Horses seem to be able to compensate for a diseased heart for many months or years without signs of heart failure. In most cases, the heart muscle is weakened and begins to lose the ability to provide adequate circulation to meet the body's needs.
Horses racing at full speed
The horses' heart is responsible for delivering oxygenated and nutrient-rich blood throughout the body and removing metabolic waste and any disruption can have detrimental effects.
© 2008 by Louis New window.
Although acquired heart disease is uncommon in horses, when it develops it is accompanied by a reduction in exercise capacity and shortness of breath and the horse may collapse with congestive heart failure.
In horses, humans and all other mammals, the heart is responsible for delivering oxygenated and nutrient-rich blood throughout the body and removing metabolic waste through a vast network of blood vessels, therefore any disruption in this process can have detrimental effects.
According to Jen Roytz, in horse racing, and most other equestrian sports, the term “heart attack” has become a catch-all phrase for suspected fatal cardiac events, as was the case recently with the passing of G1 Dubai Golden Shaheen winner XY Jet (Kantharos), who died of an apparent cardiac event the morning of Jan. 8, 2020.
While in humans a heart attack, or myocardial infarction, is commonly the result of a loss of blood flow (clogged arteries) which damages part of the heart muscle, in the equine the scenario is much different. As such, it is exceedingly rare for a horse to suffer a “heart attack” in the truest sense of the term, however horses can still be at risk for other heart-related maladies.
While sudden death due to a cardiac event is rare, especially in horses of racing age, it is not out of the realm of possibility. The types of heart disease most often associated with equine deaths include electrical irregularities known as cardiac arrhythmias, heart valve defects resulting in murmurs, congenital defects, aortic rupture and inflammation or degradation due to illness or toxins.
Equine veterinarian Dr. Foster Northrop, DVM, who practices primarily on Thoroughbred racehorses at Churchill Downs, Keeneland and Palm Meadows, offered his insights to help give clarity to what are often referred to as “heart attacks” in horses.
Sudden death in horses relating to the heart is usually an aortic arch rupture or an electrical event, such as a rhythm deficiency, like atrial fibrillation. Valve deficiencies also may be a factor in heart deaths in horses.”
While aortic arch ruptures are in general uncommon, if and when they occur it is more often in 2-year-olds, according to Northrop. In such instances, the horse often has a previously undiagnosed defect in the aortic arch that, once they are working at or near sustained maximum exertion for the first times in their lives, becomes compromised.
Once the aorta–the largest artery in the body–ruptures, the horse’s blood pressure falls rapidly as blood rushes uncontrollably into the chest cavity. While this is often a massive and near-instantly fatal event, it is possible in rare cases for a horse to experience a smaller rupture and experience a steady decline in blood circulation over the course of hours or days.
Another type of cardiac event that can result in sudden death in a horse is an arrhythmia, or abnormal heartbeat, which can cause the heart to stop suddenly.
Arrythmias are often triggered by adrenaline, such as when a horse’s heart rate is elevated during morning exercise or racing. The risk of such events can increase in extreme heat, which exacerbates the potential for arrhythmias due to calcium loss through excessive sweating.
While an aortic rupture can be identified in a necropsy, arrythmias are electrical events that do not leave visible effects on the heart muscle itself, so often a definitive diagnosis is hard to make.
Edited press release by Thoroughbred News - Note: Edited press release was originally posted on EquiMed.com in 2020.