Myocarditis and Dilated Cardiomyopathy

Myocarditis, inflammation of the heart muscle, is a prominent cause of heart failure, especially in children and young adults. It can be genetic in origin, the consequence of exposure to a drug or toxin, or a sequela of infection. The possible infectious agents include protozoa, bacteria, and viruses. A number of viruses have been implicated, especially enteroviruses and adenoviruses. During or following the infection, some individuals develop evidence of autoimmunity in the form of heart-specific antibodies and T cells. The autoimmune phase of the disease can be mimicked by direct immunization with cardiac antigens, including myosin heavy chain and troponin. The clinical diagnosis of myocarditis remains a challenge and definitive diagnosis often depends upon findings at autopsy or biopsy. Dilated cardiomyopathy is a chronic form of heart disease involving dilatation, especially of the left ventricle and often leading to congestive heart failure. It may be a sequela of myocarditis. The disease has a high case fatality rate. Investigations of the pathogenesis of viral and immune-mediated myocarditis and dilated cardiomyopathy have benefited from the development of experimental models in the mouse and rat. The disease can be reproduced in genetically selected hosts by infection with a cardiotropic virus or by immunization with an appropriate cardiac antigen.