Inhomogeneity of action potential waveshape assists frequency entrainment of cardiac pacemaker cells

In this paper, we have employed ionic models of sinoatrial node cells to in vestigate the synchronization of a pair of coupled cardiac pacemaker cells from central and peripheral regions of the sinoatrial node. The free-runnin g cycle length of the cell models was perturbed using two independent techn iques and the minimum coupling conductance required to achieve frequency en trainment was used to assess the relative ease with which various cell pair s achieve entrainment. The factors effecting entrainment were further inves tigated using single-cell models paced with an artificial biphasic coupling current. Our simulation results suggest that dissimilar cell types, those with large ly different upstroke velocities entrain more easily, that is, they require less coupling conductance to achieve 1 :1 frequency entrainment. We, there fore, propose that regional variation in action-potential waveshape within the sinoatrial node assists frequency synchronization in vivo.