Abstract
BackgroundFour-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.ResultsSame-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).ConclusionsLA 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.
Highlights
Stroke is the second most common cause of death and the third most common cause of disability worldwide [1]
atrial fibrillation (AF) patients had profoundly altered left atrial (LA) flow characteristics compared to subjects in sinus rhythm (SR), as characterised by greater stasis, lower peak velocity, lower vorticity, and larger vortex size, as well as changes in other LA flow measurements (Additional file 1: Table S2)
Exploratory analyses assessing LA 4D Flow parameters by age and gender, and their correlation with clinical characteristics are reported in Additional file 1: Tables S3, S4
Summary
Stroke is the second most common cause of death and the third most common cause of disability worldwide [1]. Atrial fibrillation (AF) is a strong risk factor for embolic stroke mainly as it causes pro-thrombotic alterations in atrial blood flow and consequent thrombus formation. Higher scores are linked to higher risk of incident ischaemic stroke, this and other similar clinical prediction tools are limited by a modest predictive capacity both in AF and in sinus rhythm (SR) patients [9, 10]. The ability to assess parameters such as LA blood flow characteristics comprehensively (i.e. absolute flow velocities, the degree of stasis, and vortical flow patterns) both in AF and in SR is very attractive, since these features contribute directly to the downstream pathophysiologic substrate for thrombus formation and may be mechanistically relevant to the risk of embolic stroke [2]. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) allows sophisticated quantifica‐ tion 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)
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