No abstract

This work reports the results of the theoretical investigation of nonlinear dynamics and spiral wave breakup in a generalized two-variable model of cardiac action potential accounting for thermo-electric coupling and diffusion nonlinearities. As customary in excitable media, the common Q 10 and Moore factors are used to describe thermo-electric feedback in a 10-degrees range. Motivated by the porous nature of the cardiac tissue, in this study we also propose a nonlinear Fickian flux formulated by Taylor expanding the voltage dependent diffusion coefficient up to quadratic terms. A fine tuning of the diffusive parameters is performed a priori to match the conduction velocity of the equivalent cable model. The resulting combined effects are then studied by numerically simulating different stimulation protocols on a onedimensional cable. Model features are compared in terms of action potential morphology, restitution curves, frequency spectra and spatio-temporal phase differences. Two-dimensional long-run simulations are finally performed to characterize spiral breakup during sustained fibrillation at different thermal states. Temperature and nonlinear diffusion effects are found to impact the repolarization phase of the action potential wave with non-monotone patterns and to increase the propensity of arrhythmogenesis. Systemic temperature is kept approximately constant through many delicate physiological feedbacks. In the heart, temperature changes greatly affect the features of the excitation wave and occur because of pathological conditions, during surgery or because of various unfortunate events. It is therefore practically relevant to determine how thermo-electric feedbacks can alter normal cardiac pacing or sustain fibrillating scenarios. Recent studies have demonstrated that structural heterogeneity of cardiac tissue is a key ingredient for understanding dispersion of repolarization and tendency to arrhythmogenesis. Here we investigate whether a generalized two-variable reaction-diffusion model of cardiac electrophysiology can highlight the dual nonlinear effects induced by thermo-electricity and diffusive nonlinearities under several simulated tests. Our aim is to provide evidence of non negligible differences in the spatiotemporal behavior of the system when these contributions are considered and to stimulate the investigation of more reliable physiological cardiac models.