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

Abstract

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. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:136–145.

A smaller heart-aorta-angle associates with ascending aortic dilatation and increases wall shear stress

“…The patients' clinical treatment was unaffected by the study. The populations of the present study have also been analyzed in the prior publications [10,12,13].…”

“…Peak systolic WSS was obtained for the analysis. Intra-and interobserver reproducibility analyses for the flow parameters of the 4D flow have been previously published and proved to be moderate [10].…”

“…The imaging parameters were selected in line with the 4D flow consensus statement [14]. The detailed imaging procedure has been presented in a previous study [10].…”

“…The aortic ring was divided into six 60°segments. The starting point (0°) was defined to be in the inner curve of AA and segment 1 covering from 0°to 60°in a counter-clockwise direction [10]. Peak systolic WSS was obtained for the analysis.…”

“…In patients with AA dilatation, the aortic blood flow has been shown to be displaced even in the case of normal tricuspid aortic valve [10]. Furthermore, the displaced flow may lead to increased wall shear stress (WSS) on the displaced side of the AA [10]. A bicuspid aortic valve (BAV) and aortic stenosis have also been shown to associate with increased WSS values [11].…”