be causative.

PATHOPHYSIOLOGY
Mechanisms—toxin production, direct invasion of myocardial tissue, and immune-mediated myocardial damage; vasculitis associated with systemic disease; allergic reactions and direct myocyte damage caused by pharmacologic agents. Protozoa (e.g., Trypanosoma cruzi) lead to granulomatous myocarditis; viral myocarditis is associated with cell-mediated immunologic reactions.
Myocardial involvement may be focal or diffuse. Clinical manifestations depend on the extent of the lesions. Diffuse, severe involvement may lead to global myocardial damage and CHF; discrete lesions involving the conduction system may cause profound arrhythmias.