Fulminant Myocarditis Across the Aetiological Spectrum in the Era of Mechanical Circulatory Support: A Case Series

Background Fulminant myocarditis is a rare but life-threatening condition characterised by acute haemodynamic compromise, malignant arrhythmias, and rapid progression to cardiogenic shock. Although the clinical presentation is often uniform, the underlying aetiology is heterogeneous and carries important implications for diagnosis, therapeutic strategy, and prognosis. Case summary We report three patients presenting within months of each other with fulminant myocarditis of distinct aetiologies: eosinophilic myocarditis associated with amoxicillin-clavulanate in a 71-year-old male; lymphocytic myocarditis in a 25-year-old male with a posthumously identified pathogenic FLNC (Filamin C) variant; and lymphocytic myocarditis with extensive replacement fibrosis in a 68-year-old male. All three required mechanical circulatory support. Despite maximal therapy, two patients died and one survived with durable left ventricular assist device (LVAD) support. Conclusion Endomyocardial biopsy was pivotal in establishing the underlying diagnosis and guiding management, particularly in cases where cardiac magnetic resonance imaging (CMR) was technically limited. These cases illustrate that fulminant myocarditis represents a haemodynamic phenotype rather than a final diagnosis. Systematic histological, virological, and – where clinically indicated – genetic evaluation is essential, as aetiology informs management but does not reliably predict outcome in mechanical circulatory support (MCS) -dependent presentations.