Background

Pulsed-field ablation (PFA) is a new ablation modality for atrial fibrillation (AF) employing trains of short-duration high amplitude electrical pulses that ablate myocardium by electroporation of the sarcolemmal membrane without tissue heating. With its different mechanism of tissue ablation, it is assumed that lesion creation is divergent to thermal energy sources. ⁶⁸Ga-fibroblast-activation protein inhibitor (FAPI) PET/CT targets FAP-alpha which is expressed by activated fibroblasts. The aim of this study was to assess ⁶⁸Ga-FAPI uptake in the pulmonary vein (PV) region of the left atrium after pulmonary vein isolation (PVI) with PFA and cryoballoon ablation (CBA) as a surrogate for ablation damage.
Methods

Nineteen patients (12 PFA, 7 CBA) underwent ⁶⁸Ga-FAPI-PET/CT 27.4 ± 12.8 days after PVI. Five patients without AF or previous ablation served as controls. Standardized uptake values of localized tracer uptake were assessed.
Results

Mean age of the PVI patients was 64.5 ± 11.3 years (79% male), thereof 10/19 (52.6%) with paroxysmal AF. Echocardiographic parameters were comparable, with a left ventricular ejection fraction and a left atrial volume index of 52.2 ± 2.7 vs. 54.3 ± 2.3 (p=0.5) and 34.9 ± 3.2 vs. 30.3 ± 4.7 (p=0.8) for PFA and CBA patients, respectively. Focal FAPI uptake around the PVs was observed in 3/12 (25%) PFA and 7/7 (100%) CBA patients (p<0.01), respectively, while no uptake was observed in all controls. Patients after PVI had significant higher FAPI uptake in PVs compared to controls (SUV_max: 3.8 ± 4.4 vs. 1.6 ± 0.1; p<0.01). Patients after PFA had significantly lower FAPI uptake around PVs compared to CB-ablated individuals (SUV_max: 2.8 ± 0.2 vs. 5.4 ± 0.9, p < 0.01; SUV_peak: 2.4 ± 0.1 vs. 3.7 ± 0.6, p < 0.01); SUV_mean: 2.2 ± 0.1 vs. 3.1 ± 0.5, p < 0.05.)

Conclusion

We confirm recent data showing the ability of ⁶⁸Ga-FAPI PET/CT of in-vivo visualization of tracer uptake as surrogate for fibroblast activation after PVI. Tissue response to PFA as non-thermal energy source seems to be different to established thermal ablation systems as fibroblast activation is far less pronounced. This functional assessment of fibroblast activation might contribute to a better understanding of lesion formation between thermal and PFA ablation potentially translating into better clinical efficacy and safety outcomes.