A similar relationship was found between a left ventricular ejection fraction < 50%, increased mortality, and increased major adverse cardiovascular events.Myocarditis has been reported to be a major cause of sudden cardiac death (SCD) in infants, adolescents, and young adults, but the reported rates show wide variation (1 to 14 percent) among young people depending on differences in SCD definition and classification/ definition of myocarditis post-mortem as well as inhomogeneity in the study populations. And one has also to distinguish between studies about myocarditis in general and fulminant myocarditis. Epidemiology
The exact incidence of myocarditis is unknown since many cases are not associated with any symptoms. However, in series of routine autopsies, 1–9% of all patients had evidence of myocardial inflammation. The prevalence rate of myocarditis is estimated to be about 22 cases per 100,000 persons annually. Fulminant myocarditis, the most severe subtype, has been shown to occur in up to 2.5% of known myocarditis presentations. When looking at different causes of myocarditis, viral infection is the most prevalent, especially in children; however, the prevalence rate of myocarditis is often underestimated since the condition is easily overlooked. Viral myocarditis being an outcome of viral infection depends heavily on genetic host factors and the pathogenicity unique to the virus. If one tests positive for an acute viral infection, clinical developments have discovered that 1-5% of said population may show some form of myocarditis.In regard to the population affected, myocarditis is more common in pregnant women, children, and those who are immunocompromised.
Diagnosis
Myocarditis refers to an underlying process that causes inflammation and injury of the heart. It does not refer to inflammation of the heart as a consequence of some other insult. Many secondary causes, such as a heart attack, can lead to inflammation of the myocardium and therefore the diagnosis of myocarditis cannot be made by evidence of inflammation of the myocardium alone.Myocardial inflammation can be suspected on the basis of electrocardiographic (ECG) results, elevated C-reactive protein (CRP) and/or erythrocyte sedimentation rate (ESR), and increased IgM (serology) against viruses known to affect the myocardium. Markers of myocardial damage (troponin or creatine kinase cardiac isoenzymes) are elevated.The ECG findings most commonly seen in myocarditis are diffuse T wave inversions; saddle-shaped ST-segment elevations may be present (these are also seen in pericarditis).The gold standard is the biopsy of the myocardium, in general done in the setting of angiography. A small tissue sample of the endocardium and myocardium is taken and investigated. The cause of the myocarditis can be only identified by a biopsy. Endomyocardial biopsy samples are assessed for histopathology (how the tissue looks like under the microscope): myocardial interstitium may show abundant edema and inflammatory infiltrate, rich in lymphocytes and macrophages. Focal destruction of myocytes explains the myocardial pump failure. In addition samples may be assessed with  immunohistochemistry to determine which types of immune cells are involved in the reaction and how they are distributed. Furthermore, PCR and/or RT-PCR may be performed to identify particular viruses.