Long-Term Prognosis and Early Clinical Predictors in Acute Myocarditis: Insights from a 10-year, Unselected Hospital Cohort

Background: Acute myocarditis (AM) is an inflammatory cardiac condition with variable prognosis, ranging from complete recovery to progressive heart failure (HF) or death. While advances in diagnostics, such as high-sensitivity troponins and cardiac magnetic resonance imaging (CMR), have facilitated detection of milder cases, prognostic insights across unselected, real-world populations remain limited. Methods In this retrospective cohort study, we analyzed 471 consecutive patients hospitalized with a discharge diagnosis of AM between 2009 and 2019. Inclusion was based on clinical diagnosis. Baseline clinical features, laboratory data, and imaging results were extracted and systematically reviewed. The primary composite outcome comprised all-cause mortality, heart transplantation, use of mechanical circulatory support, new-onset HF, ventricular arrhythmias, and cardiac device implantation. Results The median age was 34 years, 32% were female. Chest pain was the predominant presenting symptom (87%), while ST-segment elevation was observed in 48% of cases. At admission, 24.2% of patients had hypokinesia on echocardiography, and 11.6% had a left ventricular ejection fraction (LVEF) <50%. Within the first year of follow-up, 41 patients (8.7%) experienced the composite outcome. Older age, dyspnea at presentation, and elevated biomarkers were associated with adverse events in the first year. Over a median follow-up of 8.2 years, multivariable analysis revealed age (HR 1.05 per year, 95% CI: 1.03-1.07, p<0.001), signs of HF (HR 3.27, 95% CI: 1.25-8.52, p=0.015), and hypokinesia on echocardiography (HR 19.77, 95% CI: 4.10-95.36, p<0.001) as independent predictors of poor outcomes. No sex-based difference in the primary outcome was observed (HR 0.78, 95% CI: 0.31-1.96, p=0.592) despite different clinical presentation. Conclusions In this real-world, decade-long cohort, the majority of patients had favorable outcomes. However, a small subset experienced poor outcomes in both the short and long term, highlighting the need for early risk stratification and targeted management of high-risk individuals.