Variation of cycle length in epicardial electrograms: a quantification of chaos of ventricular fibrillation using a sock electrode array

In order to quantify the randomness of ventricular fibrillation (VF) the variance in electrogram in the heart was measured. Cycle length (CL) of activation was determined, and 10936 activations were used to calculate the variance of CL globally and at each electrode on the surface of the heart. A fractal dimension and chaotic trajectory analysis using a nonlinear dynamic model indicated that VF signal is a non-specific random event with chaotic measurement. It is concluded that CL and its variance become progressively greater with time. The change in the variance is linear, suggesting an orderly increase in conduction time during VF. The VF is not completely random. These findings suggest that complete VF can be described by a linear part (constant increase of variance of CL) and nonlinear part (mean CL)