Atrial fibrillation is linked to increased left ventricular fibrosis and inflammation measured by CMR with prognostic implications.

Approximately 30% of patients with atrial fibrillation (AF) develop heart failure (HF), but the underlying mechanisms and their impact on the left ventricle (LV) remain unclear. Fibrosis and inflammation are suspected contributors. This study aimed to investigate LV tissue characteristics in patients with and without AF using cardiac magnetic resonance imaging (CMR). Patients from a single-center CMR registry were categorized by AF status, adjudicated by two blinded investigators. LV fibrosis was assessed by native T1 and extracellular volume (ECV), while T2 indicated inflammation. Results were adjusted for LV ejection fraction (LVEF), end-systolic volume index (ESVi), and late gadolinium enhancement mass (LGEmass). Prognostic value was tested with multivariable Cox regression, using all-cause mortality or HF hospitalization at one year as the endpoint. Of 2,879 patients with one-year follow-up, 590 had AF. They showed lower LVEF and higher ESVi and LGEmass. After adjustment, AF was linked to higher T1 (p = 0.006), T2 (p = 0.01), and ECV (p < 0.001). Eighty-five patients reached the endpoint. In multivariable analysis, only T1 independently predicted outcome. Kaplan-Meier analysis showed patients with T1 above the median (1125 ms) had worse outcomes than those below, even without AF. The combination of AF and elevated T1 carried the poorest prognosis (p = 0.001). AF is closely associated with LV fibrosis and inflammation, with T1 emerging as an independent predictor of outcome. These findings suggest a mechanistic pathway with important prognostic implications. Prospective studies are warranted to confirm these associations and explore their role in patient stratification and management.