Effect of variations in Left Atrial Wall Thickness levels and epicardial adipose tissue quantified by photon-counting CT on potential lesion creation for perimitral flutter

Background: 
Creating linear lesions is often necessary for the ablation of macro-reentrant tachycardia and despite technological advancements, sufficient and durable linear lesions are often difficult to achieve. Variability of wall thickness (WT) and epicardial adipose tissue (EAT) levels, is likely to affect the durability of ablation lines.

Objective:
We aimed to investigate patterns of WT and EAT levels along simulated standardly used ablation lines for perimitral flutter.

Methods:
High-resolution photon counting atrial CT was performed in 40 patients prior to AF ablation as part of a prospective observational study. 3D biatrial segmentation was performed to precisely quantify left atrial (LA) and right atrial (RA) EAT levels (ml) as well as wall thickness levels (mm).

Extracted datapoints on WT and EAT were than linked to simulated linear lesions (Figure 1) using additional image processing software. An additionally developed software tool was used to calculate the lengths of the linear lesions. Total WT was considered as the sum of myocardial WT and EAT.

Results:
Regarding length, the anteroseptal line was the longest line with a mean length of 59.5 ± 7.1 mm compared to 49.0 ± 8.9 mm of the anterolateral line (p < 0.01) and both mitral isthmus lines (superior MI line 47.4 ± 6.8 mm; inferior MI line 37.7 ± 9.8 mm; both p < 0.01). Mean myocardial WT was highest at the superior MI line (2.2 ± 1.2 mm) with a high variation and values up to 8 mm in some patients, lower mean values were observed for the anteroseptal line (1.6 ± 0.6 mm, p < 0.01) ((Figure 2). Highest EAT levels were along the AL line 3.2 ± 2.5 mm) and close to the MI lines, resulting in high values of total WT for these lines.

Conclusion:
WT and EAT are distributed very heterogeneously along potential ablation lines with highest values of myocardial
thickness at the MI. Despite of lower values of total WT the AS line was the longest. The biggest variance in WT levels were observed for the superior MI line.

This data indicates that LA WT and EAT levels may vary in between patients and “one fits all approach” may not be the best strategy for optimised linear lesion creation.