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.

The impact of atrial fibrillation and stroke risk factors on left atrial blood flow characteristics

“…CMR examinations were performed on 3T MRI systems (Verio syngo MRB17 or MAGNETOM Prisma VE11C, both Siemens, Germany). LA flow characteristics were assessed using ECG-gated time-resolved 3D phase-contrast CMR with 3-directional velocity encoding imaging (‘4D flow’), using a post-processing tool which we have recently validated 9 and made available on the Oxford University Research Archive platform ( https://doi.org/10.5287/bodleian:ey4ovzdbB ). Briefly, data analysis included 3D segmentation of LA volume, and determination of two sets of parameters ( Figure 1 ): firstly, LA peak and mean velocities, since low atrial velocities are thought to be linked to activation of the coagulation cascade with increased red blood cell and plasma protein aggregation 1 ; secondly, ‘rotational’ flow parameters, since the normal flow pattern within the LA is characterized by vortexes, 10 and disruption of vortical flow is associated with altered shear stress and platelet adhesion and aggregation in computational and silicone replica models of intra-cardiac blood flow.…”

“…the tendency of flow to rotate by using the area under the vorticity–time curve over the averaged cardiac cycle using volume-weighted vorticity measures, in radians). 9 The equations used for calculating the LA 4D flow parameters are available on the Oxford University Research Archive platform at the following link: https://doi.org/10.5287/bodleian:ey4ovzdbB . All data were acquired using a 4D flow sequence with retrospective gating except for one participant where a prospectively gated sequence was used.…”

“…Sequence parameters and details of analysis methods are provided in reference 9 and in Supplementary data online, Methods for LA/LV function/volumes.…”

“…A difference of 0.06 m/s in LA peak velocity was chosen based on published data indicating that LA peak velocity in AF patients with CHA 2 DS 2 VASc ≥3 is 0.06 m/s lower than that in AF patients with CHA 2 DS 2 VASc 0–2 (13). Based on our previous work 9 showing that LA peak velocity in patients in AF is 0.22 ± 0.07 m/s, recruitment of at least 17 participants with persistent AF would provide >90% power (two-tailed alpha = 0.05) to detect a 0.06 m/s change in peak velocity after successful DCCV. Further, recruitment of at least 22 subjects per group (i.e.…”

Four-Dimensional Flow Magnetic Resonance Imaging and Applications in Cardiology

“…However, the limited spatial resolution of 4D flow MRI may not satisfy the minimum number of voxels needed to segment the LAA accurately and reliably in a certain number of cases [6]. In a recent study, reliability and reproducibility of 4D flow parameters in AF patients were reported [60]. Left atrial peak velocity Four-Dimensional Flow Magnetic Resonance Imaging and Applications in Cardiology DOI: http://dx.doi.org/10.5772/intechopen.99362 and vorticity were found to be more reproducible and independent of physiological factors than mean velocity, vortex volume and stasis.…”