Low-frequency oscillations of atrial fibrillation cycle length in goats: characterization and potentiation by class III antiarrhythmic almokalant.

Background: In chronically fibrillating goats, low-frequency oscillations (LFOs) of atrial fibrillation cycle length (AFCL) with a deceleration-acceleration sequence have been observed. The present investigation characterized such oscillations in control conditions and during the infusion of class III antiarrhythmic almokalant, trying to understand their mechanism and possible relevance.

Methods And Results: The study was performed on fibrillating goats instrumented with multiple electrodes. LFOs were characterized in 64-s recording samples (1 electrode/atrium) before and during almokalant infusion. Filtering was applied to the raw sequence of AFCL. LFOs were completely random, non-flutterlike and potentiated by almokalant, as evinced by increases in oscillation frequency, duration and amplitude. As compared with nonoscillation periods, the upper part of LFOs displayed an increase in single (84.0 +/- 11.4% vs 72.5 +/- 12.9%) and a reduction in double spikes (12.1 +/- 8.3% vs 20.2 +/- 8.6%), suggesting an improvement of propagation. This was supported by the features of activation maps during LFOs: fast conduction, few wave fronts and many linking beats.

Conclusions: Chronically fibrillating goats exhibit random LFOs, which are enhanced by almokalant. The improvement of propagation during oscillations suggests an increase in the excitable period/excitable gap. These findings raise the question of LFOs involvement in atrial fibrillation termination.