Abstract 12402: Infiltrated Atrial Fat Characterizes Underlying Atrial Fibrillation Substrate in Patients at Risk

Background: The substrate of early atrial fibrillation (AF) genesis is not fully understood. We hypothesized that infiltrated intraatrial fat is associated with discontinuous atrial conduction and AF risk (as determined by the AF risk score) in individuals with structural heart disease without AF history. Methods: Patients in sinus rhythm (N=90, age 57±10y; 55 men [63.2%]) at risk of AF as determined by the ARIC AF risk score [low (≤11 points; n=15), moderate (12-18 points; n=40), high (≥19 points; n=23) risk of AF], and patients with paroxysmal AF (n=12) underwent cardiac magnetic resonance study. Intraatrial and epicardial fat were analyzed with a Dark-blood DIR-prepared Fat-Water-separated sequence in the horizontal longitudinal axis. OsiriX DICOM viewer (Geneva, Switzerland) was used to quantify the intra-atrial fat area. All local P-wave extrema were identified on SAECG leads during sinus rhythm. A P-wave fragmentation (Pf ) was defined as an absolute difference between adjacent extrema which was above 3 standard deviations of noise, and was normalized by the duration of the P-wave in the corresponding lead. Results: Intraatrial fat monotonically increased with growing AF risk in study groups (low AF risk 16±4 vs. moderate AF risk 32±18 vs. high AF risk 81±83 mm2; ANOVA P=0.012). After adjustment for sex, race, left and right atrial area indices, and body mass index, log-transformed intraatrial fat predicted ARIC AF risk score in multivariate ordered probit regression (β-coefficient 0.50 [95%CI 0.03-0.97]; P=0.037). Interatrial septum width showed similar association (3.0±1.4 vs. 5.0±1.8 vs. 7.1±2.7 mm; ANOVA P≤0.001; adjusted β-coefficient 2.80 [95%CI 1.19-4.41]; P=0.001). Pf on the Z lead correlated with intraatrial fat index (r=0.544; P=0.001). After adjustment for BMI, left atrium (LA) size, epicardial fat and interatrial septum width, intraatrial fat was independently associated with Pf on the Z lead [β-coefficient 0.009 (95%CI 0.0003-0.019); P=0.043]. Conclusion: Infiltrated atrial fat correlates with discontinuous conduction on the posterior LA wall and characterizes evolving substrate in individuals at risk of AF.