SPIRAL WAVES ARE STABLE IN DISCRETE ELEMENT MODELS OF 2-DIMENSIONAL HOMOGENEOUS EXCITABLE MEDIA

The spontaneous breakup of a single spiral wave of excitation into a t urbulent wave pattern has been observed in both discrete element model s and continuous reaction-diffusion models of spatially homogeneous 2D excitable media. These results have attracted considerable interest, since spiral breakup is thought to be an important mechanism of transi tion from the heart rhythm disturbance ventricular tachycardia to the fatal arrhythmia ventricular fibrillation. It is not known whether thi s process can occur in the absence of disease-induced spatial heteroge neity of the electrical properties of the ventricular tissue. Candidat e mechanisms for spiral breakup in uniform 2D media have emerged, but the physical validity of the mechanisms and their applicability to myo cardium require further scrutiny. In this letter, we examine the compu ter simulation results obtained in two discrete element models and sho w that the instability of each spiral is an artifact resulting from an unphysical dependence of wave speed on wave front curvature in the me dium. We conclude that spiral breakup does not occur in these two mode ls at the specified parameter values and that great care must be exerc ised in the representation of a continuous excitable medium via discre te elements.