What is mitral valve disease, anyway?
MVD – mitral valve disease (endocardiosis, chronic valvular disease)
In Cavaliers, MVD onset is almost always much earlier and the disease progresses much more quickly than in other dogs. Early-onset MVD is not unique to Cavaliers – if you’re interested in Cairns, poodles, or bull terriers you should definitely ask about MVD. However, early-onset severe MVD appears to be a whole lot more common in Cavaliers than any other dog breed today. About 50% of five year old Cavaliers had a heart murmur in one UK study that examined 431 show-bred Cavaliers. Close to 100% had a murmur by age 10. My personal guess is that the percentage by the age of five is higher than that for puppy-mill and other carelessly-produced puppies, based on results of tests on rescue dogs and on the famous indifference and ignorance to health issues of puppy-millers.
Here’s a heart. This is a human heart, but there’s no need to be picky, all mammalian hearts have the same basic structure.
The pathway of blood through the body is in this order: from the body into the right atrium; from the right atrium into the right ventricle; from the right ventricle through the lungs to pick up oxygen; from the lungs to the left atrium; from the left atrium to the left ventricle; and out the left ventricle through the aorta and throughout the body, to eventually return to the right atrium.
The mitral valve separates the left atrium from the left ventricle. The most common form of MVD is caused by a defect in the mitral valve which allows blood to “backwash” from the left ventricle into the left atrium, in effect forcing the heart to pump that blood twice. The heart therefore has to work harder in order to do its job. Both the left atrium and left ventricle tend to enlarge and left-side congestive heart failure eventually occurs. The tricuspid valve on the right side of the heart may also become involved, leading to right-side congestive heart failure.
MVD can be heard as a murmur, with murmurs graded on a scale of 1-6 (low grade to severe). It’s often not wise to depend on your vet to pick up a low-grade murmur, although your vet will probably pick up a murmur by the time it’s out of the low-grade range. It’s better to have your dog checked by a board-certified veterinary cardiologist. If you have a Cavalier, you can have this done inexpensively at the heart clinics offered at almost all CKCSC – USA shows. The breeder from whom you bought your puppy would probably appreciate your sending her the results of checks at, say, the ages of 2, 5, and 7, if you think this problem is important and would like to contribute to its solution. Please keep in mind that the presence of a low-grade murmur does not mean the dog’s quality of life will be immediately impaired – there’s usually three or four years from first diagnosis of a murmur to first occurrence of symptoms. Symptoms may never progress to congestive heart failure at all, especially if your dog is first diagnosed with a low-grade murmur past the age of seven. There's no real need to check prior to the age of two.
Early low-grade murmurs do not require (or appear to benefit from) treatment. It’s a good idea to have a baseline x-ray of the heart done at the time of first diagnosis, though, because you can then compare later heart enlargement to this baseline to monitor the development of the problem.
Symptoms of MVD once congestive heart failure has begun include difficulty breathing; coughing, especially at night or while resting; a reduced ability to exercise – dogs with severe MVD go for carries, not walks; and eventually fainting, collapse, and possibly sudden death. If you want to read about what it's like to live with a dog that has developed MVD, check out the links below.
If symptoms appear – most likely coughing or intolerance of exercise -- the dog will probably be treated with drugs to reduce body fluid and dilate blood vessels. These drugs usually provide substantial relief to the dog and allow it to live a basically normal life for a good long time. In more severe cases, drugs that help regulate the heart rate may also be used. In very severe cases, crate rest and hospitalization will probably be required. New drugs and treatments may come into usage at any time -- always check for current information if you find your dog has developed MVD (or any other health problem).
MVD is a nasty problem for Cavaliers today, there’s no doubt about it. For suggestions on the handling of this polygenic problem in a breeding program, go here:
For more information about Cavaliers and MVD, you might start here: http://www.candog.com/cavaliers/Health/Heart%20CKCSC,%20USA.htm
For what it's like to live with a Cavalier after it has been diagnosed with MVD, check this out:
http://www.ckcsc.org/ckcsc/ckcsc_inc.nsf/Founded-1954/MVDHC.html