Abstract
We introduce an electromechanical model for human cardiac tissue which couples a biophysical model of cardiac excitation (Tusscher, Noble, Noble, Panfilov, 2006) and tension development (adjusted Niederer, Hunter, Smith, 2006 model) with a discrete elastic mass-lattice model. The equations for the excitation processes are solved with a finite difference approach, and the equations of the mass-lattice model are solved using Verlet integration. This allows the coupled problem to be solved with high numerical resolution. Passive mechanical properties of the mass-lattice model are described by a generalized Hooke's law for finite deformations (Seth material). Active mechanical contraction is initiated by changes of the intracellular calcium concentration, which is a variable of the electrical model. Mechanical deformation feeds back on the electrophysiology via stretch-activated ion channels whose conductivity is controlled by the local stretch of the medium. We apply the model to study how stretch-activated currents affect the action potential shape, restitution properties, and dynamics of spiral waves, under constant stretch, and dynamic stretch caused by active mechanical contraction. We find that stretch conditions substantially affect these properties via stretch-activated currents. In constantly stretched medium, we observe a substantial decrease in conduction velocity, and an increase of action potential duration; whereas, with dynamic stretch, action potential duration is increased only slightly, and the conduction velocity restitution curve becomes biphasic. Moreover, in constantly stretched medium, we find an increase of the core size and period of a spiral wave, but no change in rotation dynamics; in contrast, in the dynamically stretching medium, we observe spiral drift. Our results may be important to understand how altered stretch conditions affect the heart's functioning.
Highlights
The heartbeat is governed by electrical waves of excitation that periodically propagate through the cardiac muscle and initiate its contraction
We applied our discrete electromechanical model to study the effects of stretch-activated currents and stretch conditions on action potential duration (APD) and conduction velocity (CV) restitution, and spiral wave dynamics
We used our new model to investigate how stretch conditions and stretch-activated currents affect the heart’s functioning. For this we studied how stretchactivated currents affect action potential shape, restitution properties, and spiral wave activity in a medium which we assumed constantly stretched, and a contracting medium with isometric boundary conditions
Summary
The heartbeat is governed by electrical waves of excitation that periodically propagate through the cardiac muscle and initiate its contraction. Important examples are ‘‘commotio cordis’’ [7,8], the phenomenon that an impact on the chest can cause arrhythmia; and the ‘‘precordial thump’’, the phenomenon that an impact on the chest of a patient may stop an arrhythmic heart condition [9]. Both phenomena are believed to be a result of an abrupt deformation of the heart, and the main effect of deformation on the electrical activity is considered to be transmitted via so-called stretch-activated ion channels. The study of mechanoelectrical feedback is an important direction of research in current cardiac electrophysiology [10]
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