Determinants of Impaired Left Atrial Hemodynamics in Paroxysmal Atrial Fibrillation: A 4D Flow MRI Study

Left atrial (LA) blood flow stasis is a major contributor to thromboembolic risk in atrial fibrillation (AF) and can be measured non-invasively using four-dimensional (4D) flow magnetic resonance imaging (MRI), yet factors driving impaired LA hemodynamics in paroxysmal AF remain unclear. In this retrospective study, 107 patients with paroxysmal AF undergoing pre-ablation cardiac MRI were evaluated. LA blood flow stasis was quantified as the proportion of LA voxels with velocity < 0.1 m/s on 4D flow MRI. Multivariable linear regression assessed associations between LA stasis and demographic, cardiac structural and functional, and clinical variables in a complete-case cohort of 88 patients. Mean LA blood flow stasis was 44 ± 13%. After adjustment, higher left atrial volume index, higher hematocrit, and female sex were independently associated with greater LA stasis, while higher left ventricular ejection fraction, higher resting heart rate, and higher body mass index were associated with lower stasis (all p < 0.01). Age and diabetes status were not significantly associated with stasis. The final model explained 40.8% of the variance in LA blood flow stasis. These results underscore the multifactorial nature of LA hemodynamic impairment in paroxysmal AF and support integrating clinical and imaging markers to refine thromboembolic risk assessment.