Effects of transcatheter edge-to-edge repair on mitral valve diastolic hemodynamics

Introduction: : Mitral valve regurgitation (MR) is a prevalent and life-threatening condition caused by the failure of the mitral valve (MV) to coapt, allowing blood to backflow into the left atrium. Transcatheter edge-to-edge repair (TEER) techniques (e.g. MitraClip) offer a promising alternative, but clinical outcomes have reported highly contradictory results due to patient-to-patient variability. The effects of TEER configuration on MV function, hemodynamics, and long-term outcomes are largely unknown. Additionally, clinical studies have highlighted that the hemodynamic burden after TEER is correlated to the long-term survival rate. However, the impacts of post-TEER hemodynamic changes, such as multiple flow jets and left atrial pressure, cannot be fully demonstrated with structure-only simulations disregarding the effect of blood flow on the MV. In the present study, we aim to gain a better understanding of post-TEER hemodynamics during diastolic filling for the guidance of treatment selection for each patient. Specifically, we developed a computational fluid-structure interaction model based on immersogeometric analysis that can account for complex interactions between a patient-specific MV and blood flow in the left heart along with accurately modeling patient-specific MV behaviors. The developed FSI model was used to examine how the hemodynamic characteristic of TEER, such as a significant reduction of the effective orifice area (EOA) and transvalvular gradients. In addition, we investigate how the hemodynamic changes influence the post-operative MV functional state, geometry, and mechanical behaviors, which can help clinicians develop precise MR treatment guidance for patient-specific stratification, which is essential for personalizing and optimizing patient outcomes.

Materials and

Methods: : A patient-specific MV geometry is directly obtained by converting TEE images through state-of-the-art segmentation coupled to a 3D B-spline surface fitting approach to obtain high fidelity patient-specific geometries (See Figure 1). We detail multiple unique features of MV previously unavailable in the clinic that are important for treatment planning, including MV chordae tendineae (CT), quantified chordae-leaflet insertion points, papillary muscle locations, and patient-specific in vivo mechanical properties from our group’s computational pipeline.
To investigate the complex hemodynamic aspects of post-TEER MV with a patient-specific MV geometry, we focus on immersogeometric analysis (IMGA) for fluid-structure interaction. We focus on the Kirchhoff-Love thin shell formulation for the MV leaflets and beam elements for CTs. MV TEER causes a highly non-physiological focal stress concentration on the leaflets and hemodynamic changes in the left heart, and such an effect is further augmented for patients who receive more than one clip device. To implement clipping within the IMGA framework, we utilize an existing contact algorithm to identify the areas on the leaflets where the clip device is implanted. Once we identify the clipping regions, a clip-equivalent penalty force enforces displacement and rotational constraints on the leaflets, which allows physiologically accurate deformations and movements of the clipped geometry by interacting with the blood flow (See Figure 2).

Results, Conclusions, and Discussions:: Under the same heart function (i.e., inflow velocity condition) in both pre- and post-operative cases, we evaluate the MV effective orifice area and the transvalvular velocity. The presence of clip devices reduces the MV orifice area, generates multiple flow jets instead of a single jet in the pre-operative MV, and produces higher-velocity flow jets through the valve, in contrast to the smoother flow in the non-clipped case (See Figure 3). In addition, an excessive number of clips increases filling gradients and produces highly nonphysiological focal stresses onto the leaflet, which leads to a significant reduction in the MV effective orifice area (EOA). We compute EOA using the Gorlin formula. On the other hand, a reduced flow rate is observed under a constant pressure difference between the left atrium and ventricle due to increased energy loss (See Figure 4). The simulation results strongly indicate the significant hemodynamic changes due to the TEER device, which emphasize the importance of an individualized approach to MV treatment optimization.
This study investigated post-MV TEER hemodynamic responses by developing a realistic clip simulation using real human in vivo acquired MV geometry within a computational FSI framework. Our findings confirm that the presence of a clip device significantly changes overall hemodynamics in the left heart, such as increased transvalvular gradients, which directly affect heart functions after TEER. In addition, our simulated values of post-TEER EOA are comparable to the reported values in the previous literature (typical reduction around 25 − 40% and maximum reduction up to 50% or more in extreme cases). As an extension of our study, a realistic left heart will be used to investigate more rigorous hemodynamics after TEER, which can benefit precise MR treatment guidance in the clinic.

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