Flow displacement and decreased wall shear stress might be associated with the growth rate of an ascending aortic dilatation.

OBJECTIVES: Our goal was to evaluate whether four-dimensional (4D) flow magnetic resonance imaging (MRI) can predict the growth rate of dilatation of the ascending aorta (AA) in patients with a tricuspid, normally functioning aortic valve. METHODS: In this prospective clinical study, aortic 4D flow MRI was performed at the Kuopio University Hospital on 30 patients diagnosed with AA dilatation (maximum diameter >40 mm) between August 2017 and July 2020. The MRI was repeated after a 1-year follow-up, with AA dimensions and 4D flow parameters analysed retrospectively at both time points. The standard error of measurement was used to assess the statistical significance of the growth rate of AA dilatation. Flow displacement (FD) was transformed to a class-scaled parameter using FD ≥5% as a threshold. RESULTS: Statistically significant growth [median 2.1 mm (1.5-2.2 mm); P = 0.03] was detected in 6 male patients (20%); the AA diameter remained unchanged [0.2 mm (-0.3 to 0.9 mm)] in 24 patients (80%). An increased FD at the baseline was associated with significant growth during the 1-year follow-up in the proximal AA. An association was detected between decreased total wall shear stress and significant aortic growth in the inner curve of the sinotubular junction [529 mPa (449-664 mPa) vs 775 mPa (609-944 mPa); P = 0.03] and the anterior side of the proximal aortic arch [356 mPa (305-367 mPa) vs 493 mPa (390-586 mPa); P < 0.001]. CONCLUSIONS: FD and decreased wall shear stress seem to be associated with significant growth of AA dilatation at the 1-year follow-up. Thus, 4D flow MRI might be useful in assessing risk for AA diameter growth in patients with a tricuspid aortic valve.

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

OBJECTIVES: The aim of this study was to evaluate whether the orientation of the heart, measured as an angle between the long axis of the heart and ascending aorta midline (heart-aorta-angle, HAA), associates with ascending aortic (AA) dilatation. Furthermore, the association between HAA and wall shear stress (WSS) was studied. METHODS: HAA was retrospectively measured in 1000 consecutive coronary artery computed tomographic angiography (CCTA) images in patients with low-to-moderate pretest probability for coronary artery disease (CAD). To evaluate the effects of HAA on AA flow, 4D flow MRI was performed for 28 patients with AA dilatation (> 40 mm) and WSS was analyzed. RESULTS: The mean age of patients undergoing CCTA was 52.9 ± 9.8 years; 66.5% were women. Their median HAA was 128.7° and interquartile range 123.3-134.1°. HAA was significantly smaller in patients with dilated AA (median 126.7° [121.3-130.8°]) compared with the patients with normal AA (median 129.5° [124.3-135.3°], p < 0.001). HAA was smaller in males (p < 0.001) and in patients with diabetes (p = 0.016), hypertension (p = 0.001), CAD (p = 0.003), hypercholesterolemia (p < 0.001), and bicuspid aortic valve (p = 0.025) than without these factors. In a subpopulation without any of these underlying diseases (n = 233), HAA was still significantly smaller in the patients with dilated AA (median 127.9° [124.3-134.3°]) compared with patients with normal AA (median 131.9° [127.6-136.9°], p = 0.013). In 4D flow MRI, a smaller HAA correlated with increased total WSS in the outer curvature of the proximal AA (r = - 0.510, p = 0.006). CONCLUSION: A smaller HAA associates with AA dilatation and affects the blood flow in the proximal AA. KEY POINTS: • A smaller angle between the long axis of the heart and ascending aorta midline associated with ascending aortic dilatation. • A smaller heart-aorta-angle correlated with increased total wall shear stress in the outer curvature of the proximal ascending aorta.

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. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:136-145.