**3.3 Clinical classification**

Myocarditis is clinically classified as acute or chronic. Since it is possible to detect the exact onset of acute myocarditis, it is easier to estimate the circulatory parameters for diagnosis and establish the strategy for treatment of acute myocarditis than for chronic myocarditis. In some cases of acute myocarditis, we treat it as fulminant myocarditis that has developed suddenly and may progress to severe circulatory failure during the acute phase (Aoyama et al., 2002). The worldwide morbidity and mortality rates associated with fulminant myocarditis are not yet clear. Cupta et al. (2008) reported that the frequency of fulminant myocarditis is 10% among all cases of acute myocarditis in the United States.

The global concept of chronic myocarditis has not been established, although several studies have suggested that viral infection (Fujioka et al., 2000) or autoimmunity (Lauer et al., 2000) play a role in its development. There are clinically two types of chronic myocarditis, and they have different clinical courses. One type has persistent, continuous symptoms, and the other has unremarkable symptoms (JCS, 1996).

In an investigation of clinical types of myocarditis in 48 patients reported by Kodama et al. (2001), nine were the acute type, 21 were the fulminant type, three were the chronic persistent symptom type, and 15 were the chronic unremarkable symptom type. The mortality rates during the first admission were 22% for the acute type, 43% for the fulminant type, 33% for the chronic persistent symptom type, and 40% for the chronic unremarkable symptom type. The long-term prognosis for patients who recovered from their cardiac dysfunction during the early phase was good. However, the long-term prognosis for patients who were diagnosed with the chronic, unremarkable symptom type was not good because they developed irreversible circulatory dysfunction, such as dilated cardiomyopathy.
