A Hybrid Tissue-Level Model of the Left Ventricle: Application to the Analysis of the Regional Cardiac Function in Heart Failure

International audienceThis work contributes to the systemic interpretation of clinical data for the analysis of the regional cardiac function in the context of heart failure. A two-step patient-specific approach, combining a realistic geometry and a hybrid, tissue-level electromechanical model of the left ventricle is proposed. For the first step, a fast framework to extract a realistic geometry of the left ventricle from MSCT data is proposed. This geometry is then applied to a tissue-level model of the left ventricle, coupling a discrete electrical model, a mechanical model integrating a visco-elastic law, solved by a finite element method and a hydraulic model. A set of simulations carried out with the model are shown and preliminary results of the parameter identification approach, based on real patient data, are presented and discussed

An electromechanics-driven fluid dynamics model for the simulation of the whole human heart

We introduce a multiphysics and geometric multiscale computational model, suitable to describe the hemodynamics of the whole human heart, driven by a four-chamber electromechanical model. We first present a study on the calibration of the biophysically detailed RDQ20 active contraction model (Regazzoni et al., 2020) that is able to reproduce the physiological range of hemodynamic biomarkers. Then, we demonstrate that the ability of the force generation model to reproduce certain microscale mechanisms, such as the dependence of force on fiber shortening velocity, is crucial to capture the overall physiological mechanical and fluid dynamics macroscale behavior. This motivates the need for using multiscale models with high biophysical fidelity, even when the outputs of interest are relative to the macroscale. We show that the use of a high-fidelity electromechanical model, combined with a detailed calibration process, allows us to achieve a remarkable biophysical fidelity in terms of both mechanical and hemodynamic quantities. Indeed, our electromechanical-driven CFD simulations – carried out on an anatomically accurate geometry of the whole heart – provide results that match the cardiac physiology both qualitatively (in terms of flow patterns) and quantitatively (when comparing in silico results with biomarkers acquired in vivo). Moreover, we consider the pathological case of left bundle branch block, and we investigate the consequences that an electrical abnormality has on cardiac hemodynamics thanks to our multiphysics integrated model. The computational model that we propose can faithfully predict a delay and an increasing wall shear stress in the left ventricle in the pathological condition. The interaction of different physical processes in an integrated framework allows us to faithfully describe and model this pathology, by capturing and reproducing the intrinsic multiphysics nature of the human heart

Left-ventricular epi- and endocardium extraction from 3D ultrasound images using an automatically constructed 3D ASM

© 2014 Taylor & Francis.In this paper, we propose an automatic method for constructing an active shape model (ASM) to segment the complete cardiac left ventricle in 3D ultrasound (3DUS) images, which avoids costly manual landmarking. The automatic construction of the ASM has already been addressed in the literature; however, the direct application of these methods to 3DUS is hampered by a high level of noise and artefacts. Therefore, we propose to construct the ASM by fusing the multidetector computed tomography data, to learn the shape, with the artificially generated 3DUS, in order to learn the neighbourhood of the boundaries. Our artificial images were generated by two approaches: a faster one that does not take into account the geometry of the transducer, and a more comprehensive one, implemented in Field II toolbox. The segmentation accuracy of our ASM was evaluated on 20 patients with left-ventricular asynchrony, demonstrating plausibility of the approach

