Myocarditis is an inflammatory disease of the heart frequently resulting from viral infections and post-viral immune-mediated responses. The immune reaction in all forms of myocarditis causes structural and functional abnormalities in cardiomyocytes, which causes regional or global contractile impairment, chamber stiffening, or conduction system disease. Dilated cardiomyopathy occurs in 21% of cases of myocarditis. The most frequently identified viruses are parvovirus B19 and human herpes virus 6, with enteroviruses being an important cause is some regions. Other causes of myocarditis include infectious (bacterial, protazoa, lyme), autoimmune (rheumatic, lupus, sarcoidosis, HIV), hypersensitivity (medications), and toxins (medications/heavy metals) . In the developing world Trypanosoma cruzi, and bacterial infections such as diphtheria still contribute to many cases. Trypanosoma cruzi, is a leading cause of myocarditis in rural South and Central America. Post-mortem data identifies myocarditis as the cause of 8-12% of sudden death in young adults. Mortality for myocarditis is 20% at 1 year and 50% at 5 years.
Diagnosis of myocarditis based on the clinical presentation alone is usually not possible. Sub-clinical myocarditis is often encountered during assessment of presentations such as flu-like illness. Tachycardia, tachypnea and fever my be present. Chest pain, dyspnea, palpitations, cardiac arrhythmia, and heart failure can all occur during the course of the disease. Biomarkers (troponin) which lack specificity, may help to confirm the diagnosis of myocarditis. The ECG has low sensitivity for myocarditis. ECG findings may include: nonspecific ST and T wave changes, ST-segment elevation mimicking an acute myocardial infarction, low voltages and AV nodal blocks. QRS duration of ≥120 ms is an independent predictor for cardiac death or heart transplantation.
Cardiovascular magnetic resonance imaging is the main diagnostic tool. Some causes need conformation by endomyocardial biopsy which is considered the diagnostic gold standard. No standard treatment strategies are defined, other than standard heart failure therapy and physical rest. Immunosuppressive and immunomodulating therapies are effective for some types of myocarditis (ie. lupus).