Percutaneous Transluminal Angioplasty (PTA) is frequently used for revascularization of atherosclerotic lesions in patients with peripheral and coronary artery disease. The secondary success rate of the intervention is low due to the process of restenosis which is said to be a response of the tissue to vascular injury post dilation. The stresses and damage in the artery may be an important marker for this process. Morphology of the plaque is an important predictor for these arterial stresses and there is a need to understand the dependence of wall damage to the underlying plaque morphology. Orbital atherectomy (OA) is a minimally invasive interventional procedure used in heavily diseased and calcified lesions. Clinical studies have demonstrated that OA procedure may increase the lesion compliance. However the computational studies for OA procedure are rare. Given the increasing use of OA in clinical practice, a computational investigation of the procedure is in order. Angioplasty simulations were carried out for a peripheral lesion model based on a histological study of the superficial peripheral artery. The effect of changing the degree of calcification on stresses and damage in the vessel wall during PTA was examined. The results indicate that increasing the degree of calcification increases the peak stresses in the non-calcified portion of the wall making it more susceptible to injury. Plasticity of the lesion components and the original SFA geometry were also considered for some simulations and demonstrate similar results in stresses. In another set of simulations, the influence of decreasing the plaque stiffness on the vessel stresses and damage was investigated. The results show that under the action of a semi-compliant angioplasty balloon, the stresses in the wall decrease with decreasing stiffness of the plaque components. This necessitates the investigation of procedures like atherectomy which are hypothesized to increase lesion compliance. An experimental study was carried out at Cardiovascular Systems Inc to explore the change in compliance of the lesion post OA procedure. Cadaveric SFA lesion was internally pressurized before and after OA and the cross-sectional lumen areas were recorded using an Optical Coherence Tomography imaging catheter. The analysis of the results showed that there was an increase in compliance of the vessel after OA. A computational analysis of OA was also carried out based on experimental crown dynamics observed in a study carried out by a fellow researcher, Yihao Zheng at the University of Michigan, Ann Arbor. The same lesion model used in the PTA simulations was used for this study and the results demonstrate that the stress field in OA is quite localized the area of contact near the crown tool. The damage field and peak stresses are therefore localized to the plaque components and the peak stresses in the vessel wall are much smaller than in PTA simulations. The softening of the plaque components was evident through the damage field and compliance at low internal pressure levels similar to ones used in the experimental investigation was calculated. The results show an increase in compliance at low internal pressure levels after OA procedure. Damage energy density analysis was carried out for simulations of both the interventional procedures and the damage in the individual components was compared. The results show that the damage in the media and adventitia much smaller in the OA simulations as compared to PTA. The work presented in this thesis has provided a better understanding of the mechanical response of atherosclerotic lesions to PTA and OA interventional procedures and serve as a basis for future work for computational work in this field.
University of Minnesota M.S.M.E. thesis. August 2015. Major: Mechanical Engineering. Advisor: Barney Klamecki. 1 computer file (PDF); xii, 104 pages.
Computational Modelling and Comparative Damage Analysis of Angioplasty and Orbital Atherectomy Interventional Procedures.
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