Atrial Fibrillation Associated with Anesthesia in a Standardbred Gelding

A Standardbred gelding was anesthetized on three occasions over a 3 year period. Anesthesia was induced with xylazine and thiamylal on the first occasion, with xylazine, guaifenesin, and thiamylal on the second, and with acepromazine, guaifenesin, and ketamine on the third. Anesthesia was maintained with halothane during each episode. The horse had atrial fibrillation (AF) after induction of anesthesia on the first two occasions. Because arterial blood pressure remained within normal limits during AF and anesthesia, conversion to normal sinus rhythm with quinidine was not attempted. Reversion to normal sinus rhythm occurred within 12 hours of recovery after each of the first two anesthetic episodes. The gelding remained in normal sinus rhythm throughout the third anesthetic period and recovered uneventfully. Potential causes for AF in anesthetized horses are discussed.