Atrial fibrillation (AF) is the most common cardiac arrhythmia. Catheter ablation has become the main therapeutic strategy for the treatment of paroxysmal AF, however, results in permanent AF are not completely satisfactory; complex ablation patterns are needed, thus it is of great interest to look for an ideal pattern with a minimum number of lines. Ablation of complex fractionated atrial electrograms (CFAE) has been proposed for the termination of rotors as mechanisms of AF maintenance. The aim of this work is to characterize the CFAE by implementing approximate entropy (ApEn) and to correlate it with the tip of a simulated rotor, in order to apply simple ablation patterns to terminate the rotor activity. For this, a rotor was simulated in a 2D model of human atrial tissue, under permanent AF conditions. Electrograms were recorded and an algorithm to measure ApEn was developed. Three ablation patterns were proposed and evaluated. The ApEn allowed locating the CFAE with high precision and relating them to the tip of the rotor. The ablation pattern that enclosed the rotor tip and that was extended to a conduction boundary was effective in the termination of the rotor. The ApEn could be very effective in identifying target sites for ablation.