A novel measure of atrial fibrillation organization based on symbolic analysis

Measures of electrical activity organization in atrial electrogram (AEG) are used to guide the ablation treatment in subjects with atrial fibrillation (AF). We proposed an improved morphological index for measuring the degree of organization in AEGs. As for other indexes, the metric provides an estimate of the probability of founding couples of similar waves and it increases with a higher AF organization. However, it also considers the order of arrival of the wavefronts on a set of bipolar electrodes (BE). Doing so, the index is inherently influenced by the direction of propagation of the wavefronts. To quantify organization, the AEGs were encoded with sequences of words of six symbols: three describing the order of arrival of the wavefronts on the BEs, while the others depending on the shape of each wave. The organization degree (OD) of each AEG was finally obtained as a function of the entropy of the sequence of words. The method was tested on 10 subjects before and after infusion of isoproterenol (ISO). During sinus rhythm, the effects of ISO did not significantly altered the organization of the atria (on average OD= 0.75 before and 0.74 after). Instead, in atrial fibrillation, ISO significantly reduced the level of organization (OD= 0.35 before vs 0.32 after, p < 0.05, paired t-test). The results were coherent with the pharmacological effects expected from the drug.