Viral heart disease: molecular diagnosis, clinical prognosis, and treatment strategies.

Myocarditis is considered as a potent predisposing factor for dilated cardiomyopathy (DCM). Molecular biological proof of viral genome and immunohistochemical evaluation of intramyocardial inflammation are substantial in the identification and diagnosis of this pathological condition. Viruses are generally thought to be the common causative agents that trigger myocarditis and, therefore, several investigations are indispensable for the detection of viral genome in the myocardium in diagnosing viral myocarditis. The era of molecular diagnosis for viral myocarditis began with the establishment of the slot blot hybridization technique for the detection of viral genome in endomyocardial biopsy specimens. Due to inherent technical inadequacies, this method soon was replaced by in situ hybridization and polymerase chain reaction (PCR). Although in situ hybridization combines both morphological and molecular diagnosis, difficulty in standardization, possibility of nonspecific hybridization, and focal viral infection have led PCR to be an ideal molecular diagnostic strategy for the detection of viral myocarditis. Despite controversies over the specificity of this technique, several studies have substantiated the use of PCR in virological diagnosis. The ability to detect the state of viral replicative activity by demonstrating the presence of enteroviral minus-strand RNA has added a new dimension to studies on viral etiology of myocarditis and DCM. Advances in molecular diagnosis have indicated beyond doubt that persistence of viral infection is associated with disease deterioration and poor prognosis. Viral etiology of myocarditis and its contribution to the development of DCM have suggested antiviral therapy for myocarditis and DCM patients with proven viral infection.