Use of propafenone for conversion of chronic atrial fibrillation in horses.

Objective: To investigate effects of IV administration of propafenone for naturally occurring and experimentally induced chronic atrial fibrillation in horses.
Animals: 2 horses with naturally occurring atrial fibrillation and 4 horses with pacing-induced atrial fibrillation.
Procedures: Horses received a bolus of propafenone (2 mg/kg, IV over 15 minutes). If atrial fibrillation persisted after 20 minutes, a continuous infusion of propafenone (7 microg/kg/min) was given for 120 minutes. Before, during, and after treatment, plasma propafenone concentrations, hematologic and serum biochemical values, and electolyte concentrations analyses were determined and clinical signs were monitored. Surface ECGs were recorded. If propafenone treatment failed, quinidine sulfate was administered.
Results: Bolus and continuous infusion induced minimal adverse effects. During the 15-minute bolus administration, a slight increase in heart rate was observed and horses appeared more sensitive to external stimuli. Throughout treatment, no significant changes were observed in respiratory rate, QRS or corrected QT duration, or results of hematologic analyses. Although a significant increase in F-wave interval and atrial fibrillation cycle length was observed and plasma propafenone concentrations (569 to 1,268 ng/mL) reached the human therapeutic range (64 to 1,044 ng/mL), none of the horses cardioverted to sinus rhythm. Sinus rhythm could be restored in all horses via standard oral administration of quinidine.
Conclusions and Clinical Relevance: A slow IV bolus of 2 mg of propafenone/kg followed by a continuous infusion of 7 microg/kg/min over 2 hours was not an effective treatment for chronic atrial fibrillation in horses.