The prevalence of cardiovascular disease (CVD) has increased dramatically due in part to the increased rates of obesity in North America. Atherosclerosis, the most prevalent type of CVD, is a progressive disease characterized by the build-up of plaque within the arteries. The plaque development leads to the narrowing of arteries, referred to as stenosis, and restricts crucial blood flow to the organs of the body. This condition is often treated by the implantation of a stent, a wire mesh scaffold device placed in the region of an atherosclerotic plaque after balloon angioplasty. The stent was developed to improve the clinical outcome of angioplasty procedures by mitigating the effects of elastic recoil by the vessel wall and maintaining vessel patency after angioplasty. Since the introduction of stents as a treatment option over a decade ago, in-stent restenosis (ISR) has been an iatrogenic outcome and remains an unsolved limitation of the interventional treatment device, resulting in stent failure and additional surgical procedures to restore blood flow. Many improvements have been made in stent design in order to reduce the likelihood of ISR, but none have eliminated the problem. Endothelial cells lining vessel walls transduce local hemodynamic loading in the stent vicinity, such as wall shear stress magnitude (WSS), into biochemical signals that lead to the progression of ISR. Hence, resolving the hemodynamics in the vicinity of the stent is crucial to reducing the rates of stent failure. The objective of the study is to address the problem of ISR by clearly elucidating the flow physics induced by stent implantation, accounting in particular for vessel curvature, by first considering idealized stent models, then progressing to an actual stent model. Stent designs are typically based upon data originating solely from studies of flow in straight vessels, which, once optimized for this configuration, may lead to suboptimal performance when placed in tortuous vessels. Previous stent studies have almost categorically neglected the effects of curvature on the flow physics, despite the fact that even extremely mild curvature changes the axial WSSM distribution within the vessel and induces the development of secondary flows, which alters the advection of chemicals released into the lumen. Using computational fluid dynamics (CFD) techniques, this study seeks to (i) determine the impact of stent strut amplitude and frequency on primary and secondary flow structures; (ii) determine the significance of the stent strut shape in the size of the stagnation zone; (iii) evaluate flow behavior in the transition region from smooth walled to stented vessel; and (iv) examine the collection of these effects in a full stent model geometry in a curved tube. This study takes a systematic approach, dissecting the impact of the stent first into simplified foundational components, then investigating each component and finally synthesizing the components into a full stent model with the long-term goal of optimizing stent design to reduce the rate of restenosis. As well, the study findings can aid in understanding the signal transduction mechanisms of the endothelial cells, which play a role in the development of ISR, and reduce the cardiovascular disease mortality rate by improving the clinical outcome of treatment procedures. Further, the study findings contribute to the fundamental understanding of flow in curved pipes with wall protrusions, the impact of the choice of the constitutive model of the fluid, and the hemodynamic environment in the vicinity of the stent.

Background: Single-cohort studies suggest that second-generation stents (SGS; “mesh stents”) may improve carotid artery stenting (CAS) outcomes by limiting peri- and postprocedural cerebral embolism. SGS differ in the stent frame construction, mesh material, and design, as well as in mesh-to-frame position (inside/outside). Objectives: To compare clinical outcomes of SGS in relation to first-generation stents (FGSs; single-layer) in CAS. Methods: We performed a systematic review and meta-analysis of clinical studies with FGSs and SGS (PRISMA methodology, 3302 records). Endpoints were 30-day death, stroke, myocardial infarction (DSM), and 12-month ipsilateral stroke (IS) and restenosis (ISR). A random-effect model was applied. Results: Data of 68,422 patients from 112 eligible studies (68.2% men, 44.9% symptomatic) were meta-analyzed. Thirty-day DSM was 1.30% vs. 4.11% (p < 0.01, data for SGS vs. FGS). Among SGS, both Casper/Roadsaver and CGuard reduced 30-day DSM (by 2.78 and 3.03 absolute percent, p = 0.02 and p < 0.001), whereas the Gore stent was neutral. SGSs significantly improved outcomes compared with closed-cell FGS (30-day stroke 0.6% vs. 2.32%, p = 0.014; DSM 1.3% vs. 3.15%, p < 0.01). At 12 months, in relation to FGS, Casper/Roadsaver reduced IS (−3.25%, p < 0.05) but increased ISR (+3.19%, p = 0.04), CGuard showed a reduction in both IS and ISR (−3.13%, −3.63%; p = 0.01, p < 0.01), whereas the Gore stent was neutral. Conclusions: Pooled SGS use was associated with improved short- and long-term clinical results of CAS. Individual SGS types, however, differed significantly in their outcomes, indicating a lack of a “mesh stent” class effect. Findings from this meta-analysis may provide clinically relevant information in anticipation of large-scale randomized trials.

