Simulation of transcatheter aortic valve replacement: A patient-pathology specific approach. M., B.; R.P., G.; D., D.; G., M.; T.E., C.; M., P.; L., G.; S., K.; H.A., F.; J.R., T.; Y.X., Q.; S., J.; and D., B. Volume Washington, DC, USA, May 18-20, 2015.
abstract   bibtex   

Introduction: Severe aortic stenosis (AS) has an extremely adverse prognosis for symptomatic patients not eligible for the standard surgical aortic valve replacement (SAVR). Transcatheter aortic valve replacement (TAVR) has been emerged as a new minimally invasive treatment for such high risk patients. In the case of the Edwards SAPIEN® valve, the procedure consists of the delivery of a balloon-expandable stented tissue valve to the site of the native pathological valve via transfemoral or transapical catheterization. We hypothesize that the presence of large deposits of calcium in situ is a significant cause of intra- and post-procedural complications. Hence, the simulation of the deployment in patient-specific aortic root (AR) models encompassing the patient’s pathophysiological features may both represent a valuable procedural planning tool and lead to improved design of TAVR device. The aim of this study is to develop accurate heterogeneous patient specific models and to employ them to evaluate the effect of different deployment configurations of the Edwards SAPIEN® valve.

Materials and Methods: In accordance with IRB regulations, CTA scans in systolic phase of two TAVR patients were obtained from the Heart Institute of Stony Brook University Hospital and 3D segmentation was then performed in ITK-SNAP. Region competition snakes approach was employed, in which appropriate balance of evolutionary and smoothing forces was reached to accurately extract the lumen of the aortic root and the calcifications boundaries. The outer surface of the AR was obtained in MATLAB (Mathworks Inc, Natick, MA) by extruding the lumen surface with a constant thickness for the sinus and a variable-thickness for the AV native leaflets. A solid model was then created in ANSYS Design Modeler (ANSYS, Inc., Canonsburg, PA) while embedding the calcifications in the soft tissue. The crimped position of the SAPIEN® valve including the prosthetic leaflets was calculated ANSYS Explicits Dynamics. After combining the two models (Figure 1), a Finite Element Analysis (FEA) of the TAVR procedure was performed, in which the location of the TAVR valve with respect to the AV annulus was parameterized, to replicate different choice of the surgeon during the deployment. The native leaflets soft tissue was modeled with an anisotropic hyperelastic material calibrated with tensile-test experimental data on excised human AV leaflets, whereas the calcium material model was calibrated performing nano-indentation measurements after µCT-scanning the same calcified specimens. Computational Fluid Dynamics (CFD) analyses were also performed for the optimal deployed configurations, to estimate the paravalvular leakage volume in diastolic phase.

Results: Anchorage of the valve was assessed for three different axial configurations (70% toward the aortic side, 70% toward the ventricular side and midway). Stresses within the wall and interaction of calcium-soft tissue were investigated during the deployment. For both patients, who experienced valve migration during the procedure, incomplete expansion of the valve occurred and paravalvular leakage was confirmed in the correspondent CFD simulations. The risk-minimizing deployment configuration was assessed for both patients.

Conclusions: Accurate patient-specific AR models including the vessel wall thickness and calcification deposits represent a useful tool to guide TAVR and to help in preventing the migration of the valve during the deployment procedure. Also, optimizing the positioning of the valve during deployment, as well as alternative approaches to TAVR valves tailored to patient’s specific pathology, e.g. polymeric valves, may offer better procedural outcome.

Acknowledgements: This study is supported by the NIH-NIBIB Quantum Award Phase II-1U01EB012487 (DB). Ansys, Inc. is in an academic partnership with Prof. Bluestein.

image

Figure 1: FE model of a patient-specific aortic root and SAPIEN® valve in midway position before deployment.

