Inducibility of Atrial Fibrillation Depends Chaotically on Ionic Model Parameters

Previous work has shown that fibrillation can be induced by rapid pacing in a model of the human atria without fibrosis or repolarization heterogeneity. The purpose of this study was to investigate how sensitive this type of arrhythmia induction is to model parameters.Simulations were performed with a monodomain reaction-diffusion model with Courtemanche dynamics on a volumetric atrial mesh with all the major bundle structures and layered fiber orientation. The ionic model parameters were modified to represent electrically remodeled atria, uniformly. The model was stimulated with decreasing cycle length to drive the atria to maximum rate, and simulated over 10 seconds. This was tried with 10 different pacing locations and 46 different values of the conductivity, gCaL, of the L-type calcium current.For gCaL values up to 130% of the initial value, on average 4 out of 10 pacing sites induced AF. However, the positive sites were different for each tested gCaL level, even at 1% increments. Beyond 130%, the AF induction rate decreased. Every pacing site yielded AF for a subset of parameter values, but some sites more frequently.In conclusion, AF induction is highly sensitive to parameter values. The global decrease in induction seen for large gCaL may be due to the increased wavelength.