VIRTUAL HEART VALVE

• US 20070208550A1
• Filed: 02/28/2007
• Published: 09/06/2007
• Est. Priority Date: 03/02/2006
• Status: Active Grant

• Current Assignee: Edwards Lifesciences Corporation
• Original Assignee: Edwards Lifesciences Corporation
• Inventors: Cao, Hengchu, Sun, Wei
• Granted Patent: US 8,219,229 B2
• Time in Patent Office: Days
• US Class Current: 703/11
• CPC Class Codes: A61F 2/2412 with soft flexible valve members, e.g. tissue valves shaped like natural valves check valves with flexible valve members in general F16K15/14
• CPC Class Codes: A61F 2/2418 Scaffolds therefor, e.g. support stents
• CPC Class Codes: A61F 2220/0075 sutured, ligatured or stitched, retained or tied with a rope, string, thread, wire or cable
• CPC Class Codes: A61F 2230/0054 V-shaped
• CPC Class Codes: G06F 30/23 using finite element methods [FEM] or finite difference methods [FDM]

Abstract

A computational technique to construct a 3-D valve leaflet geometry. The invention pertains to methodology to construct a 3-D heart valve leaflet geometry using finite element analysis (FEA) to simulate the manual assembly process or, in other words, provide a virtual assembly process as an input to a subsequent simulated valve testing step. The simulated valves may be subjected to simulated cyclic valve opening and closings and the stress levels induced therein monitored. Simulated valve designs with lower principal stresses can then be selected for prototyping. Proposed valves can be subjected to cyclic fatigue stress testing under simulated physiologic conditions to study valve durability.

Claims

1. A method of modeling a prosthetic heart valve with a computer program, comprising:

entering two-dimensional geometry and material parameters of a flexible heart valve leaflet into a finite element analysis program to define a simulated leaflet;

entering the three-dimensional geometry and material parameters of a heart valve support frame using the finite element analysis program to define a simulated support frame; and

deriving the topography of a plurality of the simulated leaflets in three dimensions by imposing edge constraints on the simulated leaflets at their intersections with the support frame.

2. The method of claim 1, wherein the simulated support frame is generally tubular, wherein the plurality of simulated leaflets are arranged generally in a tube within the support frame, and wherein the edge constraints comprise a continuous line fixing the tube of simulated leaflets around an inflow end of the simulated support frame, and a plurality of generally axial lines located at the intersections of adjacent axial edges of the simulated leaflets.

3. The method of claim 2, wherein the edge constraints further include rotational constraints at the intersection of adjacent axial edges of the simulated leaflets such that they extend radially outward and parallel to each other.

4. The method of claim 3, wherein the edge constraints further include forces that displace discrete points along the adjacent axial edges of the simulated leaflets outwards and constrain the three translational degrees of freedom of the discrete points.

5. The method of claim 4, wherein inflow portions of the adjacent axial edges of the simulated leaflets are displaced outward until they intersect the simulated support frame, while outflow portions are displaced outward but remain spaced from the simulated support frame.

6. The method of claim 2, wherein the simulated support frame defines an undulating continuous line with upstanding outflow commissures and arcuate inflow cusps therebetween, wherein each simulated leaflet is arranged generally around an arcuate cusp with the edge constraints imposed along the cusps.

7. The method of claim 6, wherein the edge constraints include forces that displace discrete points on the simulated leaflets outward until they intersect the simulated support frame, the forces constraining the three translational degrees of freedom of the discrete points.

8. The method of claim 1, wherein the material parameters of the flexible heart valve leaflets are modeled biological tissues characterized by a nonlinear, anisotropic Fung type tissue model, within which the second Piola-kirchhoff stress S can be derived from a strain energy function W through:

$\begin{array}{cc}S=\frac{\partial <br><br>W}{\partial <br><br>E}& \left(1\right)\end{array}$

where E is the Green strain tensor, and wherein

a Fung elastic model is utilized with full expansion of quadric terms of Q and with the ability to characterize in-plane shear response;

$\begin{array}{cc}W=\frac{c}{2}<br><br>\left[{\mathrm{<br><br>}}^Q-1\right]<br><br><br><br>Q=A_1<br><br>E_{11}^2+A_2<br><br>E_{22}^2+2<br><br>A_3<br><br>E_{11}<br><br>E_{22}+A_4<br><br>E_{12}^2+2<br><br>A_5<br><br>E_{12}<br><br>E_{11}+2<br><br>A_6<br><br>E_{12}<br><br>E_{22}& \left(2\right)\end{array}$

where c and A_i are material constants.