@proceedings{n18,
  cpaper				   = {1},
  Title                    = {{Simulation of transcatheter aortic valve replacement: A patient-pathology specific approach}},
  Author                   = {Bianchi M. and Ghosh R.P. and Das D. and Marom G. and Claiborne T.E. and Poon M. and Gruber L. and Kort S. and Fernandez H.A. and Taylor J.R. and Qin Y.X. and Judex S. and Bluestein D.},
  Booktitle				   = {Frontiers in Medical Devices Conference: Innovations in Modeling and Simulation},
  address 				   = {Washington, DC, USA}, 
  month					   = {May 18-20}, 
  Year                     = {2015}, 

  Abstract				   = {
														<p>Introduction: Severe aortic stenosis (AS) has an extremely adverse prognosis for symptomatic patients not eligible for the standard surgical aortic valve replacement (SAVR). Transcatheter aortic valve replacement (TAVR) has been emerged as a new minimally invasive treatment for such high risk patients. In the case of the Edwards SAPIEN® valve, the procedure consists of the delivery of a balloon-expandable stented tissue valve to the site of the native pathological valve via transfemoral or transapical catheterization. We hypothesize that the presence of large deposits of calcium in situ is a significant cause of intra- and post-procedural complications. Hence, the simulation of the deployment in patient-specific aortic root (AR) models encompassing the patient’s pathophysiological features may both represent a valuable procedural planning tool and lead to improved design of TAVR device. The aim of this study is to develop accurate heterogeneous patient specific models and to employ them to evaluate the effect of different deployment configurations of the Edwards SAPIEN® valve.</p>
														<p>Materials and Methods: In accordance with IRB regulations, CTA scans in systolic phase of two TAVR patients were obtained from the Heart Institute of Stony Brook University Hospital and 3D segmentation was then performed in ITK-SNAP. Region competition snakes approach was employed, in which appropriate balance of evolutionary and smoothing forces was reached to accurately extract the lumen of the aortic root and the calcifications boundaries. The outer surface of the AR was obtained in MATLAB (Mathworks Inc, Natick, MA) by extruding the lumen surface with a constant thickness for the sinus and a variable-thickness for the AV native leaflets. A solid model was then created in ANSYS Design Modeler (ANSYS, Inc., Canonsburg, PA) while embedding the calcifications in the soft tissue. The crimped position of the SAPIEN® valve including the prosthetic leaflets was calculated ANSYS Explicits Dynamics. After combining the two models (Figure 1), a Finite Element Analysis (FEA) of the TAVR procedure was performed, in which the location of the TAVR valve with respect to the AV annulus was parameterized, to replicate different choice of the surgeon during the deployment. The native leaflets soft tissue was modeled with an anisotropic hyperelastic material calibrated with tensile-test experimental data on excised human AV leaflets, whereas the calcium material model was calibrated performing nano-indentation measurements after µCT-scanning the same calcified specimens. Computational Fluid Dynamics (CFD) analyses were also performed for the optimal deployed configurations, to estimate the paravalvular leakage volume in diastolic phase.</p>
														<p>Results: Anchorage of the valve was assessed for three different axial configurations (70% toward the aortic side, 70% toward the ventricular side and midway). Stresses within the wall and interaction of calcium-soft tissue were investigated during the deployment. For both patients, who experienced valve migration during the procedure, incomplete expansion of the valve occurred and paravalvular leakage was confirmed in the correspondent CFD simulations. The risk-minimizing deployment configuration was assessed for both patients.</p>
														<p>Conclusions: Accurate patient-specific AR models including the vessel wall thickness and calcification deposits represent a useful tool to guide TAVR and to help in preventing the migration of the valve during the deployment procedure. Also, optimizing the positioning of the valve during deployment, as well as alternative approaches to TAVR valves tailored to patient’s specific pathology, e.g. polymeric valves, may offer better procedural outcome.</p>
														<p>Acknowledgements: This study is supported by the NIH-NIBIB Quantum Award Phase II-1U01EB012487 (DB). Ansys, Inc. is in an academic partnership with Prof. Bluestein.</p>
														
														<img alt="image" src="pages/FDA15-Bianchi.png"  class="img-responsive">
														<p>Figure 1: FE model of a patient-specific aortic root and SAPIEN® valve in midway position before deployment.</p>
							}												
}
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