Comparison of Cardiac Activated Fibroblast Imaging and Magnetic Resonance Imaging in Patients with COVID-19-Related Myocarditis

Background: This study aimed to explore the association between cardiac fibroblast activation and cardiac magnetic resonance (CMR) imaging parameters in patients with myocarditis following infection with coronavirus 2019 (COVID-19). Methods: In this prospective study, four patients with COVID-19-related myocarditis underwent 99mTc-labeled–hydrazinonicotinamide–fibroblast activation protein inhibitor-04 (99mTc-HFAPi) single photon emission computed tomography/computed tomography (SPECT/CT) and CMR imaging. Segmental 99mTc-HFAPi activity was quantified as the percentage of average segmental myocardial count × global left ventricular target-to-background ratio. T1/T2 values, extracellular volume (ECV), and late gadolinium enhancement (LGE) were analyzed by CMR. The consistency between myocardial 99mTc-HFAPi activity and CMR parameters was explored. Results: In patients with myocarditis, the proportion of segments with abnormal 99mTc-HFAPi activity was significantly higher than in those with abnormal LGE (81.25% vs. 60.93%, p = 0.011), abnormal T2 (81.25% vs. 50.00%, p < 0.001), and abnormal ECV (81.25% vs. 59.38%, p = 0.007); however, they were similar in those with abnormal native T1 (81.25% vs. 73.43%, p = 0.291). Meanwhile, 99mTc-HFAPi imaging exhibited good consistency with native T1 (kappa = 0.69). Conclusions: Increased cardiac 99mTc-HFAPi activity is present in COVID-19-related myocarditis, which is correlated with the native T1 values in CMR.