Short-Term Outcomes in Influenza Virus-Related Myocarditis: A Single-Centre Real-Life Experience

Background: Myocarditis is a potentially life-threatening inflammation of the myocardium that can be triggered by viral infections, including influenza. While corticosteroids have historically been used with caution in viral myocarditis due to concerns over impaired viral clearance, recent insights—particularly those emerging from the COVID-19 pandemic—suggest that early, moderate-dose corticosteroid therapy may offer clinical benefits in selected inflammatory cardiac syndromes. This study aimed to assess the incidence and clinical features, as well as short-term outcomes of influenza-related myocarditis and/or pericarditis. Methods: A retrospective, observational study was conducted, including all consecutive patients diagnosed with acute myocarditis and/or pericarditis between December 2024 and March 2025 who presented with chest pain or dyspnea and had a confirmed Influenza A (H1N1) infection. The diagnostic evaluation included cardiac biomarkers, ECG, TTE, and cardiovascular magnetic resonance (CMR). All patients were monitored during a three-month follow-up period. Results: Of 281 patients with laboratory-confirmed H1N1 infection, six (2%) were diagnosed with myocarditis and/or pericarditis. All patients diagnosed with myocarditis received corticosteroid therapy and an antiviral drug (oseltamivir). CMR confirmed the diagnosis in all cases of inflammatory cardiomyopathy. At 30 days, median LVEF improved from 49% to 58%. No deaths or rehospitalizations were reported. Conclusions: Influenza-related myocarditis and/or pericarditis are relatively uncommon, occurring in approximately 2% of cases. When they occur, they are primarily associated with an uncomplicated clinical course and with favourable short-term outcomes, including a rapid recovery of left ventricular function and the absence of adverse events at three-month follow-up.