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Atrial Fibrillation In The Performance Horse

Updated: Mar 25

Atrial fibrillation is a condition in which the upper chamber of the heart is not functioning properly. The upper chamber or atrium acts by pumping the blood into the lower chamber or ventricle. From the ventricle, the blood is pumped to the rest of the body. In actual fact, the atrium is not necessary for life. Its main purpose is to ensure that the ventricle is completely full of blood before it contracts (gets smaller) and pushes the blood out into the arteries. On its own, the ventricle will fill itself to 90% of capacity before emptying. The atrium is necessary to supply the extra 10% so that the ventricle is 100% full.

In the case of atrial fibrillation, the atrium is not functioning and therefore the heart is working at only 90% of its capacity. For example, the result on the racetrack is quite startling! A standardbred horse going miles in 1:50 is now going in 1:58. No matter what you do, the horse is incapable of going any faster.

Researchers feel that the most probable cause of atrial fibrillation is damage to the heart during a virus infection. If you tend to rush your horses; to begin working them before they have completely recovered from a cold/virus, then you are setting the animal up for the condition.

Diagnosis of the condition is fairly simple as the quality or characteristics of the pulse is distinctive. The horse will have a double irregular rhythm. By this, we mean that there is actually nothing normal to the beat of the pulse. The pulse will throw in beats just about anywhere such that there is no way you can predict when the next beat will come.

A definitive diagnosis would have to be made through the use of an electrocardiogram. This is a machine that graphs the heartbeat so that the condition will show up readily. The treatment of the condition is by administration of drugs slowly and over a well-defined period of time. Due to the danger of the treatment, it would have to be carried out in a veterinarian clinic. For the most part, the therapy is successful. There is the odd horse however that simply refuses to be converted back to a normal beating heart.

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