  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.
