Overview

Myocarditis is a distinct clinical entity with a wide variety of cardiac manifestations including heart failure (HF). Potential etiologies may include toxins, medications, physical agents and, most importantly, infections. The most common forms appear to be postviral in origin. The pathophysiology of myocarditis has been well established in animal models with myocardial damage due not only to direct infection, but also consequent to postinfectious, autoimmune-mediated myocardial inflammatory damage. In humans, ongoing myocardial inflammation may result in dilated cardiomyopathy, restrictive cardiomyopathy, or acute left ventricular (LV) failure without dilatation (fulminant myocarditis).

Myocarditis is histologically characterized by both an active inflammatory cellular infiltrate within the myocardium and associated myocyte necrosis (the Dallas pathologic criteria).1 Although many clinicians and pathologists consider the Dallas criteria too restrictive, this classification has established uniform histologic criteria for diagnosis and has substantially reduced the wide variation in reported rates of this disease. While the inflammatory infiltrate is lymphocytic in more than 90% of cases, eosinophilic infiltration or giant cell formation may occasionally be seen. The clinical features of myocarditis are extremely varied, ranging from asymptomatic electrocardiographic abnormalities observed during viral Coxsackie B outbreaks in the community to severe dilated cardiomyopathy with fulminant HF leading to transplantation or death.2 Myocarditis may also cause ventricular arrhythmias or heart block or mimic acute myocardial infarction.3-4 Both acute and chronic dilated cardiomyopathies may result from inflammatory heart disease. The histologic differentiation of myocarditis from idiopathic dilated cardiomyopathy remains problematic, because several published series suggest no difference in long-term prognosis, regardless of the presence or absence of myocardial inflammation.5,6 Nonetheless, many clinicians believe that myocarditis is a potentially reversible form of cardiomyopathy and continue to perform endomyocardial biopsy searching for its presence.

Controversy continues to surround the best approach to the management of patients considered to have myocarditis. The following recommendation is based on a review of available data from uncontrolled and controlled evaluations of immunomodulatory therapy for the treatment of myocarditis.