When the Heart of a Champion Gives Out
Sudden death has occurred in nearly all equine sports, but the most frequent and attention-getting cases typically involve an event horse or a racehorse.
Researchers are trying to determine why healthy equine athletes suffer sudden death and if there's a way to prevent it
It is one of the biggest mysteries in equestrian sport, and its name alone is ominous: sudden death. While cases are very rare and totally unpredictable, the effects of just one horse collapsing suddenly and dying, often in the midst of a competition with thousands of spectators, are far-reaching: Most instances, which can be very upsetting to witness, attract media attention and public scrutiny of equine welfare, and an investigation into the horse’s death can shed negative light on equestrian sports, whether deserved or not.
Often, sudden death occurs at the top levels of the sport in what appear to be the healthiest of horses—mounts that have been monitored closely and maintained with the best of care. In November 2011, the death of 2008 Olympic Individual Gold and Team Silver medal winner Hickstead, during a show jumping event in Verona, Italy, shocked witnesses while devastating all those involved with the horse, including his rider, Eric Lamaze. The 15-year-old Dutch Warmblood stallion had just finished an almost perfect course. Veterinarians later determined that he had suffered a ruptured aorta.
Sudden death has occurred in nearly all equine sports, but the most frequent and attention-getting cases typically involve an event horse or a racehorse. Often, the media reports the cause of death as a “heart attack,” which is inaccurate. Peter Physick-Sheard, BVSc, FRCVS, associate professor at the University of Guelph, in Ontario, has a special interest in equine cardiology, and he and his colleague, Kim McGurrin, DVM, DVSc, Dipl. ACVIM, have studied sudden death in horses. Physick-Sheard explains that horses do not suffer heart attacks like humans do because they are free of serious disease of the coronary arteries.
Rikke Buhl, DVM, PhD, professor and section head of Medicine and Surgery in Large Animal Internal Medicine at the University of Copenhagen, in Denmark, is one of the world’s leading experts in equine cardiology. “The most important message is that we don’t really know why these horses die, but research groups all over the world are trying to elucidate these tragic events,” she says.
Causes and Frequency
Physick-Sheard says that some of the most important things for the lay public to understand about sudden death are that it is rare, it only happens with any frequency in young racehorses, and that people need to use a standard terminology for discussing it.
He defines it as “the sudden unexpected death of a horse that has shown no previous signs of a potentially life-threatening condition and in which post-mortem examination reveals no adequate explanation,” whereas others’ definitions do not include the part about post-mortem exams. He says these differences in defining the condition make it difficult to determine how many cases should truly be considered “sudden death.”
Buhl adds, “Sudden death also occurs when horses are at their private training yards with no public witnesses, so these events are not included in any registrations (records). Therefore, the exact number of cases is not known today.”
Rikke Buhl, DVM, PhD, professor and section head of Medicine and Surgery in Large Animal Internal Medicine at the University of Copenhagen, in Denmark, is conducting cardiac research that could prove promising for preventing sudden death. She’s trying to determine if potassium ion channel defects could be causing cardiac arrhythmias in horses similar to what’s been described in humans and dogs with the cardiac disease Long QT syndrome (LQTS). This condition involves an increased interval between the Q and T wave (two of the six waves that indicate electrical events during a heartbeat) on electrocardiogram (ECG) and problems with potassium ion channel function, which interrupt electrical signals in the heart that cause it to beat.
While researchers have not yet confirmed LQTS to exist in horses, they have characterized horses’ QT interval and how it changes due to heart rate and racing intensity. “With the new tools developed by the Equine Cardiac Group (at the University of Copenhagen), the presence of LQTS will be investigated in horses by screening ECGs from a large pool of horses with different genetic backgrounds,” Buhl says. “Genetic sequencing will be performed on blood samples from this population and from horses with sudden death to describe mutations in the potassium channels in horses.”
If the team finds LQTS to exist in horses, the next step might be developing a blood test, an ECG test, and possibly a genetic database that identifies mutations that cause sudden death in horses.
