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1: (a) Blood flow through the heart; (b) The heart inside the whole circulatory system. Images taken from www.pediatricheartspecialists.com (a) and www. pinterest.it (b).
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Cardiovascular diseases are the primary cause of mortality worldwide, affecting millions of people every year. Although advancements in medical practice are continuously improving the diagnosis and treatment techniques, computer-based simulations of the cardiac function are gradually becoming a powerful tool to better understand the heart function...
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... left and right hearts are separated by the inter-atrial and inter-ventricular septa, which prevent the mixing of oxygenated and deoxygenated blood, whereas the atria and the ventricles are connected by the atrioventricular valves (mitral valve, MV, and tricuspid valve, TV) that regulate the blood transfer from the upper to lower cavities. The four chambers are connected to the circulatory system: the ventricles with the aorta through the aortic valve (AV) and with the pulmonary artery via the pulmonary valve (PV); LA with the left and right pulmonary veins (LPV, RPV), whereas RA with superior and inferior caval veins (SCV, ICV), see Figure 1.1. Figure 1.2: Representation of the multiscale cardiac muscle. ...
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... four chambers are connected to the circulatory system: the ventricles with the aorta through the aortic valve (AV) and with the pulmonary artery via the pulmonary valve (PV); LA with the left and right pulmonary veins (LPV, RPV), whereas RA with superior and inferior caval veins (SCV, ICV), see Figure 1.1. Figure 1.2: Representation of the multiscale cardiac muscle. ...
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... of myofibers give rise to the fiberreinforced heart structure defining the cardiac muscular architecture [134,232,86,128]. A schematic representation of the multiscale myocardial fiber-structure is shown in Figure 1.2. Ventricular muscular fibers are well-organized as two intertwined spirals wrapping around the heart, clockwise on the sub-epicardium and counter-clockwise on the sub-endocardium, defining the characteristic myocardial helical structure [134,232]. ...
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... muscular fibers are well-organized as two intertwined spirals wrapping around the heart, clockwise on the sub-epicardium and counter-clockwise on the sub-endocardium, defining the characteristic myocardial helical structure [134,232]. Local orientation of myofibers are identified by their angle on the tangent plane and on the normal plane of the heart, called the helical and the sheet angles, respectively [232,243], see Figure 1.2. The transition inside the myocardial wall is characterized by a continuous change in helical angle from about 60 o to 90 o at the epicardial surface to nearly 0 o in the mid-wall region to −20 o to −60 o at the endocardium [134,232,242], with circumferential and longitudinal fiber orientations predominant in RV with respect to LV [214,154,9,211], see Figures 1.3(a-b). ...
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... fibers in the atria are arranged [214,212,167]. in individual bundles running along different directions throughout the wall chambers. Preferred orientation of myofibers in the human atria is characterized by multiple overlapping structures, which promote the formation of separate attached bundles [57], Figure 1.2 also 1.3(c-d). ...
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... this synchronized heart contraction governs the blood pressure inside the cardiac chambers, determining a ruled opening of the heart valves and ensuring, at each heartbeat, the physiological blood flow throughout the heart chambers and into the circulatory system [187,112]. A schematic representation of the electromechanical activity of the heart is outlined in Figure 1.4. Each cardiac cycle can be summarized into the following three phases (see also Figure 1 ...
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... schematic representation of the electromechanical activity of the heart is outlined in Figure 1.4. Each cardiac cycle can be summarized into the following three phases (see also Figure 1 ...
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... an EM/EFM model needs to account for the coupling with the rest of the circulatory system (say, the complements of the four heart chambers), usually represented by simplified lumpedparameter Windkessel models [204,53,139,80,209,130,184] or, less common, closedloop systems [19,198,113,96]. A schematic representation of the building blocks constituting a mathematical model of cardiac EM is shown in Figure 1.5. ...
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... fiber directions are mapped based on histological sectioning informations, taken from measurements on ex-vivo hearts [232,253,154,93], or on digital processing (structure tensor methods) of high-resolution volumetric imaging techniques [95,269,268,167,179], sometimes using a statistical atlas heart [250,161,174]. In cases where neither histological nor imaging information is available, myofiber structures are typically incorporated by using rule-based methods, that estimate the fiber orientations associated to each element of the volumetric mesh from pre-established patterns derived from histoanatomical findings [204,176,26,260,58]. Figure 1.6 shows a summary of the methods most commonly used to obtain the cardiac fiber architecture. ...
