Tricuspid valve edge-to-edge repair simulations are highly sensitive to annular boundary conditions

Abstract

Transcatheter edge-to-edge repair (TEER) simulations may provide insight into this novel therapeutic technology and help optimize its use. However, because of the relatively short history and technical complexity of TEER simulations, important questions remain unanswered. For example, there is no consensus on how to handle the annular boundary conditions in these simulations. In this short communication, we tested the sensitivity of such simulations to the choice of annular boundary conditions using a high-fidelity finite element model of a human tricuspid valve. Therein, we embedded the annulus among elastic springs to simulate the compliance of the perivalvular myocardium. Next, we varied the spring stiffness parametrically and explored the impact on two key measures of valve function: coaptation area and leaflet stress. Additionally, we compared our results to simulations with a pinned annulus. We found that a compliant annular boundary condition led to a TEER-induced "annuloplasty effect," i.e., annular remodeling, as observed clinically. Moreover, softer springs led to a larger coaptation area and smaller leaflet stresses. On the other hand, pinned annular boundary conditions led to unrealistically high stresses and no "annuloplasty effect." Furthermore, we found that the impact of the boundary conditions depended on the clip position. Our findings in this case study emphasize the importance of the annular boundary condition in tricuspid TEER simulations. Thus, we recommend that care be taken when choosing annular boundary conditions and that results from simulations using pinned boundaries should be interpreted with caution.

Appendix Figure 1.

Atrial view of the Texas TriValve 1.0. A. Open, end-diastolic configuration of the healthy valve. B. Open, end-diastolic configuration of the regurgitant valve. C. Closed, end-systolic view of the healthy valve and D. closed, end-systolic view of the regurgitant valve both overlaid with contours of maximum principal Cauchy stress.

Appendix Figure 2.

The selected annular boundary condition impacts leaflet stresses. A. We report on the maximum principal Cauchy stress in the belly region of each leaflet indicated by the shaded region on a two-dimensional representation of the leaflet surface. B. Peak stresses remain elevated following TEER and are generally increase with the stiffness of the elastic annular foundation. Please note the scale of average stress varies by leaflet.

Figure 1.

The (reverse)-engineering pipeline used to build the high-fidelity finite-element model of the human tricuspid valve, the Texas TriValve 1.0. Reproduced with permission from (Mathur et al., 2022).

Figure 2.

Simulating TEER in the tricuspid valve for A. Clip Position #1 and B. Clip Position #2. First, we implanted the device in the regurgitant tricuspid valve at end-systole. Second, we removed the transvalvular pressure load and allowed the leaflets to settle onto the clips. Lastly, we closed the clips and reapplied the transvalvular pressure.

Figure 3.

Atrial view of all TEER simulations for selected each annular boundary condition (elastic spring support or pinned) overlaid with maximum principal Cauchy stress. A. Results for the first clip position. B. Results for the second clip position. The spring stiffness constant, k, is listed below in units of N/mm.

Figure 4.

A more compliant elastic boundary condition increases coaptation area. A. Leaflet coaptation is computed as the sum of element areas in contact at end-systole, depicted in blue and projected on a two-dimensional representation of the leaflet surface. B. All TEER simulations increase valve coaptation area compared to the disease baseline of 0.27 but remain well below the healthy value of 0.55.

Figure 5.

The selected annular boundary condition has a significant impact on leaflet stresses. A. We report on the maximum principal Cauchy stress in the belly region of the septal leaflet indicated by the shaded region on a two-dimensional representation of the leaflet surface. B. Following TEER, peak stresses are larger than in the healthy (17 kPa) or disease (61 kPa) baselines and increase with the stiffness of the elastic annular foundation.