Reducing In-Stent Restenosis Through Novel Stent Flow Field Augmentation
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educing In-Stent Restenosis Through Novel Stent Flow Field Augmentation EOIN A. MURPHY and FERGAL J. BOYLE Department of Mechanical Engineering, Dublin Institute of Technology, Bolton Street, Dublin 1, Ireland (Received 30 May 2012; accepted 25 September 2012; published online 9 October 2012) Associate Editor Bruce H. KenKnight oversaw the review of this article.
including hypertension, stroke and coronary artery disease (CAD). CAD accounted for 49.9% of all deaths due to CVD in the US in 2007.114 In cases of CAD, atherosclerotic lesions, typically formed in the coronary arteries over the course of decades, narrow the arterial lumen area, thereby reducing the flow of blood, and consequently oxygen and nutrients, to tissue cells downstream. Balloon angioplasty was developed by Charles Dotter in the 1960s31 as a minimally invasive treatment for the arterial narrowing caused by atherosclerotic lesions in the peripheral arteries, and later in the 1970s it was applied to renal, coronary and iliac arteries by Gru¨ntzig and co-workers.49–51 Re-blockage of a treated coronary artery following this procedure, known as restenosis, was reported in 30–60% of patients,44 with these patients consequently needing re-treatment with either percutaneous methods or bypass surgery. Restenosis following balloon angioplasty is attributed to three key responses: acute elastic recoil, negative wall remodelling (reduction in lumen area without a change in wall mass) and arterial wall thickening into the lumen (due to an increase in the number of cells within the arterial wall). Bare metal stents (BMS) were incorporated into the angioplasty procedure in the 1990s to serve as a rigid scaffold, thus eliminating elastic recoil and reducing wall remodelling,56 with some cases of positive remodelling reported.102 Even though stenting reduced restenosis rates to between 22 and 32%,37,44,126 it still continued to be a burden. Restenosis with stents, known as in-stent restenosis (ISR), is mostly due to arterial wall thickening. Understanding and consequently devising ways of reducing the frequency of ISR has been a continuing goal of research into improved
Abstract—In-stent restenosis (ISR), manifested as a re-narrowing of the arterial lumen post-implantation of a stent, is a detrimental limitation of stent technology. Understanding and consequently devising ways of reducing the frequency of ISR has been a continuing goal of research into improved stent designs. The biological processes that can lead to ISR have been found to be partially flow dependent with the local hemodynamics at the arterial wall of crucial importance. This paper investigates these biological processes and their instigating factors. Furthermore, the history and theory behind three stent technologies which endeavour to reduce ISR rates through stent flow field augmentation are presented: a flow divider which increases the blood-flow velocity and consequently the wall shear stress through a stented region, and two novel stent technologies which induce helical flow that mimics the natural
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