Optimal ablation of linear lesions at the left atrial roof and posterior wall guided by wall thickness and epicardial fat using photon-counting CT imaging

Background: Treatment of macro-reentrant tachycardia often requires ablation of linear lesions in the left atrium (LA). However, sufficient and durable linear lesions are difficult to achieve, even with the latest technologies like pulsed-field ablation (PFA). This challenge may be linked to the variability of wall thickness (WT) and epicardial fat (EF), both of which could affect lesion durability.

Purpose: We aimed to investigate patterns of WT and EF in patients suffering from atrial fibrillation (AF) with the potential need for ablation of a posterior box lesion or roof dependent flutter.

Methods: High-resolution photon counting CT was performed preinterventionally in 40 patients undergoing AF ablation as part of a prospective study. 3D biatrial segmentation was performed using a dedicated software to precisely quantify WT and EF along potential linear lesions using an 3D visualization program (Figure 1). A manually programmed software tool was used to calculate the lengths of the linear lesions. Total WT was considered as the sum of myocardial WT and EF.

Positioning and abbreviations of the linear lesions are visualised in Figure 1.

Results: In total, 8920 3D data points and 160 potential linear lesions were analysed. Regarding length, the inferior line was significantly longer compared to all other lines (39.0 ± 7.0 mm compared to 34.4 ± 5.1mm/34.1 ± 5.1 mm/35.5 ± 5.1 mm of the RS/RP/VL). The IL and VL were significantly thicker than the RS and RP lines (IL/VL: 1.9 ± 0.8 mm and 1.9 ± 0.8 mm vs. RS/RP: 1.7 ± 0.7 mm and 1.7 ± 0.7 mm, all p-values <0.01). Thicker layers of EF were observed along both roof lines compared to the fat thickness at the VL and IL (Figure 2), resulting in the highest total wall thickness for these lines (posterior roof line 4.1 ± 2.1 mm; superior roof line 4.0 ± 2.1 mm vs. 2.0 ± 0.8 mm for the inferior line; p < 0.01).

Conclusion: Epicardial fat at the posterior wall is distributed inhomogeneously along potential ablation lines with highest fat thickness at the left atrial roof. The left atrial wall was significantly thicker along the roof lines. These findings implicate a more difficult ablation at the roof and raise safety concerns because of the proximity to the esophagus of inferior lines. For optimizing safety, positioning of and distance to the esophagus should be investigated additionally using this data set.