A Mechanism for Anisotropic Reentry in Electrically Active Tissue

A Mechanism for Anisotropic Reentry . Introduction : Numerical simulations of wavefront propagation were performed using a two‐dimensional sheet of tissue with different anisotropy ratios in the intracellular and extracellular spaces. Methods and Results : The tissue was represented by the bidomain model, and the active properties of the membrane were described by the Hodgkin‐Huxley equations. Two successive stimuli, delivered through a single point electrode, resulted in the formation of a reentrant wavefront when the second stimulus was delivered during the vulnerable period of the first wavefront. Conclusion : The mechanism for the development of reentry was that the bidomain tissue responded to point cathodal stimulation by depolarizing the tissue under the electrode in the direction perpendicular to the fiber axis, and hyperpolarizing the tissue in the direction parallel to the fiber axis. Such a distribution of depolarization and hyperpolarization modifies the refractory period of the action potential differently in each direction, resulting in block in the direction perpendicular to the fiber axis and leading to reentry and the formation of stable, rotating wavefronts.