In just days, the "Run for the Roses" will begin. Under the twin spires of Churchill Downs, the world will watch the finest equine athletes on the planet—miracles of muscle and heart—thunder toward the finish line. It is a moment of pure adrenaline, but for researchers like Sian Durward-Akhurst, assistant professor at the University of Minnesota (UMN) College of Veterinary Medicine (CVM), the focus isn't on who crosses the finish line first. It is on making sure every horse makes it home safely.

Exercise-associated sudden death (EASD) is the dark shadow that occasionally falls over the sport. It is a rare tragedy, but when a seemingly healthy horse collapses during or after a race, the loss is felt deeply by fans, owners, and the veterinary community. “EASD is absolutely devastating—there are few, if any, warning signs that a racehorse will suffer from EASD,” notes Durward-Akhurst. “So a healthy racehorse is sent out to race and without warning collapses and dies and doesn't return back to the barn.”

Now, two new studies featuring Durward-Akhurst’s work are tuning into the racehorse heart’s hidden messages to expose this silent killer. By using advanced mathematics and data from the horses themselves, researchers are finally learning how to predict the unpredictable.

The whisper before the storm

The greatest challenge with sudden death is that the heart often looks and sounds perfectly normal until the moment it isn't. The first breakthrough in solving this mystery comes from a study published in Nature Scientific Reports. Funded by the Grayson-Jockey Club Research Foundation, this project was led by UMN’s Molly McCue and Durward-Akhurst, along with Kamalan Jeevaratnam from the University of Surrey and Celia Marr from Rossdales Equine Hospital in the UK. Durward-Akhurst is also supported by a career development award from the National Institutes of Health (NIH).

The team hypothesized that a horse’s heart might be sending out "whispers" of distress before a crisis occurs. To find them, they turned to a field of mathematics known as non-linear analysis, which is often used to find hidden patterns within seemingly chaotic data.

By analyzing just 60 seconds of an electrocardiogram (ECG) while a horse was simply walking or trotting, the researchers discovered they could identify a specific type of disorderliness in the heart’s rhythm. Even when the heartbeat appeared steady to the naked eye, the math revealed subtle irregularities that served as a signature for danger. These irregularities were a reliable predictor of which horses would develop potentially life-threatening heart rhythms once they reached high-intensity exercise. The practical beauty of this discovery is its simplicity: veterinarians don't have to push a horse to its physical limit to find out if it's at risk; they can hear the warning signs while the horse is just walking in the shed row.

“The long-term goal will be to develop a screening tool that can be used to determine EASD risk,” describes Durward-Akhurst. High risk horses can then undergo additional diagnostics to identify the cause of the increased risk—and a way to mitigate that risk.

Lessons from the "black box"

While one study focused on the math of prevention, a second study—published in the Equine Veterinary Journal—took a sobering look at the reality of actual fatalities. The project is part of a larger study supported by the Horseracing Integrity and Safety Authority (HISA) and led by Durward-Akhurst and Cris Navas de Solis from the University of Pennsylvania. For this retrospective analysis they partnered with experts from Equine Sports Medicine Consultants and the University of Adelaide.

The researchers issued an international call for ECG data from horses that had tragically died during or shortly after exercise. This resulted in a small but vital data set that functions like a "black box" recorder, providing a rare window into what actually happens in the final moments of a racehorse's life.

The findings were unexpected and revealing. Three out of the four horses wearing a monitor at the time of death were in Atrial Fibrillation (AF), an irregular heart rhythm, when the horse left the stall. One additional horse (out of 11 total horses) left the stall in atrial fibrillation and did not die that day, but died nine days later while not wearing a monitor. AF is a well known cause of poor performance in racehorses because the heart is unable to function at the maximal capacity that is needed for high-intensity exercise; but the connection to EASD that the data suggested was unexpected.

The data also highlighted a new window of vulnerability: the late recovery period. This is the time when a horse is slowing down and cooling off after a fast run. Far from being out of the woods once the race ends, the heart undergoes a complex physiological shift during cooling that can trigger malignant arrhythmias in at-risk horses.

“Discovering the high frequency of AF at rest in horses with EASD was surprising, however, it is also a highly practical takeaway,” notes Durward-Akhurst. “AF is relatively easy to diagnose at rest. Adding this as part of a horse's pre-exercise or race routine would prevent horses in AF doing high intensity exercise and could reduce the frequency of EASD.” For EASD cases that were not known to be in AF prior to death, further work is needed to understand their increased risk of EASD.

A new standard of safety

The ultimate goal of all these studies is to help move the racing industry from a reactive stance on EASD to a proactive one. Durward-Akhurst envisions a future where heart screening is as routine as shoeing a horse or checking for lameness. By combining wearable sensors with AI-driven algorithms, the goal is to implement a scalable workflow that allows even untrained personnel to catch AF before a horse ever steps onto the track.

The research has implications for human medicine, too. “These pieces are part of the translational puzzle,” notes Durward-Akhurst. “The hope is that if we can develop methods that predict EASD in horses, these could be tested in humans.” These findings also improve our understanding of EASD and AF in horses, which helps us identify similarities and differences to EASD and AF in people—an approach Durward-Akhurst applied in another recent study, published in in Case Reports in Veterinary Medicine, to identify rare genetic mutations in ponies that mirror human conditions like Gardner Syndrome.

As the Kentucky Derby approaches, Durward-Akhurst’s work serves as a reminder that while the speed of the thoroughbred captures our imagination, it is the rhythm of their hearts that sustains the sport. By learning to listen to those hearts more closely, research is helping ensure that the only thing breathtaking about the Derby is the finish.