Elsevier

Journal of Biomechanics

Volume 45, Issue 11, 26 July 2012, Pages 1965-1971
Journal of Biomechanics

Patient-specific modeling of biomechanical interaction in transcatheter aortic valve deployment

https://doi.org/10.1016/j.jbiomech.2012.05.008Get rights and content

Abstract

The objective of this study was to develop a patient-specific computational model to quantify the biomechanical interaction between the transcatheter aortic valve (TAV) stent and the stenotic aortic valve during TAV intervention. Finite element models of a patient-specific stenotic aortic valve were reconstructed from multi-slice computed tomography (MSCT) scans, and TAV stent deployment into the aortic root was simulated. Three initial aortic root geometries of this patient were analyzed: (a) aortic root geometry directly reconstructed from MSCT scans, (b) aortic root geometry at the rapid right ventricle pacing phase, and (c) aortic root geometry with surrounding myocardial tissue. The simulation results demonstrated that stress, strain, and contact forces of the aortic root model directly reconstructed from MSCT scans were significantly lower than those of the model at the rapid ventricular pacing phase. Moreover, the presence of surrounding myocardium slightly increased the mechanical responses. Peak stresses and strains were observed around the calcified regions in the leaflets, suggesting the calcified leaflets helped secure the stent in position. In addition, these elevated stresses induced during TAV stent deployment indicated a possibility of tissue tearing and breakdown of calcium deposits, which might lead to an increased risk of stroke. The potential of paravalvular leak and occlusion of coronary ostia can be evaluated from simulated post-deployment aortic root geometries. The developed computational models could be a valuable tool for pre-operative planning of TAV intervention and facilitate next generation TAV device design.

Introduction

Aortic stenosis (AS) is the most common valvular disease in developed countries [Auricchio et al., 2011] and its prevalence is growing with an aging population [Carabello and Paulus, 2009, Conti et al., 2010]. While surgical aortic valve replacement is still the preferred choice for patients with symptomatic AS, minimally invasive transcatheter aortic valve (TAV) intervention has recently shown promise for elderly high-risk patients who have significant comorbidities [Dwyer et al., 2009, Ebenstein et al., 2009, Fung et al., 1993]. This revolutionary therapy also has a great potential to treat non high-risk patients, with the advantages of less trauma (without the rigors of open-chest surgery) and shorter recovery time, and thus may fundamentally change the current paradigm of surgical valve replacement.

During TAV intervention, the interventional cardiologist does not have direct access to the calcified aortic valve, and must rely on the interaction between the TAV stent and the host tissue to maintain proper device positioning and function. Many of the adverse effects [Fung et al., 1993, Gasser et al., 2006, Grube et al., 2007, Gurvitch et al., 2010] seen in clinical trials, such as impairment of coronary flow, cardiac tamponade, stroke, peripheral embolism, aortic injury, paravalvular leak and access site injury [Haj-Ali, 2008, Hauck et al., 2009], can be explained from the biomechanics perspective. For instance, excessive radial expansion force of the TAV stent may cause aortic injury, while insufficient force may lead to paravalvular leakage and device migration. Improper TAV positioning can also cause occlusion of the coronary ostia (CO). Thus, a quantitative understanding of the biomechanics involved in the TAV intervention is critical for the success of this procedure.

Due to the complex geometry, mechanical properties and contact between the TAV stent and the aortic root in TAV intervention, integrated experimental and computational methods are necessary to evaluate the biomechanical response. Finite element (FE) analysis has been utilized to study the biomechanics of the aortic root [Holzapfel et al., 2000, Holzapfel et al., 2004, Jeziorska et al., 1998, Kumar and Mathew, 2010, Labrosse et al., 2010] or TAV devices [Leon et al., 2010, Li and Sun, 2010, Lu et al., 2008, Mangini et al., 2011, Marrey et al., 2006] individually. However, to the best of our knowledge, the biomechanical interaction between the stenotic aortic valve and TAV stent has been largely unexplored, and therefore is the focus of the present work. Specifically, patient-specific FE models of aortic roots were reconstructed from multi-slice computed tomography (MSCT) scans, and stent expansion during TAV deployment was simulated. Contact force between the stent and aortic root, as well as stress and strain changes in aortic tissue due to the stent expansion were analyzed.

