Abstract 17900: Analysis of Left Atrial Flow Velocity Distribution by 4D Flow MRI in Patients With Atrial Fibrillation
Background: To identify atrial fibrillation (AF) patients with high stroke risk, clinicians use risk scores with mediocre predictive values (C statistic 0.55-0.64). Because blood stasis is a key factor responsible for thrombus formation in the left atrium (LA), evaluating LA 3D flow patterns may improve understanding of stroke risk in AF patients.
Objective: To assess differences in LA flow velocity distribution in AF patients and controls by 4D flow MRI
Methods: We performed 4D flow MRI in 21 AF patients in sinus rhythm during imaging (AF-sinus), 10 AF patients in AF (AF-afib), and 9 controls. Manual segmentation of LA volume enabled analysis of all LA voxel velocities over all phases of the cardiac cycle. LA flow was quantified by mean LA velocity and the percentage of LA velocities > 0.2 m/s (incidence). To evaluate the highest velocities in each voxel, varying proportions of the velocity profiles (top 5%, 25%, 50%, 65%, 100%) were analyzed.
Results: Patient ages (years) in the groups were control (59±4), AF-sinus (60±9), and AF-afib (68±9). Mean velocity and incidence were significantly different (p < 0.05) between AF-sinus and controls when more than the top 50% of the voxel velocities were analyzed. Mean velocity and incidence were significantly different when comparing AF-afib to AF-sinus or controls regardless of threshold. Analyzing data from the top 65% of flow, LA flow in AF-sinus was significantly lower than in controls, but higher than AF-afib (Figure).
Conclusions: When compared to controls, LA flow measured by 4D Flow MRI is impaired in AF-sinus and in AF-afib. In AF-sinus, the wide spread of LA flow suggests that some patients have LA flow similar to controls, while in others LA flow is more similar to AF-afib. Inclusion of LA velocities below the median improves discrimination between patient groups. Further work will help determine whether 4D Flow MRI can accurately guide decisions on anticoagulation by identifying AF patients at increased stroke risk.
- © 2013 by American Heart Association, Inc.