Analysis of aortic pressure fields from 4D flow MRI in healthy volunteers: Associations with age and left ventricular remodeling.

BACKGROUND

Aging-related arterial stiffness is associated with substantial changes in global and local arterial pressures. The subsequent early return of reflected pressure waves leads to an elevated left ventricular (LV) afterload and ultimately to a deleterious concentric LV remodeling.

PURPOSE

To compute aortic time-resolved pressure fields of healthy subjects from 4D flow MRI and to define relevant pressure-based markers while investigating their relationship with age, LV remodeling, as well as tonometric augmentation index (AIx) and pulse wave velocity (PWV).

STUDY TYPE

Retrospective.

POPULATION

Forty-seven healthy subjects (age: 49.5 ± 18 years, 24 women).

FIELD STRENGTH/SEQUENCE: 3 T/4D flow MRI.

ASSESSMENT

Spatiotemporal pressure fields were computed by integrating velocity-derived pressure gradients using Navier-Stokes equations, while assuming zero pressure at the sino-tubular junction. To quantify aortic pressure spatiotemporal variations, we defined the following markers: 1) volumetric aortic pressure propagation rates ΔP /ΔV and ΔP /ΔV, representing variations of early and late systolic relative pressure peaks along the aorta, respectively, according to the cumulated aortic volume; 2) ΔA defined in four aortic regions as the absolute difference between early and late systolic relative pressure peaks amplitude.

STATISTICAL TESTS

Linear regression, Wilcoxon rank sum test, Bland-Altman analysis, and intraclass correlation coefficients (ICC).

RESULTS

Spatiotemporal variations of aortic pressure peaks were moderately to highly reproducible (ICC ≥0.50) and decreased significantly with age, in terms of absolute magnitude: ΔP /ΔV (r = 0.70, P < 0.005), ΔP /ΔV (r = -0.45, P < 0.005) and ΔA (|r| > 0.39, P < 0.005). ΔP /ΔV was associated with LV remodeling (r = 0.53, P < 0.001) and ascending aorta ΔA was associated with AIx (r = -0.59, P < 0.001). Both associations were independent of age and systolic blood pressures. Only weak associations were found between pressure indices and PWV (r ≤ 0.40).

DATA CONCLUSION

4D flow MRI relative aortic pressures were consistent with physiological knowledge as demonstrated by their significant volumetric and temporal variations with age and their independent association with LV remodeling and augmentation index. Level of Evidence 2 Technical Efficacy Stage 3 J. Magn. Reson. Imaging 2019;50:982-993.