Mitral Valve Disease In Dogs

Mitral valve disease is also called endocardiosis, and is a type of heart disease that can affect dogs, usually those that are mature or reaching old age. It is a progressive condition that worsens as the dog gets older, and is in fact the most common heart problem to affect older dogs-in some cases, dogs will not present with symptoms until they are older than ten.

Once the condition does begin to develop and become symptomatic in affected dogs, it has an extremely negative impact on the dog’s quality of life, causing problems including respiratory distress, severe coughing and breathlessness, and exercise intolerance. Ultimately, affected dogs are usually euthanized at some point before the condition reaches its natural conclusion, which is invariably death by means of chronic heart failure.

In this article, we will look at mitral valve disease in dogs in more detail, including what sort of dogs can be affected by the condition, and why there is currently no standardised testing scheme in place for it. Read on to learn more.

More about mitral valve disease

Mitral valve disease occurs due to a malfunction of the mitral valve, the valve that separates the top and bottom halves of the left side of heart. When the dog is healthy, the mitral valve opens to let blood move from the atria to the ventricles, and then closes again as the heart pumps the blood out into the blood vessels to stop the blood from flowing back.

However, when a dog has mitral valve disease, a type of plaque accumulates within the valve itself, causing deformation of the valve and so, allowing blood to flow back into the atrium. This means that the blood pumped by the heart is weaker and less prolific than it should be, and the fact that the mitral valve allows blood to flow back into the atrium also leads to a murmur.

This leads to the heart dilating abnormally and increasing the volume of blood it pumps, which masks the symptoms of the condition for some time so that the dog appears to be normal and healthy-however, it actually makes the disease worse at the same time, and ultimately, causes congestive heart failure.

Once the condition becomes symptomatic, affected dogs will suffer from exercise intolerance, and a tendency to have a soft, dry cough that is worse at night and after exercise.

How do dogs develop mitral valve disease?

There is often a hereditary element to mitral valve disease in dogs, and a breed line history of the condition does increase the risk of other dogs of the breed line also being affected by the condition. However, as dogs age and their bodies begin the gradual slow down towards the end of their lives, heart conditions such as mitral valve disease become more and more prevalent, within dogs from previously unaffected breed lines as well as those with a history of heart problems.

What sort of dogs can be affected by the condition?

Any breed or type of dog can be affected by mitral valve disease, and it is much more common in dogs that are mature or approaching old age. However, certain breeds of dog are much more prone to developing the condition than others, with the Cavalier King Charles spaniel topping the list; in fact, the Cavvie is around twenty times more likely to develop the condition than any other breed of dog.

Other breeds where the condition tends to present regularly include the Chihuahua, Miniature poodle, Norfolk terrier and the miniature Schnauzer.

Additionally, males are around twice as likely to develop the condition than females.

Can pre-breeding screening be performed for mitral valve disease?

Because there is a hereditary element to mitral valve disease in some cases, particularly in breeds with high incidence rates of the condition such as the Cavalier King Charles spaniel, many breed organisations and clubs concerned with the welfare of commonly affected breeds have lobbied The Kennel Club to have the condition included within their umbrella health screening schemes by breed, and arrange a DNA testing protocol for the condition.

However, this has not proven possible to date due to the complexity of the condition and so, the challenges of establishing a test that will return reliable results. Instead, The Kennel Club advises Cavalier King Charles spaniel breeders to have their potential breeding stock checked on an annual basis by a veterinary surgeon or veterinary cardiologist, who will use a stethoscope to listen to the dog’s heart and so, pick up on the earliest indications of the condition.

This form of checking is not conclusive, however, and a dog whose heart appears healthy one year may show signs of the condition the next. For this reason, it is impossible to mandate a registry for healthy dogs and refuse registration to dogs that are diagnosed with the condition, as the condition may not become apparent for many years.

Ergo, the best that any expert can tell you when it comes to your own dog and their mitral valve health is whether or not they appear to have the early symptoms of the condition or not at any given point in time, but this does not protect against the potential later development of the condition.


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