Spiral waves and target patterns in an excitable medium — the math behind cardiac arrhythmias
Click on grid to create a stimulus. Activator u shown (blue=rest, white=excited, red=refractory)
FitzHugh-Nagumo PDE: ∂u/∂t = Du∇²u + u − u³/3 − v + I_ext, ∂v/∂t = ε(u + β − γv).
u is the fast activator (membrane voltage analog), v is the slow inhibitor (recovery variable).
Spiral waves arise from broken wave fronts and are self-sustaining. They model cardiac re-entry arrhythmias.
ε controls the ratio of activator/inhibitor timescales; smaller ε → sharper wavefronts.