MYOCARDITIS is an inflammation affecting the myocardium. The diverse clinical presentations make the diagnosis challenging, and the pathophysiology is not well understood.

Patients with myocarditis may be asymptomatic and do not seek medical treatment. It can be easily mistaken for acute coronary syndrome because of similar symptomatology and is often diagnosed by exclusion of other cardiac diseases. A wide variety of triggers, including infectious and non-infectious agents, can result in myocarditis, with viral infection being the most common cause of the disease.

The majority of patients recover spontaneously; however, infrequently, patients may develop acute heart failure, chronic dilated cardiomyopathy or sudden death. 1 Cardiac magnetic resonance( CMR) is a non-invasive imaging method that

forms the backbone of the diagnostic workup. Endomyocardial biopsy( EMB) incorporating the histological Dallas criteria still plays an important role in the diagnosis of myocarditis.

Despite its low complication rates, the latter is not commonly performed on account of the invasiveness of the procedure and the relatively low diagnostic yield. Treatment of myocarditis is mainly supportive.

Definitions Myocarditis The World Heart Federation Expert Committee( 1997) defined myocarditis as a“ process characterised by an inflammatory infiltrate of the myocardium. In acute myocarditis, necrosis and / or degeneration of adjacent myocytes is required, whereas in chronic myocarditis, necrosis is not an obligatory feature”. 2

The European Society of Cardiology Working Group on Myocardial and Pericardial Diseases adopts the definition of myocarditis from the WHO / International Society and Federation of Cardiology:“ An inflammatory disease of the myocardium diagnosed by established histological, immunological and immunohistochemical criteria.” 3

According to the histological Dallas criteria, the presence of myocyte necrosis and / or degeneration with an inflammatory infiltrate adjacent to these myocytes is required to establish the diagnosis. 4

As for the immunohistochemical criteria, the definition of abnormal inflammatory infiltrate is proposed to consist of greater than or equal to 14 leucocytes / mm 2, including up to four monocytes / mm 2 with the presence of CD3 positive T-lymphocytes greater than or equal to seven cells / mm 2 contained within

cardiacmyocytes. 3 When myocarditis is associated with cardiac dysfunction, it is categorised as inflammatory cardiomyopathy.

Viral myocarditis Myocarditis with histological evidence and positive viral PCR is classified as viral myocarditis.

Autoimmune myocarditis In the subgroup of autoimmune myocarditis, viral PCR analysis is negative on myocardium, with or without serum cardiac autoantibodies. 3

Fulminant myocarditis Fulminant myocarditis is myocarditis with signs of acute heart failure, cardiogenic shock or life-threatening rhythm disturbances.

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