Left atrium MRI 4D-flow in atrial fibrillation: Association with LA function

Left atrium (LA) is a principal site of thrombus formation inducing thromboembolic events, which have been associated with LA low flow velocities. Recent developments in magnetic resonance imaging (MRI) 4D flow analysis enable a non-invasive visualization of LA flow patterns. Our main objective was to investigate modifications of the main vortices in the LA with regards to LA functional indices in 4 patients with atrial fibrillation (AF) and 6 healthy volunteers. Vorticity threshold and Q-criterion indices were computed from the centered vorticity calculation on filtered 4D velocity MRI images. Phasic LA longitudinal strains were computed on cine MRI images using LA feature tracking algorithm. LA dilation in AF came along with a drop in LA longitudinal strains. Best correlations between LA flow and functional changes were found for velocity vs. longitudinal strains corresponding to reservoir and LA contraction phases (r=0.69 and r=0.81, p<;0.03). Similarly, the highest correlation was found during LA contraction phase for associations between LA longitudinal strains and Q-criterion (r=0.52). In AF, LA functional changes are tightly associated with flow disorganization during the cardiac cycle especially during LA contraction phase.