SIMULATION OF REENTRY IN A PIECE OF MYOCARDIAL TISSUE - STRONG SENSITIVITY TO SPATIAL AND TEMPORAL CONDITIONS

A simple model for the simulation of re-entrant excitation was created . The model consists of a matrix of 15 x 15 compartments, where each c ompartment has its own action potential that depends dynamically on fo ur ion currents (I-Na, I-Ca, I-K and I-b) having time and voltage-depe ndent activation and inactivation kinetics. The compartments were comb ined with resistors to simulate electrotonic interaction. At short exc itation intervals the action potential was shortened in duration, and at even shorter coupling intervals decremental propagation occurred. R e-entry around an obstacle could be elicited in response to a properly ti:med extra stimulus. A time dependent unidirectional block was made by making some of the action potentials longer in duration. An obstac le was not a necessary substrate for re-entry, but the timing of the e xtra stimulus was critical. In the presence of an obstacle, the induct ion of re-entry was critically dependent on the shape of the obstacle. The most important result of the simulations is that the system is hi ghly sensitive to the initial spatial and temporal conditions. These s ensitivities are generic features of dynamic systems that are describe d by non-linear differential equations and are typical for chaotic sys tems. The system studied shows features associated with deterministic chaos.