Better heartbeats for better hoofbeats.

Defibrillation can help a horse ’s heartbeat recover.

An article by Clare Illingworth, SPARK writer, University of Guelph.


When human heart won’t beat normally and the arrhythmia is life-threatening, emergency-care technicians place paddles on the patient’s chest and use an electric shock to regulate the heart’s rhythm. It’s a process called defibrillation. The same treatment is used electively in people to treat some chronic rhythm disturbances.

Horses and other large animals suffer from irregular heart rhythms, too, and although electric shock treatment would be useful in some cases, external defibrillation paddles are too dangerous to use because horses’ reac-tions are unpredictable and difficult to control. Chemical treatments are available, but they’re dangerous. So University of Guelph research-ers are creating a procedure to defibrillate a horse’s heart electrically from inside the body.

Prof. Peter Physick-Sheard, Clinical Stud-ies and Population Medicine, and graduate student Kimberly McGurrin found that plac-ing electrodes inside a horse’s heart via the jugular vein allows a charge to safely pass to the heart, correcting irregular rhythm.

“We’ve been studying and treating the equine heart for many years,” says Physick-Sheard. “But irregular heart rhythms, and this one in particular, remain poorly understood, with few effective and safe treatment options. That’s why this team has been so dedicated to perfecting the new procedure.”

Atrial fibrillation (AF) is a particularly trou-blesome irregularity in heart rhythm in horses and occurs spontaneously when the top por-tion of the heart starts twitching instead of beating. This leads to reduced cardiac output, causing a significant decrease in athletic performance.

In non-racing animals, it’s often discovered only during yearly veterinary examinations, because there are few symptoms indicating something is wrong. Untreated horses remain capable of moderate exercise, but they never reach their peak performance potential. The longer the abnormal rhythm persists, the more difficult it becomes to treat, says Physick-Sheard, and stressed horses may faint, becoming a danger to themselves and others.

AF can be treated chemically when detected at an early stage, with a 75-per-cent success rate. Veterinarians administer a quinidine solution, intravenously or orally, that alters heart muscle excitability in such a way that heart cells again beat in unison. In some cases, however, drug treatment may cause serious toxic side effects or even death. The medication has a narrow margin between therapeutic and toxic doses and has to be administered carefully. Some horses react badly to even small doses, and mild toxic side effects are observed in all horses.

That’s why electrical treatment represents a desirable alternative; it’s able to “shock” the muscles into performing correctly by reset-ting the heart cells to begin beating uniformly again. In this way, the heart returns to its regular rhythm without the use of danger-ous drugs. Physick-Sheard’s veterinary team will offer the new treatment this fall at the University’s Large Animal Clinic.

“It’s our ultimate aim that treated horses will recover from the anesthesia at the clinic and be able to return home that day,” he says, “but we have a lot more work to do before the procedure becomes that routine.”

As a side to this research, Physick-Sheard and Prof. Brad Hanna, Biomedical Sciences, are also investigating a genetic link to AF by examining the lineage of reported cases in standardbred race horses. They’re building an analytical model to more reliably detect decreased performance in race horses, allow-ing them to monitor and chart the success of animals that undergo the treatment.

Other members of this research team are anesthesiologist Prof. Carolyn Kerr and equine clinician Dr. Dan Kenney. The study is spon-sored by the Grayson Jockey Club Foundation, the Ontario Ministry of Agriculture and Food, and the Department of Clinical Studies at the University of Guelph.