Cardiac Magnetic Resonance (CMR) has emerged as a reference tool for the diagnosis of myocarditis but its role in follow-up (FU) after the acute event is unknown. The objectives of our study were to assess the evolution of CMR parameters between the acute phase of infarct-like myocarditis and 12months thereafter, and to identify the predictive factors of persistent myocarditis at one year and the long-term prognosis of this infarct-like form.

All patients with infarct-like acute myocarditis confirmed by CMR were included from April 2012 to January 2018 in this prospective study at Dijon University Hospital. CMR was performed within 7days following symptom onset, at 3months and one year after the acute event. One-year FU included ECG, a cardiac stress test, Holter recording, biological assessments and medical history. Patients were classified according to the presence or absence of complete healing at one-year, based on the CMR evaluation.

One hundred and eleven patients were included. At one year, 59patients (53%) exhibited persistent myocarditis on CMR. The baseline predictive factors of persistent myocarditis at one year were a higher troponin peak (3,8 ug/L vs. 9,3 ug/L, P<0,001) and a higher initial extent of LGE based on CMR “SQS score” (4,41 vs. 8,82, P<0,001). On clinical FU, one patient experienced cardiac death before the one-year CMR control and had precisely persistent myocarditis at three months. Moreover, patients with persistent myocarditis were more likely than patients with complete recovery to have premature ventricular contractions during the cardiac stress test (25% versus 7%, P=0.014).

Less than 50% of patients with infarct-like acute myocarditis showed complete healing at one year and one patient experienced cardiac death. These results thus highlight the importance of maintaining long-term FU in patients with infarct-like myocarditis.