Activation maps during ventricular fibrillation are constructed from the analysis of two-second time windows. Each map is classified into three categories according to its complexity: low (type I), comprising a single broad wavefront with no conduction block or areas of slow conduction; intermediate (type II), consisting of two wavefronts or a wavefront with areas of conduction block or slow conduction; and high (type III), comprising three or more wavefronts associated with areas of slow conduction and conduction block. The degree of complexity is expressed as a quantitative variable using the formula: CI = (number of type I maps x 0.1 + number of type II maps x 1 + number of type III maps x 2) / total number of activation maps.