Organizational index mapping to identify focal sources during persistent atrial fibrillation

Localized rotors have been implicated in the mechanism of persistent atrial fibrillation (AF). Although regions of highest dominant frequency (DF) on spectral analysis of the left atrium (LA) have been said to identify rotors, other mechanisms such as wavefront collisions will sporadically also generate an inconsistent distribution of high DF. We hypothesized that if drivers of AF were present, their distinctive spectral characteristics would result more from their temporal stability than their high frequency.

Ten patients with persistent AF underwent LA noncontact mapping. Following subtraction of far-field ventricular components, noncontact electrograms at 256 sites underwent fast Fourier transform. Mean absolute difference in DF between 5 sequential 7-second segments of AF was defined as the DF variability (DFV) at each site. Mean ratio of the DF and its harmonics to the total power of the spectrum was defined as the organizational index (OI). Mean DFV was significantly lower in organized areas (OI > 1 SD above mean) than at all sites (0.34 ± 0.04 vs 0.46 ± 0.04 Hz; P < 0.001). When organized areas were ablated during wide-area circumferential ablation, AF organized in remote regions (LA appendage ΔOI ablated vs unablated: +0.21 [0.06-0.41] vs -0.04 [-0.14-0.05]; P = 0.005).

At sites of organized activation, the activation frequency was also significantly more stable over time. This observation is consistent with the existence of focal sources, and inconsistent with a purely random activation pattern. Ablation of such regions is technically feasible, and was associated with organization of AF in remote atrial regions.