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... the years, myofibers orientation has been studied using mainly histological data, anatomical dissections and Diffusion Tensor Imaging (DTI) acquisitions [232,9,211,8,104,95,167,97,165,240,100,98,16,51,93], see Figure 1.3. DTI is a Magnetic Resonance Imaging (MRI) technique able to produce useful structural information about heart muscle fibers and largely applied to explanted ex-vivo hearts, coming from animal experiments [104,95,217,267,174] or from human corpses [134,167]. ...
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... there is a paucity of imaging data on atrial fibers orientation with respect to the ventricles, mainly due to imaging difficulties in capturing the thin atrial walls [57]. Only recently, ex vivo atrial fibers have been analysed owing to submillimeter Diffusion Tensor MRI (DT-MRI) [167,268,269], see Figure 1.3(d). Moreover, since the atrial thickness is smaller than the DTI voxel size, it is not possible to obtain in-vivo myofibers in the atria [101]. ...
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... (CT) scan, or using detailed Computer Aided Design (CAD) models (see Figure 1.7). Given the geometry, the creation of a whole heart mesh is a challenging procedure mainly because the atrial wall is about an order of magnitude thinner than the ventricular wall. ...
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... Investigate the effect of several myofiber architectures on EM simulations. Figure 1.8: Graphical map of the thesis. ...
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... thesis is organized along the following chapters. A graphical map illustrating the main topic and the link of these chapter is shown in Figure 1.8. ...
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... orientations obtained for the three LDRBMs (R-RBM, B-RBM and D-RBM) in the idealized biventricular model are shown in Figures 2.14(a-f). The input angles values α endo,, , α epi,, , α endo,r , α epi,r , β endo,, , β epi,, , β endo,r and β epi,r were chosen for all the three methods based on the observations of histological studies in the human heart [134,86,9,99,210,136,229] (see also [58]): ...
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... observe that all the LDRBMs represent the characteristic helical structure of LV and a compatible fiber orientations both in the right endocardium, not facing to the septum, and in the right epicardium, far enough from the inter-ventricular junctions. Most of the differences occur in the right ventricular endocardium facing the septum (see Figures 2.14(a-c)), in the inter-ventricular junctions between the two ventricles and in the right epicardial lower region (see Figures 2.14(d-f)). ...
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... observe that all the LDRBMs represent the characteristic helical structure of LV and a compatible fiber orientations both in the right endocardium, not facing to the septum, and in the right epicardium, far enough from the inter-ventricular junctions. Most of the differences occur in the right ventricular endocardium facing the septum (see Figures 2.14(a-c)), in the inter-ventricular junctions between the two ventricles and in the right epicardial lower region (see Figures 2.14(d-f)). ...
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... initiate the action potential propagation we applied four endocardial stimuli: two for each ventricle, one in the mid-septal zone and one in the lateral endocardial wall. In Figures 2.15(ac) we report the activation maps obtained with the three fibers configurations. The activation time of a given point in the cardiac muscle is computed as the time when the transmembrane potential derivative du dt reaches its maximal value. ...
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... different orientations of the septal fibers produced a significant impact in terms of EP numerical results. A dissimilar activation pattern and timing were observed at the septum, especially in the right endocardial region, confirmed by the highest discrepancy between R-RBM and the other two methods reaching 28-29% of the total activation time (Figure 2.15). Conversely, D-RBM and B-RBM yield almost the same activation pattern, thanks to the extensions introduced in B-RBM (Figure 2.15). ...
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... dissimilar activation pattern and timing were observed at the septum, especially in the right endocardial region, confirmed by the highest discrepancy between R-RBM and the other two methods reaching 28-29% of the total activation time (Figure 2.15). Conversely, D-RBM and B-RBM yield almost the same activation pattern, thanks to the extensions introduced in B-RBM (Figure 2.15). The above results confirmed the importance of including specific fiber orientations in RV with respect to those of LV. ...
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... observe that the biatrial LDRBM captures the arrangement of fiber directions in all the principal anatomical atrial regions of RA, with the inclusion of PM (see Figures 2.19(b-d)), of LA, with the prescription of different transmural variations (e.g. in BB, LPV and RPV), see Figure 2.19(a). Moreover, it physically includes the principal IC connecting RA to LA: BB IC , FO IC , see Figure 2.19(c). ...
