Two horses lost their lives on the cross-country course at the spring Red Hills International Horse Trials in Tallahassee, Florida, in 2008. The deaths of both horses, Jonathan Holling’s Direct Merger and Missy Miller’s Leprechaun’s Rowdy Boy, were ultimately attributed to heart-related problems. Certainly it wasn’t the first time an eventing horse had died on course or from heart trouble. But those two losses were, perhaps, the pair of straws that finally broke the camel’s back and helped spark a research effort by the U.S. Eventing Association that continues to this day, aimed at preventing such tragedies.
Raising the Question
Not long after Red Hills, the USEA officially launched its Equine Cardiopulmonary Research Group, led by Catherine Kohn, VMD; A. Kent Allen, DVM; Mark Revenaugh, DVM and Eleanor M. Green, DVM.
“If you look back at what was going on in eventing when we started, there were concerns about what seemed to be a surge of horses that died in competition,” says Dr. Kohn. “These were seemingly healthy horses at well-run competitions. Incidents like this are catastrophic for the horse, of course, but also for the rider and the eventing community.”
The CRG was formed, she adds, in an attempt to apply science to the question of what was causing these unexpected deaths. And, since 2008, members have been working toward an answer.
Setting the Stage
CRG members started the project by looking at horse deaths on cross country. They identified two categories: fatalities attributed to injuries from falls and fatalities where the horse did not appear to be injured. CRG research has focused on this second group.
Next, researchers reviewed deaths of human athletes in competition and found that cardiac problems were often implicated. “So we decided to start [our study] by looking at the cardio and respiratory health of horses competing in eventing,” says Dr. Kohn.
At the 2009 Plantation Field Horse Trials, the researchers ran a pilot study, completing electrocardiograms (ECG) and heart and lung ultrasounds on 20 horses the day before and immediately following the cross-country test.
An ECG records the heart rhythm and heart rate. An ultrasound, or “echo” study, uses ultrasound waves to make images of the heart muscle and the portion of the lungs closest to the skin. One type of echo study, an echocardiogram, specifically makes images of the heart muscle as it moves so that the size, shape, quality of the motility of the heart muscle and the functioning of the heart valves can be assessed.
Veteran four-star eventer Allison Springer was one of the volunteer participants at that first trial, competing in the CIC*** with Destination Known. “The study can be successful only with a broad range of data gathered from participants like me,” says Allison, explaining her decision to join the study. “The welfare of my horses is of the utmost importance to me. I feel that participation is a responsibility that I owe to all the amazing horses that compete in my sport.”
Dr. Kohn recaps the results of that first study, saying, “We didn’t find anything egregious in those horses. There was nothing to suggest that the horses tested had unsuspected heart or lung abnormalities that might lead to a catastrophic incident on course. As 20 horses is a small study population, we consider this a pilot study. However, our results did not support the hypothesis that undetected structural heart or lung disease is common in healthy event horses.”
The researchers carried out several other studies, including one looking at levels of cardiac troponin, a protein released when the heart muscle is damaged. In this study, researchers collected blood samples from horses at rest and following the cross-country test at two competitions.
“The horses were all healthy with no obvious heart disease, yet several showed a substantial increase in troponin levels after the cross-country test,” says Dr. Kohn. “We were intrigued by these results. However, we tested horses at additional competitions and did not find concerning increases in post-cross country troponin levels. This information, as well as the expense of troponin assays, led us to decide not to commit resources to this line of investigation. We are hopeful that we may obtain funding for additional troponin studies in the future.”
The Devil Is in The Details—or the Device
The result of those initial field studies was the creation of this hypothesis: Horses may develop transient cardiac arrhythmias (an irregular heartbeat) while on cross country. In this condition, the heart rhythm breaks down, making it difficult for the horse to pump blood efficiently. In some instances, these arrhythmias may compromise exercise tolerance and could lead to falls, injury or fatalities.
How to prove or disprove the theory? “We needed to look at the electrical activity of the horses’ hearts while they were competing to try to answer the question, ‘What’s happening on the field of play?’” says Dr. Kohn.
To do that, researchers needed a recording device that would remain in position on the horse during the twists, turns, ups, downs and speed of a cross-country run. However, such a device wasn’t commercially available and, says Dr. Kohn, “It soon became apparent that the ‘devil was in the details,’ and fabricating a device that would stay in place would be a challenge.”
