Effect of positioning and heart beating on transcatheter aortic valve performance. M., B., R.P., G., G., M., O.M., R., M.J., S., & D., B. Volume Minneapolis, MN, USA, October 5-8, 2016.
abstract   bibtex   

Introduction: Transcatheter aortic valve replacement (TAVR) is a minimally invasive procedure for inoperable patients with severe aortic stenosis. Adverse events, such as intra-procedural valve migration and post-procedural paravalvular leakage (PVL), have been hindering the use of TAVR for lower-risk and younger patients. Therefore, a deeper understanding of the interaction between the device and the surrounding calcified native tissues may help in guiding procedural planning and minimizing the risk of such complications. In this study we assessed the effect of TAVR deployment positioning on the risk of the valve migration, and its performance during heart beating.

Materials and Methods: We have evaluated the performance of both balloon- and self- expandable TAVR devices. First, CTA images of a failed Edwards Sapien balloon-expandable TAVR case at Stony Brook University Hospital were collected and used for segmentation after IRB approval. The entire diseased aortic root (AR) was reconstructed and the soft tissue thickness was calculated by an in-house algorithm to assure embedding the calcium deposits of the diseased aorta. The valve was modeled and its crimping into the catheter was simulated prior the deployment. The deployment and recoil phases of the TAVR procedure were then simulated in Abaqus Explicit 6.14 (Simulia, Dassault Systèmes, Providence, RI). The deformed configurations were used to estimate the PVL through the gaps for each investigated scenario by employing a computational fluid dynamics (CFD) model. The fluid domain was extracted and meshed with ANSYS SpaceClaim and Fluent Meshing 17.0 (ANSYS Inc., Cannonsburg, PA). In parallel, performances of self-expandable TAVR devices during the heart beating were evaluated for a commercially available Medtronic Evolut R and for a novel polymeric valve developed by our group (Polynova Cardiovascular, Inc., Stony Brook, NY). These valves’ crimping and deployment were simulated in the beating Living Heart Model (LHM) (Simulia).

Results and Discussion: Three deployment locations were studied: distal, midway and proximal. Similar stress distribution patterns and magnitudes were observed in the distal and the midway cases (Fig. 1), where the maximum values were in the contact region. The mean contact pressure in the recoil phase of the proximal model was higher as a result of the more localized interaction; however the total contact force resulted to be lower than the other two configurations (Ftot, proximal = 10.2 N, Ftot, mid = 26.3 N, Ftot, distal = 28.8 N). Similar to the clinical experience, the proximal deployment experienced a loss of almost 75% of the contact area at the end of the recoil when the stent dislocated into the left ventricle. The CFD for the other two configurations shows the presence of substantial PVL, being more pronounced in proximity of the fusion region between each pair of leaflets and for the midway case. Simulations in the LHM show larger post-deployment interaction between the Evolut R stent and the AR, whereas the LHM native leaflets experienced overall lower stresses when in contact with the deployed Polynova stent.

Conclusions: The model was capable of assessing and predicting the migration risk and PVL, suggesting that a more distal deployment offers optimal positioning for this patient-specific TAVR migration case. Devices deployment in the LHM demonstrated the effect of heart beating on the valves’ final position and highlighted the possible complications such as contact stability and potential interference with the atrioventricular node. Prototypes of the Polynova polymeric TAVR valves are being tested in vitro for hemodynamics performance in the Vivitro Left Heart Simulator, with effective orifice area and transvalvular regurgitant fraction calculated (ISO 5840-3 2013). Durability of the valves is being tested in the Vivitro HiCycle and their thrombogenicity measured in the Berlin LVAD and compared to other valves such as our polymeric surgical valve and the Edwards Sapien valve.

Acknowledgements: This study is supported by the NIH-NIBIB Quantum Award Phase II-1U01EB012487 (DB). ANSYS, Inc. and Simulia Living Heart Project are in academic partnership with Prof. Bluestein.

image

Figure 1: (Top) Stresses on the native leaflets at 50% of the Edwards Sapien deployment. (Left bottom) Contact area between native leaflets and stent over the time for the three configurations. (Right bottom) CoreValve Evolut R deployed in the beating LHM showing stresses on the native leaflets.

