Electronic consequences of action potential collision in cardiac tissue: computer simulations and tissue experiments.

The electrical effects of action potential collision were studied using a computer simulation of one-dimensional action potential propagation and tissue experiments from isolated cardiac Purkinje fibers. The effects of collision when compared with normal one-way propagation included quantitative changes in all of the measured indices of action potential depolarization and repolarization. These changes can be attributed to spatiotemporal changes in the net membrane current. Parameter sensitivity and analytic techniques identified five factors which determine the collision-induced decrease in action potential area: conduction velocity, action potential height, cable radius, specific intracellular resistivity and the specific membrane resistance during action potential repolarization. The simulations demonstrated that collision effects were independent of inhomogeneity in action potential duration, the spatial extent of the collision effects was greater than the resting space constant and certain simulated abnormal conditions (e.g., discontinuous propagation, ischemia) increased the magnitude of the collision effects. The tissue experiments supported the simulations regarding the changes in action potential configuration directly at and on each side of the collision site. Elevated [K(+)]o and exposure to tetrodotoxin increased the changes in action potential duration in the Purkinje fiber experiments. Action potential collision is a common occurrence in the heart. Under certain conditions, the resulting collision-induced changes may significantly contribute to the electrical inhomogeneities which are thought to be involved in the formation of cardiac arrhythmias.