Left atrial vortex size and velocity distributions by 4D flow MRI in patients with paroxysmal atrial fibrillation: Associations with age and CHA₂DS₂‐VASc risk score

Abstract

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.

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

“…Overall, LA peak velocity and vorticity are the most reproducible, temporally stable, and robust to rhythm differences and heart rate changes over time. Furthermore, these markers provide a non-invasive readout of LA haemodynamics that are potentially mechanistically relevant to thrombus formation and embolic stroke [ 12 , 13 ].…”

“…Further, for all scans, after flow denoising using divergence free wavelets [ 30 ], the volumes of the largest vortex rings inside the LA were calculated automatically using the lambda2 (λ2) method [ 26 ]. In each case, a specific lambda threshold for vortices was defined as half the mean λ2 value over the cardiac cycle [ 13 ]. LA vortex volume (ml) is reported as the mean of LA vortex volumes throughout the cardiac cycle alongside peak LA vortex volumes (ml) within systole and diastole.…”

“…ECG-gated time-resolved phase-contrast cardiovascular magnetic resonance (CMR) with 3-directional velocity encoding (4D flow) is an established CMR technique that allows comprehensive in-vivo visualisation and quantification of cardiovascular flow velocities [ 11 ]. Recent proof-of-principle studies have shown that peak and mean velocity and stasis measurements derived from LA 4D flow are associated with clinical stroke risk in patients in SR with history of AF [ 12 , 13 ] and low blood flow velocities have been linked to activation of the coagulation cascade [ 2 , 3 ]. Furthermore, assessment of the pattern of blood flow within the LA [ 14 ] may also be relevant to embolic risk, since loss of normal vortical flow has been found in patients in SR with a history of paroxysmal AF at higher stroke risk [ 13 ] and is associated with platelet aggregation and thrombus formation [ 15 , 16 ].…”

“…Recent proof-of-principle studies have shown that peak and mean velocity and stasis measurements derived from LA 4D flow are associated with clinical stroke risk in patients in SR with history of AF [ 12 , 13 ] and low blood flow velocities have been linked to activation of the coagulation cascade [ 2 , 3 ]. Furthermore, assessment of the pattern of blood flow within the LA [ 14 ] may also be relevant to embolic risk, since loss of normal vortical flow has been found in patients in SR with a history of paroxysmal AF at higher stroke risk [ 13 ] and is associated with platelet aggregation and thrombus formation [ 15 , 16 ]. Together, these observations raise the intriguing possibility that parameters derived from 4D flow could eventually be used as imaging biomarkers to improve embolic risk stratification in clinical practice, particularly in patients with SR.…”

“…Although analysis of LA 4D flow parameters by CMR is more time-consuming than the collection of simpler measurements, such as LA volume and emptying fraction, direct assessment of a key component of the Virchow’s triad would be highly attractive if able to identify patients who may benefit from anticoagulation, either in SR or with a low AF burden (e.g., not identified by short-term electrocardiographic (ECG) monitoring [ 17 ]). In the present study, we aimed to evaluate and compare the reproducibility of a number of LA flow characteristic parameters [ 12 , 13 ], both within the same session and over time. We included subjects with AF or SR and a wide range of clinical stroke risk, to provide information on reproducibility across a heterogeneous and clinically-relevant population.…”