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Bicuspid aortic cusp fusion morphology alters aortic three-dimensional outflow patterns, wall shear stress, and expression of aortopathy.

ABSTRACT: BACKGROUND:Aortic 3-dimensional blood flow was analyzed to investigate altered ascending aorta (AAo) hemodynamics in bicuspid aortic valve (BAV) patients and its association with differences in cusp fusion patterns (right-left, RL versus right-noncoronary, RN) and expression of aortopathy. METHODS AND RESULTS:Four-dimensional flow MRI measured in vivo 3-dimensional blood flow in the aorta of 75 subjects: BAV patients with aortic dilatation stratified by leaflet fusion pattern (n=15 RL-BAV, mid AAo diameter=39.9±4.4 mm; n=15 RN-BAV, 39.6±7.2 mm); aorta size controls with tricuspid aortic valves (n=30, 41.0±4.4 mm); healthy volunteers (n=15, 24.9±3.0 mm). Aortopathy type (0-3), systolic flow angle, flow displacement, and regional wall shear stress were determined for all subjects. Eccentric outflow jet patterns in BAV patients resulted in elevated regional wall shear stress (P<0.0125) at the right-anterior walls for RL-BAV and right-posterior walls for RN-BAV in comparison with aorta size controls. Dilatation of the aortic root only (type 1) or involving the entire AAo and arch (type 3) was found in the majority of RN-BAV patients (87%) but was mostly absent for RL-BAV patients (87% type 2). Differences in aortopathy type between RL-BAV and RN-BAV patients were associated with altered flow displacement in the proximal and mid AAo for type 1 (42%-81% decrease versus type 2) and distal AAo for type 3 (33%-39% increase versus type 2). CONCLUSIONS:The presence and type of BAV fusion was associated with changes in regional wall shear stress distribution, systolic flow eccentricity, and expression of BAV aortopathy. Hemodynamic markers suggest a physiological mechanism by which the valve morphology phenotype can influence phenotypes of BAV aortopathy.

SUBMITTER: Mahadevia R

PROVIDER: S-EPMC3946057 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature

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Bicuspid aortic cusp fusion morphology alters aortic three-dimensional outflow patterns, wall shear stress, and expression of aortopathy.

Mahadevia Riti R Barker Alex J AJ Schnell Susanne S Entezari Pegah P Kansal Preeti P Fedak Paul W M PW Malaisrie S Chris SC McCarthy Patrick P Collins Jeremy J Carr James J Markl Michael M

Circulation 20131217 6

<h4>Background</h4>Aortic 3-dimensional blood flow was analyzed to investigate altered ascending aorta (AAo) hemodynamics in bicuspid aortic valve (BAV) patients and its association with differences in cusp fusion patterns (right-left, RL versus right-noncoronary, RN) and expression of aortopathy.<h4>Methods and results</h4>Four-dimensional flow MRI measured in vivo 3-dimensional blood flow in the aorta of 75 subjects: BAV patients with aortic dilatation stratified by leaflet fusion pattern (n=1 ...[more]

PMID: 24345403

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Project description:OBJECTIVES:The objectives of this study were to investigate an association between the magnitude of flow-mediated aortic wall shear stress (WSS) and medial wall histopathology in patients with bicuspid aortic valve (BAV) with aortopathy. METHODS:Patients with BAV (n = 27; 52 ± 15 years; 3 women; proximal thoracic aorta diameter = 4.4 ± 0.7 and 4.6 ± 0.5 cm) who underwent prophylactic aortic resection received preoperative 3-dimensional time-resolved phase-contrast magnetic resonance imaging with 3-dimensional velocity encoding to quantify WSS relative to a population of healthy age- and sex-matched tricuspid aortic valve control participants (n = 20). Quantitative histopathology was conducted on BAV aorta tissue samples resected at surgery (n = 93), and correlation was performed between elastic fiber thickness and in vivo aortic WSS as continuous variables. Validation of elastic fiber thickness was achieved by correlation relative to tissue stiffness determined using biaxial biomechanical testing (n = 22 samples). RESULTS:Elastic fibers were thinner and WSS was higher along the greater curvature compared with other circumferential regions (vs anterior wall: P = .003 and P = .0001, respectively; lesser curvature: both P = .001). Increased regional WSS was associated with decreased elastic fiber thickness (r = -0.25; P = .02). Patient stratification with subanalysis showed an increase in the correlation between WSS and histopathology with aortic valve stenosis (r = -0.36; P = .002) and smaller aortic diameters (<4.5 cm: r = -0.39; P = .03). Elastic fiber thinning was associated with circumferential stiffness (r = -0.41; P = .06). CONCLUSIONS:For patients with BAV, increased aortic valve-mediated WSS is significantly associated with elastic fiber thinning, particularly with aortic valve stenosis and in earlier stages of aortopathy. Elastic fiber thinning correlates with impaired tissue biomechanics. These novel findings further implicate valve-mediated hemodynamics in the progression of BAV aortopathy.

Project description:ObjectivesA bicuspid aortic valve (BAV) is characterized by variable phenotypic manifestations, as well as longitudinal evolution of valve dysfunction and ascending aorta dilatation. The present study investigated the impact of severe aortic stenosis (AS) on the flow patterns and wall shear stress (WSS) distribution in BAV patients with right-left (RL) and right-non-coronary (RN) cusp fusion types, and the study aimed to reveal whether aortic dysfunction could further alter intrinsic aortic haemodynamic aberrations generated by abnormal BAV cusp fusion patterns.MethodsFour-dimensional flow magnetic resonance imaging was performed in 120 BAV subjects and 20 tricuspid aortic valve controls. BAV patients were evenly categorized into 4 cohorts, including RL and RN BAV with no more than mild aortic dysfunction as well as RL and RN BAV-AS with isolated severe AS.ResultsBAV subjects exhibited eccentric outflow jets resulting in regional WSS elevation at the right-anterior position of the ascending aorta in the RL group and the right-posterior location in the RN group (P?<?0.005). The presence of severe AS resulted in accelerated outflow jets and more prominent flow and WSS eccentricity (P?<?0.005) by marked helical (P?=?0.014) and vortical flow formation (P?<?0.005), as well as increased prevalence of tubular and transverse arch dilatation. The changes to the flow jet in BAV-AS subjects blurred the differences in peak flow velocity and WSS distribution between RL and RN BAV. Differences in the phenotypes of aortopathy were associated with changes in functional haemodynamic parameters such as flow displacement and WSS eccentricity.ConclusionsSevere AS markedly exacerbated aortic flow aberrations in BAV patients and masked the existing distinct flow features deriving from RL and RN fusion types. Longitudinal studies are needed to investigate the evolution of ascending aortic dilatation relative to the interaction between intrinsic cusp fusion types and acquired severe valve dysfunction.

Dataset Information

Bicuspid aortic cusp fusion morphology alters aortic three-dimensional outflow patterns, wall shear stress, and expression of aortopathy.

Publications

Bicuspid aortic cusp fusion morphology alters aortic three-dimensional outflow patterns, wall shear stress, and expression of aortopathy.

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