Volume 14 Number 3	July 1998

In Vivo Deployment of Palmaz-Schatz Stent Sparse Matrix Methods Fluid Phase Equilibria Modeling the Dynamics of RNA Seminar Synopsis Visitors Research Reports alloon angioplasty has proven to be an effective alternative to more invasive surgical procedures for the treatment of coronary disease, the leading cause of death in the United States. The goal of balloon angioplasty is to permanently increase the luminal size of a blood vessel that has been expanded by the inflation of a balloon at high pressure within the narrowed vessel segment to mechanically remove plaque deposition responsible for occlusion. During angioplasty, a mechanical device known as a stent may be deployed at the site of vascular injury. Stents may be fabricated from a number of biocompatible materials, typically metals, and are preferably radio-opaque. Optimal stent deployment technique leads to uniform circumferential expansion and very close apposition to the vessel wall. Unfortunately, balloons and stents are not designed for deployment as matching systems. Physicians often rely on personal preference and experience in selecting a combination of angioplasty balloons and stents. This may lead to inconsistent expansion of system components against the vascular wall. Stent deployment in an irregularly occluded or eccentric lumen can be particularly problematic. Undeployed stent eccentric arterial lumen Professor William Gleason in the Department of Laboratory Medicine and Pathology at the University of Minnesota and Svenn Borgersen of BIOSIMulations Inc., Eagan, Minnesota used a Palmaz-Schatz type stent geometry as the basis for development of a three dimensional finite element analysis (FEA) model to simulate stent deployment within a partially occluded, asymmetric arterial lumen as shown in the figures. The purpose of the analysis was to examine the effects of an asymmetric lumen on deployed stent geometry and stress levels. Model development and analysis were based on the mentat/marc k6.2 fea software from MARC Analysis Research Corporation, Palo Alto, California. The model consisted of eight noded, isoparametric, hexahedral elements. This element type has three translational degrees-of-freedom per node and a total of twenty-four degrees-of-freedom per element with eight Gaussian integration points. The model allows for large displacement, geometric stiffening, non-linear material properties, and full three dimensional contact. For this study, vascular walls and lumen occlusion surfaces were represented as three dimensional mathematically rigid boundaries. In order to evaluate anticipated stress concentration effects due to geometry at junctions of longitudinal and circumferential stent members, model mesh refinement was included at these locations. Expansion of the stent to its maximum design configuration was accomplished using a uniformly distributed loading by use of a follower force on the internal surfaces of the stent. The magnitude of the pressure load was increased incrementally until the stent conformed to the simulated vascular geometry or the ultimate strength of the material was exceeded. The obtained results clearly illustrated the inherent risks of deploying this type of stent in an asymmetric lumen: asymmetric deployed geometry, crippling of the structure, and non-conformity of the stent to the vascular lumen. A stent deployed under these conditions could be succeptible to collapse. Lack of structural stability and high stress level implied that sharply reduced mechanical fatigue design life may be anticipated. These researchers have conducted a number of modeling studies of various stent types, geometries, and materials. These have included stent only, stent and catheter balloon only, and stent/catheter balloon/arterial wall. In general, good qualitative correlation has been achieved between the predicted deployed stent geometry obtained from the stent models and the observed deployed stent geometry obtained empirically. Additional work is in progress to extend the computational results for other stent geometries, types, materials, stent coating materials, effects of stent/balloon combinations, and evaluation of deployment strategies. Eccentric arterial lumen with 50% stent deployment Eccentric arterial lumen with 80% stent deployment     Side view of fully expanded stent design condition End view of fully expanded stent design condition   HOME | BULLETINS | CONTACT US| NEXT ARTICLE | THIS ISSUE   This information is available in alternative formats upon request by individuals with disabilities. Please send email to alt-format@msi.umn.edu or call 612-624-0528.   URL: http:// This page last modified on   Website related questions or problems should be directed to webmaster@msi.umn.edu The Supercomputing Institute does not collect personal information on visitors to our website. For the University of Minnesota policy, see www.privacy.umn.edu.