UF Large Animal Hospital
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.
Symptoms of Atrial Fibrillation in Horses
- Poor performance
- Shortness of breath
- Easily exhausted
- Coughing
- Discharge from nose
- Sudden deceleration during a race
- Irregular heart beat will be heard on auscultation
Atrial Fibrillation is often discovered when a veterinarian listens to the horse’s heart for another reason, or as a part of a wellness exam.
How is Atrial Fibrillation Treated?
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. There are potential side effects such as ataxia, nasal edema, colic, hives, laminitis and rarely death.
Transvenous electrical cardioversion (TVEC) is our preferred method for conversion of atrial fibrillation in horses. Electrical cardioversion of the atrial fibrillation back to sinus rhythm using TVEC has a high success rate without the risk of toxicity signs that can occur with medical conversion using quinidine. However, medical conversion can be a preferred approach in some situations.
UF Large Animal Hospital is the only equine veterinary clinic in Florida that can treat atrial fibrillation with transvenous electrical cardioversion.
About Transvenous Electrical Cardioversion
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 the thoracic radiograph pictured above. The horse is placed under general anesthesia, and then a synchronized shock, timed to the QRS complex, is delivered.
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 are treated with transvenous electric cardioversion for atrial fibrillation have a complete recovery and return to athletic performance.
Can Atrial Fibrillation be Prevented?
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, schedule an evaluation with the cardiology experts at UF Large Animal Hospital by calling (352) 392-2229. Their specialized team has the experience and tools to diagnose and manage a wide range of equine cardiac conditions.
