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HELICAL STE NTS

HELICAL STE NTS. C.G.Caro Department of Bioengineering Imperial College. ARTERIAL STENTING. Arterial stenting for atherosclerosis increasing Challenges of stenting: Intimal hyperplasia (IH), stent kinking and fracture

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HELICAL STE NTS

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  1. HELICAL STENTS C.G.Caro Department of Bioengineering Imperial College

  2. ARTERIAL STENTING • Arterial stenting for atherosclerosis increasing • Challenges of stenting: Intimal hyperplasia (IH), stent kinking and fracture Drug-eluting stents retard IH development, but can delay endothelial repair and risk of in-stent thrombosis

  3. INTIMAL HYPERPLASIA • Highly important disease : causes failure of arterial stents, bypass grafts, vascular access grafts, balloon angioplasty, a-v fistulae • Pathology: accumulation of smooth muscle cells and extracellular matrix in intima • Causation: possibly vessel damage but, like atherosclerosis, IH influenced by flow - favours low wall shear/stagnation regions

  4. LARGER ARTERY FLOW AND GEOMETRY Reynolds number >> 1 (inertially dominated flow) Three-dimensional (non-planar) geometry

  5. FEATURES OF INERTIALLY DOMINATED NON-PLANAR FLOWS • Swirling • Cross-mixing Inhibition of flow stagnation, separation and instability Relatively uniform distribution of wall shear Enhanced blood-wall mass transport (including oxygen)

  6. Toe 1-D 3-D Planar MRI of flow in model bypass graft Non-planar

  7. Computational study of swirling and mixing in a helical tube Reynolds number 200, amplitude ratio 0.5, pitch 5 diameters

  8. Re = 1000 from “Studies of Planar & Non-Plaar flow”July 1998 Files: bend side.avi, bend top.avi approx 0’20”

  9. U-bend

  10. Helical Stent

  11. Angiograms post stent implantation in pig common carotid arteries Rt Straight Lt Helical Rt Straight Lt Helical 3547 Helical stent: helical deformation of artery and swirling of blood flow immediately after implantation of stent Straight stent: no swirling of flow

  12. Transverse sections of pig common carotid arteries one month post stent implantation

  13. MECHANICAL PROPERTIES OF HELICAL STENTS • Cadaver superficial femoral artery: helical stents kink less than conventional stents on flexing knee • Computational studies: lower local stresses on deforming helical than conventional stents • Bench tests: helical stents far less likely to fracture than conventional stents

  14. CONCLUSIONS • Less intimal hyperplasia with helical than conventional (straight) stents • Improvement due to swirling and mixing, improving wall shear and blood-wall mass transport, including of oxygen? • Intimal hyperplasia caused by vessel injury and compromised wall shear and mass transport? • First-in-man studies planned

  15. ACKNOWLEDGEMENTS To many colleagues over many years, including at Veryan Medical Limited

  16. U-bend movie

  17. MRI Toe y Toe wall Bed wall Bed x CFD

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