9. The method of claim 1, wherein the material parameters of the simulated leaflets are modeled elastomeric polymer thin sheet characterized by a nonlinear hyperelastic property.

10. The method of claim 1, wherein the material parameters of the simulated leaflets are modeled polymer thin sheet approximated by a linear elastic property.

11. A method of testing a simulated prosthetic heart valve, comprising:

providing a two-dimensional drawing of a simulated heart valve leaflet having a cusp edge and a free edge;

simulating a valve assembly procedure to form a simulated heart valve by attaching the cusp edge of a plurality of the leaflets to a simulated 3-dimensional heart valve support frame using finite element analysis software, and applying edge constraints at the support frame to the cusp edges;

applying nonlinear tissue material constitutive properties in the finite element analysis software;

applying simulated valve opening and closing fluid cycles to the simulated heart valve; and

monitoring simulated stresses induced in the simulated heart valve by the application of simulated valve opening and closing cycles.

12. The method of claim 11, wherein the simulated support frame is generally tubular, wherein the plurality of simulated leaflets are arranged generally in a tube within the support frame, and wherein the edge constraints comprise a continuous line fixing the tube of simulated leaflets around an inflow end of the simulated support frame and a plurality of generally axial lines located at the intersections of adjacent axial edges of the simulated leaflets.

13. The method of claim 11, wherein the edge constraints include forces that displace discrete points on the simulated leaflets outward until they intersect the simulated support frame, the forces constraining the three translational degrees of freedom of the discrete points.

14. The method of claim 11, wherein the simulated support frame defines an undulating continuous line with upstanding outflow commissures and arcuate inflow cusps therebetween, wherein each simulated leaflet is arranged generally around an arcuate cusp with the edge constraints imposed along the cusps.

15. The method of claim L, further including subjecting the simulated heart valve to cyclic fatigue stress testing under simulated physiologic conditions to study valve durability.

16. A method of selecting a prosthetic heart valve design for prototyping, comprising:

providing a two-dimensional drawing of a simulated heart valve leaflet having a cusp edge and a free edge;

simulating a valve assembly procedure by attaching the cusp edge of a plurality of the leaflets to a simulated 3-dimensional heart valve support frame using finite element analysis software;

imposing edge constraints on the leaflets at their intersections with the support frame;

applying nonlinear tissue material constitutive properties in the finite element analysis software;

applying simulated valve opening and closing fluid cycles;

obtaining a stress distribution in the leaflets;

performing the steps above for at least two simulated heart valves; and

building a prototypical valve based on a comparison of the observed stress distribution in the leaflets of the simulated valves.

17. The method of claim 16, further including:

building a prototypical valve based on the simulated valve in which the lowest principal stresses in the leaflets throughout the opening and closing cycles are observed.

18. The method of claim 16, wherein the simulated support frame is generally tubular, wherein the plurality of simulated leaflets are arranged generally in a tube within the support frame, and wherein the edge constraints comprise a continuous line fixing the tube of simulated leaflets around an inflow end of the simulated support frame and a plurality of generally axial lines located at the intersections of adjacent axial edges of the simulated leaflets.

19. The method of claim 16, wherein the edge constraints include forces that displace discrete points on the simulated leaflets outward until they intersect the simulated support frame, the forces constraining the three translational degrees of freedom of the discrete points.

20. The method of claim 16, wherein the simulated support frame defines an undulating continuous line with upstanding outflow commissures and arcuate inflow cusps therebetween, wherein each simulated leaflet is arranged generally around an arcuate cusp with the edge constraints imposed along the cusps.