A Heart-To-Heart on Severe Subaortic Stenosis

Marley was barely eight-weeks old in 2008 when his veterinarian heard a severe heart murmur in the hound-mix’s chest. Marley’s owner, Debbie Suttles, adoption team leader at the Gainesville (Florida) Humane Society, was referred to Herbert Maisenbacher, VMD, at the University of Florida College of Veterinary Medicine, also in Gainesville. After Maisenbacher confirmed the diagnosis of severe subaortic stenosis (SAS), a congenital heart disease, the veterinary researcher told Suttles about a new 2008-2010 study funded by an AKC Canine Health Foundation grant.

The 12-dog study had three aims: (a) to test the safety of a double balloon valvuloplasty (similar to an angioplasty) on dogs with SAS; (b) to significantly decrease the heart’s pressure gradient post-operatively; and (c) to determine if the cutting balloon reduced the pressure gradient and prevented re-stenosis, or re-narrowing of the area below the aortic valve. Although the study’s success partially depended on no re-stenosis for at least one year after surgery, Cardiology Chief Amara Estrada, DVM, intended to track the dogs for the rest of their lives.

Common in larger-breed dogs such as Dobermans, Golden Retrievers, Boxers, Dogue de Bordeaux and German Shepherds, SAS has, in the past, been treated with beta blocker medications or a low-pressure balloon valvuloplasty. With either protocol, the dogs lived an average of only 55 months. Doctors speculated that a more aggressive approach with earlier intervention might increase longevity and improve the animal’s quality of life.

On July 2, 2009, veterinary researcher Mandi Schmidt, DVM, performed the mildly invasive two-hour procedure on Marley. Under general anesthesia and via the carotid artery in the neck, she inserted a cutting balloon with 2mm blades followed by a strong, part-Kevlar, high-pressure balloon. The object was to inflate and dilate the abnormal area of the heart below the aortic valve.

"He still has a murmur," says Suttles about Marley, "but his systolic pressure gradient (the indicator of the heart’s effort to pump blood) was over 300mmHG (before surgery), and it dropped to around 190mmHG."

To qualify for the study, SAS-affected dogs had to have a minimum Doppler systolic pressure gradient of 80mmHG, be less than two years of age and not have a systemic or metabolic disease. "At between 8 and 30 months," Estrada says,"each dog had a fully developed lesion, but not a lot of secondary effects. You could see the stenotic ridge on the echocardiogram."

Although study dogs were treated gratis, the experimental procedure—if privately done--would cost around $5,000, says Estrada. Furthermore if a pediatric surgeon repaired the abnormality, the surgery could easily cost $10,000 to $15,000. "That would be prohibitive for most owners," Estrada says. Finding a safe, effective, affordable treatment is important—one reason Estrada is planning a second study to see if the high-pressure balloon alone can decrease the pressure gradient. Since the cutting balloon costs $1,000 and can be used only once (while the $600 high-pressure balloon can be used repeatedly), the savings would be significant. "We want to get the cost down to $2,000 to $3,000," says Estrada.

SAS is so common that breeders regularly screen for it in their puppies. But owners who "really do their homework" often are knowledgeable about it, says Estrada. "Dogs can be asymptomatic, but it depends on the severity of the individual case." Although Marley, for example, behaved like a typical, frisky puppy, some dogs with high pressure gradients can act lethargic. That was Moe’s problem.

After Frank and Janet Diaz purchased golden retrievers "Moe" and "Max" on the Internet, they discovered that compared to her littermate, Moe appeared less energetic and short of breath. "She did not run around like her sister (who has a less severe murmur)," says Frank, who knew Golden Retrievers might develop hip dysplasia but was not warned of SAS. "In hindsight, if I’d known of the condition, I would have checked the breeder more," he says. "Goldens are such sweet wonderful dogs, it’s sad they’re cursed with this problem.

"Without any intervention," he says, "her life expectancy and quality of life would be compromised…, so we wanted to do something if it was possible." The couple was apprehensive about the 2009 surgery ("there’s always a chance of not making it through," says Frank), but Moe tolerated it well and her pressure gradient dropped 30 percent. According to Moe’s owners, her "night and day" improvement enables her to complete a one-mile walk every day and play with Max in the house and backyard. "It was not guaranteed," says Frank, "but it was what we hoped would happen if it were successful."

Since the valvuloplasty procedure produced no complications in all 12 dogs, they went home the next day. Six months later, they showed an average decrease of 33 percent in pressure gradient with no re-stenosis. Estrada thinks there’s a "good chance" the stenosis won’t return; long-term maintenance of the improved pressure gradient is still an unknown. If stenosis reforms, the team would probably repeat the valvuloplasty. Says Estrada, "I’ll know more when the dogs come back for their 18-month check."

The University of Florida’s commitment to translational medicine and cooperation between the medical and veterinary colleges means the SAS study results will impact the pediatric interventional cardiology team. Says Estrada, "It (the procedure) will probably be done in newborns (with SAS) as a bridge before surgeons do open heart surgery to repair the heart or replace the valve." In July of this year the study was presented at the Pediatric Interventional Cardiac Catheterization Symposium in Chicago.

Meanwhile doctors prescribe the beta blocker atenolol and moderate exercise (no running or jogging) for the study dogs, including Marley and Moe, whose one-year checkups indicate neither re-stenosis nor an increase in pressure gradient. "I would have paid for a procedure to prolong her life and its quality," says Frank. "I count my blessings."