(A) Membrane potential of a simulation at t = 1 s (introduction of connections) and t = 7 s. (B) Continuation of the simulation in panel A after removing all connections (step 3ii in methods section 2.2). (C) Continuation of the simulation in panel A without changing connections (step 3i in methods section 2.2). (D) Kaplan–Meier curve showing atrial fibrillation persistence in single and dual-layer simulations (n = 17 for single layer and n = 8 for double layer).