Three-dimensional left atrial blood flow characteristics in patients with atrial fibrillation assessed by 4D flow CMR

Abstract

Aims: To apply 4D flow cardiac magnetic resonance (CMR) for the volumetric measurement of 3D left atrial (LA) blood flow to evaluate its potential to detect altered LA flow in patients with atrial fibrillation (AF) and to investigate associations of changes in systolic and diastolic LA flow with the current clinical risk score (CHA₂DS₂-VASc) used for the assessment of thromboembolic risk in AF.

Methods and results: 4D flow CMR was performed in 40 patients with a history of AF (in sinus rhythm during CMR scan, age = 61 ± 11 years), 20 age-appropriate controls (59 ± 7 years), and 10 young healthy volunteers (24 ± 2 years) to measure in vivo time-resolved 3D LA blood flow. LA velocities were characterized with respect to atrial function and timing by calculating normalized LA flow velocity histograms during ventricular systole, early diastole, mid-late diastole, and the entire cardiac cycle. Mean, median, and peak LA velocity steadily decreased when comparing young volunteers, age-appropriate controls, and AF patients by 10-44% and 8-26% for early diastole and the entire cardiac cycle, respectively (P < 0.01 for all comparisons except median velocity for young vs. older volunteers and peak velocity for older volunteers and AF patients). There were moderate but significant inverse relationships between increased CHA₂DS₂-VASc score and reduced mean LA velocity (early diastole: r = -0.37, P < 0.001; entire RR-interval: r = -0.33, P = 0.005), median LA velocity (r = -0.33, P = 0.003; r = -0.25, P = 0.017), and peak velocity (r = -0.36, P = 0.001; r = -0.45, P < 0.001). LA flow indices also correlated significantly with age and LA volume (R² = 0.44-0.62, P < 0.001), but not with left ventricular ejection fraction.

Conclusion: Left atrial 4D flow CMR demonstrated significantly reduced LA blood flow velocities in patients with AF. Further study is needed to determine whether these measures can improve upon the CHA₂DS₂-VASc score for stroke risk prediction and enhance individual decisions on anticoagulation in patients with AF.

Keywords: 4D flow CMR; atrial fibrillation; cardiovascular MRI; flow; stroke.