Atrial Fibrillation in Horses

Information provided by Dr. Amara Estrada, Veterinary Internal Medicine (Cardiology) Specialist and Dr. Sarah Reuss, Large Animal Veterinary Internal Medicine Specialist

What is atrial fibrillation in horses?

Atrial fibrillation (or “A-Fib”) is an abnormal rhythm of the heart and is one of the most common cardiac problems in horses. The heart has an important role – it provides vital support to all other structures in the body – and when there is a medical issue involving the heart, it can drastically affect the horse’s overall health.

What causes atrial fibrillation in horses?

An underlying heart disease with atrial enlargement can lead to A-Fib, but most cases occur in horses with structurally normal hearts. There are some medical issues that have been known to cause atrial fibrillation, including potassium depletion due to furosemide (Lasix), colic, and excessive sweating. Some reports indicate a higher incidence in Standardbreds, Draft horses, and Warmbloods.

What are the symptoms of atrial fibrillation in horses?

  • Poor performance
  • Shortness of breath
  • Easily exhausted
  • Coughing
  • Discharge from nose
  • Sudden deceleration during a race
  • None – Many times this condition is only discovered when the veterinarian listens to the horse’s heart for another reason or as part of a wellness exam
  • Irregularly irregular heart beat will be heard on auscultation

What can I do if my horse has atrial fibrillation?

Horses that have abnormal heart rhythms will undergo a full workup, including physical examination, blood work, electrocardiogram (“ECG”), and echocardiogram (“echo”) to diagnose A-Fib and rule out any other underlying conditions.

Once diagnosed, atrial fibrillation can be treated with the drug quinidine, but there are potential side effects such as ataxia, nasal edema, colic, hives, laminitis and rarely death. The University of Florida Large Animal Hospital is the only equine veterinary clinic in Florida that can treat atrial fibrillation with electrocardioversion for A-Fib.

Electrical cardioversion (or transvenous electrical cardioversion) is indicated for horses that are resistant to conversion with quinidine therapy or develop signs of toxicity with attempted conversion with quinidine. Transvenous electrical cardioversion is our preferred method for conversion of atrial fibrillation in horses.

For this procedure, a catheter is placed in the jugular vein. Electrical leads are then threaded into the right atrium and left pulmonary artery using echocardiographic guidance with the horse standing. Correct lead position is shown in this thoracic radiograph. The horse is placed under general anesthesia, and then a synchronized shock, timed to the QRS complex, is delivered. (See figure above – Images illustrating transvenous electrical cardioversion for a horse with atrial fibrillation.)

Once energy is delivered, the patient converts to a normal sinus rhythm, and is then allowed to wake up from anesthesia.

In most cases, horses that have an electrocardioversion for atrial fibrillation have a complete recovery and return to athletic performance. However, some horses may be prone to this or other cardiac problems and will need the treatment repeated.

How can I prevent atrial fibrillation in my horse?

While you can’t prevent this condition, the sooner your horse is diagnosed and treated for atrial fibrillation the better the outcome will be. The longer a horse has been in atrial fibrillation, the less likely it will be successfully converted back to and maintain a normal rhythm. Be observant of your horse’s behavior. If you notice any decreases in performance, call your veterinarian immediately as this could be the cause of a cardiovascular problem like atrial fibrillation. You can also learn how to listen to your horse’s heart and learn what is “normal” for your horse.

More Information

If you suspect your horse has atrial fibrillation or is exhibiting any signs of poor performance, call your veterinarian or contact the veterinary specialists at the UF Large Animal Hospital at (352) 392-2229.

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