• Kimberly

Atrial Fibrillation in Standardbreds

What is AF & why are we talking about it?

Commonly called "A-fib", this is an abnormal heartbeat rhythm and is one of the most common cardiac problems you can find in horses. Especially those that are high level athletes. The heart is an extremely important organ that provides vital necessary support to all parts of the equine system - so when it has a medical issue, it can cause major overall health issues to the horse. We are not vets nor trained medical professionals. This is an information blog only and if you have more questions or fear your horse may be dealing with Atrial Fibrillation - please contact your veterinarian.


Most often A-fib happens in horses with normal sized hearts, but it can be especially common in horses with abnormally large hearts. Known causes of a-fib can be potassium depletion (which can happen to horses receiving 'Lasix'), colic, and excessive sweating. In many studies conducted by Veterinary Colleges over the years, it has been determined that the Standardbred breed is of the most "at-risk" breeds for this medical issue. They've also been doing many recent studies on the potential of it being genetically passed on through the breed as well. For the purpose of this blog, we will stick to the basic information; although if you are interested in the scientific side - be sure to look at the Guelph University studies that have been done on Atrial Fibrillation!

A-fib is something that most of us, with retired Standardbreds, likely will not see in our horses. They're no longer at the top of their athletic regime and live a more relaxed lifestyle. However, your horse may have a history of A-fib or may have had A-Fib that went undiagnosed and untreated. Which means, you should watch for the symptoms!


Symptoms of Atrial Fibrillation:

* Shortness of Breath

* Easily Exhausted

* Coughing

* Nasal Discharge

* Sudden deceleration of speed

* irregular heart beat


However - often times you may not notice any symptoms until your veterinarian is doing a wellness exam on your horse or has to listen to their heart beat for another reason.

Horses that are suspected to have A-Fib will go through a full workup, including a physical exam, electrocardiogram (ECG), echocardiogram (echo) to rule out any other underlying conditions and diagnose it as A-Fib. Atrial Fibrillation is then treated with the drug Quinidine, however it does come with side affects including the potential for ataxia, nasal edema, colic, hives, laminitis, and rarely, death. Electrical cardioversion can be done for horses that are resistant to the quinidine therapy or develop potential signs of toxicity when attempted conversion with quinidine. Transvenous electrical cardioversion is typically the preferred method for horses with atrial fibrillation. This is a procedure however that requires the horse to be put under anesthesia. Once the energy has been delivered through the cardioversion and the heart returns to normal sinus rhythm, the horse is allowed to awake from the anesthesia.


Most horses who receive treatment in time will return to complete athletic ability. Some horses may however end up prone to A-Fib or have other cardiac problems (such as a heart murmur) and may need repeated treatments. The sooner you can get your horse diagnosed and treated, the better the outcome will be. The longer a horse stays in A-Fib, the less likely the treatments will be successful in reverting to regular sinus rhythm. Horses could end up with permanent heart murmurs from A-Fib, and have to retire to light working lifestyles in order to keep the heart working to the best of its ability.

Atrial Fibrillation may not be something that we see happening to our retired horses, but there are times that horses come into our program who have been through A-Fib in the past, or unfortunately A-Fib was undiagnosed and they have permanent health conditions that have arisen because of this. It always helps to understand what it is and where it comes from!

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