B-PO04-077 HEART RATE VARIABILITY AND LEFT ATRIAL HEMODYNAMICS IN ATRIAL FIBRILLATION MEASURED WITH 4D FLOW MRI

Introduction: Clinical scores used for stroke risk estimation in atrial fibrillation (AF) have limited predictive accuracy. 4D Flow MRI can acquire blood flow in a volume data set encompassing the entire left atrium (LA) with quantification of blood velocity in 3 orthogonal directions for every voxel at multiple time points throughout the cardiac cycle (4D = 3D coverage + time). Hypothesis: 4D Flow MRI can assess 3D LA flow abnormalities in AF patients, which may potentially be linked to stroke. Methods: We performed 4D flow MRI in 30 volunteers (10 young, 20 older) and 70 patients with a history of AF: 40 in sinus rhythm (AF-sinus) and 30 in AF during MRI scan (AF-afib). The typical LA contained 3000 voxels and 18 phases per voxel. LA flow velocity histograms for each patient were quantified by mean LA velocity, median LA velocity, and the percentage of LA velocities < 0.2 m/s (%stasis). CHA2DS2-VASc scores were calculated for each patient. Results: Mean LA velocity, median LA velocity, and %stasis were significantly different between groups: young volunteers (0.26±0.02 m/s, 0.23±0.02 m/s, 37.3±7.6%), older volunteers (0.21±0.03 m/s, 0.20±0.03 m/s, 52.2±16.0%), AF-sinus (0.18±0.03 m/s, 0.17±0.03 m/s, 67.5±16.9%), and AF-afib (0.16±0.01 m/s, 0.14±0.03 m/s, 78.2±12.9%), p < 0.0125 for all comparisons. CHA2DS2-VASc had moderate but significant correlations with mean LA velocity (R 2 =0.27, p<0.001), median LA velocity (R 2 =0.23, p<0.001), and stasis% (R 2 =0.26, p<0.001). LA flow indices also correlated significantly with age, LA volume, and left ventricular ejection fraction (LVEF) as seen in the Table. Conclusions: Left atrial 4D flow MRI is a novel approach to identify patients with reduced LA blood velocities and increased LA stasis. Further study is needed to determine whether these measures can improve upon the CHA2DS2-VASc score for stroke risk prediction and enhance individual decisions on anticoagulation in patients with AF.

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

Journal of Cardiovascular Magnetic Resonance ◽

10.1186/s12968-021-00729-0 ◽

2021 ◽

Vol 23 (1) ◽

Author(s):

Marco Spartera ◽

Guilherme Pessoa-Amorim ◽

Antonio Stracquadanio ◽

Adam Von Ende ◽

Alison Fletcher ◽

...

Keyword(s):

Atrial Fibrillation ◽

Blood Pressure ◽

Heart Rate ◽

Cardiovascular Magnetic Resonance ◽

Magnetic Resonance ◽

Sinus Rhythm ◽

Left Atrial ◽

Peak Velocity ◽

4D Flow ◽

Mean Velocity

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.

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Sildenafil Administration Improves Right Ventricular Function on 4D Flow MRI in Young Adults Born Premature

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00824.2020 ◽

2021 ◽

Author(s):

Philip A Corrado ◽

Gregory P Barton ◽

Christopher J François ◽

Oliver Wieben ◽

Kara N Goss

Keyword(s):

Heart Rate ◽

Young Adults ◽

Kinetic Energy ◽

Right Ventricular ◽

Right Atrial ◽

4D Flow Mri ◽

4D Flow ◽

Direct Flow ◽

Flow Mri ◽

Rv Function

Background: Extreme preterm birth conveys an elevated risk of heart failure by young adulthood. Smaller biventricular chamber size, diastolic dysfunction, and pulmonary hypertension may contribute to reduced ventricular-vascular coupling. However, how hemodynamic manipulations may affect right ventricular (RV) function and coupling remains unknown. Methods: As a pilot study, 4D flow MRI was used to assess the effect of afterload reduction and heart rate reduction on cardiac hemodynamics and function. Young adults born premature were administered sildenafil (a pulmonary vasodilator) and metoprolol (a beta blocker) on separate days, and MRI with 4D flow completed before and after each drug administration. Endpoints include cardiac index (CI), direct flow fractions, and ventricular kinetic energy including E/A wave kinetic energy ratio. Results: Sildenafil resulted in a median CI increase of 0.24 L/min/m2 (P=0.02), mediated through both an increase in heart rate (HR) and stroke volume. Although RV ejection fraction improved only modestly, there was a significant increase (4% of end diastolic volume) in RV direct flow fraction (P=0.04), consistent with hemodynamic improvement. Metoprolol administration resulted in a 5-bpm median decrease in HR (P=0.01), a 0.37 L/min/m2 median decrease in CI (P=0.04), and a reduction in time-averaged kinetic energy (KE) in both ventricles (P<0.01), despite increased RV diastolic E/A KE ratio (P=0.04). Conclusions: Despite reduced right atrial workload, metoprolol significantly depressed overall cardiac systolic function. Sildenafil, however, increased CI and improved RV function, as quantified by the direct flow fraction. The preterm heart appears dependent on HR, but sensitive to RV afterload manipulations.

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