Wall Shear Stress In Ascending Aorta Research Articles

Leaflets fusion length in bicuspid aortic valve is related to ascending and aortic root dilation and ascending aorta wall shear stress

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Spanish Ministry of Science, Innovation and Universities, Instituto de Salud Carlos III Background Bicuspid aortic valve (BAV) is the most common congenital heart defect, consisting in the fusion of two aortic valve leaflets. Altered flow patterns have been related to aortic wall degeneration in BAV patients and may be responsible for the high prevalence of aortic disease in these patients. A number of studies on excised BAV or using advanced imaging modalities reported a wide variability of fusion extent between leaflet, but no previous study assessed whether leaflet fusion length may be used to stratify BAV patients. Purpose We aimed to test whether leaflet fusion extent can be quantified by cardiac magnetic resonance imaging (CMR) and whether it is related to aortic dilation and flow abnormalities in non-dysfunctional BAV. Methods One hundred and twenty BAV adults with no previous aortic or aortic valve surgery or significant valvular disease were consecutively enrolled. Patients with two sinuses of Valsalva (true BAV) or fusion of the left and non-coronary cusps, both being rare forms of BAV, were excluded. Twenty-eight healthy volunteers were also included for comparison. A 4D flow CMR sequence was acquired and circumferential wall shear stress and pulse wave velocity were assessed in the ascending aorta. A stack of double-oblique cine images of the aortic valve were used to quantify the length of the fusion between leaflets. Results The length of the fusion between leaflets was effectively measured in 112/120 patients (93%). Reproducibility was good (ICC = 0.826). Fusion length varied greatly (range 2.3 – 15.4 mm, 7.8 ± 3.2 mm, tertiles cut-off points were 6 and 9.3 mm). After correction for age, BSA, stroke volume and BAV fusion morphotype, fusion length was independently associated with diameter at the sinus of Valsalva (p = 0.002). Moreover, once corrected for age, stroke volume and ascending aorta pulse wave velocity, fusion length was positively related to ascending aorta diameter (p = 0.028). The comparison of maps of circumferential peak-systolic WSS in healthy volunteers (left) and BAV patients pertaining to the three leaflet fusion length tertiles is shown in Figure 1. Circumferential WSS progressively increase with larger fusion length. This trend was statistically significant (p < 0.05) in the right and outer regions of the proximal and mid ascending aorta. Conclusions Bicuspid aortic leaflet fusion length varies considerably and it is independently associated with ascending aorta and aortic root dilation, possibly through flow alterations. Abstract Figure 1

Ascending aortic wall shear stress and distensibility are different in patients with corrected atrioventricular septal defect compared to healthy controls: a comprehensive CMR and 4D flow MRI evaluation

Background In patients with an atrioventricular septal defect (AVSD), the left ventricular outflow tract (LVOT) and the ascending aorta (AAo) are located more anteriorly due to the position of the common AV valve. This may alter proximal aortic flow, and we hypothesize that this can result in impaired LV systolic function and AAo wall degeneration. We aimed to quantify differences in AAo wall shear stress (WSS), distensibility (Dist), aortic arch pulse wave velocity (PWV) and LV ejection fraction (EF) in these patients versus healthy controls using cardiovascular magnetic resonance (CMR) and four dimensional (4D) flow MRI.

Bicuspid aortic valve hemodynamics does not promote remodeling in porcine aortic wall concavity.

To investigate the role of type-I left-right bicuspid aortic valve (LR-BAV) hemodynamic stresses in the remodeling of the thoracic ascending aorta (AA) concavity, in the absence of underlying genetic or structural defects. Transient wall shear stress (WSS) profiles in the concavity of tricuspid aortic valve (TAV) and LR-BAV AAs were obtained computationally. Tissue specimens excised from the concavity of normal (non-dilated) porcine AAs were subjected for 48 h to those stress environments using a shear stress bioreactor. Tissue remodeling was characterized in terms of matrix metalloproteinase (MMP) expression and activity via immunostaining and gelatin zymography. Immunostaining semi-quantification results indicated no significant difference in MMP-2 and MMP-9 expression between the tissue groups exposed to TAV and LR-BAV AA WSS (P = 0.80 and P = 0.19, respectively). Zymography densitometry revealed no difference in MMP-2 activity (total activity, active form and latent form) between the groups subjected to TAV AA and LR-BAV AA WSS (P = 0.08, P = 0.15 and P = 0.59, respectively). The hemodynamic stress environment present in the concavity of type-I LR-BAV AA does not cause any significant change in proteolytic enzyme expression and activity as compared to that present in the TAV AA.

Beta-blocker therapy does not reduce ascending aorta wall shear stress in patients with bicuspid aortic valve

Methods Right-left coronary leaflet fusion BAV patients on b-blockers (BB+) (n = 30, M:F = 23:7, age: 46 ± 14 years) and not on b-blockers (BB-) (n=30, M:F = 23:7, age: 46 ± 13 years) and healthy controls (n=15, age:43±11 years) underwent time-resolved, 3D phase contrast (4D flow) MRI. Patient groups were matched by systolic blood pressure (SBP), degree of aortic stenosis (AS), and AAo diameter (3.9 ± 0.7 vs. 3.9 ± 0.6 cm, p = 0.70). A 3D segmentation of the thoracic aorta was performed (MIMICS, Materlise, Belgium). Systolic 3D WSS was calculated in the thoracic aorta from 4D flow velocity acquisition and a sagittal maximum intensity projection (MIP) of WSS was generated.

Impact of beta-blocker therapy on thoracic aorta 3D wall shear stress in patients with bicuspid aortic valve

Background Beta-blockers are the recommended medical treatment for slowing ascending aorta (AAo) dilation in patients with bicuspid aortic valve (BAV). Wall shear stress (WSS) has been shown to promote endothelial cell dysfunction [1] and AAo WSS may play a role in aortic aneurysm growth. Time-resolved 3D phase contrast (4D flow) MRI allows for the quantification of 3D WSS regionally in the thoracic aorta. The aim of this study was to assess changes in thoracic aorta WSS associated with b-blocker therapy in BAV patients.

From unicuspid to quadricuspid: the impact of aortic valve morphology on 3D hemodynamics

Background The purpose of this study was to assess the impact of aortic valve morphology on aortic 3D blood flow dynamics and wall shear stress (WSS) in normal and a wide range of congenitally altered aortic valves ranging from unicuspid to quadricuspid morphology. Methods In-vivo aortic 3D hemodynamics were evaluated by MRI in 17 patients with unicuspid (n=3), bicuspid (n=9, 3 true bicuspid, 3 right-left (RL) coronary leaflet fusion, and 3 right-non (RN) coronary leaflet fusion), trileaflet (n=3), and quadricuspid aortic valves (n=2). Valve morphology and dynamics were assessed using 2D CINE MRI. Aortic blood flow was measured using ECG and respiration synchronized 4D flow MRI with full volumetric coverage of the aorta. Data analysis included co-registered visualization of aortic valve morphology with systolic 3D blood flow and grading of valve-specific aortic out-flow patterns. The influence of valve geometry on aortic hemodynamics was quantified by calculation of valve flow angle and segmental distribution of ascending aorta WSS. Results All congenitally altered valves showed marked flow derangement, elevated velocity jets along the aortic wall and distinct flow impingement locations. While all RLBAV valves were associated with flow jets directed towards the right anterior aortic wall, RN-fusion and unicuspid valves showed jet patterns towards the right-posterior wall. Quantitative analysis revealed higher flow angles for unicuspid, true BAV, RN-BAV, RL-BAV, and quadricuspid