The Horse

MAR 2019

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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YOUR GUIDE TO THE 2018 AAEP CONVENTION A6 March 2019 The Horse | AAEP Wrap-Up TheHorse.com/AAEP2018 MICHELLE ANDERSON T he horse's heart generally gets far less attention than other body sys- tems, said Virginia B. Reef, DVM, Dipl. ACVIM, ACVSMR, during the 2018 Frank J. Milne State-of-the Art Lecture. Reef, a professor and section chief at the University of Pennsylvania School of Veterinary Medicine's New Bolton Center, has spent her career studying the equine cardiovascular system and treating heart disease. It's an area vet schools used to overlook. "But there's more and more recognition that cardiac disease actually is important, and there's concern from the public and veterinarians about horse safety and sud- den cardiac death," she said. The horse is an amazing athlete in part because of the efficient way its cardiovas- cular system pumps blood and oxygen to the body, Reef said. During exertion, cardiac output increases eight to 12 times over resting values, and heart rate increas- es up to eightfold. This, combined with a large lung capacity and capillary network, allows a horse to consume up to 40 times more oxygen exercising than at rest. When all goes right, blood flows smoothly and efficiently through the heart. When things go wrong, horses can exhibit poor performance and even die. Vets might identify cardiac issues inci- dentally during prepurchase or wellness exams or performance. Reef described the basic cardiac exam and diagnostics vets can pursue if they suspect a murmur or an arrhythmia: electrocardiography, which measures the heart's electrical activity; echocardiography, which uses sound waves to collect imagery of the moving heart; and the 4D echocardio- gram, which looks at 3D images over the fourth dimension of time. Reef then described a variety of heart issues. Horses are born with some condi- tions (they're congenital), while others are caused by exercise, drugs, infectious dis- ease, toxin exposure, metabolic problems, electrolyte imbalances, and bites from venomous animals. Many conditions, specifically certain murmurs, occur along with or cause additional cardiac prob- lems and lead to compounding health problems. Murmurs These are either congenital or acquired and occur frequently in horses. Reef said the vet's job is to differentiate benign murmurs from those associated with underlying heart disease. Whether a murmur affects a horse's performance or life expectancy depends on its cause, severity, and location. Reef said mitral (valve) regurgitation is the murmur vets encounter most fre- quently. It doesn't affect performance or life span unless it occurs at an early age. For moderate murmurs, drugs such as ACE inhibitors can extend career and life span for low-intensity work. More serious cases have a poorer prognosis and limit a horse from high-intensity sports, she said. Arrythmias Irregular equine heartbeats have many causes that result in different signs. Horses with atrial fibrillation, for example, might start strong in a race, only to slow halfway to the wire. However, certain atrioventricular blocks occur in fit horses, disappear during exercise, and don't affect performance, Reef said. Treatment might include cardioversion to restore normal heartbeat either with drugs or by shocking the heart. Myocardial disease Exposure to certain toxins and drugs, as well as hypoxia (lack of oxygen), are a few causes of heart tissue (myocardium) damage. Specifi- cally, myocardial disease in horses can be related to ionophore (antibiotics some- times added to cattle and chicken feed) consumption. The death of one or more horses is often the first sign of ionophore exposure, Reef said. Surviving horses can suffer long-term negative effects. Pericardial disease Infection of the pericardium (the membrane enclosing the heart) is rare but has been associated with pleuropneumonia and mare reproductive loss syndrome. Early diagnosis and ag- gressive treatment with pericardial drain- age, lavage, and antimicrobials are needed for a positive outcome, Reef said. Congestive heart failure A variety of heart conditions can cause this heart weakness and fluid buildup in the lungs and surrounding body tissues. Because of the interplay between the cardiac and pulmonary system, the lungs and pulmonary artery are often affected, Reef said. So, many of these horses are misdiagnosed with lower airway disease, she said. Sudden cardiac death This is a risk for horses with certain heart conditions that can result in catastrophic death. It oc- curs during or shortly after exertion and can be caused by events such as internal hemorrhage from ruptured heart vessels. Horses with these conditions are unsafe to ride, Reef said. Thanks to researchers like Reef, vets are learning more about cardiac disease, its risk to horse and rider, and treatments to improve performance and quality of life. To read about her talk in its entirety, see TheHorse.com/166169. h COURTESY AAEP Giving the Equine Heart Some Love Dr. Virginia Reef described the equine cardiovascular system and cardiac abnormalities.

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