The Relationship between Epicardial Fat and Atrial Fibrillation Cannot Be Fully Explained by Left Atrial Fibrosis

Background: Epicardial adipose tissue (EAT) has been associated with atrial fibrillation (AF), but its pathophysiological mechanisms remain unclear. Objectives: To measure the correlation between EAT and left atrium (LA) fibrosis, and to assess their ability to predict relapse after pulmonary vein isolation (PVI). Methods: Patients with AF enrolled for a first PVI procedure underwent both cardiac computerized tomography (CT) and cardiac magnetic resonance (CMR) imaging within less than 48 hours. EAT LM was quantified on contrast-enhanced CT images at the level of the left main. LA fibrosis was quantified on isotropic 1.5 mm 3D delayed enhancement CMR. After pulmonary vein isolation (PVI), patients were followed up for AF relapse. Statistical significance was set at p<0.05. Results: Most of the 68 patients (46 men, age 61 +/- 12 years) had paroxysmal AF (71%, n=48). Patients had a median EAT LM volume of 2.4 cm(3)/m(2) (interquartile range [IQR] 1.6-3.2 cm(3)/m(2)), and a median amount of LA fibrosis of 8.9 g (IQR 5-15 g). The correlation between EAT LM and LA fibrosis was statistically significant but weak (Spearman's R=0.40, p=0.001). During a median follow-up of 22 months (IQR 12-31), 31 patients (46%) had AF relapse. Multivariate analysis yielded two independent predictors of AF relapse: EAT LM (HR 2.05, 95% CI 1.51-2.79, p< 0.001), and non-paroxysmal AF (HR 2.36, 95% CI 1.08-5.16, p=0.031). Conclusion: The weak correlation between EAT and LA suggests that LA fibrosis is not the main mechanism linking EAT and AF. EAT was more strongly associated with AF relapse than LA fibrosis, supporting the existence of other more important mediators of EAT and AF.