Propagation of the cardiac action potential from an ectopic focus into a two-dimensional sheet of ventricular cells

We have carried out computer simulations in which a model of an ectopic focus is incorporated as the central element of a two-dimensional sheet of ventricular cells in which the coupling conductances may be different in the X and Y directions and a specific region of lack of coupling conductance may serve as a resistive barrier. We determined the critical size of the central element for successful propagation of its action potential into the sheet and found that this critical size was decreased when anisotropy was present compared to the isotropic case and was further decreased when the central site of stimulation was close to the resistive barrier. We conclude that the normal existence of anisotropy and enhancement of the degree of anisotropy under pathophysiological conditions may play a facilitating role in the development of ectopic foci which may lead to cardiac arrhythmias.