Le traitement endovasculaire des anévrismes de l’aorte (Endovascular Aneurysm Repair ou EVAR) est une chirurgie mini-invasive qui consiste à faire glisser une endoprothèse par voie fémorale jusqu’au niveau de l’anévrisme afin de re-canaliser le flux sanguin. Les principales complications qui peuvent survenir sont les phénomènes de migration et d’endofuites (écoulement persistant de sang dans le sac anévrismal) de type Ia. Ces phénomènes apparaissent lorsque l’étanchéité n’est plus assurée entre l’extrémité proximale de l’endoprothèse et le vaisseau sanguin. Dans ce travail, des simulations paramétrées de déploiement complet d’un système de pose de stent ont été développées en utilisant la Méthode des Éléments Finis (FEM) afin d’étudier la stabilité du contact lors du largage d’une endoprothèse en nitinol dans un Anévrisme de l’Aorte Thoracique (AAT) réaliste. Les facteurs suivants associés à ces complications ont été étudiés : (1) la longueur de la zone de fixation proximale (PASL), (2) la valeur de surdimensionnement ou « oversizing » du stent (O %), (3) la valeur du coefficient de frottement entre le stent et l’aorte (µ) et (4) l’angulation du collet proximal. L’influence de la présence de calcifications sur le comportement biomécanique de l’endoprothèse lors de son déploiement dans les zones de fixation a également été analysée. Les résultats des simulations ont montré qu’une PASL supérieure à 18 mm est un facteur décisif pour éviter la migration de l’endoprothèse pour une angulation du collet de l’anévrisme de 60° et dans des conditions de contact glissant (µ=0,05). L’augmentation de la valeur de l’oversizing de 10 % à 20 % améliore la résistance de la fixation de la prothèse. En revanche, un oversizing supérieur à 25 % pour une angulation du collet de 60° entraine des déformations excentriques ainsi que la ruine du stent. D’autre part, aucune migration n’a été observée dans un modèle d’aorte idéalisé où l’angulation du collet était de 0°, la PASL de 18 mm et le coefficient de frottement µ de 0,05. Afin d’améliorer le contact et de prévenir l’apparition de phénomènes de migration et d’endofuite de type Ia chez des patients présentant une aorte tortueuse et calcifiée avec un anévrisme fortement angulé, un nouveau design de stent a été proposé, basé sur les résultats des simulations numériques effectuées. La principale difficulté était de trouver un compromis entre flexibilité et raideur. Les résultats des simulations réalisées avec ce nouveau stent ont montré une amélioration de la stabilité de contact, ce qui a pour effet de limiter l’apparition des phénomènes de migration et donc de réduire les complications liées à la procédure endovasculaire. / The main mechanical related problems of endovascular aneurysm repair are migration and endoleak type Ia. They occur when there is no effective seal between the proximal end of stent-graft and the vessel. In this work, we have developed parameterized-deployment simulations of a complete stenting system using finite element method (FEM) to investigate the contact stiffness of a nitinol stent in a realistic Thoracic Aortic Aneurysm (TAA). Therefore, the following factors associated with these complications have evaluated: (1) Proximal Attachment Site Length (PASL), (2) stent Oversizing value (O %), (3) different contact friction situations (stent/aorta) and (4) proximal neck angulation. The calcification impact on the biomechanical behaviour of the deployment at the attachment zone has also been investigated. The simulation results showed that PASL>18mm was a crucial factor to prevent migration at a neck angle of 60⁰and smoothest contact condition (μ=0.05). The increase in (O %) ranging from 10% to 20% improved the fixation strength; however, O % ≥ 25% at 60° caused eccentric deformation and stent collapse. No migration was reported in an idealized aorta model with a neck angle of 0⁰, PASL=18mm and μ=0.05. The numerical observations are used as a guide to optimize the stent design in such neck morphology to strengthen the contact and prevent migration or endoleak type Ia. The optimized stent results showed better contact stability to resist the migration. They also showed a good compromise of stent design requirements (flexibility and stiffness). Moreover, the new design can also prevent the risk of folding or collapse of stent struts by mitigating the energy of eccentric deformation caused by high angulation and oversizing.