6 minute read
CARDIOLOGY
Moving to a Different Rhythm
When Rio, an 8-year-old American Quarter Horse gelding, was diagnosed with atrial fibrillation (AFib), Alana Alpern, DVM, took him to her alma mater, the UC Davis School of Veterinary Medicine.
When Dr. Alpern was a student at UC Davis more than 15 years ago, the school was one of the few places in the United States performing transvenous electrical cardioversion (TVEC). Since Dr. Alpern graduated in 2007, the school has performed only a handful of TVEC procedures, due to a lack of essential equipment over the past decade.
“It’s been a long time since we’ve performed a TVEC at UC Davis,” said Jessica Morgan, DVM, of the Equine Field Service. “But I gained a lot of experience with them in my time as a clinician at the University of Pennsylvania, so we have the right team and equipment to offer that option again.”
Dr. Morgan consulted with Fiona Wensley, DVM, in the Equine Medicine Service treating Rio, the Cardiology Service, and the Anesthesia Service—as well as Dr. Alpern—about the possibility of a TVEC being an option for Rio, after quinidine, a medication commonly used for cardioversion failed to correct his arrhythmia, according to Dr. Morgan.
Rio is doing well
Electrodes on the tips of catheters were placed in Rio's chest to perform the TVEC procedure.
Image courtesy of UC Davis
“Dr. Alpern was looking for an opportunity to try something else, and we agreed that a TVEC was the answer,” Dr. Morgan said.
A cutaneous method—placing electrode paddles on the chest— is the preferred way to perform an electrical cardioversion on dogs and people, but a horse’s large muscle mass does not allow the shock wave to reach the heart without causing deadly complications. Veterinarians must approach the horse’s heart with electrodes on the tips of catheters placed across the heart through the horse’s veins.
Electrodes on the tips of catheters were placed in Rio's chest to perform the TVEC procedure.
Two catheters were placed in Rio’s right jugular vein–one was advanced into the left pulmonary artery and the other into the right atrium. Their positions were placed with the assistance of echocardiography and confirmed with radiographs of his chest.
Rio was then anesthetized, and a shock wave produced by a life pack was sent to the electrodes with the intention of stunning the atrium, then allowing it to restart.
The procedure was successful, and Rio’s heart was shocked back into a normal sinus rhythm, confirmed by a post-procedure electrocardiogram. A follow-up echocardiogram several days later revealed improvement of previous findings.
“From a cardiovascular standpoint, Rio has a good prognosis for return to athletic function, as long as he is able to maintain sinus rhythm,” Dr. Morgan said. “He didn’t have any major complications with the procedure, and he hasn’t gone back into atrial fibrillation.”
The many people involved in Rio's cardiovascular procedure.
Image courtesy of UC Davis
Rio was placed on medication to reduce the risk of recurrence, and Dr. Alpern has a cell-phone-based electrocardiogram unit to monitor him at home.
After 2 months, Dr. Alpern reports that Rio is doing well and is back to giving short rides to her children. She remains optimistic about his recovery.
TVEC on the East Coast
TVEC was also used recently at Cornell University College of Veterinary Medicine, in New York.
Rose, a 9-year-old Warmblood mare, had just the right amount of energy and feistiness to become a successful show jumper when her owner, Claudia, bought her in January 2022.
But 9 months later at a series of classes in Tryon, N.C., Claudia noticed a change. While Rose had initially performed well, during the last class she began knocking fences down. When they left the ring, Rose developed a nosebleed.
And while 3 other horses developed nosebleeds that day, Sarah Allendorf, DVM, the veterinarian on site, noticed something additional in Rose. She had an arrhythmia.
Claudia and her horses traveled home to Cazenovia, N.Y., and a few weeks later, Rose’s heart still had not improved. Claudia set up an evaluation at the Cornell Equine and Nemo Farm Animal Hospitals (ENFAH), where Katharyn Mitchell, DVM, assistant professor in the Section of Large Animal Medicine with a subspecialty in cardiology, reviewed Rose’s case and had suspicions of AFib.
Because Rose’s heart had not spontaneously returned to sinus rhythm, Dr. Mitchell, with Beth Williams Louie, DVM, and Hanna Sfraga, a resident in large animal medicine, evaluated Rose to determine the cause of the AFib.
“While AFib can be a secondary condition that’s caused by underlying heart disease, bigger horses like Rose are more at risk for arrhythmias simply due to their size and their naturally larger hearts,” Dr. Mitchell said.
Rose’s evaluation involved multiple components, including an echocardiography, exercise test at the walk, trot and canter while Rose wore a portable ECG device that transmits to a computer so the heart rate and rhythm can be monitored in real time.
Although the evaluation ruled out underlying cardiac disease, Dr. Mitchell found that Rose experienced tachycardia during exercise, making it dangerous for Rose to do so.
Based on Rose’s risk factors and tachycardia, Dr. Mitchell and her team decided to perform TVEC, which also just returned to Cornell.
For the procedure, Dr. Mitchell and other members of the ENFAH Cardiology Service guided catheters to the heart while Rose was standing and lightly sedated. Starting from the right jugular vein, the specially designed long catheters pass into the right atrium, right ventricle and pulmonary artery. The correct placement was evaluated in real time using ultrasonography, and then once again with a radiograph taken by the Imaging Service.
Then, the Anesthesia and Pain Medicine Service induced general anesthesia and monitored Rose’s health status so Dr. Mitchell and her team could watch the ECG and time the TVEC shocks appropriately. The TVEC stops the arrhythmia, giving Rose’s heart a chance to resume a normal sinus rhythm. It took 4 shocks for Rose’s heart to do so, which Dr. Mitchell says is average for this procedure.
Rose recovered from the anesthesia and TVEC well. She rested for 1 month and a recheck at Cornell showed good results. Claudia started jumping Rose, working with her incrementally to ensure she wasn’t doing too much too quickly.
6 months after the procedure, Rose was back to jumping nearly as high as she was prior to the AFib diagnosis.
Because she’s a bigger horse with a naturally larger heart, she has a risk of another AFib recurrence, but other factors are in her favor. Because of Dr. Allendorf’s quick diagnosis and Claudia’s rapid contact with Cornell, she was not in AFib for very long prior to her procedure, and she has not had any other known AFib episodes.
Both horses are doing well. MeV
The report is a combination of 2 reports on the UC Davis and Cornell University websites. The originals were written by Rob Warren (UC Davis) and Jamie Crow (Cornell). You can find the originals here: https://www. vetmed.ucdavis.edu/news/electrical-shock-procedurecorrects-horses-irregular-heartbeat and https://www. vet.cornell.edu/news/20230614/cornell-helps-horseirregular-heartbeat-return-jumping
