Myocarditis is an inflammatory disease of the myocardium. Although associated with a number of infections and systematic diseases, myocarditis is most frequently the result of a viral infection, with coxsackievirus B and echovirus being the most frequently implicated infectious agents.
However, any virus may replicate in the heart and induce myocardial inflammation. The true incidence of this disease is unknown because most cases resolve spontaneously and never reach medical attention. However, myocardial involvement has been re-ported to occur in 1% to 5% of patients with acute viral infections.
Myocardial damage is believed to be secondary to direct viral invasion of the myocytes, as well as to the immunologic response to the infection. Initially, replication of the virus in the myocytes leads to cell damage and death. At this early phase, the virus is eliminated primarily by humoral and cell-mediated immune processes,and, in most cases, myocardial inflammation promptly resolves. If this initial immune response fails to clear the viral agent, it has been hypothesized that an autoimmune response directed against the myocardium may be triggered, leading to further myocardial inflammation and injury. The clinical presentation of myocarditis is quite variable. Many patients are asymptomatic and will have complete resolution of the myocarditis without complications. others may present with nonspecific complaints typical of a viral syndrome, such as fever, malaise, and myalgias. Pleuritic chest pain secondary to pericardial inflammation is common, although some patients may have typical of myocardial ischemia.
If cardiac dysfunction is present ,patients may present with symptoms of congestive heart failure and, instances, cardiogenic shock. Life-threatening arrhythmias can occur in patients with myocarditis even in the presence of preserved left ventricular systolic function. On physical examination, patients are often tachycardic.