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Research Papers

Simulation Based Design and Evaluation of a Transcatheter Mitral Heart Valve Frame

[+] Author and Article Information
Melissa Young1

Department of Biomedical Engineering, Cleveland Clinic, Cleveland, OH 44195;  Medical Device Solutions (MDS) Core, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195youngm7@ccf.org

Ahmet Erdemir

Department of Biomedical Engineering, Cleveland Clinic, Cleveland, OH 44195;  Computational Biomodeling (CoBi) Core, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195

Samantha Stucke, Brian Davis

 Medical Device Development Center, Austen BioInnovations Institute in Akron, Akron, OH 44308

Ryan Klatte

 Medical Device Solutions (MDS) Core, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195

Jose L. Navia

Department of Biomedical Engineering, Cleveland Clinic, Cleveland, OH 44195;  Cardiothoracic Surgery, Miller Family Heart and Vascular Institute, Cleveland Clinic, Cleveland, OH 44195

1

Corresponding author.

J. Med. Devices 6(3), 031005 (Aug 14, 2012) (8 pages) doi:10.1115/1.4007182 History: Received November 23, 2011; Revised June 18, 2012; Published August 14, 2012; Online August 14, 2012

In certain populations, open heart surgery to replace a diseased mitral valve is not an option, leaving percutaneous delivery a viable alternative. However, a surgical transcatheter based delivery of a metallic support frame incorporating a tissue derived valve puts considerable constraints on device specifications. Expansion to a large diameter from the catheter diameter without mechanical fracture involves advanced device design and appropriate material processing and selection. In this study, a new frame concept is presented with a desirable feature that incorporates wings that protrude during expansion to establish adequate fixation. Expansion characteristics of the design in relation to annulus fixation were quantified through finite element analysis predictions of the frame wing span and angles. Computational modeling and simulation was used to identify many favorable design features for the transcatheter mitral valve frame and obtain desired expansion diameters (35–45 mm), acceptable radial stiffness (2.7 N/mm), and ensure limited risk of failure based on predicted plastic deformations.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Several design geometries were tested through computational simulation. Only the periodic circumferential segments (representative of semiaxisymmetry) are shown. All the designs incorporated some form of a wing type structure. Many possibilities including but not limited to overall design size, e.g., diameter, shape of individual components, i.e., of the wings, strut thickness, were considered. The highlighted design, on the far right side, shows the favorable geometry which has a starting tube diameter of 15 mm.

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Figure 2

A tetrahedral mesh was utilized to discretize frame geometries. The undeformed mesh of the favorable design (also see highlighted design in Fig. 1) was shown here along with a local coordinate system and boundary conditions. A cylindrical local coordinate system helped implement semiaxisymmetric deformation of the mitral valve frame. Arrows indicate the location and direction of displacement boundary conditions. Prescription of the translational degrees of freedom at these locations provided the simulation of the expansion of the device to a desired diameter.

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Figure 3

The wing span, depth, and angle measurement locations were acquired from predicted expansion of the favorable design. A cross section of the device at the circumferential plane is shown.

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Figure 4

Expanded geometry of a failed (on the left) and the working (favorable, on the right) design. Finite element analysis provided the prediction of the designs at expanded states as well as the stress-strain distributions within. Red regions denote plastic strain magnitudes higher than 50%. The failed design had significant plastic deformation even before it expanded to the desired diameter.

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Figure 5

(a) Deployed three-dimensional geometry of the favorable percutaneous mitral valve stent frame as predicted by finite element analysis. The predictions utilized a simplified expansion scenario of the frame, prescribed by radial translation of various device regions to a desired diameter (also see Fig. 2). Full geometry was generated through circumferential stacking of the semiaxisymmetric model. (b) A close-up view of recessed indentation that provided the capacity for wing opening upon valve deployment.

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Figure 6

Wing span, depth, and angle of the favorable design (see highlighted design in Fig. 1) as a function of inner diameter dictated during initial expansion. These variables were predicted by finite element analysis, prescribed by incremental radial translation of the design to the desired diameter (in this case 44 mm). See Fig. 3 for more detailed description of these expansion variables.

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Figure 7

The plastic strain magnitudes of the favorable design (see highlighted design in Fig. 1) at the fully deployed diameter (∼44 mm) were found to be less than 30%. Plastic strain magnitude distribution in the device is shown from a top view of the expanded frame. Predictive strains of 55% did occur with the coarse mesh analysis due to a meshing artifact, and this was confirmed by a fine mesh analysis (outermost right subcells).

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Figure 8

Predicted plastic strain magnitude distribution for the crimped frame (∼10 mm). Results for the favorable design (see highlighted design in Fig. 1) are shown, where the observed plastic strains were 15%. Provided analysis results were obtained using the coarse mesh (also see Fig. 7).

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Figure 9

An illustration of the transcatheter valve frame deployed in its final configuration in the mitral valve annulus, anterior to the fossa ovalis and papillary muscles. The coronary sinus is superior to the mitral valve annulus and located along the left arterial wall. The device is crimped on the catheter system and positioned across the native mitral valve. Balloon expansion of the device triggers the anchoring fixation wings to secure around the tissue annulus.

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Figure 10

Transcatheter mitral heart valve frame with wing fixation system securely deployed and secured in a cadaver sheep annulus. An axial view is shown.

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