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... example of LDRBM boundary-value solutions for the fiber generation procedure (of D-RBM type) is sketched in Figure 3.1(b). For further details about ventricular LDRBMs we refer the reader to Section 2.1. ...
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... the normalized inter-ventricular distance, defined in Section 3.1.1, and C rv ∈ (0, 1] represents the left-right ventricular contractility ratio, see Fig- ure 3.1(b). Finally, problem (A ) is closed by the initial condition (3.3b). ...
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... R-RBM and D-RBM feature a linear transition passing from the endocardium to the epicardium, while B-RBM employs a bidirectional spherical interpolation bislerp (see [176,26,58,188]). In Figure 3.13(b) the PV-loop curves (for both ventricles) 1 s) and the time trace of the average, minimum and maximum axial stresses S f f (top-left), S ss (bottom-left) and S nn (bottom-right) for the three LDRBMs. Table 3.8: Comparison of relevant mechanical biomarkers among EM simulations using D-RBM,B-RBM and R-RBM for the myofiber architecture. ...
Citations
... The whole-heart EM model includes a detailed myocardial fiber architecture built upon a total-heart Laplace-Dirichlet Rule-Based Method [84], which couples together different methods for the atria [85] and the ventricles [86], to properly reproduce the characteristic features of the cardiac fiber bundles in all the four-chambers [85], see Fig. 1a. ...
... The whole-heart EM model includes a detailed myocardial fiber architecture built upon a totalheart Laplace-Dirichlet Rule-Based Method [78], which couples together different methods for the atria [79] and the ventricles [80], to properly reproduce the characteristic features of the cardiac fiber bundles in all the four-chambers [79], see Figure 1a. ...
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 activation 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 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). 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.
... • an accurate myocardial fiber architecture using a novel whole-heart Rule-Based-Method (RBM) that takes into account also the characteristic atrial fiber bundles [45,55]; ...
... To prescribe the muscular fiber architecture in the myocardium Ω myo 0 , we rely on a particular class of Rule-Based-Methods (RBMs), known as Laplace-Dirichlet RBMs (LDRBMs) [22,72,73] recently reviewed in a communal mathematical description and also extended to account for atrial geometries in [45]. Specifically, we use the whole-heart LDRBM proposed by Piersanti et al. [45] in its improved version detailed in [55,Chapter 4]. ...
... Fig. 4 shows that the whole-heart LDRBM is able to accurately reproduce the myocardial fiber architecture, capturing the helical structure of LV, the characteristic fibers of RV, the outflow tracts regions and the fiber bundles of LA and RA, including the inter-atrial connections, the Crista Terminalis (CrT) and the Pectinate Muscles (PeMs). For further details about this whole-heart LDRBM we refer to [55]. ...
While ventricular electromechanics is extensively studied, four-chamber heart models have only been addressed recently; most of these works however neglect atrial contraction. Indeed, as atria are characterized by a complex physiology influenced by the ventricular function, developing computational models able to capture the physiological atrial function and atrioventricular interaction is very challenging. In this paper, we propose a biophysically detailed electromechanical model of the whole human heart that considers both atrial and ventricular contraction. Our model includes: i) an anatomically accurate whole-heart geometry; ii) a comprehensive myocardial fiber architecture; iii) a biophysically detailed microscale model for the active force generation; iv) a 0D closed-loop model of the circulatory system; v) the fundamental interactions among the different core models; vi) specific constitutive laws and model parameters for each cardiac region. Concerning the numerical discretization, we propose an efficient segregated-intergrid-staggered scheme and we employ recently developed stabilization techniques that are crucial to obtain a stable formulation in a four-chamber scenario. We are able to reproduce the healthy cardiac function for all the heart chambers, in terms of pressure-volume loops, time evolution of pressures, volumes and fluxes, and three-dimensional cardiac deformation, with unprecedented matching (to the best of our knowledge) with the expected physiology. We also show the importance of considering atrial contraction, fibers-stretch-rate feedback and suitable stabilization techniques, by comparing the results obtained with and without these features in the model. The proposed model represents the state-of-the-art electromechanical model of the iHEART ERC project and is a fundamental step toward the building of physics-based digital twins of the human heart.
