Interaction of pacemakers as generating mechanism of atrial fibrillation

We study, if mechanisms for the generation of fibrillation patterns observed recently in studies of the FitzHugh-Nagumo (FHN) model can be seen also in the model of Bueno-Orovio, Cherry and Fenton (BOCF), that has been adapted specifically to the atrial electrophysiology. The mechanisms are associated with the interference of two spatially separated pacemakers that are connected by a small bridge of the conducting tissue. One of the two pacemakers represents the sinus node, while the second one represents a self-excitatory source in the left atrium, as an ectopic focus or microreentrant circuit. In the FHN model, three different types of irregular patterns are observed and which type occurs depends on the frequency ratio of the two pacemakers. However, only one of these types is observed in the BOCF model. Particularly interesting is the fact that the strength of the irregularity is determined by the sinus node frequency. This may be an explanation why AF is typically intermittent at its beginning.