Aortic dilatation associates with flow displacement and increased circumferential wall shear stress in patients without aortic stenosis: A prospective clinical study

Background The relationship between blood flow characteristics and ascending aortic (AA) dilatation has not been studied in patients with a tricuspid aortic valve (TAV) without aortic stenosis. Purpose To evaluate whether 4D flow characteristics determined in MRI are related to AA dilatation by comparing dilated AA and nondilated AA subjects with TAV. Study Type Prospective. Population Twenty patients with dilated AA and 20 age-matched patients with nondilated AA. Field Strength/Sequence 1.5T/4D flow, 2D flow, and anatomic images. Assessment Altogether, 16 different 4D flow parameters were assessed in 10 planes in the thoracic aorta. Intra- and interobserver reproducibility were analyzed. Statistical Tests Independent t-test for normally distributed and the Mann-Whitney test for skewed distributed parameters were used. A paired-samples t-test was used to compare 2D and 4D flow parameters. Intraclass correlation coefficient (ICC) was used in intra- and interobserver reproducibility analysis. Results Aortic flow was displaced from the centerline of the aorta in the proximal and tubular planes. Flow displacement (FD) was greatest in the proximal plane of AA and was higher in dilated AA (4.5%, range 3.0-5.8%) than in nondilated AA (2.0%, 1.0-3.0%, P < 0.001). Total wall shear stress (WSS) values were 1.3 +/- 0.4 times higher on the displaced side than on the opposite side of the aorta (P < 0.01). The circumferential WSS (WSSC) ratio to total WSS was greater in dilated AA, being 0.48 +/- 0.11 vs. 0.32 +/- 0.09 in the inner curvature of the proximal AA (P < 0.001) and 0.37 +/- 0.11 vs. 0.26 +/- 0.07 in the whole aortic ring in the distal AA (P < 0.001). Depending on 4D flow parameters, reproducibility varied from excellent (ICC = 0.923) to very low (ICC = 0.204). Data Conclusion The present study demonstrates that 4D flow measurements help to visualize the pathological flow patterns related to aortic dilatation. Flow displacement and an increased WSSc/WSS ratio are significantly associated with AA dilatation. Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:136-145.