In fact, it took several years of trial, error and modification to develop an effective system. Two CRG members, Doctors Ric Birks and Mary Durando, had engineered a recording system that they were using successfully on racehorses. They made some modifications to this system for use in event horses during competition.
“In 2013 and 2014, we were able to acquire interpretable recordings of heart rhythm during the cross country in approximately 65 to 70 percent of the horses we tested,” explains Dr. Kohn. “We are very pleased with the performance of this system.”
The recording system consists of electrodes in the area of the girth and on the horse’s back with wires connecting the electrodes to the recorder itself. The recorder is secured inside a small pouch sewn to a saddle pad. Researchers affix the system before the horse goes to the cross-country warm-up, and the system remains in place until after the cross-country test. The researchers are then able to record the electrical activity of the heart at rest, during the less-intense work of the warm-up, during the cross-country test itself and during at least the early few minutes of the recovery period.
Allison, who also participated in a field study at the Plantation Field CIC** in 2015 aboard Cascani, attests to the advancement of the system. “The equipment used to gather information has improved significantly in the past years, allowing for more accurate information-gathering,” she says.
For study participants, Allison explains, the process is simple. “A couple of vets came to my stall when we were tacking up for cross country. They have a thin quilt saddle pad that held the sensors. They were very mindful about me being 100 percent comfortable with the placement of the pad, that the wires were comfortably tucked away and that no piece of extra equipment would influence my performance in any way. The vets were excellent to work with.”
“Having developed the device, now we need to accumulate a large number of recordings from a diverse group of eventing horses,” says Dr. Kohn. “Our goal is 100 ECGs.”
By the end of 2015, CRG members had conducted studies at the 2014 Waredaca Horse Trials, the 2015 horse trials at the Horse Parks of New Jersey and Fair Hill, the 2015 Plantation Field CIC, and the 2015 Fair Hill Three-Day Event. Participants—all volunteers—have included approximately 65 horses competing at Beginner Novice through the CCI*** level. Researchers briefly examine each recording at the event and inform riders if significant heart irregularities are detected.
“Our next task was to determine how many of our recordings were of sufficiently high quality to be interpretable,” says Dr. Kohn. For that step, two to four veterinarians specializing in equine cardiology make a preliminary review of each of the recordings. Those that pass this screening test are then examined in detail by the same veterinarians.
“Recordings vary in length from 30 minutes to as long as 90 minutes,” explains Dr. Kohn. “Detailed review of these recordings is time-consuming, especially considering that all of our researchers are volunteers with full-time jobs. We are currently working on the detailed analyses of our 2015 data.”
The researchers hope that during the 2016 competition season they’ll hit 100 useable recordings—a large enough number, says Dr. Kohn, “to give us a good idea of the electrical activity of the hearts of healthy horses in the cross-country phase of an eventing competition.”
Since the group’s key researchers live on the East Coast, studies to date have taken place in the East for the sake of convenience and to minimize expenditures. The group hopes to extend their studies to the Midwest and possibly the West Coast this year. “We want to give more riders an opportunity to volunteer and thus ensure that we have as broad a population of eventing horses in our study as possible,” says Dr. Kohn.
“We are very pleased to be able to obtain, for the first time as far as we know, interpretable recording of the electrical activity of the hearts of horses galloping and jumping their way around a competition cross-country course,” says Dr. Kohn. “We are now focused on studying sufficient horses to get our 100 interpretable recordings and an analysis of the large amount of data we have in hand.”
Dr. Kohn refrains from offering conjecture on results from data that is still being evaluated. “Speculation is dangerous,” she says. “Our goal is to be open-minded and approach our data in a scientific way so that our conclusions will be valid. You formulate a hypothesis, test it and then the data proves whether your hypothesis is right or wrong.”
One thing Dr. Kohn doesn’t expect the studies to include: recordings from horses who collapse on course. Luckily, such incidents remain uncommon, she explains, making it extremely unlikely statistically that the group will capture recordings from such a horse during one of the field studies.
Dr. Kohn is also willing to share her hopes: “I hope that we don’t find significantly abnormal heart rhythms or occult heart disease in any recording from our 100 horses. If we don’t find evidence of unsuspected heart disease, then we can conclude that recommending specialized screening tests for heart disease in apparently healthy horses is unlikely to be helpful in preventing equine fatalities during competition,” she says.
