Successful conversion of equine atrial fibrillation using oral flecainide

Atrial fibrillation is the most common arrhythmia affecting performance in horses. Conversion to sinus rhythm carries a good prognosis if no significant underlying cardiac disease is present and horses commonly return to performance at the previous level or above. The drug most commonly used to convert equine atrial fibrillation is quinidine. However, quinidine has the potential for a number of adverse effects including colic, nasal mucosal edema, dyspnea and laminitis. Quinidine also requires administration through a nasogastric tube, as the drug is very bitter and acidic and may cause oral ulcerations if administered PO. Flecainide is an antiarrhythmic agent of Singh-Vaughan Williams class Ic, whereas quinidine belongs to class Ia. Intravenously administered flecainide has been reported to be a safe and effective drug for treatment of induced atrial fibrillation in the horse, with fewer adverse effects compared to quinidine, but has been less effective when administered to horses with naturally occurring atrial fibrillation. The pharmacokinetics of oral flecainide and the oral dosage required to treat equine atrial fibrillation have been determined. To the authors' knowledge, there are no reports describing treatment of equine atrial fibrillation with oral flecainide. This report describes the successful conversion of naturally occurring atrial fibrillation, by means of oral flecainide, in a horse.