Cardiac magnetic resonance (CMR) has emerged as a reference for the non-invasive 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 at 12 months after infarct-like myocarditis.

All patients with acute myocarditis confirmed by CMR [i.e. typical non-ischemic late gadolinium enhancement (LGE)] were prospectively included from 2012 to 2018 at Dijon University Hospital. CMR was performed<7 days following symptom onset, at 3 months and 1 year after the acute event. FU included ECG, cardiac stress test, Holter recording, biological assessments, medical history and a QoL questionnaire. Patients were classified according to complete healing at CMR.

In total, 111 patients were included. At one year, 59 patients (53%) exhibited persistent myocarditis on CMR. The predominant location of LGE was inferolateral in 76% of the patients. 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. We found minor ventricular dysrhythmia at one year and especially a cardiac death in the FU. These results thus highlight the importance of maintaining long-term FU in patients with infarct-like myocarditis, and may lead to modifications in the clinical and therapeutic management of acute myocarditis in routine practice.