PBEC Success Story: A Chemical Cardioversion Gives Pontecini A Boost

Francesca Giarrusso and Poncho. Photo by Shawn McMillen Photography

BY Lindsay Berreth

Trainer Patti Harnois of Holly Hill Farm spends winters in Wellington, Florida, with her group of clients and is very familiar with how heat can affect horses.

When student Francesca Giarrusso’s 19-year-old warmblood gelding Pontecini started exhibiting signs of fatigue in the 3’3” jumper and equitation rings, Harnois assumed it was the Florida weather.

“I was getting 100 percent performance, but then it would drop to about 60 percent performance as the day went on when he had to come out again. He still performed and did his job; it was just the amount of energy was lower,” she said.

During a routine insurance health check, it was discovered that “Poncho” had atrial fibrillation, the most common type of cardiac arrythmia in horses, and suddenly the gelding’s unusual fatigue made sense.

Harnois took Poncho to nearby Palm Beach Equine Equine Clinic (PBEC) where Internal Medicine Specialist Dr. Fernando J. Marqués, DVM, Diplomate ACVIM, Diplomate ACVSMR, conducted several tests on Poncho. 

Photo courtesy of Dr. Marques

Dr. Marqués said that poor performance is the most common clinical sign of atrial fibrillation in horses. Poncho showed no other signs of discomfort or pain, he was just “running out of gas.”

“During exercise, they just can’t do anymore because they don’t get enough oxygen into the muscles,” he said. “The heart is inefficient to supply the amount of oxygen at a high level of intensity of exercise. It’s just, boom, they cannot go anymore.”

Atrial contraction of the heart is important, said Dr. Marqués. “In an atrial fibrillation, the atria just fibrillates [rapid rhythm] instead of having a nice organized contraction pumping blood from the atria to the ventricles. That contraction is needed under strenuous exercise.”

The first step was to confirm that the horse had atrial fibrillation by an electrocardiographic study (ECG). Then it was important to rule out why this was happening to Poncho—was it a primary cardiac problem or was it secondary to other issues like an electrolyte imbalance? If it was a secondary issue, the arrythmia could possibly be fixed without cardiac intervention.

Dr. Marqués ran bloodwork on Poncho including cardiac troponins, which are proteins released as a result of myocardial damage. Then he did an echocardiogram (ultrasonographic study of the heart) to take measurements of the heart, including the atria, ventricles, and ventricular function. There were no issues with Poncho’s bloodwork and nothing of concern on the echocardiogram.

Dr. Marqués opted for a chemical cardioversion procedure, which converts a cardiac arrhythmia to a normal rhythm. It’s one of two ways to treat atrial fibrillation. The other is an electrical cardioversion, which involves shocks to the heart under general anesthesia. Dr. Marqués prefers to do a chemical cardioversion as it’s less invasive.

At the clinic, a nasogastric tube was passed into Poncho’s stomach. He was given one dose of the drug Quinidine and had a telemetry ECG monitor with electrodes attached to his body to monitor his heart rate and rhythm remotely on an iPad outside the stall.

Quinidine absorbs into the bloodstream and after two hours, there should be a change to the rhythm of the heart. If not, up to three doses may be given. Poncho required three doses during the day until cardioversion to a normal sinus rhythm occurred, and he stayed overnight to be monitored.

Photo courtesy of Dr. Marques

“You start seeing changes slowly and gradually on the ECG,” said Dr. Marqués. “The amplitude and the shape of the different waves on the ECG tracing start changing for the better. Then you see evidence of atrial contraction, which is indicated by the P wave. Horses with atrial fibrillation lack P waves because the atria doesn’t contract. Instead, you see F waves, or fibrillation waves which appear as a wavy baseline on the tracing.”

By the next day, Poncho had a normal rhythm to his heart, so he went home. He was rechecked after 10 days, and everything still looked good.

“It was a really nice case where everything went in the right direction,” said Dr. Marqués. “When I started, I told the owner and trainer that this horse was probably in atrial fibrillation for a long time, and maybe the chances of cardioversion were slim. But that wasn’t the case luckily.”

For Harnois, who’s now back at her base in Marston Mills, MA, and Harvard, MA, the experience at PBEC was smooth and easy. “The clinic, the vet, the care, the treatment was amazing,” she said. 

After getting several opinions but no answers, she was grateful to Dr. Marqués for finding the problem and solving it.

“The hardest part is getting the diagnosis and the treatment,” she said. “The clinic is right next to my barn, and it’s much easier on the horse. They had a vet on him 24/7 while they were doing the conversion. He was watched every moment of the whole process.”

Poncho’s chemical cardioversion was performed in late March, and after some handwalking and small paddock turnout, Harnois gradually built up his under saddle work, and he’s just started jumping at the two-month mark.

She’s excited to see Giarrusso back in the ring with her partner of two years soon.

“He’s taught her everything. He’s taken her from basically a two-foot rider up to 3’3”. It’s been a great partnership,” she said.