Associated factors for in-hospital mortality in patients with fulminant myocarditis: a systematic review and meta-analysis

Background Fulminant myocarditis (FM) progresses rapidly and carries high all-cause in-hospital mortality. Patients in the early phase often develop cardiogenic shock and malignant ventricular arrhythmias, with widely varying mortality rates reported across studies. Existing single-center cohorts yield conflicting prognostic findings with marked cross-cohort heterogeneity, and no standardized meta-analysis with GRADE certainty grading has been published to guide risk stratification. This meta-analysis pooled prognostic associations of all-cause in-hospital mortality in FM to inform acute risk evaluation and personalized care. Methods Eleven Chinese and English electronic databases were searched from database establishment through June 2025. Eligible studies were observational cohorts reporting prognostic associations of all-cause in-hospital mortality among FM patients. Two independent reviewers completed screening, data extraction and quality assessment separately. The Newcastle-Ottawa Scale (NOS) and AHRQ checklist were adopted to evaluate methodological quality. Pooled analyses were performed via the statsmodels package in Python, and the GRADE framework was applied to rate the certainty of evidence. Results 26 retrospective cohort studies with 4,890 FM patients were enrolled. Ten potential factors were meta-analyzed, of which six showed statistically significant associations with in-hospital mortality ( P < 0.05), including age (OR = 1.03, 95% CI: 1.02–1.04), cardiac arrest or CPR (OR = 2.57, 95% CI: 1.49–4.44), lactate (OR = 1.08, 95% CI: 1.00–1.16), cTnI (OR = 1.04, 95% CI: 1.01–1.07), LVEF (OR 0.94, 95% CI 0.90–0.97), and intravenous immunoglobulin therapy (OR = 0.12, 95% CI: 0.02–0.86). CK-MB, serum creatinine, total bilirubin, and VT/VF showed no statistically significant association (all P > 0.05). GRADE evidence ratings indicated low-certainty evidence for age and cTnI, and very-low-certainty evidence for the remaining significant factors. Sensitivity analyses indicated unstable pooled estimates for lactate and intravenous immunoglobulin therapy. Conclusions Four factors showed positive associations with elevated all-cause in-hospital mortality. LVEF was inversely associated with mortality, whereas the inverse association for IVIG represents a fragile treatment-related signal. These findings may inform acute risk screening, but most associations were supported by low or very low certainty evidence and should not be interpreted as causal. All included data were derived from retrospective cohorts. Standardized multicenter prospective studies are required to verify these prognostic associations. Systematic Review Registration https://www.crd.york.ac.uk/PROSPERO/view/CRD420261399446 , identifier CRD420261399446.