Experimental Quantification of Chaos in Cardiac Tissue; Examples of Period 3 and Other Complex Dynamics.

Many models of cardiac cells exhibit chaotic dynamics implying the possibility of a nonlinear approach to stabilize irregular heart rhythms of cardiac disease. However, little experimental evidence has been collected to justify this description. This study aims to both quantify and qualify the chaotic nature of cardiac tissue from the system's arrhythmic electrical response to fast periodic stimuli. Leading Lyapunov Exponents were calculated from time series of single cell action potential durations (APDs) from within a frog ventricle, showing a cascade into chaos as a function of period. Additionally, several examples of period-three orbits and unstable periodic orbits of action potentials were observed. Similarly, we identified transient coherent structures and periodic orbits from multicellular optical mapping measurements of voltage activity during ventricle fibrillation in explanted, live pig and human heart experiments. These observations further illustrate that cardiac tissue response is not stochastic but rather chaotic suggesting methods to control and terminate arrhythmias.