UW veterinarians try new drug for equine heart fibrillations

A drug routinely used in humans is now being tested for veterinary applications that could revolutionize the treatment of atrial fibrillation (irregular heartbeats) in horses.

Quinidine, the drug currently used to treat this problem in horses, is complicated to administer. The horse must receive frequent stomach tube placement or be fitted with an indwelling tube. Side effects, including depression and colic, are significant.

Veterinarians at School of Veterinary Medicine believe they’re the first to use the oral drug flecainide to resolve a chronic case of atrial fibrillation in a horse. The ease with which the drug can be delivered will make it easier for veterinarians to treat this problem.

“It’s too early to tell if there are fewer side effects, but flecainide is much easier to administer than quinidine,” says Åse Risberg, one of the veterinary school’s large animal internal medicine doctors.

Flecainide has been administered intravenously to horses in Japan and England, but Risberg has not seen any reports of flecainide use in the United States, and to her knowledge, it has never been used orally to treat atrial fibrillation in horses.

“We read about the drug in the veterinary literature and decided to try it,” she says.

Her colleague, Sheila McGuirk, a large animal internal medicine veterinarian who is known for her knowledge of cardiology in large animals, was involved in developing the initial treatment protocols for quinidine, which resulted in fewer side effects and changed the way atrial fibrillation was treated in large animals.

The new use of this human drug may further change the way this problem is treated in horses.

McGuirk notes that the prognosis for atrial fibrillation is dependent on the horse’s age, heart rate, and how long the animal has had the disease. Signs of atrial fibrillation include exercise intolerance at maximum performance. As a result, the condition is most commonly diagnosed in equine athletes, including racehorses, as well as performance and show horses. While heart problems in horses are not common, atrial fibrillation is the most common heart problem that affects performance.