Interaction of spiral waves with external fields in excitable media

The problem of spiral waves interacting with weak external fields in two-dimensional reaction-diffusion excitable media is considered. The velocity and the angle of the drift of the spiral resulting from the interaction with the field is calculated analytically. We find that a field coupled to the fast variable causes the spiral to drift at an angle with respect to the direction of the field, whereas a field coupled to the slow variable induces a drift parallel to the field. Numerical simulations are presented that demonstrate a good qualitative agreement with the theory. (c) 1995 The American Physical Society