When a horse develops heart problems, poor performance usually is the first tip-off

by Denise Steffanus

THE DEATH of Dubai World Cup (UAE-G1) winner Electrocutionist from a suspected heart attack stunned his connections and the racing world.

The five-year-old Red Ransom horse was one of the most accomplished racehorses in the Godolphin Racing stable. In three seasons and 12 starts, the winner of Group 1 races in three countries was never off the board. He won eight times, was second three times, and third once. In what was to be his final start six weeks earlier on July 29, Electrocutionist mounted a late challenge against eventual winner Hurricane Run in the King George VI and Queen Elizabeth Stakes (Eng-G1) at Ascot and finished second by a half-length.

Typically, when a horse is suffering from a heart ailment, a decrease in performance is the first sign. But with his racing career in high gear, the only complaint about Electrocutionist's performance leading up to that race came from the British racing press, which alleged the horse had been exhibiting stiffness in morning training.

Then in August, Godolphin Racing Manager Simon Crisford announced, "Electrocutionist aggravated an old splint injury in the King George which needs to be cooled out. And as a consequence, he will not run in the Irish Champion Stakes (Ire-G1) at Leopardstown in September. The plan at this time is to run him in the Champion Stakes (Eng-G1) at Newmarket [on October 14]."

Unfortunately, early in the week of September 3, Electrocutionist was found in distress and sweating profusely, according to trainer Saeed bin Suroor, and he was admitted to a veterinary hospital in Newmarket. Clinicians there began to treat him for a heart abnormality. On September 9, the day he had been expected to be the favorite in the Irish Champion Stakes, Electrocutionist died.

"He appeared to be responding well to treatment, but during the night he suffered what seems to have been a fatal heart attack," Crisford said.

A Godolphin spokesperson said on October 6 the exact type of heart abnormality that killed Electrocutionist would not be made public.

Unusual scenario

Not knowing exactly what killed Electrocutionist, a seemingly robust horse, has made some horsemen uneasy. If a heart attack could claim such an outstanding athlete, could one of their horses be next?

"Two things come to my mind that might cause a problem acutely--rapidly instead of having a long-term problem," said Mary Rose Paradis, D.V.M., M.S., associate professor of clinical sciences at Tufts University, where she teaches a course in equine cardiology. "One would be an arrhythmia [irregular heartbeat] of some sort. Probably the most common arrhythmia in the racehorse is atrial fibrillation, which is generally not going to cause acute death in the horse unless there is some underlying heart disease. If it wasn't atrial fibrillation, there is another arrhythmia called ventricular tachycardia, and that is a possibility, but it is not as common as atrial fibrillation. Usually it is associated with something else, such as trauma to the chest wall or electrolyte abnormalities, say when [a horse has] real severe diarrhea, or it could be secondary to a drug reaction."

Electrocutionist's symptoms were not typical of a cardiac problem, said Lynne Nelson, D.V.M., M.S., an assistant professor and board-certified veterinary cardiologist at Washington State University who specializes in interventional cardiology and heart-failure mechanisms.

"I would usually think fever, more than anything else," she said of the distress and sweating that reportedly led Godolphin to send him to a Newmarket clinic. "But, certainly, other alterations in the nervous system could cause that. If the animal had a fever and had more acute infection on one of the heart valves, then those things could tie, because acute infection on one of the valves can sometimes cause fatal emboli [blood-vessel blockages]. But sweating isn't a typical symptom."

Arrhythmias

Cardiac arrhythmias are more common in the horse than any other domestic animal. Arrhythmias, such as atrial fibrillation, can profoundly affect athletic performance.

More severe rhythm disturbances can be life-threatening, such as the ventricular tachycardia suspected in the sudden death of 1984 Kentucky Derby (G1) and Belmont Stakes (G1) winner Swale. After a light morning gallop, Swale collapsed and died while being bathed at trainer Woody Stephens's barn.

Heart muscle is unique in that special conducting pathways direct electrical current through the heart, which stimulates a wave-like contraction of muscles that pumps blood through the chambers. Electrical impulses must fire in precise order for the heart to function properly. Any disruption in that circuitry may lead to chaos when the equine heart races up to 240 beats per minute during peak competition.

The only way in the past to restore proper heart rhythm was through the administration of the drug quinidine. Given via nasogastric tube because of its high toxicity, quinidine can produce serious side effects. Administration of quinidine is sometimes fatal even in healthy horses, yet some horses may require as many as six doses given at two-hour intervals to achieve the desired effect. A horse undergoing quinidine treatment must be monitored constantly via electrocardiograph, and special attention is paid to notice any signs of toxicity, such as colic or diarrhea. Moreover, quinidine treatment is unsuccessful in 20% of cases.

More recently, clinicians have begun to use electric shock to treat arrhythmias. The technique, which is called electrical conversion, entails threading two catheters specially made for equine use through the horse's jugular vein and into the atrium, the upper right chamber of the heart, and into the pulmonary artery on the left side of the heart. A short electrical shock is delivered between the two poles formed by the electrodes at the ends of the catheters, which stops the heart action for an instant and causes all the cells to begin to work again in synchronicity. A good analogy is pressing the reset button on an electronic device.

Paradis said admitting a horse to a veterinary clinic is no guarantee it will survive a fatal arrhythmia, even if it occurs while the horse is under surveillance.

"If it's going to happen, there's not a whole lot you can really do if the horse is going into a fatal arrhythmia," she said. "In the best of all circumstances, if the person who is treating the horse is right there, sees it on the [electrocardiograph] that is running all the time, and can recognize it enough to give drugs immediately, you still may lose them."

