Numerical experiments in a modified Beeler-Reuter cable model: Initiating fast (Na) and slow (Ca) waves

We have modified the Beeler-Reuter model of cardiac muscle cells to account for the action of catecholamines. This model reveals the ability for slowly propagating calcium waves to coexist with the normal rapidly propagating wavefront associated with sodium activation. Either slowly propagating calcium waves or rapidly propagating sodium waves may be selectively invoked by changing the slope of a ‘ramp’ stimulus pulse. Rapid changes in stimulus potential evoke fast sodium wavefronts while stimulation with a gradual ramp with a rate of change adequate to inactivate sodium channels will initiate a slowly propagating calcium wavefront. Possible mechanisms for transitions between fast- and slow-propagating wavefronts are considered. Transition between calcium and sodium wavefronts may result in chaotic medium dynamics.