Atrial Fibrillation Reentrant Circuit: Cardiac Rotor Simulator

Atrial fibrillation is sustained not by a single faulty pacemaker cell but by a self-perpetuating electrical wave chasing its own tail through heart tissue — a reentrant circuit, or rotor. This simulator models a patch of atrial muscle as a grid of Mitchell–Schaeffer cardiac cells coupled by diffusion, the same minimal-ionic-model approach used in computational electrophysiology research. Trigger a normal planar beat (S1), then fire a precisely timed premature beat (S2) into its refractory wake to induce a unidirectional conduction block — the textbook mechanism that spins up a spiral wave. From there you can tune refractory period, conduction velocity and fibrosis density to see, live, why shortened atrial refractoriness and diffuse fibrosis make fibrillation easier to start and harder to stop.