Effect of Stent Design on Intra-stent Hemodynamics
Date Issued
2012
Date
2012
Author(s)
Lee, Kuang-Huei
Abstract
The stent has been a major breakthrough for the treatment of atherosclerotic vascular disease. The permanent vascular implant of a stent, however, changes the blood flow hemodynamics and may consequently affect the restenosis process – a re-narrowing of stented artery. Computational Fluid Dynamics (CFD) has been widely used to analyze the hemodynamic behavior, such as wall shear stress (WSS) and wall shear stress gradient (WSSG) distribution, in stented arteries since clinical research indicated that low WSS, oscillatory WSS, flow recirculation, and high WSSG are the most critical factors in restenosis process. In this study, two CFD models (the axisymmetric model and the 3-D stent model) were developed to investigate the effects of stent design patterns, strut geometry, and blood rheology on the intra-stent hemodynamics. The velocity profile, flow recirculation, WSS distribution, oscillatory WSS, and WSSG distribution of various stent geometries were studied. Results show strong correlations between the intra-stent hemodynamics and strut geometry. The intra-stent blood flow is very sensitive to the stent thickness and fillet size, while the strut width and the radius of the most curved part of stent are relatively unimportant. The effect of fillet size suggests that electrochemical polishing, a surface-improving process during stent manufacturing, strongly influences the hemodynamic behavior in stented arteries and should be controlled precisely in order to achieve the best clinical outcome. Rheological effects on the wall shear stress are minor in axisymmetric model. Newtonian simulation increase distal recirculation length by only 6% as compared with non-Newtonian simulation; however, it becomes significant in the 3-D stented artery model, with Newtonian flow simulation tending to give more conservative estimates of restenosis risk. Newtonian simulation increase low shear area by average 14.7% as compared with non-Newtonian simulation. Moreover, the non-Newtonian effect varies with stent design. Besides, the simulated results based on 3-D stent model also show strong correlations between the intra-stent hemodynamics and stent design patterns. Asymmetric stent design and uneven head of a stent increase low shear area by 3.9% and 3.7%, decrease average WSSG by 6.2% and 3.5%, and intensify the WSS oscillation by 50.2% and 12.6%, respectively, while pulsatile blood flow is considered. The proposed methodologies and findings will provide great insights for stent design optimization, facilitate stent testing process, and then reduce potential restenosis rate of the future stent designs.
Subjects
Restenosis
Wall Shear Stress
Stent Design
Hemodynamics
Computational Fluid Dynamics.
Type
thesis
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