Integrated Cardiac Electromechanics: Modeling and Personalization

Cardiac disease remains the leading cause of morbidity and mortality in the world. A variety of heart diagnosis techniques have been developed during the last century, and generally fall into two groups. The first group evaluates the electrical function of the heart using electrophysiological data such as electrocardiogram (ECG), while the second group aims to assess the mechanical function of the heart through medical imaging data. Nevertheless, the heart is an integrated electromechanical organ, where its cyclic pumping arises from the synergy of its electrical and mechanical function which requires first to be electrically excited in order to contract. At the same time, cardiac electrical function experiences feedback from mechanical contraction. This inter-dependent relationship determines that neither electrical function nor mechanical function alone can completely reflect the pathophysiological conditions of the heart. The aim of this thesis is working towards building an integrated framework for heart diagnosis through evaluation of electrical and mechanical functions simultaneously. The basic rational is to obtain quantitative interpretation of a subject-specific heart system by combining an electromechanical heart model and individual clinical measurements of the heart. To this end, we first develop a biologically-inspired mathematical model of the heart that provides a general, macroscopic description of cardiac electromechanics. The intrinsic electromechanical coupling arises from both excitation-induced contraction and deformation-induced mechano-electrical feedback. Then, as a first step towards a fully electromechanically integrated framework, we develop a model-based approach for investigating the effect of cardiac motion on noninvasive transmural imaging of cardiac electrophysiology. Specifically, we utilize the proposed heart model to obtain updated heart geometry through simulation, and further recover the electrical activities of the heart from body surface potential maps (BSPMs) by solving an optimization problem. Various simulations of the heart have been performed under healthy and abnormal conditions, which demonstrate the physiological plausibility of the proposed integrated electromechanical heart model. What\u27s more, this work presents the effect of cardiac motion to the solution of noninvasive estimation of cardiac electrophysiology and shows the importance of integrating cardiac electrical and mechanical functions for heart diagnosis. This thesis also paves the road for noninvasive evaluation of cardiac electromechanics

Myocardial motion estimation combining tissue Doppler and B-mode echocardiographic images

International audienceWe present a registration framework that combines both tissue Doppler and B-mode echocardiographic sequences. The estimated spatiotemporal transform is diffeomorphic, and calculated by modeling its corresponding velocity field using continuous B-splines. A new cost function using both B-mode image voxel intensities and Doppler velocities is also proposed. Registration accuracy was evaluated on synthetic data with known ground truth. Results showed that our method allows quantifying wall motion with higher accuracy than when using a single modality. On patient data, both displacement and velocity curves were compared with the ones obtained from widely used commercial software using either B-mode images or TDI. Our method demonstrated to be more robust to image noise while being independent from the beam angle

