Regulatory veterinarians say it's not as easy as you'd think to pick up on heart problems in racehorses.
That was one of the takeaways from this year's Welfare and Safety of the Racehorse Summit, held this year through a series of online webinars due to COVID-19. In the conclusion of the series, veterinary epidemiologist Dr. Tim Parkin noted that while equine fatalities due to musculoskeletal injury have gone down in the decade he has tracked injuries, fatalities due to other causes have not improved. Musculoskeletal injuries make up 93 percent of fatal injuries, but on-track deaths can sometimes have other causes, like cardiac problems. Parkin said he believed the reason musculoskeletal injuries had gone down was because most of the health and welfare reforms initiated around the country thus far were focused on limbs and lameness.
The trouble is, cardiac problems aren't that easily detected in horses.
In 2016, we spoke to Dr. Sophy Jesty of the Charleston Veterinary Referral Center who is board certified in large animal internal medicine and cardiology. Jesty explained that horses do not have “heart attacks” the way humans do. A human heart attack is the result of a blocked artery which kills part of the heart muscle. Horses do not experience this, but they can experience things that look like heart attacks — including a ruptured aorta, which may be undetectable until the horse bleeds out internally and collapses, or an arrhythmia (abnormal beat).
At the time of that interview, regulatory veterinarians were growing more curious about the best way to screen horses for arrhythmias. In a separate session of the Welfare and Safety Summit this year, New York's equine medical director revealed he had done some informal screenings with an inexpensive handheld ECG device, but he didn't find much.
“One of the problems I encountered in our necropsy program we had a number of horses had experienced exercise-induced sudden death on our racetracks and nearly 70 percent of those horses were necropsy negative, meaning there was no obvious answer for what had happened,” said Dr. Scott Palmer. “This backs us in to the conclusion that cardiac arrhythmias could be the cause of death, and I thought, 'Gee, we probably ought to look at that a little bit.'
“Interestingly, I've examined more than 200 horses so far with this thing and have never found a cardiac arrhythmia where I'd say this horse can't race.”
In Maryland, veterinarians listen to horses with a stethoscope as part of the standard pre-race exam and have done so for the past four to five years, according to Mike Hopkins, executive director of the Maryland Racing Commission. Hopkins said the team of veterinarians estimate they have discovered fewer than ten cases of arrhythmias in that time. There were 3,883 starters in the state of Maryland last year.
Those familiar with arrhythmias in horses probably wouldn't find that surprising. Although the scientific community is still learning about cardiac problems in horses, many experts believe that some equine arrhythmias probably show up only when the horse is in work, and may be induced by the adrenaline rush a horse experiences in a race.
Palmer said that although he didn't find any rhythms of concern, that wouldn't discourage him from continuing to look.
“With that said, I believe that we should at least be looking at these horses for arrhythmias,” he continued. “I know horses have normal murmurs and I know they can have normal arrhythmias that disappear at exercise. I also know that horses do die of exercise-induced arrhythmias. I think the presence of atrial fibrillation or other significant arrhythmias, I think those horses should be scratched. And to be honest, if we don't look for it, we certainly never will find it.”
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