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 of cardiac fibroblast activation and cardiac magnetic resonance (CMR) imaging parameters in patients with myocarditis following coronavirus disease 2019 (COVID-19) infection. 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 at 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 those with abnormal LGE (81.3% vs. 60.9%, p = 0.011), abnormal T2 (81.3% vs. 50.0%, p < 0.001), and abnormal ECV (81.3% vs. 59.4%, p = 0.007) but was similar in those with abnormal native T1 (81.3% vs. 73.4%, p = 0.291). Meanwhile, 99mTc-HFAPi imaging had good consistency with native T1 (kappa = 0.69). Conclusion Increased cardiac 99mTc-HFAPi activity is present in COVID-19–related myocarditis, which is correlated with the native T1 values in CMR.