Fluid-electro-mechanical model of the human heart for supercomputers

The heart is a complex system. From the transmembrane cell activity to the spatial organization in helicoidal fibers, it includes several spatial and temporal scales. The heart muscle is surrounded by two main tissues that modulate how it deforms: the pericardium and the blood. The former constrains the epicardial surface and the latter exerts a force in the endocardium. The main function of this peculiar muscle is to pump blood to the pulmonary and systemic circulations. In this way, solid dynamics of the heart is as important as the induced fluid dynamics. Despite the work done in computational research of multiphysics heart modelling, there is no reference of a tightly-coupled scheme that includes electrophysiology, solid and fluid mechanics in a whole human heart. In this work, we propose, develop and test a fluid-electro-mechanical model of the human heart. To start, the heartbeat phenomenon is disassembled in the different composing problems. The first building block is the electrical activity of the myocytes, that induces the mechanical deformation of the myocardium. The contraction of the muscle reduces the intracavitary space, that pushes out the contained blood. At the same time, the inertia, pressure and viscous stresses in this fluid exerts a force on the solid wall. In this way, we can understand the heart as a fluid-electro-mechanical problem. All the models are implemented in Alya, the Barcelona Supercomputing Center simulation software. A multi-code approach is used, splitting the problem in a solid and a fluid domain. In the former, electrophysiology coupled with solid mechanics are solved. In the later, fluid dynamics in an arbitrary Lagrangian-Eulerian domain are computed. The equations are spatially discretized using the finite element method and temporally discretized using finite differences. Facilitated by the multi-code approach, a novel high performance quasi-Newton method is developed to deal with the intrinsic issues of fluid-structure interaction problems in iomechanics. All the schemes are optimized to run in massively parallel computers. A wide range of experiments are shown to validate, test and tune the numerical model. The different hypothesis proposed — as the critical effect of the atrium or the presence of pericardium — are also tested in these experiments. Finally, a normal heartbeat is simulated and deeply analyzed. This healthy computational heart is first diseased with a left bundle branch block. After this, its function is restored simulating a cardiac resynchronization therapy. Then, a third grade atrioventricular block is simulated in the healthy heart. In this case, the pathologic model is treated with a minimally invasive leadless intracardiac pacemaker. This requires to include the device in the geometrical description of the problem, solve the structural problem with the tissue, and the fluid-structure interaction problem with the blood. As final experiment, we test the parallel performance of the coupled solver. In the cases mentioned above, the results are qualitatively compared against experimental measurements, when possible. Finally, a first glance in a coupled fluid-electro-mechanical cardiovascular system is shown. This model is build adding a one dimensional model of the arterial network created by the Laboratório Nacional de Computação Científica in Petropolis, Brasil. Despite the artificial geometries used, the outflow curves are comparable with physiological observations. The model presented in this thesis is a step towards the virtual human heart. In a near future computational models like the presented in this thesis will change how pathologies are understood and treated, and the way biomedical devices are designed.El corazón es un sistema complejo. Desde la actividad celular hasta la organización espacial en fibras helicoidales, incluye gran cantidad de escalas espaciales y temporales. El corazón está rodeado principalmente por dos tejidos que modulan su deformación: el pericardio y la sangre. El primero restringe el movimiento del epicardio, mientras el segundo ejerce fuerza sobre el endocardio. La función principal de este músculo es bombear sangre a la circulación sistémica y a la pulmonar. Así, la deformación del miocardio es tan importante como la fluidodinámica inducida. Al día de hoy, solo se han propuesto modelos parciales del corazón. Ninguno de los modelos publicados resuelve electrofisiología, mecánica del sólido, y dinámica de fluidos en una geometría completa del corazón. En esta tesis, proponemos, desarrollamos y probamos un modelo fluido -electro -mecánico del corazón. Primero, el problema del latido cardíaco es descompuesto en los distintos subproblemas. El primer bloque componente es la actividad eléctrica de los miocitos, que inducen la deformación mecánica del miocardio. La contratación de este músculo, reduce el espacio intracavitario, que empuja la sangre contenida. Al mismo tiempo, la inercia, presión y fuerzas viscosas del fluido inducen una presión sobre la pared del sólido. De esta manera, podemos entender el latido cardíaco como un problema fluido-electro-mecánico. Los modelos son implementados en Alya, el software de simulación del Barcelona Supercomputing Center. Se utiliza un diseño multi-código, separando el problema según el dominio en sólido y fluido. En el primero, se resuelve electrofisiología acoplado con mecánica del sólido. En el segundo, fluido dinámica en un dominio arbitrario Lagrangiano-Euleriano. Las ecuaciones son discretizadas espacial y temporalmente utilizando elementos finitos y diferencias finitas respectivamente. Facilitado por el diseño multi-codigo, se desarrolló un novedoso método quasi-Newton de alta performance, pensado específicamente para lidiar con los problemas intrínsecos de interacción fluido-estructura en biomecánica. Todos los esquemas fueron optimizados para correr en ordenadores masivamente paralelos.Se presenta un amplio espectro de experimentos con el fin de validar, probar y ajustar el modelo numérico. Las diferentes hipótesis propuestas tales como el efecto producido por la presencia de las aurículas o el pericardio son también demostradas en estos experimentos. Finalmente un latido normal es simulado y sus resultados son analizados con profundidad. El corazón computacional sano es, primeramente enfermado de un bloqueo de rama izquierda. Posteriormente se restaura la función normal mediante la terapia de resincronización cardíaca. Luego se afecta al corazón de un bloqueo atrioventricular de tercer grado. Esta patología es tratada mediante la implantación de un marcapasos intracardíaco. Para esto, se requiere incluir el dispositivo en la descripción geométrica, resolver el problema estructural con el tejido y la interacción fluido-estructura con la sangre. Como experimento numérico final, se prueba el desempeño paralelo del modelo acoplado.Finalmente, se muestran resultados preliminares para un modelo fluido-electro-mecánico del sistema cardiovascular. Este modelo se construye agregando un modelo unidimensional del árbol arterial. A pesar de las geometrías artificiales usadas, la curva de flujo en la raíz aórtica es comparable con observaciones experimentales. El modelo presentado aquí representa un avance hacia el humano virtual. En un futuro, modelos similares, cambiarán la forma en la que se entienden y tratan las enfermedades y la forma en la que los dispositivos biomédicos son diseñados.Postprint (published version