Viral myocarditis: Balance between viral infection and immune response

Myocarditis is an inflammatory disorder of the heart muscle, and is often underdiagnosed in clinical practice. It presents more dramatically in the young with acute heart failure and more insidiously in adults with chronic dilated cardiomyopathy. The etiology is most often viral in North America, with a wide spectrum of natural history. The majority of patients recover spontaneously, but those with persistent ventricular dysfunction face a 20% one-year mortality. Myocarditis initiates as viral disease, and molecular techniques have confirmed viral persistence. The immune response follows as a two-edged sword - both inadequate and excessive immune responses lead to disease. Finally, the myocyte is the target of the above processes, and expresses molecular, cytokine and vascular changes that lead to dilated cardiomyopathy and heart failure. The gold standard for diagnosis still relies on the overly strict Dallas criteria for evaluating myocardial biopsies. Molecular techniques are playing an increasingly important role in both diagnosis and prognosis. Clinical suspicion is still the key towards an early diagnosis. Treatment must be early and persistent - generally supportive initially, with immunosuppression now playing a secondary role in temporizing those with exuberant immune response. Newer treatments for dilated cardiomyopathy such as amlodipine and carvedilol are equally appropriate for postmyocarditis patients. Future treatment may involve specific biological agents, immune therapy, antiviral strategies and molecular gene therapy.