Patient-Specific FSI Modelling of the Left Heart for Pre-Operative Planning of Valve Surgery
Cardiac valves, and especially the mitral valve (MV), are complex anatomical structures. Their proper function depends on a delicate force distribution and synchronized function of all their components. Pathological changes in valve components are common indicators for valvular surgery. There is a large variety of valve implants (mechanical/ biological), sizes and implantation techniques, as well as valve repair techniques. The success of the operation is highly dependent on the surgeons’ experience in terms of surgical technique and choosing the most appropriate prosthesis and intervention for the individual patient. This project developed a novel prognostic/forecasting fluid-solid interaction (FSI) simulation tool that can provide patient-specific pre-operative optimization of MV repair or replacement.
Materials & Methods
CT images were acquired from a 62 years old male, segmented in Simpleware, and the 3D anatomy of the left heart, including the MV and aortic valve (AV) root, was reconstructed and meshed. Porcine anterior and posterior MV leaflets were tested under biaxial displacement, whereas aortic valve (AV) leaflets, aortic wall and MV chordae were tested under uniaxial tension. The stress-strain profiles (Figure 1) were imported into the model of the left heart (Figure 2A) and a fibre-reinforced transversely isotropic material model was used for the MV and AV leaflets and aortic wall, whereas a cable material model was used for the MV chordae. The model was imported into LS-DYNA, where an FSI simulation was performed for one cardiac cycle. The ventricle motion was prescribed according to the patient’s specific systolic geometry so that to reach peak systole in 0.35s (Figure 2B). The aortic pressure was used as boundary condition at the aortic inlet/outlet and a zero pressure boundary condition was applied at the atrial side. The models were validated against in vitro testing in a pulse simulator (MV) and clinical data (whole left heart).
The simulations predicted MV and AV leaflet regions with elevated stress concentrations during the cardiac cycle (Figures 3A, 3B and 4A), which were in accord with failure regions observed clinically. Moreover, the simulations indicated variable loading of the different MV chordae during the cardiac cycle. The whole left heart model demonstrated the interdependent function of the MV and AV, whereas the predicted fluid patterns developed during the cardiac cycle indicated varying wall shear stress levels on the wall of the different components (Figure 4B).
This study demonstrated that different components of the MV experience different levels of stress and strain, with direct implications in the selection of appropriate materials for MV reconstruction. Future work will focus on parametric studies with different repair materials for MV leaflet and chordae reconstruction, and different prostheses for MV replacement.