Anomalous drift of spiral waves in heterogeneous excitable media

We study the drift of spiral waves in a simple model of heterogeneous excitable medium, having gradients in local excitability or cellular coupling. For the first time, we report the anomalous drift of spiral waves towards regions having higher excitability, in contrast to all earlier observations in reaction-diffusion models of excitable media. Such anomalous drift can promote the onset of complex spatio-temporal patterns, e.g., those responsible for life-threatening arrhythmias in the heart.