An integrated heart-torso electromechanical model for the simulation of electrophysiogical outputs accounting for myocardial deformation

TL;DR

This work addresses the limitation of static heart-torso representations in predicting electrophysiological outputs by introducing an integrated heart-torso electromechanical (EMT) model. It couples a 3D cardiac electromechanical model with a torso Laplace conduction problem and uses a torso lifting approach to account for deformation, enabling simulations on moving domains with a segregated intergrid scheme. Key contributions include the incorporation of mechano-electrical feedbacks (MEFs), a reduced 0D circulatory model, and a flexible numerical framework that supports static, moving, or hybrid heart-torso configurations, demonstrated in healthy and VT scenarios with significant effects on ECGs and BSPMs. The framework facilitates quantitative assessment of deformation-induced changes in EP outputs and offers a path toward non-remeshing, moving-domain simulations useful for personalized cardiac digital twins and clinical planning.

Abstract

When generating in-silico clinical electrophysiological outputs, such as electrocardiograms (ECGs) and body surface potential maps (BSPMs), mathematical models have relied on single physics, i.e. of the cardiac electrophysiology (EP), neglecting the role of the heart motion. Since the heart is the most powerful source of electrical activity in the human body, its motion dynamically shifts the position of the principal electrical sources in the torso, influencing electrical potential distribution and potentially altering the EP outputs. In this work, we propose a computational model for the simulation of ECGs and BSPMs by coupling a cardiac electromechanical model with a model that simulates the propagation of the EP signal in the torso, thanks to a flexible numerical approach, that simulates the torso domain deformation induced by the myocardial displacement. Our model accounts for the major mechano-electrical feedbacks, along with unidirectional displacement and potential couplings from the heart to the surrounding body. For the numerical discretization, we employ a versatile intergrid transfer operator that allows for the use of different Finite Element spaces to be used in the cardiac and torso domains. Our numerical results are obtained on a realistic 3D biventricular-torso geometry, and cover both cases of sinus rhythm and ventricular tachycardia (VT), solving both the electromechanical-torso model in dynamical domains, and the classical electrophysiology-torso model in static domains. By comparing standard 12-lead ECG and BSPMs, we highlight the non-negligible effects of the myocardial contraction on the EP-outputs, especially in pathological conditions, such as the VT.

Figures (20)

• Figure 1: Schematic representation of the implemented electro-mechano-torso model.
• Figure 2: Left: Domains $\Omega_T$ (torso), $\Omega_H$ (biventricular geometry), and $\Omega_C$ (caps). The external surface of the torso is indicated as $\Gamma_T^{\text{ext}}$. Center and right: partitioned of the boundary $\partial \Omega_H$ in epicardium $\Gamma_H^{\text{epi,LV}}$ and $\Gamma_H^{\text{epi,RV}}$, base $\Gamma_H^{\text{base}}$, and left and right endocardium $\Gamma_H^{\text{endo,LV}}$ and $\Gamma_H^{\text{endo,RV}}$ . The portion of $\partial \Omega_C$ representing the surface directed to the torso, both left and right $\Gamma_C^{\text{epi,LV}}$ and $\Gamma_C^{\text{epi,RV}}$, and directed to the cardiac endocardium, both left and right $\Gamma_C^{\text{endo,LV}}$ and $\Gamma_C^{\text{endo,RV}}$, are also indicated.
• Figure 3: Time-advancing scheme for the coupled EMT model. The number referred to the computational order for a single time step $t_n$.
• Figure 4: (a) Volumetric geometries for the EMT model. (b) Cardiac imaging configuration, reference configuration $\Omega_H^0$ and diastasis configuration computed from the EM simulation at the diastasis phase of the heart beat. The active tension $T_a$ for the diastasis configuration is also displayed.
• Figure 5: (a) Location of the spherical impulses on the reference cardiac geometry $\Omega_H^0 \cup \Omega_C^0$ used to activate the heart for the test case in healthy conditions. (b) Cardiac reference geometry $\Omega_H^0$ with the idealized distribution of scar (black), grey zones (grey), and healthy tissue (white) over the myocardium. The site of the activation point for the S1, S2, S3 and S4 pacing protocol is also depicted with a red sphere. (c) Position of the 9 electrodes to compute the 12-lead ECG.

Theorems & Definitions (5)

• Remark 1
• Remark 2
• Remark 3
• Remark 4
• Remark 5