Influence of Stent Flexibility on Artery Wall Stress and Wall Shear Stress in Bifurcation Lesions

Figures

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  Figure 1. Flattened surface view of the Multi-link 8 and Kaname stents compared in this study for implantation in bifurcated artery sites and an illustration of the test method of stent flexibility. (A) The Multi-link 8 stent is made from L605 cobalt chromium with a strut thickness of 81 μm. The inner diameter is 3.0 mm and the surface consists of six crowns with a strut width ranging from 76 μm to 102 μm.31 The data used to create the flattened surface view were created by reverse engineering of the product. (B) The Kaname stent is also made from L605 cobalt chromium and has a similar strut thickness (80 μm) and inner diameter (3.0 mm). The surface consists of eight crowns with a strut width ranging from 90 μm to 100 μm. (C) Stent flexibility was evaluated as a force required for a 0.5-mm displacement when a point on the stent 7 mm from the fixture was nudged.

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  Figure 2. Changes in bifurcation geometry following stent implantation. (A) Angiographic images of the artery before (left) and after (right) implantation of the Multi-link 8 stent. (B) Angiographic images of the artery before (left) and after (right) implantation of the Kaname stent. The degree of artery angulation is defined as the angle between the proximal artery segment and the distal artery segment. The proximal edge angle is the angle between the proximal artery segment and the stented artery segment, and the side branch angle is the angle between the daughter artery and the side branch. The change in angulation was numerically greater in the Multi-link 8 implantation group, while other metrics showed no consistent group differences (see Table 1).

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  Figure 3. Histological abnormalities at artery bifurcations following stent placement. Shown are longitudinal hematoxylin-eosin (HE)-stained sections (×12.5) of bifurcation artery sites implanted with the Multi-link8 stent (A) or the Kaname stent (B) for 28 days. Adventitia inflammation and internal elastic lamina (IEL) injury (▲) and neointima hyperplasia (↑) were observed mainly at distal sites opposite side branches. Lower images (C) Elastica trichrome staining (×12.5 and ×100) of the bifurcation artery site from animal No. 2 implanted with the Multi-link 8 stent for 28 days.

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  Figure 4. Scanning electron microscopy (SEM) images of the endothelium at bifurcating artery sites implanted with the Multi-ink 8 stent and their binarized images showing distinct cell morphology according to the level of wall shear stress. Endothelial cells at the distal region opposite side branches were round or cobblestone in shape with adherent leukocytes. The binarized images were obtained by the binarization of original images, and the cell shape index (Y long axis divided by X short axis) was analyzed using the image processing program ImageJ.

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  Figure 5. Representative 3-D wall shear stress distribution in bifurcation artery sites implanted with the Multi-link8 stent (A) or Kaname stent (B) on day 0 and corresponding longitudinal histopathological and angiographic images on day 28. In both stent groups, the distribution of neointima hyperplasia (arrows) matched regions of low wall shear stress (blue areas) simulated by computational fluid dynamics (CFD).

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  Figure 6. Changes in flow velocity vector contours and low WSS areas at a bifurcating artery following stent placement. Left upper panel: The 2-D velocity contours for the curved bifurcation model (subject to Murray’s law) in the non-stented condition (Model A). Left lower panel: Worse-case stent placement model (Model B) created by extreme straightening (reduced bifurcation angle). The high-velocity blood flow in the curved bifurcation is further shifted toward the outer curve in Model B, and the blood flow near the inner curve is decreased with the generation of neither vortex flow nor inverted flow (left panels). The low WSS (<1.0 Pa) region is expanded by stenting (right panels).