Effect of flecainide on atrial fibrillatory rate in a large animal model with induced atrial fibrillation

Background: Atrial fibrillatory cycle length has been considered one of the indices of atrial electrical remodelling during atrial fibrillation (AF), which can be assessed from surface ECG by computer-assisted calculation of atrial fibrillatory rate (AFR). Horses have been suggested as a bona fide model for AF studies since horses too, develop lone AF, however data on AF characteristics in horses are extremely sparse and non-invasive characterization of AF complexity using surface ECG processing has not been reported. Aim: The aim was to study characteristics of induced AF and its modification by flecainide. Methods: The study group consisted on 3 horses with spontaneous persistent AF and 13 with pace-induced AF. Seven horses were treated with saline (control) and eight with flecainide (2 mg/kg). ECGs were analysed using spatiotemporal cancellation of QRST complexes and calculation of AFR from the residual atrial signal. Results: At AF onset, AFR was 295 +/- 52 fibrillations per minute (fpm) in the horses with induced AF treated with flecainide, 269 +/- 36 fpm in the control group (ns), and 364 +/- 26 fpm in the horses with spontaneous persistent AF (P < 0.05 compared to the control group). Flecainide caused a decrease in AFR in all animals and restored sinus rhythm in the animals with induced AF. In the control animals, AFR increased from 269 +/- 36 fpm to a plateau of 313 +/- 14 fpm before decreasing to 288 +/- 28 fpm during the last 10% of the AF episodes preceding spontaneous conversion (P < 0.05). Conclusion: AFR in horses with induced AF resembles AFR in humans with paroxysmal AF. Flecainide caused a rapid decrease in AFR in all horses, further supporting the method to be a non-invasive technique to study the effect of antiarrhythmic compounds.