Increased Left Ventricular Mass Index and Atrial Volume Index Are Associated with Atrial Fibrosis in Patients with Atrial Fibrillation

<b>Objectives:</b> Our aim was to determine imaging-derived parameters from echocardiography associated with the presence of atrial fibrosis in a cohort of atrial fibrillation (AF) patients. <b>Methods:</b> Initially, 123 participants were included in this prospective cross-sectional observational study (clinicaltrials.gov: NCT03584126); after exclusion criteria, 112 full datasets were analyzed. All participants underwent clinical evaluation, echocardiography, and cardiac MRI. Overall, 29 patients with AF and left atrial (LA) fibrosis at MRI, 37 with AF and without LA fibrosis at MRI, and 46 healthy controls were included in the final database. Results: The cardiac structural parameters as assessed by MRI were not significantly different between AF patients with and without fibrosis, apart from LA volume. The area under the curve (AUC) reached a value of 0.69 when using body-surface-area-indexed LA volume (LAVi) determined by echocardiography as a factor associated with LA fibrosis in AF patients. Moreover, when detecting LA fibrosis using LAVi, an optimal cut-off value of 42.7 mL/m² was obtained, resulting in 41.67% specificity and 88.46% sensitivity with a total accuracy of 65.06%. Testing BSA-indexed left ventricular mass (LVMi) as a factor associated with LA fibrosis, the optimal cut-off value was 140.2 g/m², with 76.92% sensitivity, 58.33% specificity and 67.62% total accuracy for the discrimination between AF patients with and without LA fibrosis. A strong association between body-surface-area-indexed left atrial volume (LAVi) and the presence of atrial fibrillation was identified (54.5 mL/m² vs. 29.8 mL/m² in controls, <i>p</i>-value < 0.0001). <b>Conclusion:</b> LA volume indexed to BSA could be a promising tool for the identification of cardiac fibrosis in AF patients.