A two-dimensional cellular automaton model of parasystole

Under normal cardiac conditions, the sinoatrial node is the pacemaking region which initiates depolarization in the heart; in parasystole, there also exists an ectopic pacemaker which may initiate depolarization waves. Parasystole is a form of arrhythmia caused by the influence of the secondary pacemaker on cardiac behaviour. Specifically, we consider cases of pure parasystole, where the two pacemakers are protected from each other. Previous theoretical models of pure parasystole consider the interaction of two pacemakers without incorporating physical space. The objective here is to create a simple, theoretical, two-dimensional model of pure parasystole where the distance between the pacemakers may be adjusted. A cellular automaton model was created using Python 3.8.3 and associated packages. The model was used to evaluate how changes in space influenced cell activation cycles and the number of intervening sinus beats (the number of times cells were activated by the sinus node versus being activated by the ectopic pacemaker). The model dynamics were further compared to experiments using optogenetic methods to stimulate a cardiac monolayer from two sites. This model provides insight into the physical dynamics of parasystole in its most basic form so that it may be built upon to eventually be used in a clinical context.