Use of intravenous flecainide in horses with naturally-occurring atrial fibrillation.
Authors: van Loon G, Blissitt K J, Keen J A, Young L E
Journal: Equine veterinary journal
Summary
# Editorial Summary: Intravenous Flecainide for Equine Atrial Fibrillation Van Loon and colleagues evaluated intravenous flecainide as a treatment for naturally-occurring atrial fibrillation in ten horses, building on earlier experimental data suggesting high efficacy and safety. The team administered 2 mg/kg flecainide intravenously at 0.2 mg/kg/min, with three horses receiving extended infusion to a maximum dose of 3.0 mg/kg, whilst measuring heart rate, QRS duration and fibrillation cycle length before, during and after treatment. Disappointingly, only one horse—with acute AF of 12 days' duration—converted to normal sinus rhythm; all nine horses with chronic AF failed to respond, despite significant increases in QRS duration and fibrillation cycle length (P = 0.006 and 0.002 respectively). Two horses developed potentially dangerous ventricular dysrhythmias within 15 minutes of treatment, and three exhibited tachycardia exceeding 100 bpm. In contrast, oral quinidine sulphate (22 mg/kg every 2 hours) successfully restored sinus rhythm in eight of nine horses with minimal adverse effects. For practitioners, these results suggest flecainide offers limited benefit for chronic AF in horses and carries a concerning risk of serious dysrhythmias, rendering oral quinidine a substantially safer and more effective alternative for this common performance-limiting arrhythmia.
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Practical Takeaways
- •Do not use IV flecainide as a treatment strategy for chronic AF in horses — it is ineffective and carries risk of dangerous dysrhythmias
- •IV flecainide may have limited utility only in cases of very acute AF (<2 weeks), but oral quinidine is a more reliable and safer alternative
- •Monitor cardiac rhythm closely during any antiarrhythmic drug administration, as ventricular dysrhythmias can develop rapidly in the first 15 minutes of flecainide infusion
Key Findings
- •Intravenous flecainide (2 mg/kg) failed to convert sinus rhythm in all 9 horses with chronic AF, with only 1 horse with acute AF (12 days duration) responding successfully
- •QRS duration and fibrillation cycle length increased significantly during flecainide infusion (P = 0.006 and P = 0.002), but heart rate did not increase significantly despite 3 horses developing rates >100 bpm
- •Two horses developed potentially dangerous ventricular dysrhythmias within the first 15 minutes of flecainide treatment at 2.0 mg/kg
- •Oral quinidine sulphate (22 mg/kg every 2 hours) restored sinus rhythm in 8 of 9 horses with minimal adverse effects after flecainide failure