Epicardial intramyocardial fat coupling detected by cardiac tomography in candidates to atrial fibrillation ablation

Background Low-attenuation epicardial adipose tissue (I-EAT) has been implicated in atrial myopathy and AF severity. [1-3] Whether I-EAT affects intramyocardial fat (InFAT) and how it relates with anterior (AW) and posterior (PW) left atrial (LA) wall remains unclear. Purpose To investigate the relationship between I-EAT, InFAT (total, total%, and borderzone, BZ%) across AW and PW. Methods We retrospectively enrolled 22 consecutive patients undergoing pre-ablation cardiac CT. Images were processed with a dedicated software to quantify LA wall thickness, burden and distribution of intramyocardial fat (InFAT total% and InFAT BZ%, areas where InFAT intermingles with healthy myocardium), and presence of I-EAT. The LA was divided into segments according to a method previously described to ensure data comparability: segments 3–6 as the posterior wall (PW), segments 8–11 as the anterior wall (AW). [4] After excluding non-suitable segments, a segment-level analysis was performed on 174 segments (88 from AW and 86 from PW). Left atrial thickness heterogeneity (D-LAWT) was defined as the within-segment difference between the maximum and minimum wall thickness values. Predefined HU thresholds from prior literature were applied: I-EAT −96.6 to −45 HU; InFAT Total −194 to −5 HU; InFAT BZ −50 to −5 HU. Results Segments with I-EAT showed greater D-LAWT in both PW (2.5±0.9 vs 1.7±0.9 mm; p<0.001) and AW (2.5±0.9 vs 2.1±0.8 mm; p=0.049), and a higher InFAT burden (InFAT Total% 17.4±10.6 vs 11.6±8.9; InFAT BZ% 13.1±7.6 vs 8.5±5.8; both p<0.001) [Figure 1A] InFAT displayed an epicardial-to-endocardial gradient, with a greater InFAT burden in the more epicardial layers, InFAT BZ% gradient was stronger when I-EAT was present (Spearman’s Rho 0.6; p<0.001 when I-EAT was present vs 0.5; p<0.001, when I-EAT was absent, Z-score 3.5; p < 0.0001). [Figure 1B] I-EAT was more frequent in AW, whereas InFAT burden was greater in PW (BZ% 12.1±7.2 vs 7.8±5.8; Total% 17.5±10.9 vs 9.9±7.7; PW vs AW). D-LAWT correlated with InFAT BZ% in PW (p=0.006) but not in AW (p=0.069). [Figure 2] Conclusions In vivo CT suggests that I-EAT is associated with greater InFAT and higher D-LAWT. Intramyocardial fat showed to be more nuanced in the PW compared to the AW.