title: Antiarrhythmic and electrophysiologic effects of flecainide on acutely induced atrial fibrillation in healthy horses.
abstract: BACKGROUND
  Only few pharmacologic compounds have been validated for treatment of atrial fibrillation (AF) in horses. Studies investigating the utility and safety of flecainide to treat AF in horses have produced conflicting results, and the antiarrhythmic mechanisms of flecainide are not fully understood.
  
  
  OBJECTIVE
  To study the potential of flecainide to terminate acutely induced AF of short duration (≥ 15 minutes), to examine flecainide-induced changes in AF duration and AF vulnerability, and to investigate the in vivo effects of flecainide on right atrial effective refractory period, AF cycle length, and ventricular depolarization and repolarization.
  
  
  METHODS
  Nine Standardbred horses. Eight received flecainide, 3 were used as time-matched controls, 2 of which also received flecainide.
  
  
  METHODS
  Prospective study. The antiarrhythmic and electrophysiologic effects of flecainide were based on 5 parameters: ability to terminate acute pacing-induced AF (≥ 15 minutes), and drug-induced changes in atrial effective refractory period, AF duration, AF vulnerability, and ventricular depolarization and repolarization times. Parameters were assessed at baseline and after flecainide by programmed electrical stimulation methods.
  
  
  RESULTS
  Flecainide terminated all acutely induced AF episodes (n = 7); (AF duration, 21 ± 5 minutes) and significantly decreased the AF duration, but neither altered atrial effective refractory period nor AF vulnerability significantly. Ventricular repolarization time was prolonged between 8 and 20 minutes after initiation of flecainide infusion, but no ventricular arrhythmias were detected.
  
  
  CONCLUSIONS
  Flecainide had clear antiarrhythmic properties in terminating acute pacing-induced AF, but showed no protective properties against immediate reinduction of AF. Flecainide caused temporary prolongation in the ventricular repolarization, which may be a proarrhythmic effect.
authors.affiliation: Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Taastrup, Denmark.
authors.forename: M M
authors.initials: MM
authors.lastname: Haugaard
authors.forename: S
authors.initials: S
authors.lastname: Pehrson
authors.forename: H
authors.initials: H
authors.lastname: Carstensen
authors.forename: M
authors.initials: M
authors.lastname: Flethøj
authors.forename: E Z
authors.initials: EZ
authors.lastname: Hesselkilde
authors.forename: K F
authors.initials: KF
authors.lastname: Praestegaard
authors.forename: J G
authors.initials: JG
authors.lastname: Diness
authors.forename: M
authors.initials: M
authors.lastname: Grunnet
authors.forename: T
authors.initials: T
authors.lastname: Jespersen
authors.forename: R
authors.initials: R
authors.lastname: Buhl
mesh_terms: D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000627:therapeutic use*; D001281:Atrial Fibrillation / Q000188:drug therapy* / Q000209:etiology; D002304:Cardiac Pacing, Artificial; D005260:Female; D005424:Flecainide / Q000627:therapeutic use*; D006734:Horse Diseases / Q000188:drug therapy* / Q000209:etiology; D006736:Horses; D008297:Male
chemical_list: D000889:Anti-Arrhythmia Agents; D005424:Flecainide
keywords: Atrial electrophysiology; Equine; Pacing; Programmed electrical stimulation