We developed a new phenomenological model for ventricular epicardial cells. The proposed model is based on the Rogers-McCulloch formulation of the FitzHugh-Nagumo equations and consists of only three state variables. Furthermore, our model includes a simplification parameter rγ which allows increasing time and space integration by a factor equal to rγ. Our three-variable model can reproduce the main tissue-level characteristics of epicardial cells, such as action potential amplitudes and shapes, upstroke velocities, and action potential duration and conduction velocity restitution curves. Except for a reduced upstroke velocity, the simplification included in the model does not significantly affect action potential characteristics and restitution properties. In a 2D sheet, integral characteristics of reentry dynamics, such as dominant period, are only slightly influenced by the simplification. However, the trajectory of the spiral tip changes for different values of rγ.
