Sohrab Behnia - Urmia University of Technology (UUT)
Javid Ziaei
Marjan Ghiassi

The study of cardiac dynamics by mathematical models has a long history that has been started by using nonlinear oscillators to generate such rhythms. Since cardiacrhythms may exhibit chaotic behaviors, the chaos theory as a powerful tool in studying nonlinear dynamical systems, can beused for analyzing cardiac system. In this paper, based on Grudziński and Żebrowski's model, the effects of external factors on pacemaker rhythms were studied using a newmeasure, called the scale index. Obtained results showed that the scale index can detect special behaviors in the actionpotential whereas the Lyapunov exponent is not capable of uncovering them. Moreover, it was found that the nonperiodicity of pacemaker rhythms in the presence of externalperiodic force is not high. Finally, it was discovered that the scale index can provide a non-invasive assessment of the heart in real-life conditions.