(229bb) A Study of the Effects of Heat Therapy through Thermomechanical Coupling on Action Potential Properties and Spiral Wave Dynamics in a Cardiac Electromechanical Model

The heartbeat is triggered by electrical impulses that travel along a special pathway through the cardiac muscle and initiate its contraction. Abnormal electrical activity, such as spiral waves, in cardiac tissue have been largely linked to the onset of cardiac arrhythmias, such as Ventricular Fibrillation (VF) [1], which lead to cardiac arrest and results in over 300 000 deaths annually in the United States. In its turn, contraction of the heart causes cardiac tissue deformation which feeds back on the wave propagation and affects electrophysiological properties via mechanoelectrical feedback (MEF) [2]. Electrical-excitation and contraction of the heart can be linked by an electromechanical model of cardiac tissue. The heat therapy has been used in medicine. When a hyperelastic material is subjected to heat, it deforms. The hyperelastic material [3] model has been used to describe the mechanical behavior of passive myocardium. The therapeutic effects of heat include decreasing joint stiffness; increasing the extensibility of collagen tissues, etc.

In this work, we introduce a thermo-electromechanical model for cardiac tissue, which is provided by thermomechanical coupling. Mathematically, this mechanism of thermomechanical coupling is based on the theory of thermoelasticity [4]. The electrical activity is represented by the Luo-Rudy [5] model, and the mechanical properties are described using the Mooney-Rivlin material response [3]. The active tension that couples the electrophysiological model with the cardiac mechanics model is generated using the Niederer-Hunter-Smith [6] model which is the most advanced model, including all features contained in other models. We apply the model to study how thermomechanical coupling affect the action potential shape, restitution properties, and dynamics of spiral waves. We show that deformation caused by heat transfer through the thermomechanical coupling affect these properties via MEF.

To the authors' best knowledge, this is the first work that studies the effects of coupling the heat with the soft tissue mechanics of the heart on the properties and dynamics of action potential. This will serve to demonstrate that heat therapy can be pursued in the design of therapeutic strategies and algorithms for implantable devices capable of preventing or treating life-threatening cardiac arrhythmias, VF for example, where the electrical therapy is currently the most widely used treatment.

[1] M. E. Zevitz, Ventricular fibrillation [online]. eMedicine http://www.emedicine.com/med/topic2363.htm (2004).

[2] M. J. Lab, Mechanoelectric feedback (transduction) in heart: concepts and implications, Cardiovasc.Res, vol.32, p. 3-14, 1996.

[3] A. Hazim, Y. Belhamadia, and S. Dubljevic, Control of cardiac alternans in an electromechanical model of cardiac tissue, Comput in Biol and Medicine, vol. 63, p. 108-117, 2015.

[4] R. B. Hetnarski, â??and M. R. Eslami, Thermal Stresses: Advanced Theory and Applications. Springer 2009.

[5] C. Luo, and Y. Rudy, A model of the ventricular cardiac action potential. Depolarization, repolarization, and their interaction, Circ Res, vol. 68, p. 1501-1526, 1991.

[6] S. A. Niederer, P. J. Hunter, and N. P. Smith, A quantitative analysis of cardiac myocyte relaxation: a simulation study, J Biophysics, vol. 90, p. 1697-722, 2006.