Section snippets

Methods

Patient-specific aortic root geometry. Full phase cardiac MSCT scans were collected from patients at Hartford Hospital (Hartford, CT). Institutional Review Broad approval to review de-identified images was obtained for this study. One stenotic patient with a tricuspid aortic valve and an aortic annulus size of 21 mm was identified from the database. Severe calcification was found in the leaflets of the patient. The MSCT examination was performed on a GE LightSpeed 64-channel volume computed

Results

Material models. The best-fitted material properties of aortic tissue as well as the corresponding biaxial test data are illustrated in Fig. 4. The obtained material parameters are listed in Table 1. It can be seen in Fig. 4 that there was very good correlation between simulation and biaxial results. From the biaxial results it can be seen that the sinus and aortic leaflet tissues had stiffer mechanical response in the circumferential direction, while the ascending aorta was stiffer in the

Discussion

Successful TAV deployment and function are heavily reliant on the aortic root-TAV stent interaction. Since the human aortic valve has a large variation of anatomic structures, e.g. different annulus size, sinus height, CO location [Martin et al., 2011, Wang et al., 2011, Webb and Cribier, 2010] and tissue stiffness [Stolzmann et al., 2009], determination of appropriate interaction forces between the TAV and the native tissue using either in vivo or ex vivo measurements is a challenging task. In

Conclusions

Patient-specific FE models of stenotic aortic roots were reconstructed from MSCT scans; and TAV stent deployment was simulated. The results showed that mechanical responses of the aortic root model directly reconstructed from MSCT scans were significantly lower than those of the model at the rapid ventricular pacing phase. In addition, inclusion of the myocardium slightly increased the mechanical responses. It was observed that maximum stresses and strains were in the region of leaflet

Conflict of interest statement

All authors disclose any financial and personal relationships with other people or organizations that could inappropriately influence (bias) their work.

Acknowledgments

This work was supported in part by the State of Connecticut Department of Public Health Biomedical Research Grant DPH2010-0085, a NSF GRFP fellowship, NIH 1R01HL104080 and 1R21HL108239 grants. We would like to thank Dr. Charles Primiano and Dr. Raymond McKay for providing CT scans. We would also like to thank Thuy Pham and Caitlin Martin for providing experimental data of the aortic tissues.

References (41)

  • L.F. Tops et al.

    Noninvasive evaluation of the aortic root with multislice computed tomography implications for transcatheter aortic valve replacement

    JACC Cardiovascular Imaging

    (2008)
  • A. Zajarias et al.

    Outcomes and safety of percutaneous aortic valve replacement

    Journal of the American College of Cardiology

    (2009)
  • R. Zegdi et al.

    Is it reasonable to treat all calcified stenotic aortic valves with a valved stent? Results from a human anatomic study in adults

    Journal of the American College of Cardiology

    (2008)
  • F. Auricchio et al.

    A computational tool to support pre-operative planning of stentless aortic valve implant

    Medical Engineering & Physics

    (2011)
  • D.M. Ebenstein et al.

    Nanomechanical properties of calcification, fibrous tissue, and hematoma from atherosclerotic plaques

    Journal of Biomedical Materials Research. Part A

    (2009)
  • Y.C. Fung et al.

    Remodeling of the constitutive equation while a blood vessel remodels itself under stress

    Journal of Biomechanical Engineering

    (1993)
  • T.C. Gasser et al.

    Hyperelastic modelling of arterial layers with distributed collagen fibre orientations

    Journal of the Royal Society Interface

    (2006)
  • R. Gurvitch et al.

    Transcatheter aortic valve implantation: durability of clinical and hemodynamic outcomes beyond 3 years in a large patient cohort

    Circulation

    (2010)
  • F. Hauck et al.

    A new tool for the resection of aortic valves: in-vitro results for turning moments and forces using Nitinol cutting edges

    Minimally Invasive Therapy & Allied Technologies

    (2009)
  • G.A. Holzapfel et al.

    A new constitutive framework for arterial wall mechanics and a comparative study of material models

    Journal of Elasticity

    (2000)
  • Cited by (80)

    View all citing articles on Scopus
    View full text