Computational analysis of the electromechanical performance of mitral valve cerclage annuloplasty using a patient-specific ventricular model

We aimed to propose a novel computational approach to predict the electromechanical performance of pre- and post-mitral valve cerclage annuloplasty (MVCA). Furthermore, we tested a virtual estimation method to optimize the left ventricular basement tightening scheme using a pre-MVCA computer model. The present model combines the three-dimensional (3D) electromechanics of the ventricles with the vascular hemodynamics implemented in a lumped parameter model. 3D models of pre- and post-MVCA were reconstructed from the computed tomography (CT) images of two patients and simulated by solving the electromechanical-governing equations with the finite element method. Computed results indicate that reduction of the dilated heart chambers volume (reverse remodeling) appears to be dependent on ventricular stress distribution. Reduced ventricular stresses in the basement after MVCA treatment were observed in the patients who showed reverse remodeling of heart during follow up over 6 months. In the case who failed to show reverse remodeling after MVCA, more virtual tightening of the ventricular basement diameter than the actual model can induce stress unloading, aiding in heart recovery. The simulation result that virtual tightening of the ventricular basement resulted in a marked increase of myocardial stress unloading provides in silico evidence for a functional impact of MVCA treatment on cardiac mechanics and post-operative heart recovery. This technique contributes to establishing a pre-operative virtual rehearsal procedure before MVCA treatment by using patient-specific cardiac electromechanical modeling of pre-MVCA.

Consideraciones en la definición del modelo específico al paciente de la tibia / Considerations about the definition of a patient specific model of the tibia

INTRODUCCIÓN: los análisis por elementos finitos se usan para entender y predecir los procesos biológicos. En la biomecánica ortopédica, los modelos específicos al paciente se generan a partir de Tomografía Computarizada y empleados en la toma de decisiones médicas. Algunos procesos correctivos ortopédicos pueden simularse a través, de los análisis por elementos finitos. Para obtener modelos biomecánicos confiables, es muy recomendable reducir los errores en la definición del modelo en la etapa de pre-procesamiento del análisis por elementos finitos. OBJETIVO: analizar la influencia de la densidad del mallado y las propiedades mecánicas durante la definición del modelo específico al paciente en los resultados del análisis por elementos finitos. MÉTODOS: se empleó el Método de Elementos Finitos en la simulación de la tibia a compresión. La geometría de la tibia del paciente se generó a partir de Tomografía Computarizada. Se emplearon mallas con tamaño de elementos no uniforme y uniforme. Al modelo se le aplicaron propiedades mecánicas homogéneas y no homogéneas. RESULTADOS: los elementos de bajo orden convergen a la solución, las tensiones para las mallas con estos elementos son inferiores a las correspondientes las mallas con elementos de tamaño uniforme y de alto orden. Por otra parte, las propiedades mecánicas no homogéneas reducen la diferencia en el cálculo de las tensiones. CONCLUSIONES: para obtener modelos específicos al paciente confiables se recomienda, generar la geometría del hueso con superficies suavisadas, controlar la calidad de la malla superficial, usar propiedades mecánicas no homogéneas, y utilizar la malla generada directo en Abaqus con elementos de bajo orden y tamaño no uniforme.

INTRODUCTION: finite element analysis is used to understand and predict biological processes. In orthopedic biomechanics patient specific models are generated by computed tomography and used for medical decision making. Some corrective orthopedic processes may be simulated by means of finite element analysis. In order to obtain reliable biomechanical models it is highly advisable to reduce the number of errors in the definition of the model during pre-processing of the finite element analysis. OBJECTIVE: analyze the influence of mesh density and mechanical properties on the results obtained by finite element analysis during the stage of definition of the patient specific model. METHODS: the finite element method was used to simulate tibial compression. The geometry of the patient's tibia was generated by computed tomography. Meshes were used with non-uniform and uniform element sizes. Homogeneous and non-homogeneous mechanical properties were applied to the model. RESULTS: low-order elements converge to the solution. Tensions for meshes with these elements are lower than those for meshes with uniform size and high-order elements. On the other hand, non-homogeneous mechanical properties reduce the difference in the estimation of tensions. CONCLUSIONS: to obtain reliable patient specific models it is recommended to generate the bone geometry with softened surfaces, control the quality of the surface mesh, use non-homogeneous mechanical properties, and use the mesh generated directly on Abaqus with low-order elements and non-uniform size.