Virtually every owner of a King Charles Cavalier Spaniel encounters mitral valve disease if the dog lives long enough. So it’s important to understand what MVD is – and what it isn’t.
It leads to congestive heart failure when untreated, but it’s not a death sentence. It’s the most common disease in all adult dogs but 20 times more frequent in Cavaliers. It’s treatable with medicines that lengthen life and make it better, but it’s not curable.
That’s why the CKCS Health Research Endowment was established at N.C. State University’s College of Veterinary Medicine, a national leader in studying canine diseases. The goal is for owners, breeders and people who love these spaniels to help pin down the genetic cause of the disease and eliminate it.
“What’s particularly sad about MVD in Cavaliers is that it’s age-related,” says Dr. Sandy Tou, a cardiologist at the college. “The onset for most dogs often comes in their geriatric years, but Cavaliers get it quite young.
“Many dogs go a long time without developing complications from it. If you get the disease when you’re 10 or 12, you may live out a normal life with it. If you get it at 3 as a Cavalier, even if you’re asymptomatic for five years, you’re still only 8.”
The mitral valve sits between the heart’s left atrium (upper chamber) and left ventricle (lower chamber), opening and closing to keep blood flowing in the proper direction. Unoxygenated blood from the body comes back to the heart via the right atrium and goes down to the right ventricle, which sends it to the lungs for oxygen. This oxygen-rich blood then comes back to the left atrium and goes down to the left ventricle, which pumps it to the rest of the body.
But because the left ventricle operates under high pressure from the strongest muscles around the heart, the mitral valve can wear out and leak. Blood flows backward into the heart, which causes multiple problems that end in congestive heart failure.
Luckily, owners get a warning sign. Dr. Tou says vets usually refer dogs to her after hearing heart murmurs at annual wellness exams:
“Your vet will listen with a stethoscope to the heart and lungs. If there’s an audible murmur, the vet may ask a specialist to do an echocardiogram or heart ultrasound. At that stage, if the leak is mild and there’s no heart enlargement, there’s no evidence that treatment is necessary. If the heart has enlarged, it’s time to slow down the disease.”
That can happen with changes in diet or medication, which vets adjust as the illness progresses. Tou says the biggest breakthrough in recent years has been Pimobendan, a.k.a. Vetmedin: That drug (which is also used by humans in Japan) can delay the onset of heart failure in dogs for 15 months, a significant span for animals who develop the disease late in life.
Valve surgery has become an expensive option, though Tou says few specialists perform it in the United States. The leading practitioner, Japanese doctor Masami Uechi, has done more than 400 mitral valve repair surgeries with his team, mostly in his home country.
Researchers trying to cure the disease in humans have made slow progress: Just three years ago, an international team isolated the first gene in which mutations cause the common form of it. Animal researchers, who have much less money at their disposal, haven’t done that.
“We hope to find genetic variants associated with disease development, ” says Dr. Tou. “Our (NC State) veterinary geneticists look for genetic causes; if we can find those, we can develop tests for both prevention and treatment.”