[Contribution of cardiac MRI in the initial evaluation and follow-up of myocarditis mimicking acute coronary syndrome: a series of 43 patients]

Aims: The diagnosis of acute myocarditis is complex, especially when the clinical presentation mimics an acute coronary syndrome. This condition may promote the progression to dilated cardiomyopathy and the occurrence of severe arrhythmias. A reassessment integrating a cardiac MRI at three months after the acute episode could help identify patients with a poor prognosis.

Patients and results: This prospective series of 43 consecutive patients hospitalised for acute myocarditis included 36 men and seven women, with a mean age of 32 years, with no indication of heart failure. All patients presented elevated levels of troponin I. Echocardiography showed moderate left ventricular dysfunction in six cases and segmental wall motion abnormalities in 22 cases. After gadolinium injection, a subepicardial late enhancement was observed in 39 cases. Three months after the acute episode, all patients were asymptomatic. The echocardiography and laboratory tests were normal. In 23 cases, the MRI showed persistence of the late enhancement without segmental wall motion abnormality. After a mean follow-up of three years, one patient was lost to follow-up and only one suffered a heart failure revealing a dilated cardiomyopathy complicated by ventricular arrhythmias.

Conclusion: On admission, the subepicardial localisation of late enhancement in the cardiac MRI is reliable criteria for the diagnosis of acute myocarditis, enabling to rule out an acute coronary syndrome. During follow-up, the persistence of late enhancement has no impact on prognosis. In this series, after a mean follow-up of three years, it was not associated with clinical or paraclinical abnormalities, except in one patient.