In addition, she notes, the group would be able to say that transient, potentially performance-limiting heart-rhythm abnormalities didn’t occur in the study population. That would suggest that such abnormalities are unlikely to be common in healthy competition horses and unlikely to be an important cause of collapse or fatality during competition, she explains.
While Dr. Kohn notes that this phase of the research won’t answer all the questions about why fatalities may occur in horses who are competing, it will provide essential baseline data that’s not currently available. “Defining the range of electrical activity of the hearts of healthy horses in competition is essential for interpretation of potentially abnormal exercising ECGs in eventing horses,” she says.
What Riders Can Do Now
While the study moves forward, Dr. Kohn has advice that event riders can act on today. Most important, she says, know your horse’s heart. Ask your vet to listen carefully to the heart. If your vet finds an arrhythmia or a heart murmur, make sure he or she does a comprehensive cardiac exam, including an echocardiogram.
“Consult with a veterinary cardiologist who has experience working with horses and follow his/her advice for ongoing monitoring of your horse,” she encourages. “You will then have the information necessary to make an educated decision as to whether or not your horse should enter a strenuous competition. Refraining from competing horses known to have an increased risk of a heart problem during strenuous exercise will reduce the risk of injuries and fatalities during competitions.”
Allison explains one of the precautions she has implemented: “I take fitness very seriously and have been regularly using heart-rate monitors on my horses for fitness work.”
Dr. Kohn thinks it’s important to point out that all participants in the research study are volunteers. “We are very grateful to the riders who have helped us. Without them, we can’t do anything,” she says. “So if you’re competing and you see our USEA Cardiopulmonary Research Program sign, come talk to us and, if you can, volunteer to be part of our study. We welcome your participation!”
Jonathan Holling: Gaining Something Positive
Jonathan Holling sat aboard his horse, a 1996 Irish Thoroughbred gelding, Direct Merger, in the cross-country start box at the Red Hills International Horse Trials in March 2008. He had every reason to expect the horse to turn in a clean, fast round, just like the year before. But this time, something went wrong.
Clearing a vertical and heading on a three-stride line to a narrow, the typically brave Direct Merger uncharacteristically ran out. “He got wobbly, reared up and died,” recalls Jonathan, emotion still evident in his voice. “I was lucky that it didn’t happen while he was jumping. I walked away unscathed, physically.”
But for Jonathan, it wasn’t enough to feel lucky. He’d seen other riders not walk away. He wondered what if it had been a kid in the saddle—would a smaller, younger person have been unhurt? And most of all, the question haunting him was why his healthy, athletic horse had suddenly died under him.
“I was so upset at the time,” he recalls. “Every time I would ask a vet—really smart, experienced professionals—they would [give an answer] and it seemed to make sense. But eventually they would all get to a point where they had to say, ‘I don’t know,’ because there is not enough research on this issue with eventing horses.”
When Jo Whitehouse of the U.S. Eventing Association approached Jonathan about the fledgling idea of putting together a cardiopulmonary research group, he knew he had to throw his support behind it.
“This was a way to focus on getting something positive out of it all,” says Jonathan. I couldn’t continue to ride horses and event at the top levels if I was not doing something to help understand why this could happen.
“I was shocked at how amazing people were at the time,” he continues. “The whole equine community. I had to take this outpouring of support and turn it into a push for this study.”
Ultimately, he hopes the study will yield a better understanding of why incidents like this occur—maybe allowing riders to identify risk factors sooner as an aid to prevention.
“I’m so appreciative that these really intelligent people are willing to donate their time and support,” says Jonathan. “Right now, I’m looking at a photo of Direct jumping into the Head of the Lake in Kentucky in 2007. I still tear up about [the accident]. It had a huge impact on my life. But if what happened to my horse had any small thing to do with getting the study going, that helps.”
Jonathan Holling and his wife, Jennifer, run Holling Eventing, a full-service training, lesson and sales business based at Willow Run Farm in Ocala, Florida. Jonathan has competed through the CCI**** level at events including the Rolex Kentucky Three-Day Event, Burghley Horse Trials and the Nations Cup™ in Boekelo, the Netherlands. He has also coached the USEA Area IV young riders team to two gold medals.
This article originally appeared in the May 2016 issue of Practical Horseman.