Sarah Evers Conrad
In a previous study (TheHorse.com/27151), Catriona Lyle, RCVS, of the University of Edinburgh’s Royal School of Veterinary Studies, in Scotland, looked at cause of death in 268 cases of sudden death in Thoroughbred racehorses from California, Pennsylvania, Australia (Victoria and Sydney), Hong Kong, and Japan. On post-mortem examinations, researchers identified cardiac failure, presumptive pulmonary (lung) failure, pulmonary hemorrhage, hemorrhage associated with pelvic fractures and blood vessel rupture, and spinal cord injury. Only 53% of the deaths had a definitive cause, 25% had a presumptive cause, and 22% were unexplained. Interestingly, aortic rupture, which the public considers to be a common cause of sudden death, occurred in only 1% of the cases in the study.
Another problem that contributes to the difficulty in diagnosing sudden death’s cause is the variation in post-mortem techniques and lesion descriptions during necropsy. Standards for dissecting and examining horses post-mortem would be helpful going forward, says Lyle.
Another diagnostic challenge is that sudden death can have more than one cause. “Due to the limited knowledge of the pathophysiological background for these fatal events, it’s difficult to identify risk factors, whether this could be pre-existing conditions like congenital or acquired disorders,” says Buhl. “Among the horses that suffer sudden death, 20-68% of cases do not have structural lesions sufficient to account for death on necropsy. Cardiac and/or pulmonary failure are found to be the most common causes diagnosed on post-mortem examinations, but also trauma, neurologic lesions, and acute hemorrhage are reported.”
Doug Corey, DVM, of Associated Veterinary Medical Center, in Walla Walla, Washington, who has worked with the Professional Rodeo Cowboys Association, also adds blood vascular issues (aneurisms), stroke, stress, and abnormalities in the horse’s internal systems to the list of possible causes. He says cases are very rare in the rodeo industry, and he has only seen one, which he believes was due to a heart condition; however, no autopsy was performed. In 35 years as an official event veterinarian in Western disciplines, Jerry Black, DVM, of Colorado State University, says he has never seen a case.
Elsbeth Swain, DVM, Dipl. ACVIM, also of Colorado State University, says there is little warning at maximal exercise before a horse collapses. “The veterinarian present may be able to intervene with supportive care after a horse acutely collapses, but depending on the cause, all efforts may be futile.”
She has a few recommendations for ways horse owners might avoid a tragedy: “The most important thing for prevention is to have your horse evaluated by a veterinarian at least once per year, especially prior to big events. Assessing the physical examination, diet, and conditioning of the equine athlete may aid in prevention. It is also important to ensure that supplements or medications will not negatively affect the horse in competition.”
Understanding the Equine Heart
During Buhl’s 15 years of studying the equine heart, her research results have correlated race performance to heart size: the larger the heart, the better. Her studies have also shown that training can induce significant cardiac hypertrophy, or thickening of the heart muscle. Studies in humans have shown that this can increase an athlete’s risk of collapsing and even dying during exercise. She is also studying atrial fibrillation, an irregular and often rapid heart rate that can cause poor blood flow, in racehorses. “The synergy between equine and human research is strong and visible, and we hope our research will gain new insight into diseases that are of importance for both horse and man,” says Buhl.
Meanwhile, Physick-Sheard and McGurrin have been at the forefront of defining horses’ normal heart rhythm. They’ve shown that horses’ heart sounds, rhythms, and rate vary greatly. Heart rate ranges from 16 beats per minute during rest to more than 200 beats per minute during intense exercise. At the end of an intense exertion, it’s normal for the horse to experience irregular heartbeats. In most cases the heart rate eventually returns to normal. Yet, sometimes this rhythm disturbance can be fatal. “The frequency with which these seem to occur without consequence, and in horses that continue to race successfully, has been a significant observation,” says Physick-Sheard.
His latest research includes looking at biomarkers in a blood test to detect heart muscle damage in horses, which he says could be used as a screening tool for at-risk horses.
