Spiral breakup in model equations of action potential propagation in cardiac tissue

Two-variable model equations that capture some essential dynamical features of quantitative electrophysiological models of cardiac tissue are introduced. In one dimension, these equations naturally reproduce an experimentally observed oscillatory pulse instability that causes an alternation in action potential duration. In two dimensions, spontaneous spiral breakup leading to a spatially disorganized electrical wave activity is shown to occur as a direct consequence of this instability.