Vessel wall reactions to endovascular stent implantation

In order to gain insight in the effects of stenting, we studied the process of wound healing and the short- and long-term effect of these permanently present foreign bodies. Both thrombogenic and less thrombogenic metals were evaluated with respect to thrombogenicity and tissue response. Synthetic polymers were evaluated with respect to improving the haemocompatibility and tissue-compatibility profile of these devices. Stenting of normal porcine arteries. In Chapter 2, a balloon-expandable tantalum stent is described, tested in normal porcine coronary arteries for one and four weeks, and an indication is given of the process of wound healing and of the extent of intimal hyperplasia in these arteries. In chapter 3 a self-expanding stainless steel stent was tested in normal porcine coronary arteries. Luminal change was assessed at one, four, and twelve weeks using quantitative angiography, while histologic analysis was performed at twelve weeks only. Additionally, the efficacy of a polymer coating as well as pharmacological treatment (antiplatelet and anti-coagulant treatment) aimed at reducing acute thrombotic complications and intimal hyperplasia was studied. In an attempt to improve some of the features of stents, early thrombogenicity and barotrauma, a polymeric stent was developed and tested in vitro and in vivo and the results are discussed in Chapter 4, Stenting of vein grafts. Using a model of early vein graft narrowing in pigs, stenting was studied to assess the potential benefit of single and mnltiple stent implantation, compared to plain balloon angioplasty (Chapter 5). Stenting of both diseased and healthy arteries in animals of similar age and using the same stent, enables the assessment of behaviour of this stent under different circumstances. Pathologic examination of human saphenous vein bypass grafts treated with the self-expanding stainless steel stent (used in pigs in Chapter 3), is discussed in Chapters 6 and 7. This allowed for a comparison between the effect of stents when implanted in healthy porcine coronary arteries, porcine arteriovenous grafts and diseased human arteriovenous grafts. Vascular (dys)function. To assess long-term effects of stenting, a physiological study was undertaken to determine vascular function (Chapter 8). Aogiotensin metabolism in stented porcine coronary arteries was studied, as angiotensin IT is implicated as a growth factor or as a modifier of growth response of smooth muscle cells.

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