Abstract
Electrical stimulation of excitable cardiac tissue results in a variety of rhythms similar to those clinically recorded. Simplified momlinear equations and ionic models give complementary descriptions of the dynamics in cardiac preparations. Nonlinear midels often capture the essential dynamical features of the experimental observations but do not properly describe the underlying ionic mechanisms. Ionic midels are descriptive, complex, and despite their general sucess in reproducing the cardiac action potential, seldom undergo extensive testing against experimentally determined rhythms. We review work from our group devoted to the modeling of cardiac rhythms, including nonlinear models and the Shrier-Clay ionic model of electrical activity in embryonic chick heart cell aggregates. Since sustained stimulation may have long lasting consequences on the intrinsic excitability of the tissue, we also discuss recent advances in modeling the stimulation history-dependent aspects of pacemaking.