Biomechanical analysis of transcatheter valve migration in patient-specific models. M., B., T.E., C., G., M., R., G., M., P., M.H., M., E., F., L., G., H.A., F., J.R., T., & D., B. Volume San Antonio, TX, USA, October 22-25, 2014.
abstract   bibtex   

Introduction: Transcatheter Aortic Valve Replacement (TAVR) is a minimally-invasive alternative to open heart surgery for high-risk patients with aortic stenosis. Current TAVR devices consist of animal derived tissue mounted onto an expandable metallic frame being delivered to the site of native pathological valve via a transfemoral or transapical catheter. The presence of calcifications in the annulus likely leads to complications such as migration valve post- deployment, leading to multiple implantations or failed procedures. Therefore, a deeper understanding of the interactions of the device and calcified tissue in the aortic root may lead to best clinical practice and eventually improved TAVR devices. We aimed to accomplish this by building patient-specific models from cases where Edwards SAPIEN® migration occurred including each patient’s valve, vessel thickness, and calcifications. Then, by incorporating TAVR deployment, an accurate heterogeneous model of the disease state was achieved, allowing us to investigate the valve stent anchoring.

Materials and Methods: CTA datasets were obtained from four patients who experienced Edwards SAPIEN® valve migration during TAVR at the Heart Institute of Stony Brook University Hospital. These were used as input for the open-source software ITK-SNAP, which implements a 3D active contour segmentation. After proper contrast enhancement was obtained, the segmentation process was based on the evolution of a closed surface driven by a band-pass filter that allows capturing exclusively pixels falling into a predefined range of intensity. This approach was followed to extract both lumen boundaries and calcification regions characterized by abnormal intensity values, whereas the vessel outer wall was obtained in a second phase by processing the lumen on slice level using MATLAB (MathWorks Inc., Natick, MA). In the final geometry the aortic root, the main coronary branches, the ascending aorta, the aortic arch and its branches, and part of the thoracic descending aortic were included in order to build a comprehensive vascular model for TAVR simulation. The model of SAPIEN® stent was then included and an explicit dynamics finite element model was built using ANSYS Mechanical (ANSYS, Inc., Canonsburg, PA). Normal blood pressure and contact conditions were then imposed and the effect of calcification on valve stent anchoring was investigated. The calcification regions inside the wall were modeled as nearly rigid linear elastic whereas for the soft tissue an isotropic hyperelastic model was initially employed.

Results and Discussion: Full patient-specific aortic models were reconstructed (Fig. 1) for four patients who experienced valve SAPIEN® migration. Stresses within the vessel wall, including calcium-soft tissue interaction, were investigated and the stent interaction with the annulus, especially in the aortic root portion. Ongoing simulations show how the presence of rigid, spread calcium deposits in the operative field lead to malposition of the TAVR frame and a potential loss of contact with the vessel. Furthermore, simulations with our Device Thrombogenicity Emulation (DTE)-optimized polymeric TAVR valve [1] will be carried out for comparison.

Conclusions: Patient-specific aortic models including the vessel wall thickness and calcification regions represent a useful tool to guide TAVR and to help in preventing the migration of the valve during the deployment procedure. This may aid in procedural planning and improved device designs. The future integration of the DTE-optimized polymeric valve in the model may demonstrate its superiority to tissue-based devices.

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.