Aortic aneurysm

Rupture of an aneurysm on the aorta, the main blood vessel in the heart, can cause symptoms that could be interpreted as colic. The horse feels acute pain and responds by acting anxious and distressed, looking around at its sides, pawing, and sweating. However, the heart rate becomes extremely high--between 140 and 180 beats per minute, which differentiates an aortic aneurysm from colic.

An aneurysm is like a weak spot on a rubber inner tube that bulges before it blows out. Some aneurysms are congenital and exist within the horse for years without detection. Other aneurysms are acquired from degenerative changes in the heart and are most commonly found in older breeding stallions.

"There are usually no signs or symptoms of a pre-existing aneurysm,"

said Virginia Reef, D.V.M., director of large animal ultrasonography and cardiology at the University of Pennsylvania's New Bolton Center.

Reef said an aorta can rupture outside the heart, causing death within minutes, or it can rupture into the heart, causing accelerated heart rate and significant pain.

An aneurysm can be detected with an echocardiogram, a type of diagnostic ultrasound that produces images of the beating heart. However, clinicians have been unsuccessful in developing an effective treatment for the condition.

Infection

Infections that attack the heart or the sac around it (pericardium) or systemic infections that invade the heart also can cause a cardiac episode.

Paradis said horses are susceptible to bacterial endocarditis, an infection of the inner surface of the heart or the heart valves. "If they had a viral infection or a respiratory infection with a secondary bacterial pneumonia or something, it could seed the heart valves with bacteria, which then cause an insufficient valve that results in a murmur. And they can shower these bacteria throughout their body because it's on the heart valve. Again, those don't generally die acutely. But certainly infection can cause a problem.

"Around the heart is the pericardium. We hypothesize that viral infection or even an immune reaction can cause a lot of fluid to accumulate in the pericardium [pericarditis]. That, again, would cause a problem, but we usually don't think of acute death with that, but it certainly can cause the heart not to be able to pump well because it's trapped inside this fluid-filled bag so it can't really expand the way it should."

Infections can cause permanent damage to the heart in two ways: While the infection is active, it can eat away at the structures of the heart, causing them to deform. After the infection is resolved, scar tissue can form and further deform the heart.

"What we try to do is just halt [the infection], so if the infection hasn't destroyed the valve too radically, then the horses may be able to cope with the minor defect in the valve," Nelson said. "If it's severe, then the horse may not be able to cope with that."

Horses that have had severe infections of the heart may be left with a heart murmur, the sound the blood makes when it does not flow smoothly through the heart. Heart murmurs are rated on a scale of one to six, with one being a faint sound heard through a stethoscope and six being loud enough to detect with the human ear.

Grade one or two heart murmurs that occur during the systolic (contracting) phase of the heartbeat typically are not cause for concern.

"Anything [systolic] that is a grade three or above, or anything that occurs during the relaxation stage of the heart--we call that a diastolic murmur--those would all be pathologic," Paradis said.

Drugs and anaphylactic shock

Some sudden deaths that appear to be heart-related actually may result from acute, exercise-induced anaphylactic (allergic) shock. Thomas Swerczek, D.V.M., Ph.D., a veterinary pathologist at the University of Kentucky, found that condition in his 1994 postmortem examination of Easy Goer, winner of nine Grade 1 stakes during his three-year racing career before his retirement to the breeding shed. While at stud, Easy Goer was turned out for exercise one day, and the pent-up energy that sent him bucking and running around the pasture caused a sudden, massive allergic reaction.

"Typically what happens is that you give a horse penicillin for four or five days and on the sixth day, he may get a mild case of anaphylactic shock," Swerczek said. "If the horse isn't turned out, he'll go right through it all right, but if you turn him out and he gets to running around, he may drop dead from a subtle type of hypertension from a combination of exercise and the reaction from the penicillin. I've even seen horses given a shot of penicillin and loaded onto a van who dropped dead on the van from the combination of stress and the shot. It has nothing to do with the heart per se, but rather a general reaction that causes pooling of blood due to the anaphylaxis."

Like humans, some horses are acutely allergic to bee stings and experience other allergies.

"Anaphylactic reaction will often result in death because the whole body goes into shock, essentially," Paradis said. "So in those animals, it could simulate a heart attack in the sense that their lungs will fill up with fluids, just like in congestive heart failure. Then they go into cardiac arrest."

Potential symptoms

Paradis and Nelson said the first indication of a heart problem in a horse typically is a decrease in performance--the horse pulls up short in a workout, does not want to gallop as far during training, or tires easily.

As the condition worsens, the horse's lower legs may tend to fill with fluid, it may have difficulty breathing, and at the advanced stage it may even begin to froth from the nose and mouth. But Nelson warned that in some horses, a minor change in behavior may be the only indication.

Nelson urged horsemen to order a complete veterinary examination as soon as a performance problem arises to pinpoint the cause, which could be a subtle lameness, respiratory disease, or a cardiac problem. If the examination hints at a cardiac problem, the veterinarian will order diagnostic tests to identify the exact condition.

"Our routine cardiovascular work-up includes a very good physical examination, auscultation [listening to the heart], electrocardiogram, possibly a blood-pressure measurement, and then an echocardiogram or ultrasound of the heart," Nelson said. Further diagnostics include monitoring the horse's heart while it is exercising on a treadmill, similar to a treadmill stress test in humans.

Nelson said most equine heart problems are acquired, so she advocates routine, thorough physical examinations for all horses.

"Even owners taking their own horse's heart rate, knowing how to do that, getting accustomed to what that is like during certain phases of activity, and then getting a good veterinary check are really important to pick up early diseases that are acquired," she said.

Denise Steffanus is a Thoroughbred Times contributing editor who writes frequently on veterinary and farm management topics.