Myocarditis can potentially cause sudden cardiac death. However, there are few data on the long-term rhythm risk in these patients and the last guidelines do not recommend any specific follow-up (FU). We assessed the occurrence of cardiac rhythm disorders at the acute phase and one-year after “infarct-like” myocarditis.

All patients with infarct-like acute myocarditis confirmed by CMR (with typical non-ischemic late gadolinium enhancement (LGE)) were included from April 2012 to January 2017 in this prospective single-center study at Dijon University Hospital. CMR was performed within 7 days following symptom onset, at 3 months and one year after the acute event. One-year FU included a rhythmic evaluation with ECG, a cardiac stress test and Holter recording.

Eighty-five patients were included. Cardiac monitoring showed that 10% of these patients had rhythm events in the acute phase, essentially premature ventricular contractions (PVC) and non-sustained ventricular tachycardia. At one year, 44 patients (52%) exhibited persistent myocarditis on CMR. Patients with persistent myocarditis were more likely than patients with complete recovery to have PVC during the cardiac stress test (31% versus 6%, P=0,006). In most of the patients with cardiac stress PVC, the PVC originated from the site of the persistent inflammation on the CMR (64%). On the 24–hour Holter monitor, the PVC burden was not different among groups with or without persistent myocarditis at one year (221±704 PVCs vs. 86±53 respectively, P=0.398). It was not found serious ventricular or atrial arrhythmia, neither on cardiac stress test, nor on Holter recording.

Although no serious rhythm disorders were found, ventricular dysrhythmias are frequent in patients one year after “infarct like” acute myocarditis, especially in those without complete recovery on CMR. This work highlights the importance of maintaining long-term FU in these patients, most of whom have normal LVEF.