References: [1] T. E. Claiborne, et al.; ASAIO J. 2013 May-Jun; 59(3): 275-83

image

Figure 1: (A) Representative aortic model inclusive of vessel lumen (pink) and calcification regions (green). (B) SAPIEN® valve stent; (C) DTE-optimized polymeric TAVR valve

@proceedings{n13,
  cpaper				   = {1},
  Title                    = {{Biomechanical analysis of transcatheter valve migration in patient-specific models}},
  Author                   = {Bianchi M. and Claiborne T.E. and Marom G. and Ghosh R. and Poon M. and Musani M.H. and Feldmann E. and Gruberg L. and Fernandez H.A. and Taylor J.R. and Bluestein D.},
  Booktitle				   = {BMES Annual Meeting 2014 (BMES2014)},
  address 				   = {San Antonio, TX, USA}, 
  month					   = {October 22-25}, 
  Year                     = {2014}, 

  Abstract				   = {
														<p>Introduction: Transcatheter Aortic Valve Replacement (TAVR) is a minimally-invasive alternative to open heart surgery for high-risk patients with aortic stenosis. Current TAVR devices consist of animal derived tissue mounted onto an expandable metallic frame being delivered to the site of native pathological valve via a transfemoral or transapical catheter. The presence of calcifications in the annulus likely leads to complications such as migration valve post- deployment, leading to multiple implantations or failed procedures. Therefore, a deeper understanding of the interactions of the device and calcified tissue in the aortic root may lead to best clinical practice and eventually improved TAVR devices. We aimed to accomplish this by building patient-specific models from cases where Edwards SAPIEN® migration occurred including each patient’s valve, vessel thickness, and calcifications. Then, by incorporating TAVR deployment, an accurate heterogeneous model of the disease state was achieved, allowing us to investigate the valve stent anchoring.</p>
														<p>Materials and Methods: CTA datasets were obtained from four patients who experienced Edwards SAPIEN® valve migration during TAVR at the Heart Institute of Stony Brook University Hospital. These were used as input for the open-source software ITK-SNAP, which implements a 3D active contour segmentation. After proper contrast enhancement was obtained, the segmentation process was based on the evolution of a closed surface driven by a band-pass filter that allows capturing exclusively pixels falling into a predefined range of intensity. This approach was followed to extract both lumen boundaries and calcification regions characterized by abnormal intensity values, whereas the vessel outer wall was obtained in a second phase by processing the lumen on slice level using MATLAB (MathWorks Inc., Natick, MA). In the final geometry the aortic root, the main coronary branches, the ascending aorta, the aortic arch and its branches, and part of the thoracic descending aortic were included in order to build a comprehensive vascular model for TAVR simulation. The model of SAPIEN® stent was then included and an explicit dynamics finite element model was built using ANSYS Mechanical (ANSYS, Inc., Canonsburg, PA). Normal blood pressure and contact conditions were then imposed and the effect of calcification on valve stent anchoring was investigated. The calcification regions inside the wall were modeled as nearly rigid linear elastic whereas for the soft tissue an isotropic hyperelastic model was initially employed.</p>
														<p>Results and Discussion: Full patient-specific aortic models were reconstructed (Fig. 1) for four patients who experienced valve SAPIEN® migration. Stresses within the vessel wall, including calcium-soft tissue interaction, were investigated and the stent interaction with the annulus, especially in the aortic root portion. Ongoing simulations show how the presence of rigid, spread calcium deposits in the operative field lead to malposition of the TAVR frame and a potential loss of contact with the vessel. Furthermore, simulations with our Device Thrombogenicity Emulation (DTE)-optimized polymeric TAVR valve [1] will be carried out for comparison.</p>
														<p>Conclusions: Patient-specific aortic models including the vessel wall thickness and calcification regions represent a useful tool to guide TAVR and to help in preventing the migration of the valve during the deployment procedure. This may aid in procedural planning and improved device designs. The future integration of the DTE-optimized polymeric valve in the model may demonstrate its superiority to tissue-based devices.</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>
														<p>References: [1] T. E. Claiborne, et al.; ASAIO J. 2013 May-Jun; 59(3): 275-83</p>
														
														<img alt="image" src="pages/BMES14-TAVR.png"  class="img-responsive">
														<p>Figure 1: (A) Representative aortic model inclusive of vessel lumen (pink) and calcification regions (green). (B) SAPIEN® valve stent; (C) DTE-optimized polymeric TAVR valve</p>
							}																								
}
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