@proceedings{n27,
  cpaper				   = {1},
  Title                    = {{Effect of positioning and heart beating on transcatheter aortic valve performance}},
  Author                   = {Bianchi M. and Ghosh R.P. and Marom G. and Rotman O.M. and Slepian M.J. and Bluestein D.},
  Booktitle				   = {BMES Annual Meeting 2016 (BMES2016)},
  address 				   = {Minneapolis, MN, USA}, 
  month					   = {October 5-8}, 
  Year                     = {2016}, 

  Abstract				   = {
														<p>Introduction: Transcatheter aortic valve replacement (TAVR) is a minimally invasive procedure for inoperable patients with severe aortic stenosis. Adverse events, such as intra-procedural valve migration and post-procedural paravalvular leakage (PVL), have been hindering the use of TAVR for lower-risk and younger patients. Therefore, a deeper understanding of the interaction between the device and the surrounding calcified native tissues may help in guiding procedural planning and minimizing the risk of such complications. In this study we assessed the effect of TAVR deployment positioning on the risk of the valve migration, and its performance during heart beating.</p>
														<p>Materials and Methods: We have evaluated the performance of both balloon- and self- expandable TAVR devices. First, CTA images of a failed Edwards Sapien balloon-expandable TAVR case at Stony Brook University Hospital were collected and used for segmentation after IRB approval. The entire diseased aortic root (AR) was reconstructed and the soft tissue thickness was calculated by an in-house algorithm to assure embedding the calcium deposits of the diseased aorta. The valve was modeled and its crimping into the catheter was simulated prior the deployment. The deployment and recoil phases of the TAVR procedure were then simulated in Abaqus Explicit 6.14 (Simulia, Dassault Systèmes, Providence, RI). The deformed configurations were used to estimate the PVL through the gaps for each investigated scenario by employing a computational fluid dynamics (CFD) model. The fluid domain was extracted and meshed with ANSYS SpaceClaim and Fluent Meshing 17.0 (ANSYS Inc., Cannonsburg, PA). In parallel, performances of self-expandable TAVR devices during the heart beating were evaluated for a commercially available Medtronic Evolut R and for a novel polymeric valve developed by our group (Polynova Cardiovascular, Inc., Stony Brook, NY). These valves’ crimping and deployment were simulated in the beating Living Heart Model (LHM) (Simulia).</p>
														<p>Results and Discussion: Three deployment locations were studied: distal, midway and proximal. Similar stress distribution patterns and magnitudes were observed in the distal and the midway cases (Fig. 1), where the maximum values were in the contact region. The mean contact pressure in the recoil phase of the proximal model was higher as a result of the more localized interaction; however the total contact force resulted to be lower than the other two configurations (F<sub>tot, proximal</sub>  = 10.2 N, F<sub>tot, mid</sub>  = 26.3 N, F<sub>tot, distal</sub>  = 28.8 N). Similar to the clinical experience, the proximal deployment experienced a loss of almost 75% of the contact area at the end of the recoil when the stent dislocated into the left ventricle. The CFD for the other two configurations shows the presence of substantial PVL, being more pronounced in proximity of the fusion region between each pair of leaflets and for the midway case. Simulations in the LHM show larger post-deployment interaction between the Evolut R stent and the AR, whereas the LHM native leaflets experienced overall lower stresses when in contact with the deployed Polynova stent.</p>
														<p>Conclusions: The model was capable of assessing and predicting the migration risk and PVL, suggesting that a more distal deployment offers optimal positioning for this patient-specific TAVR migration case. Devices deployment in the LHM demonstrated the effect of heart beating on the valves’ final position and highlighted the possible complications such as contact stability and potential interference with the atrioventricular node. Prototypes of the Polynova polymeric TAVR valves are being tested in vitro for hemodynamics performance in the Vivitro Left Heart Simulator, with effective orifice area and transvalvular regurgitant fraction calculated (ISO 5840-3 2013). Durability of the valves is being tested in the Vivitro HiCycle and their thrombogenicity measured in the Berlin LVAD and compared to other valves such as our polymeric surgical valve and the Edwards Sapien valve.</p>
														<p>Acknowledgements: This study is supported by the NIH-NIBIB Quantum Award Phase II-1U01EB012487 (DB). ANSYS, Inc. and Simulia Living Heart Project are in academic partnership with Prof. Bluestein.</p>
																					
														<img alt="image" src="pages/BMES2016-Bianchi.png"  class="img-responsive">
														<p>Figure 1: (Top) Stresses on the native leaflets at 50% of the Edwards Sapien deployment. (Left bottom) Contact area between native leaflets and stent over the time for the three configurations. (Right bottom) CoreValve Evolut R deployed in the beating LHM showing stresses on the native leaflets.</p>
							}												
}
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