Introduction:

Esophageal thermal injury (ETI) following atrial fibrillation (AF) ablation is associated with rare but serious complications such as atrio-esophageal fistula. Besides invasive diagnostic techniques (gastro-duodenoscopy) there is no established imaging method in the assessment of ETI. ⁶⁸Ga-Fibroblast-activation protein inhibitor (FAPI) positron-emission tomography (PET) is a novel technique targeting the protein FAP-alpha enabling the visualization of activated fibroblasts after tissue injury. The aim of this retrospective study was to assess the feasibility of FAPI-PET imaging in the evaluation of ETI after pulmonary vein isolation (PVI) with cryoballoon (CBA) and radiofrequency ablation (RFA).

Methods:

Data of 12 patients having undergone ⁶⁸Ga-FAPI-PET/CT after PVI were analyzed. Five oncologic patients, matched for sex, age and LVEF without known esophageal affection, AF or previous ablation, served as controls. We analyzed FAPI-PET/CT visually and quantitatively, using standardized uptake parameters (SUV_max) of the region of interest (ROI) placed at the esophageal wall at the CT level of the origin of left superior pulmonary vein (LSPV). We assessed clinical baseline characteristics, imaging parameters from echocardiography and procedural PVI data.

Results:

Visually, a focal unspecific esophageal tracer uptake on the atrial level was observed along the esophageal wall in 1/5 (20%) control and 8/12 (66.7%) PVI patients, p=0.11. Quantitatively, patients after PVI had significantly higher FAPI uptake in the predefined esophageal loci at the level of origin of LSPV compared to controls (SUV_max: 2.8±0.9 vs. 1.9±0.5, p=0.02). There was no statistical difference between esophageal FAPI uptake between CBA and RFA patients (SUV_max 2.8±1.0 vs. 2.8±0.8; p=0.76).

Conclusion

We demonstrate the feasibility of the use of ⁶⁸Ga-FAPI-PET/CT to assess FAPI uptake as a surrogate for thermal damage in terms of ETI after PVI. Standardized measures demonstrated significantly higher tracer uptake in ablation patients compared to controls demonstrating the proof-of-principle of this method to assess ETI. CBA doesn`t seem to cause more pronounced fibroblast activation in esophagus following tissue injury than RFA. Further studies, especially in combination with endoscopic work-up, are warranted to assess if this modality might provide the potential to better describe the entity of ETI with special regard to temporal pattern of fibroblast activation after thermal damage for PVI.

Table 1. Patient characteristics

LVEF, left ventricular ejection fraction; AF, atrial fibrillation; CHF, chronic heart failure; LAVI, left atrial volume index; BMI, body mass index; TIA, transient ischemic attack; RF, radiofrequency ablation; PVI, pulmonary vein isolation; CBA, cryoballoon ablation;