Visualization of thermal damage using ⁶⁸ Ga-FAPI-PET/CT after pulmonary vein isolation

Purpose: ⁶⁸ Ga-fibroblast-activation protein inhibitor (FAPI) positron emission tomography (PET) is a novel technique targeting FAP-alpha. This protein is expressed by activated fibroblasts which are the main contributors to tissue remodeling. The aim of this proof-of-concept study was to assess ⁶⁸ Ga-FAPI uptake in the pulmonary vein (PV) region of the left atrium after pulmonary vein isolation (PVI) with cryoballoon ablation (CBA) and radiofrequency (RFA) as a surrogate for thermal damage. Methods: Twelve PVI patients (5 RFA, 7 CBA) underwent ⁶⁸ Ga-FAPI-PET 20.5 ± 12.8 days after PVI. Five patients without atrial fibrillation or previous ablation served as controls. Standardized uptake values of localized tracer uptake were calculated. Results: Focal FAPI uptake around the PVs was observed in 10/12 (83.3%) PVI patients, no uptake was observed in 2 PVI patients and all controls. Patients after PVI had higher FAPI uptake in PVs compared to controls (SUV_max: 4.3 ± 2.2 vs. 1.6 ± 0.2, p < 0.01; SUV_peak: 2.9 ± 1.4 vs. 1.3 ± 0.2, p < 0.01). All CBA patients had an intense uptake, while in the RFA, group 2 (40%), 1 (20%), and 2 (40%) patients had an intense, moderate, and no uptake, respectively. We observed higher uptake values (SUV_peak) in CBA compared to RFA patients (4.4 ± 1.5 vs. 2.5 ± 0.8, p = 0.02). Conclusion: We demonstrate in-vivo visualization of ⁶⁸ Ga-FAPI uptake as a surrogate for fibroblast activation after PVI. CBA seems to cause more pronounced fibroblast activation following tissue injury than RFA. Future studies are warranted to assess if this modality can contribute to a better understanding of the mechanisms of AF recurrence after PVI by lesion creation and gap assessment.