REVIEW – February 2007

Viral myocarditis, contemporary diagnostic methods

Authors: Kristin Lamp, Vello Sõgel

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Myocarditis is an elusive illness to study, diagnose and treat, as its clinical presentation may range from nearly asymptomatic to heart failure (dilate cardiomyopathy). Myocarditis in defined as inflammatory changes in the heart muscle and it is characterized by myocyte necrosis. Viral myocarditis is the most common form of myocarditis. A number of cardiotropic viruses have been identified as causative factors of myocarditis. Among them the most common are Coxsackie – adenovirus (A, B), influenza virus (A, B) Epstein – Barr virus, cytomegalovirus, herpes simplex virus, parvovirus B19 and HIV. In the initial stage of viral infection cytotoxic necrosis of myocytes develops due to uptake of viral RNA without appearance of the interstitial infiltrate. Classical, histologically apparent infiltration of mononuclear cells in the myocardial tissue develops in 4-14 days. Tumor necrosis factor, T-lymphocytes and antiviral antibodies are activated for eliminating the virus from the tissue.
In the chronic phases the deleterious effects of either inadequate or inappropriately strong immune response can lead to hazardous long term sequelae of dilate  cardiomyopathy and heart failure.
The clinical diagnosis of myocarditis is usually based on clinical findings and/or laboratory tests (cardiac enzyme and cardiac tropin levels). In severe acute cases cardiac catheterization is necessary to differ entiate the inflammatory process from the ischemic damage of the heart. Echocardiography can reveal oedema of the heart tissue, systolic and diastolic dysfunction and changes of myocardical contractility function.
Endomyocardial biopsy is traditionally considered a diagnostic procedure of choice, however, it is an invasive method and has definite limitations. MRI, a nonivasive method involving use of a contrast medium, has been shown to have sensitivities and specificities approaching 100 % for diagnosis. The findings of MRI correspond almost entirely to histological findings.
The paper present two cases of viral myocarditis and demonstrates the sensitivity of MRI for appropriate diagnosis.