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

Abstract

BackgroundThe 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. PurposeTo evaluate whether four-dimensional (4D) flow characteristics determined in MRI are related to AA dilatation by comparing dilated AA and non-dilated AA subjects with TAV. Study type Prospective.Population 20 patients with dilated AA, 20 age-matched patients with non-dilated AA. Field Strength/Sequence1.5T/4D flow, 2D flow and anatomic images. AssessmentAltogether 16 different 4D flow parameters were assessed in 10 planes in the thoracic aorta. Intra-and inter-observer reproducibility were analyzed. Statistical testIndependent T-test for normal-distributed and Mann-Whitney-test for skewed distributed parameters were used. Paired-samples T-test was used to compare 2D and 4D flow parameters. Intraclass correlation coefficient (ICC) was used in intra-and inter-observer reproducibility analysis. ResultsAortic flow was displaced from the center line 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 non-dilated 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 whole aortic ring in the distal AA (p<0.001). Depending on 4D flow parameter, reproducibility varied from excellent (ICC=0.923) to very low (ICC=0.204). Data conclusionThe 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.

High prevalence of ascending aortic dilatation in a consecutive coronary CT angiography patient population

“…Intra-and interobserver reproducibility analyses for measurements of AA diameter were not performed in the present study. However, in our prior study with 1.5-T aortic magnetic resonance angiography, interobserver reproducibility was shown to be excellent (ICC = 0.917) with 20 dilated AA and 20 non-dilated AA patients [7]. Lu et al showed in a small 30-patient CT population that the maximum variability was 1.2 mm in the measured AA diameter and low variability indicated that AA diameter is a reliable measurement [25].…”

“…Furthermore, it has been related to hypertension and smoking [4][5][6]. The hemodynamic conditions in the aorta play a significant role in determining TAD [7]. In particular, the bicuspid aortic valve (BAV) often causes valvular dysfunction (stenosis and regurgitation) and abnormal flow in the ascending aorta.…”

Automated Quantitative Extraction and Analysis of 4D flow Patterns in the Ascending Aorta: An intraindividual comparison at 1.5 T and 3 T

“…It is known that somehow bigger and longer helices with a "mismatch" between the volume of the helix and aorta could lead to aortic dilatation or elevated wall shear stress 21,31,32 . However, further studies are needed to evaluate which parameters are best for the assessment of pathologic flow patterns.…”

Assessment of hemodynamic responses to exercise in aortic coarctation using MRI-ergometry in combination with computational fluid dynamics

“…Increased WSS has been associated with aortic dilatation 32 , 33 , endothelial cell dysfunction 34 , 35 , development of atherosclerotic plaque 36 , as well as the formation of intracranial aneurysms 31 . WSS and secondary flow have already shown to be increased in patients with aortic coarctation 37 , 38 at rest.…”