Frequency gradients during two different forms of fibrillation in the canine atria

Background: Atrial fibrillation (AF) is thought to be sustained by multiple reentrant wavelets or firing foci. Objective: The aim of this study was to compare the spectral domain characteristics in the left atrium (LA) and right atrium (RA) in two different models of AF. Methods: Rectangular 8 × 14 electrode arrays were placed on the LA and RA of 14 anesthetized dogs. AF episodes were induced with burst pacing and aconitine in each dog. For each model, AF was induced from the RA in six dogs and from the LA in six dogs. Dominant frequencies (DFs) were obtained using the fast Fourier transform of the unipolar recordings obtained from each electrode of the array. Standard deviation (SD) was used to compute the frequency dispersion within an atrium. Regularity of the signal was quantified using an organization index (OI). Results: DFs were largest in the atrium where aconitine was applied. Aconitine AF had larger gradients than burst-pacing AF (5.0 ± 4.5 vs. 0.9 ± 1.0 Hz: P <.006). Aconitine AF when compared with burst-pacing AF had greater absolute LA-RA differences in the SD of DFs (2.3 ± 1.9 vs. 0.2 ± 0.2 Hz; P <.001) and in OI (0.11 ± 0.07 vs. 0.06 ± 0.07; P <.07). Conclusions: Differences in frequency gradients and organization were observed during AF induced by burst pacing and aconitine. This suggests that different mechanisms of AF are possible and may be identified with frequency domain analysis.