Acute myocarditis is associated with cardiac arrhythmia in 25% of cases; a third of these arrhythmias are ventricular tachycardia (VT) or ventricular fibrillation (VF). The implantation of a cardiac defibrillator (ICD) following sustained ventricular arrhythmia remains controversial in these patients.

We sought to assess the risk of major arrhythmic ventricular events (MAE) over time in patients implanted with an ICD following sustained VT/VF in the acute phase of myocarditis compared to those implanted for VT/VF occurring on myocarditis sequelae.

Our retrospective observational study included patients implanted with an ICD following VT/VF during acute myocarditis or VT/VF on myocarditis sequelae, from 2007 to 2017, in 15 French university hospitals. MAE was defined as any appropriate intervention of the defibrillator (antitachycardia pacing or shock) on VT/VF.

Over a median follow-up period of 3 years, 11(39%) patients of the acute myocarditis group and 24(60%) patients of the myocarditis sequelae group experienced one or more MAE. Kaplan–Meier MAE rate estimates at one and three years follow-up were 19% and 45% in the acute group, and 43% and 64% in the sequelae group, respectively. There was no significant difference in the number or type of MAEs in the two groups.

Patients who experienced sustained ventricular arrhythmias during acute myocarditis had a very high risk of VT/VF recurrence during follow-up. These results challenge current guidelines for ICD implantation in acute myocarditis associated with VT/VF by showing that the risk of MAE recurrence remains high after the resolution of the acute episode.