Cardiologist searches for keys to mitral valve disease

Manhattan, Kan—About 70 percent of dogs affected by mitral valve disease do not develop heart failure or die as a result, according to a new study out of Kansas State University's College of Veterinary Medicine (KSU).

Large breeds are prone, too: Borgarelli’s research has shown that it’s not just small-breed dogs that are affected by chronic mitral valve disease, but large breeds such as German Shepherds as well.(MARTIN RUEGNER /GETTY IMAGES)

Michele Borgarelli, DVM, PhD, Dipl. ECVIM-CA, has studied heart disease in dogs for more than 15 years. He found that some breeds are more prone to mitral valve disease—a deterioration of the mitral valve that causes blood to backflow through the valve. Some cases progress to congestive heart failure.

"We know that the disease affects geriatric dogs very commonly," says Borgarelli, associate professor of cardiology at KSU. "I'm interested to know why some dogs progress faster and die from the disease when other dogs do not."

Small-breed dogs, such as Cavalier King Charles Spaniels, Cocker Spaniels, Dachshunds, Miniature Poodles and Yorkshire Terriers, are more prone to chronic mitral valve disease. But Borgarelli's research has shown that the disease can also affect large-breed dogs, such as German Shepherds. Borgarelli wants to research a list of factors to identify dogs more likely to progress to a severe disease state.

"You don't want to wait until they get to an age where it is too late," Borgarelli says. "You want to identify these patients as early as possible."

But most dogs affected by mitral valve disease do not progress to heart failure, he says. In fact, 70 percent of the preclinical dogs studied that had signs of the disease are still alive after six years. The dogs that experienced heart failure had a median survival time of nine months after severe heart failure to 33 months after moderate heart failure, according to Borgarelli's research.

"That's very similar to people," Borgarelli says. "There are some people who don't progress to heart failure even without any treatment. Treatment options are also different between people and dogs. Severely afflicted humans can have their deteriorated valve repaired or replaced. You cannot do that with dogs, yet. But surgery is going to be an option in the future for dogs. Because not every dog will be affected by heart failure, it is important to be able to identify dogs at higher risk for progression of the disease."

Borgarelli and his team conducted two studies involving more than 300 dogs over a period of five years. They found some indicators for severe forms of the disease, including an enlarged left atrium in the heart. Other indicators include biomarkers and brain natriuretic peptide, or BNP. Borgarelli began a study last year on BNP. It will conclude in 2015 and seeks to find out if treatment with a combination of two drugs can delay the onset of clinical signs of mitral valve disease and to evaluate if any biomarker, including the peptide, can be used to identify patient risk.

Although the disease is not often fatal, Borgarelli says there is room for more research on the topic.

"This disease was first described in the 1960s. What we knew about the disease in the 1960s was about the same as what we knew up until a few years ago," he says. "Many questions have been resolved in just a few years."

Key scientific questions remain, however. Scientists do not know if the disease is genetic. Nor do researchers completely understand why some patients progress to heart failure and others do not.