Abstract 16784: Utility of 4D Flow MRI to Quantify Improvement of Left Atrial Hemodynamics Following Cardioversion for Atrial Fibrillation

Abstract

Background: Cardioversion (CV) for persistent atrial fibrillation (PeAF) restores sinus rhythm (SR) but its effects on left atrial (LA) and LA appendage (LAA) flow are not well established. Research question: Does restoring sinus rhythm improve LA/LAA hemodynamics in patients with PeAF? Aims: To compare changes in LA/LAA 4D flow MRI characteristics post-CV for PeAF versus repeated measurements in a control group without AF. Methods: We performed 4D flow MRI (3T Skyra) in 9 PeAF patients (8 males, age 68±8 yrs, 78% HTN, 44% DM, 22% CAD, CHA2DS2-VASc 2.7±1.5, LVEF 53±17%) prior to and 62±44 days after CV (in SR) (minimum 4 weeks after CV). We also performed repeat MRIs in 9 SR controls (6 males, age 51±11 yrs, 78% HTN, 22% DM, 11% CAD, CHA2DS2-VASc 1.6±0.9, LVEF 62±4%) 60±19 days apart, both in SR (minimum 4 weeks apart). Data analysis included 3D segmentation of LA and LAA for evaluation of atrial velocity data. Absolute atrial velocities were calculated for each voxel and time frame inside the LA and LAA, and used to derive blood stasis (quantified by determining number of cardiac time frames with velocities below a threshold of 20 cm/s, normalized by the total number of cardiac time frames: Stasis%= (Nstasis/ NTotal)*100 ) and median velocity. Results: In PeAF, restoring SR improved 4D flow characteristics by reducing stasis and increasing median velocity (p<0.003, figure). In the controls, there was no significant change in median velocity or stasis % between the two scans in either the LA or LAA. Bland-Altman analysis for the two control scans showed no significant differences in the controls. Pre-CV median velocities and stasis% in PeAF significantly differed from controls while post-CV, they did not. Conclusion: AF is associated with impaired LA and LAA flow characteristics that improve substantially with CV toward control values. Use of 4D MRI to quantify LA and LAA hemodynamic function is feasible; future studies are needed to correlate 4D MRI measurements to thromboembolic risk.