CMR and FDG PET/CT Imaging Phenotypes and their Association with Outcomes in Patients with Known or Suspected Myocarditis.

INTRODUCTION: Cardiac magnetic resonance imaging (CMR) is a powerful tool in evaluating myocarditis. The role of fluorodeoxyglucose-positron emission tomography/computed tomography (FDG PET/CT) in known or suspected myocarditis remains unknown. We aimed to investigate whether FDG PET/CT adds prognostic value to CMR in patients with known or suspected myocarditis. METHODS: From a registry of 1,646 patients at Brigham and Women's Hospital who underwent FDG PET/CT for known or suspected inflammatory cardiomyopathy, we applied the following criteria: 1) had a primary clinical diagnosis of myocarditis, including focal late gadolinium enhancement suggestive of myocarditis on CMR, 2) underwent both FDG PET/CT and CMR within 12 months, and 3) had no evidence of cardiac or extracardiac sarcoidosis via histology or metabolically active extracardiac sarcoidosis via FDG PET/CT. Imaging findings were categorized as 1)'concordant' if there was at-least one matched myocardial segment with focal LGE on CMR and FDG uptake on PET/CT or 2) 'discordant' if there were no matched segments. The primary outcome was major adverse cardiovascular event (MACE), a composite of heart failure hospitalization, sustained ventricular tachycardia (VT)/ventricular fibrillation, VT ablation, left ventricular assist device placement, cardiac transplant, and death at one-year. RESULTS: We identified 100 patients (59±13 years, 74% male, LVEF 51±13%) who met inclusion criteria. Concordant imaging findings were present in 45 patients (61±11, 73% male, LVEF 50±13%) and discordant in 55 (57±15, 75% male, LVEF 52±13%). Patients in the concordant group were most likely to be treated with immunosuppression after imaging than the discordant group (31% vs 9.1% p=0.005). In an adjusted model, patients with concordant imaging findings had a higher risk of MACE than patients with discordant imaging findings (aHR: 3.61 [95% CI: 1.14, 11.39], p=0.028). CONCLUSION: FDG PET/CT may have prognostic value in select patients with known or suspected myocarditis as patients in our study with concordant CMR and FDG PET/CT findings were at increased risk of MACE in follow-up.