Cardiac Function Consequences of the Persistence of Acute Myocarditis Somatostatin-PET Criteria Four Months Post-Acute Phase

Background. Somatostatin-positron emission Tomography (PET) imaging of inflammatory cells is an effective approach for detecting Acute Myocarditis (AM) based on the Myocardial Uptake Volume (MUV) criteria of > 18 cm3. The current study further characterizes patients for whom this criterion persists at the 4-month Follow-Up (FU) from apparently uncomplicated AM. Methods. Twenty-seven patients [median age 26.5, inter-quartile range: 21.9-31.9 years] underwent Cardiac Magnetic Resonance (CMR) and [68Ga]Ga-DOTA-TOC PET at the acute phase and 4.5 [4.2-5.0] months later. Patients with > 18 cm3 MUV (FU.PET+) at the 4-month follow-up were compared to FU.PET- patients. Results. At 4 months, inflammation by CMR was only identified in two patients but in 11 patients by PET (FU.PET+ group), with 5 of these 11 patients exhibiting a baseline-to-4-months expansion in MUV. Ejection Fractions (EFs) at four months were generally lower in FU.PET+ than FU.PET- patients (Left Ventricular (LV).EF, 52.9 [48.6; 55.0] % vs. 56.0 [54.3; 57.8] %, p=0.001). In addition, the 5 FU.PET+ patients with expansion of the MUV had a worse LV.EF evolution (4-month follow-up minus baseline difference in LV.EF: (-5.0) [(-12.9)-(-1.0)] %) vs. + 3.1 [0.94-8.0] % for the other patients, p=0.004) and the highest plasma high-sensitivity troponin-Ic at 4-months (13.0 [7.5-22.00] ng/l vs. 3.0 [2.0-9.5] ng/l, p=0.045) suggestive of a more persistent active disease. In contrast, the evolution profile of the 6-remaining FU.PET+ patients was consistent with a longer recovery time as a consequence of a more severe initial insult (i.e., with lower LV.EF and higher MUV at baseline vs. the other patients, both p < 0.05). Conclusions. Myocardial inflammation is detected by somatostatin-PET at 4 months from an apparently uncomplicated AM in as many as 41% of patients. It is associated with a poorer recovery of cardiac function, consistent with more persistent active disease or a more severe initial insult.