Research in the Field
The eventing world has also been on the forefront of sudden death research. The United States Eventing Association’s (USEA) Cardiopulmonary Research Group (CPRG) is comprised of veterinarians, physicians, and EMTs dedicated to applying scientific principles to the study of death or collapse of event horses. Catherine Kohn, VMD, professor emeritus in the Department of Veterinary Clinical Sciences at The Ohio State University and co-chairperson of the CPRG, says the group has been working to perfect a system that reliably records an electrocardiogram (ECG, a measure of the heart’s electrical efficiency) of a horse as it competes on cross-country and analyze that data.
The CPRG has a special interest in the heart, as cardiac and lung issues have been the leading cause of collapse and sudden death in human athletes. In their first study they performed echocardiograms (ultrasound examinations of the heart’s structure) of 20 horses before and immediately after the cross-country phase at the 2009 Plantation Fields Horse Trials, in Kennett Square, Pennsylvania. They noted no dramatic abnormalities in heart rate, rhythm, or function or fluid buildup in the lungs. “We hypothesized that some horses might develop arrhythmias during intense exercise that resolve when exercise is discontinued,” says Kohn. “Therefore, we think it is important to actually record the heart rhythm, the electrocardiogram, while horses compete to describe the transient cardiac arrhythmias while horses compete.”
Kohn says it’s also important to monitor horses during the early part of the recovery period because that’s when arrhythmias are seen. “Now that we have a more reliable way to record exercising ECGs in the field, our next step will be to study a large group of eventing horses at all levels of competitions,” Kohn continues. “Our goal is to describe the electrical activity of the heart in healthy horses during cross-country competition.”
While studying what happens to horses during exercise and competition has been important to the CPRG, learning as much as possible after a case of sudden death is also crucial. Kohn hopes to help educate horse owners about the importance of obtaining necropsies on horses that die during competition. “Some people understandably find the thought of allowing a necropsy on their horse quite distasteful and are unwilling to give permission for the procedure,” she says. “Perhaps if horse owners understood how important a contribution their particular horse might make to our understanding of causes of sudden death, owners/riders would be more accepting of the necropsy.”
Due to the importance of this information, the USEA now requires and pays for a necropsy of every horse that dies in competition. The USEA’s research group has developed a protocol to forward to the person responsible for performing the necropsy on a horse that dies in competition so that each report is standardized.
“Post-mortem drug testing of these horses is also mandatory,” says Kohn. “We want to know what medications the horse has been given so that we can identify associations that may exist between administration of a particular drug and sudden death during competition.”
The CPRG has also discussed banking the heart and other tissues for additional detailed examinations and future tests of sudden death cases in eventing.
The USEA is not the only group requiring necropsies. Kohn says the Fédération Equestre Internationale (FEI) now mandates necropsies and collects data on all horses that die in FEI competitions.
Prior to 2013, it was nearly impossible to determine how frequently collapse or sudden death occurred at United States Equestrian Federation (USEF) events because a reporting procedure wasn’t in place. On August 1, 2013, GR 843, a new USEF rule, also known as the “collapse rule,” took effect as part of an overarching “Catastrophic Incident Protocol.” The goal is to keep USEF informed of any collapses and give it the power to investigate by appointing a veterinarian to examine the horse or pony. In addition, the animal can be drug tested, according to other USEF rules. The rule requires owner, rider, and/or trainer cooperation.
The USEF also has a Horse Welfare Review Panel that reviews fatalities and collapses, says Stephen Schumacher, DVM, chief administrator of USEF’s Drugs and Medications Department. This panel reviews necropsy and drug test results, steward/technical delegate reports, veterinary records, eyewitness reports, personal accounts of those involved with the horse, any available videos, and more—all in an effort to get a clear picture of what happened and why. Because even with a necropsy, says Schumacher, the cause of death can be impossible to pinpoint.
Despite the current research and various organizations’ efforts, the reasons why sudden death happens remain a puzzle. “I don’t think anyone should expect that we’re going to find a cure or a way to prevent all fatalities in equestrian sport,” says Kohn. “Fatalities do occur in other sports and among human athletes, as well. Still we aim to prevent the preventable and mitigate risk by thoroughly studying this problem among equine athletes.”
It might be a puzzle that always has some missing pieces, but as more becomes known, a partial picture of this malady might emerge that can help save lives.
About the Author
Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.
POLL: University Equine Hospitals