Incidence and predictors of major arrhythmic events following acute myocarditis complicated by ventricular arrhythmias: a systematic review and meta-analysis

Background Acute myocarditis (AM) complicated by ventricular arrhythmias (VA) account for up to 9% of AM presentations, yet their epidemiology and prognosis remain incompletely defined. The risk of VA recurrence after discharge is still unclear, with predictors poorly established, complicating risk stratification and implantable cardioverter-defibrillator (ICD) decision-making. Purpose To assess the incidence and predictors of major arrhythmic events (MAE) during follow-up in patients with sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) in the acute phase of AM. Methods This systematic review and meta-analysis was registered in PROSPERO. PubMed, Web of Science, and Cochrane Library were searched up to December 2024 for studies reporting post-discharge VA recurrence in AM. Additional unpublished data were obtained from study authors to restrict analysis to sustained VT and VF at presentation or before discharge from index hospitalization for AM. The primary outcome was MAE at follow-up, defined as documented sustained VA, appropriate ICD therapy or sudden cardiac death. Pooled recurrence rates and predictors were assessed using random-effects models. Results After 1652 records identified, 27 full-text articles were assessed for eligibility and 8 studies met inclusion criteria. A total of 355 patients were included in the analyses. Additional data were obtained from the authors of 6 out of the 8 studies. The pooled incidence of MAE was 46.4% (95% CI 38.1-54.9; I²=50.0, Figure 1) during a mean pooled follow-up of 3.8 years (95% CI 2.7–5.1). The reconstructed pooled Kaplan-Meier curve for MAE-free survival is shown in Figure 2. Neither demographic factors (age, sex) nor ICD implantation prior to discharge were significantly associated with MAE at follow-up. Reduced left ventricular ejection fraction, using cut-offs of 50% and 35% were not predictive, with respective RRs of 1.22 (95% CI 0.86-1.74) and 1.38 (95% CI 0.82-2.33). The presence of late gadolinium enhancement on cardiac magnetic resonance was also not predictive of MAE, with a RR of 1.00 (95% CI 0.52-1.94), regardless of its anteroseptal or inferolateral localization. VT as initial arrhythmia was not associated with an increased risk of MAE recurrence in comparison to VF as initial arrhythmia (RR 1.61, 95% CI 0.88-2.95). Traditional cardiovascular risk factors—including hypertension, diabetes, and dyslipidemia—did not influence recurrence. Conclusion MAE recurrences in AM affect nearly half of patients with sustained VA during the acute phase of AM. However, no single clinical, imaging, or demographic factor consistently predicted recurrence. These findings highlight the complexity of risk stratification and support 2025 ESC recommendations to consider ICD implantation after a first sustained VA episode in the acute phase of myocarditis.