Complex irregular dynamics in a computer model of vagal control of the cardiac pacemaker

Summary form only given. The electrical-discharge patterns of the natural pacemaker region of the heart, the sinoatrial node can be accurately reproduced in a two-dimensional mathematical model in which 225 individual pacemaker cells mutually entrain to a common frequency. This model was perturbed periodically with acetylene (ACh) pulses to mimic repetitive reflex-mediated vagal stimulation. A range of vagal stimulus intensities and cycle lengths was used and the stimulus:response patterns for individual cells of the array were monitored. As revealed in a map of the parameter space, patterns of phase-locking (e.g. 1:1, 2:1, 3:2) that followed the typical Farey sequence were obtained at lower stimulus intensities and low frequencies, whereas regions of irregular (possibly chaotic) dynamics were apparent at higher intensities and higher frequencies. Qualitatively similar results were obtained when only a single pacemaker cell was repetitively stimulated with vagal pulses using the same protocols