Measuring Stress on a Third-Generation Balloon-Expandable Aortic Valve During Expansion

Summary

The following protocol outlines simulations conducted to evaluate the influence of systemic pressure loading on the structural integrity of a 26-mm SAPIEN 3 valve. The stress level was determined by utilizing finite element analyses, which indicated that the highest stresses during the crimping phase were concentrated at the commissural tips.

Abstract

This study aimed to determine the mechanical stresses experienced by third-generation, balloon-expandable transcatheter aortic valves in the presence of aortic calcification, defined by an elevated Agatston score index for calcium. The device under investigation was the Edwards SAPIEN 3 valve (referred to as S3-TAV henceforth), a 26-mm commercial device. Five steps were undertaken. The first was the reconstruction of the three-dimensional (3D) computer-aided design (CAD) model of the device. The second was a simulation of the crimping and reopening process. The third was evaluating the crimping effect on leaflet stress and a comparison to an ideal condition. The fourth was a simulation of real clinical cases. Finally, the subsequent phase of the study entails the post-processing of the simulation results and a comparison with the follow-up data. A high-resolution micro-computed tomography scan was used to develop an accurate 3D geometric mesh of the stent and the valve. The material properties of the leaflets were derived from surgical bioprostheses; the material properties of the stents were based on those of cobalt-chromium. A series of simulations were conducted to assess the impact of systemic pressure loading on the structure. Stress was quantified through the application of finite element analyses. A stress analysis of the valve, conducted using exact geometry derived from high-resolution scans, revealed that peak stresses during the crimping phase were concentrated at the commissural tips, where the leaflets were attached. These regions were identified as the most likely sites for thrombosis and degeneration. The persistence of bulky calcifications following the device expansion results in the formation of paravalvular leakages (PVLs), which act as precursors to thrombosis and structural valve degeneration.

Introduction

Transcatheter aortic valve implantation (TAVI) has been demonstrated to be an effective treatment for severe aortic stenosis (AS), particularly in patients who are at intermediate or high risk of undergoing surgery or in those who are not eligible for surgical intervention^1,2,3,4. The SAPIEN 3 represents the third generation of transcatheter balloon expandable aortic valves (TAVs). It was initially released for provisional commercial use in Europe in January 2014 and subsequently in the United States in June 2015. The valve was the pioneerin....

Protocol

The use of these data for research was approved by the Institutional Review Board, with patient consent waived. IRB ID: 202201057, Approval Number assigned by the IRB: IRB-MTP_2022_03_202201057; ClinicalTrials.gov ID: NCT05261204.

NOTE: A summary of the protocol is provided in Table 1.

1. Investigated device biomodeling study

1. Computed biomodelling study
   NOTE: One patient exhibited a malfunction attributable to a PVL. The device was subsequently removed and utilized for the biomechanical study.
   1. Perform a micro CT scan for the patient in question.

Results

Evaluation of the crimping effect on leaflet stress: general consideration
The stress values on prosthetic leaflets in the diastolic phase were obtained following the completion of the following steps: (a) Leaflet closure was achieved by applying uniform physiological pressure (0.005 MPa ≈80 mmHg) to their external surface. (b) Leaflet apposition was then facilitated by re-expansion of the stent frame. (c) Finally, the leaflets were included in a systolic configuration throughout the crimping phase (.......

Discussion

The biomechanical performance of S3-TAV has been evaluated in relation to the device's technological advances, which represent a third generation of such devices. However, this analysis has also taken into account the ongoing challenges that remain in the implantation region and the geometry of the aortic annulus and root or solid bulky calcification. The present study demonstrates that the maximum and minimum principal stresses occurring in the 26 mm S3-TAV are localized to the cells situated immediately adjacent to.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Abaqus	Dassault Systèmes (Simulia, Providence, RI, USA)	2017	commercial finite element solver
Edwards SAPIEN 3 valve	Edwards Lifesciences, Inc. of Irvine, California	https://www.edwards.com/healthcare-professionals/products-services/transcatheter-heart/transcatheter-sapien-3-ultra	Sapien valve studied
ITK-SNAP	www.itksnap.org	Version 3.6	Identifying anatomy on pre-operative DICOM images
Matlab	Mathworks Inc., Natick, MA, USA)	v.R2018b	Generate a suitable mesh of the aortic wall
MicroCT-40	Scanco Medical AG, Basel, Switzerland		Desktop cone-beam micro-computed tomography scanner
Revolution Apex	GE Healthcare, Chicago, Illinois, USA		Dual-source computed tomography scanner
Rhinoceros	McNee and Associates, Seattle, WA, USA	Version 5.0	Construct a definitive 3D Computer-aided design