Background Characterization of left atrial (LA) hemodynamics in paroxysmal atrial fibrillation (PAF) may provide valuable insights for thromboembolic risk. Purpose To evaluate LA vortex formation and velocity distributions by 4D flow MRI and identify associations with age, LA/LV (left ventricle) function, and established risk scores. Study Type Prospective clinical. Population Patients with PAF (n = 45, 46 ± 14 years) and healthy controls (n = 15, 54 ± 9 years) were enrolled. MRI Sequences 3T standardized cardiac MRI protocol inclusive of 4D flow MRI. Assessment Flow analysis planes were prescribed at each pulmonary vein. Velocity distribution analysis and vortex size quantification by the Lambda2 (λ2) method were performed in the LA. Statistics Pearson or Spearman's correlation coefficients, r, were calculated to identify relationships between 4D flow‐derived LA parameters and age, LA/LV function, and CHA2DS2‐VASc stroke risk score. Univariate and multivariate determinants of stroke risk were assessed using linear regressions. To compare parameters within multiple groups, one‐way analysis of variance or Kruskal–Wallis was used. Results LA vortice sizes were observed in all subjects using λ2 showing inverse correlations with peak pulmonary vein inflow velocities (P < 0.05), and positive correlations with LA volume (P < 0.05). Vortex size was elevated in PAF at all phases of the cardiac cycle, being most prominent at end early diastole (3.98 ± 1.84 cm3 vs. 6.93 ± 3.11 cm3, P = 0.001). Velocity distribution analysis showed a greater incidence of flow stasis among patients with PAF (P < 0.05). In univariate regression, vortex size was associated with the CHA2DS2‐VASc risk score at peak systole (0.457 ± 0.038, P ≤ 0.001). However, in multivariate regression age was the dominant determinant of stroke risk (0.348 ± 0.012, P = 0.006). Data Conclusion This study demonstrated that LA vortex size is increased among low‐risk patients with PAF and is associated with the CHA2DS2‐VASc risk score. Age remained the dominant determinant of stroke risk. Level of Evidence: 2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2020;51:871–884.
A utosomal dominant polycystic kidney disease (AD-PKD) is the most common inherited renal disease and is the fourth-leading cause of end-stage renal disease (1-3). ADPKD is progressive in nature, but the rate of progression is variable (4); in light of this variability, a readily available tool to determine individualized rate of progression is valuable in ADPKD management (5). Increases in renal cyst number and size leading to observable enlargement of the kidneys (4) precedes renal dysfunction in ADPKD, often by many years to decades (4). Therefore, quantifying renal enlargement emerged as a robust marker of progression in ADPKD (6,7). This concept was extended to imaging-based classifications (6) used to individualize prognosis and make treatment decisions (8-10). It is now recommended that all patients with ADPKD have an assessment of renal size as part of their initial evaluation (8,10,11). Whereas various methods of renal size assessment have been reported (6,7,12), total kidney volume (TKV) has emerged as the most accurate assessment method and is most strongly associated with clinical outcomes (5). MRIderived TKV is accurate and reproducible but the reference standard method of manual planimetry is time consuming (11,13,14), which limits translation into clinical practice. Alternative methods have been developed that estimate TKV on the basis of a more rapidly obtained series of measurements, although familiarity with these methods is limited in many clinical settings (6,14-16). In addition, image acquisition can be a challenge for clinicians who practice in settings where MRI access is limited (17). CT is known to help provide accurate TKV assessment (6,18), but there are concerns regarding radiation exposure; however, this has not been re-evaluated in the context of modern dosereducing imaging techniques (19).
Atrial fibrillation (AF) is associated with systemic thrombo-embolism and stroke events, which do not appear significantly reduced following successful pulmonary vein (PV) ablation. Prior studies supported that thrombus formation is associated with left atrial (LA) flow alterations, particularly flow stasis. Recently, time-resolved three-dimensional phase-contrast (4D-flow) showed the ability to quantify LA stasis. This study aims to demonstrate that LA stasis, derived from 4D-flow, is a useful biomarker of LA recovery in patients with AF. Our hypothesis is that LA recovery will be associated with a reduction in LA stasis. We recruited 148 subjects with paroxysmal AF (40 following 3–4 months PV ablation and 108 pre-PV ablation) and 24 controls (CTL). All subjects underwent a cardiac magnetic resonance imaging (MRI) exam, inclusive of 4D-flow. LA was isolated within the 4D-flow dataset to constrain stasis maps. Control mean LA stasis was lower than in the pre-ablation cohort (30 ± 12% vs. 47 ± 18%, p < 0.001). In addition, mean LA stasis was reduced in the post-ablation cohort compared with pre-ablation (36 ± 15% vs. 47 ± 18%, p = 0.002). This study demonstrated that 4D flow-derived LA stasis mapping is clinically relevant and revealed stasis changes in the LA body pre- and post-pulmonary vein ablation.
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