Use of intravenous flecainide in horses with naturally-occurring atrial fibrillation.

The research article discusses a trial to evaluate the effectiveness of intravenous flecainide treatment on horses with naturally-occurring atrial fibrillation (AF). The study revealed that for most cases, particularly chronic AF, the drug showed limited effectiveness and some cases even resulted in dangerous dysrhythmias.

Methodology

• Ten horses with naturally-occurring AF were selected for the study. They were treated with intravenous (i.v.) flecainide at a rate of 0.2 mg/kg bodyweight (bwt)/min up to a total dosage of 2 mg/kg bwt.
• In three of the horses, the i.v. flecainide infusion was continued at a slower rate (0.05-0.10 mg/kg bwt/min) until a total dose of 3.0 mg/kg bwt had been administered.
• Heart rate, QRS duration (a measure of ventricular depolarization and repolarization) and average interval between fibrillation waves were measured before, during, and after the flecainide treatment.
• If the treatment did not successfully restore normal sinus rhythm, the horses were given oral doses of quinidine sulphate (22 mg/kg bwt every 2 hours).

Results

• The treatment was unsuccessful in converting the rhythm of horses with chronic AF (9 out of the 10 horses). Only one horse, which had acute AF of 12 days’ duration, successfully converted to normal sinus rhythm.
• The QRS duration and fibrillation cycle length significantly increased during and after the flecainide infusion.
• The heart rate overall did not significantly change, though 3 horses developed heart rates in excess of 100 beats/min.
• Two horses developed potentially dangerous ventricular dysrhythmias within the first 15 minutes of the treatment.
• Oral quinidine sulphate was able to restore sinus rhythm in 8 out of the 9 horses that did not respond to the i.v. flecainide treatment, and it had minimal side effects.

Conclusions

• The study concluded that while flecainide could potentially be successful in treating acute AF, it was not capable of restoring sinus rhythm in horses with chronic, naturally-occurring AF at the dosages used in this study.
• Additionally, 2.0 mg/kg bwt flecainide resulted in potentially dangerous dysrhythmias in two of the horses, indicating its potential risks.

This reveals intravenous flecainide treatment may not be the most suitable approach in treating chronic AF in horses. Rather, oral quinidine sulphate may be a more viable option. Further study could provide deeper insight into appropriate dosage and safety measures while using flecainide, or highlight more effective alternatives.