Models Of Cardiac Electromechanics Research Articles

Intra- and interventricular asynchrony of electromechanics in the ventricularly paced heart

The degree of restoration of pump function by ventricular pacing depends on the pacing site and timing of pacing. Numerical models of cardiac electromechanics could be used to investigate the relation between the ventricular pacing site and timing on the one side, and pump function on the other. In patient-specific models, these numerical models could be used to optimize location and timing for best pump function. The aim of this study was to demonstrate the potential for modeling patient-specific electromechanic during ventricular pacing by means of the extension of an existing three-dimensional finite-element model of LV electromechanics with the right ventricle. A parametrized geometry of the LV and RV was made from canine (non-invasively obtained) cine-MR short axis images. Depolarization was modeled using the eikonal-diffusion equation. Mechanics was computed from balance of momentum, with nonlinear anisotropic passive and time-, strain-, and strainrate-dependent uniaxial active behavior. Simulations of complete cardiac cycles were performed for a normal heart beat with synchronous activation and ventricular pacing at the right ventricular apex and left ventricular free wall. We focused on timing of LV and RV hemodynamics, asynchrony in depolarization and myofiber shortening, regional stroke work, and systolic septal motion. In the simulation of sinus rhytm, ventricular ejection was found to start earlier for the right side than for the left side, which is in agreement with experimental data. In simulations with ventricular pacing, results agreed with experimental findings in the following aspects: 1) depolarization sequence; 2) the spatial distributions of sarcomere length and stroke work density depended mainly on timing of depolarization; 3) maximum pressure and maximum increase of pressure were lower than during sinus rhythm; 4) the earliest activated ventricle had the earliest start of ejection, and 5) the septum moved towards the last activated ventricle at the onset of systole. As a first step, the potential of patient-specific modeling in simulating conduction disturbances has been demonstrated by inserting a ventricular geometry, obtained from non-invasively measured short axis MR images. Later steps would include the implementation of adaptation models to estimate patient myofiber orientation and to assess the effects of pacing in the long term.

Computational model of three-dimensional cardiac electromechanics

We coupled a continuum model of impulse propagation with a three-dimensional model of regional ventricular mechanics. Equations for action potential propagation, myofilament activation and active contraction were solved in an anatomically detailed finite element model of canine left and right ventricular geometry, muscle fiber architecture and Purkinje fiber network anatomy. Finite element equations for time-dependent excitation and recovery variables were assembled using a collocation method and solved using adaptive Runge---Kutta integration. Resting tissue mechanics were modeled as nonlinear, orthotropic and hyperelastic. A Windkessel model for arterial impedance was coupled to ventricular pressure and volume to compute hemodynamic boundary conditions during ejection. Ventricular volume constraints were imposed during the isovolumic phases. This model showed good agreement in the time course of regional systolic strains with experimental measurements during normal sinus rhythm and demonstrates the importance of the Purkinje fiber system in determining the mechanical activation sequence.

The modelling of a primitive ‘sustainable’ conservative cell

The simple sustainable or 'eternal' cell model, assuming preservation of all proteins, is designed as a building block, a primitive element upon which one can build more complete functional cell models of various types, representing various species. In the modelling we emphasize the electrophysiological aspects, in part because these are a well-developed component of cell models and because membrane potentials and their fluctuations have been generally omitted from metabolically oriented cell models in the past. Fluctuations in membrane potential deserve heightened consideration because probably all cells have negative intracellular potentials and most cells demonstrate electrical activity with vesicular extrusion, receptor occupancy, as well as with stimulated excitation resulting in regenerative depolarization. The emphasis is on the balances of mass, charge, and of chemical species while accounting for substrate uptake, metabolism and metabolite loss from the cell. By starting with a primitive representation we emphasize the conservation ideas. As more advanced models are generated they must adhere to the same basic principles as are required for the most primitive incomplete model.

A model of cardiac cellular electromechanics

A coupled electromechanics model of a single cardiac cell is used to interpret a wide variety of experimental tests and is compared to a limited extent (since no other cardiac model dealing with the full range of mechanical tests is available) with other models of myofilament mechanics. We consider the passive elasticity of the cell, troponin–C–calcium binding kinetics, thin filament kinetics, the length dependence of steady–state tension, cross–bridge kinetics, and the coupling of mechanics to cell electrophysiology (the Noble 98 model) via the calcium transient.

Three-dimensional analysis of regional cardiac function: a model of rabbit ventricular anatomy.

The three-dimensional geometry and anisotropic properties of the heart give rise to nonhomogeneous distributions of stress, strain, electrical activation and repolarization. In this article we review the ventricular geometry and myofiber architecture of the heart, and the experimental and modeling studies of three-dimensional cardiac mechanics and electrophysiology. The development of a three-dimensional finite element model of the rabbit ventricular geometry and fiber architecture is described in detail. Finally, we review the experimental results, from the level of the cell to the intact organ, which motivate the development of coupled three-dimensional models of cardiac electromechanics and mechanoelectric feedback.