Cornell Cardiologists Calm Horses' Fluttering Hearts

Cornell Cardiologists Calm Horses' Fluttering Hearts

Dr. Bruce Kornreich placed 3-foot long catheter tipped with electrodes into On-Star's right atrium, while a second catheter continued down into the right ventricle and up into the pulmonary artery.

Photo: Cornell University College of Veterinary Medicine

When traditional treatments for atrial fibrillation (AF) fail, a new procedure offered by cardiologists at the Cornell University College of Veterinary Medicine, in Ithaca—called transvenous electrical cardioversion (TVEC)— provides an alternative way to reset the quivering heart of a horse back to its normal heartbeat.

“I’m very excited to be able to offer this procedure,” said Bruce Kornreich, DVM, PhD, Dipl. ACVIM, associate director of the Feline Health Center and staff cardiologist. “AF is a very common condition in horses that we’re often asked to diagnose and treat. This is another tool in our toolbox to convert these patients back to a normal heart rhythm.”

The Cornell University Equine Hospital offered TVEC, which involves placing electrodes in the heart to reset its rhythm with an electric shock, until about five years ago when the hospital could no longer purchase catheters needed for the procedure. Recently, the catheters came back onto the market.

At around the same time, Cornell veterinary students examined On-Star, a 19-year-old mare from the Cornell Equine Park teaching herd. “The students picked up the arrhythmia, and we diagnosed it as AF,” said Gillian Perkins, DVM, Dipl. ACVIM, medical director of the Equine and Nemo Farm Animal Hospitals, who coordinated the procedure.

Veterinarians use a cardiac ultrasound to monitor their progress and then perform an X ray (below) to verify that the metal electrodes are sandwiching the right atrium.

Photo: Cornell University College of Veterinary Medicine

Photo: Cornell University College of Veterinary Medicine

Atrial fibrillation is the most common cause of irregular heartbeat in horses, and veterinarians often diagnose the condition in racehorses. It occurs when the organized electrical signals that normally control heart rate and contraction become disorganized, causing a rapid and erratic heartbeat. Horses can survive for years with AF, but the condition often causes poor performance.

Traditionally, veterinarians have treated AF with quinidine, a drug that can reverse irregular heartbeat in about 85% of treated horses. The drug has several possible side effects, however, and for horses that don’t respond well to quinidine, or that have had AF for several years, TVEC might be a better treatment option.

The procedure works like the paddles of a defibrillator doctors use on humans, and even makes the horses “jump” from the muscle spasm. But horses’ thick chest muscles and lungs make it impossible to shock the heart from the outside; veterinarians place 3-foot-long catheters tipped with electrodes into the heart via the right jugular vein.

“The most difficult part of the procedure for us is to guide the catheter,” said Cornell cardiologist Romain Pariaut, DVM, Dipl. ACVIM, ECVIM-CA. “In horses, it’s a long path to the heart from the outside.”

Veterinarians use a cardiac ultrasound to monitor their progress and perform an X ray to verify the metal electrodes are sandwiching the right atrium. Finally, they anesthetize the horse, stand back, and apply a timed electric shock to return the heart to a normal rhythm.

On-Star’s procedure took approximately four hours and required a veritable village of clinicians: cardiologists, internists, radiologists, anesthesiologists, and licensed veterinary technicians. Combined with the expense of the catheters, the initial diagnostic evaluation, and hospitalization, the procedure costs $3,500 to $4,000.

The procedure carries its own risks, not the least of which are associated with the general anesthesia. With this in mind, Pariaut and Kornreich tried to reduce the amount of time On-Star was under anesthesia through careful attention to electrode placement. Additionally, with both TVEC and quinidine there is also the possibility that horses will spontaneously go back into AF. One recent study found that between one-third and one-half of horses successfully converted from AF to normal heart rhythm will revert after treatment. So far, On-Star is doing well and has had no complications.

Funding from the Harry M. Zweig Memorial Fund and the large animal medicine and cardiology sections made TVEC possible for On-Star and for future patients diagnosed with AF.

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