Left atrial 4D flow cardiovascular magnetic resonance: a reproducibility study in sinus rhythm and atrial fibrillation

Abstract

Background: Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) allows sophisticated quantification of left atrial (LA) blood flow, and could yield novel biomarkers of propensity for intra-cardiac thrombus formation and embolic stroke. As reproducibility is critically important to diagnostic performance, we systematically investigated technical and temporal variation of LA 4D flow in atrial fibrillation (AF) and sinus rhythm (SR).

Methods: Eighty-six subjects (SR, n = 64; AF, n = 22) with wide-ranging stroke risk (CHA₂DS₂VASc 0-6) underwent LA 4D flow assessment of peak and mean velocity, vorticity, vortex volume, and stasis. Eighty-five (99%) underwent a second acquisition within the same session, and 74 (86%) also returned at 30 (27-35) days for an interval scan. We assessed variability attributable to manual contouring (intra- and inter-observer), and subject repositioning and reacquisition of data, both within the same session (same-day scan-rescan), and over time (interval scan). Within-subject coefficients of variation (CV) and bootstrapped 95% CIs were calculated and compared.

Results: Same-day scan-rescan CVs were 6% for peak velocity, 5% for mean velocity, 7% for vorticity, 9% for vortex volume, and 10% for stasis, and were similar between SR and AF subjects (all p > 0.05). Interval-scan variability was similar to same-day scan-rescan variability for peak velocity, vorticity, and vortex volume (all p > 0.05), and higher for stasis and mean velocity (interval scan CVs of 14% and 8%, respectively, both p < 0.05). Longitudinal changes in heart rate and blood pressure at the interval scan in the same subjects were associated with significantly higher variability for LA stasis (p = 0.024), but not for the remaining flow parameters (all p > 0.05). SR subjects showed significantly greater interval-scan variability than AF patients for mean velocity, vortex volume, and stasis (all p < 0.05), but not peak velocity or vorticity (both p > 0.05).

Conclusions: LA peak velocity and vorticity are the most reproducible and temporally stable novel LA 4D flow biomarkers, and are robust to changes in heart rate, blood pressure, and differences in heart rhythm.

Keywords: 4D flow; Cardioembolic risk; Cardiovascular magnetic resonance; Left atrium; Reproducibility; Stasis; Velocities; Vortex; Vorticity.

Fig. 1

Comparison in left atrial (LA) flow characteristics in sinus rhythm (SR) and atrial fibrillation (AF) at baseline. Upper panel: representative cases of study participants in SR and in AF. Map legends are colour-coded such that hot colours represent deranged 4D flow values. 4D flow imaging in a SR participant (70 year-old male with BMI 30 kg/m² and CHA₂DS₂-VASc = 1) shows a typical vortex (see Additional file 2: Video S1 showing pathlines emitted from pulmonary veins). Similar imaging in a patient with AF (67 year-old male with body mass index 26 kg/m² and CHA₂DS₂VASc = 3) shows a short-range vortex (see Additional file 2: Video S1). Lower panel: LA mean vortex volume (a), LA vorticity (b), LA peak velocity (c), and LA stasis (d) in the overall study cohort stratified per rhythm at the time of the scan. Data expressed as mean ± SD. Statistically significant p values are marked (*p < 0.05), and smaller p values are stratified by size (**p < 0.01, ***p < 0.001). PV pulmonary veins, RU right upper, RL right lower, LU left upper, LL left lower

Fig. 2

Variability assessment of LA 4D flow parameters. Coefficients of variation (CV) for each flow parameter for intra-observer (grey), inter-observer (blue), rescan (green), and interval scan (red).CV are expressed as proportion (0–1). Statistically significant p values are marked *(< 0.05), and smaller p values are stratified by size (**p < 0.01, ***p < 0.001)