Nonlinear dynamics, fractals and chaos: Applications to cardiac electrophysiology

This abstract summarizes selected applications of nonlinear dynamics and chaos theory to cardiac physiology and clinical medicine. A detailed description of this work (along with additional citations) is given in the accompanying references (2-11, 13-15). The term nonlinear describes a wide class of systems (including all physiological systems) whose output is not linearly proportional to the strength of an applied stimulus. Evidence for nonlinearities in cardiac physiology includes the finding of abrupt changes (bifurcations), self-sustained and complex oscillations, chaotic behavior, fractal structures, and hysteresis (2,3,7,10,11,15). Until recently, it was generally accepted that sudden cardiac death represented a bifurcation from the seemingly periodic state of normal sinus rhythm to the "chaotic" dynamics of ventricular fibrillation and related lethal arrhythmias. We have contested the notion that the dying heart is best described as a chaotic attractor (4,6,9). Instead, we have proposed a countervailing view of cardiac dynamics summarized by the two following propositions (6):