(H-290) Simulating the Expansion of a Metal Stent in Coarctation of the Aorta

Introduction:: Coarctation of the Aorta (COA) is a narrowing or stricture in the descending aorta that causes elevated blood pressure and reduced blood flow. If left untreated these patients can have high blood pressure, chest pains, aortic tearing / dissection, aneurysms, premature coronary artery disease and stroke. Stent dilation of obstructed vessels in pediatric patients with metal stents has become necessary in treatment of congenital heart disease. In this study, a 3D COA model was created from magnetic resonance imaging (MRI) of a pig study investigating stenting of the COA. A contact structural simulation with a Genesis XD stent was performed to investigate the mechanical stresses of the arterial wall during stent-artery expansion to 10 mm diameter and relaxation of the stent to explore risks of aortic wall injury.


Materials and Methods:: A COA model was created and examined with a genesis metal stent following IACUC protocols at UT Southwestern. Solid 3D models of a Genesis XD stent (Cordis Corp., Warren, NJ), reproduced from images taken with a Nikon D70 with a macro lens (Sigma 50 mm DG) using Solidworks 2022 (Dassault Systemes SolidWorks Corp., Concord, MA, USA), and COA of a pig model of the descending aorta were created using 3D Slicer. These models were next imported into ABAQUS (Dassault Systemes Simulia Corp., Providence, RI, USA) to perform nonlinear, large deformation analysis for different steps in a stent analysis: crimp, relaxation, expand and relaxation. The crimper and balloon were modeled as rigid cylinders. The stent was modeled as 316L stainless steel using nonlinear combined hardening with material data derived from tensile tests described by Poncin et al (1). The descending aorta was modeled using an Ogden model fitted from material data derived from tensile tests performed by Kamenski et al (2).

Results, Conclusions, and Discussions:: Model validation was performed by comparing stent lumen measurements with the in-vivo study in a pig. Histology also showed lumen measurements similar to simulation measurements. The artery simulation showed high von mises stresses upon full expansion within the threshold of tearing the internal elastic lamina of the artery. Simulation stresses approached 2291 kPa circumferential stress and 2121 kPa axial stress compared to 2510 ± 979 kPa circumferential stress and 753 ± 228 kPA axial stress from experimental aortic tissue failure (3). These high stress zones are located at the narrowest region of the COA. The average expanded IVUS COA lumen measurement was 9.97 ± 1.3 mm (n=3) and the simulation COA lumen was 10 mm.
In conclusion, we used our validated 10 mm Palmaz genesis XD stent model based upon bench top testing to simulate the stent expansion in a COA model. The COA simulation shows the stent implantation into the aorta causes high mechanical stresses at the contact regions of the stent with the narrowest region of the aorta wall. Thus showing a region of risk of arterial tissue failure during stent implantation. For children aging the stent is further dilated to force the stent to grow with the patient. We believe these arterial stresses will further increase upon further dilatation procedures and potentially put the vessel at aortic wall injury and potentially stent fracturing.

Acknowledgements (Optional): :

References (Optional): : < ! 1. Poncin, P., Materials & Processes for Medical Devices Conference 2003. 810:7.
2. Kamenski, A.V., Biomech Model Mechanobiol. 2014. 13:1341-1359.
3. Witzenburg CM, J Biomech Eng. 2017 Mar 1;139(3):0310051–03100514