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What is it?

This condition, also known as endocardiosis, chronic degenerative valvular disease, chronic valvular fibrosis and acquired mitral &/or tricuspid regurgitation or insufficiency, is by far the most common heart disease of dogs, accounting for about 75% of all heart disease cases in dogs.

The disease becomes increasingly prevalent as dogs get older, and affects predominantly the smaller breeds. In the past, it has mostly been reported in Miniature and Toy Poodles, Miniature Schnauzers, Chihuahuas, Dachshunds and small terriers. However, in the last 10 years there has been an alarming increase in its prevalence in the Cavalier. Unfortunately, the Cavalier is showing the disease at a much younger age, with around 10% of dogs under one year of age having a heart murmur, and probably more than 50% of 5 year olds having murmurs. Although not all of these dogs will die or even become ill because of the disease, probably 60% of dogs over 9 years of age are likely to have advanced disease. As we shall see later, there is now strong evidence of a genetic basis for mitral valve disease in both Cavaliers and Dachshunds.

What goes wrong?

Over a period of time we see progressive deterioration of the heart valves. The most commonly affected is the mitral valve, on the left side, followed by the tricuspid valve (on the right) and occasionally the aortic valve (on the left). The normally flexible thin valve leaflets become gnarled, fibrous and thickened, and their restraining tendons also thicken and sometimes rupture. The result is an incompetent leaky valve, which allows progressively more and more backflow. Eventually up to 80% of the output from the heart is leaking back through the valve (termed regurgitation) and only 20% is moving forward. As a result, the heart chambers enlarge, the heart muscle works harder and eventually the muscle may fail. In some cases, the thin-walled atrial chambers may rupture, and in others the valve tendons give way, both having disastrous (ie fatal) consequences.

What are the signs?

In the early stages, you (the owner) will not be aware that anything is wrong. However, your veterinarian will be able to hear a swishing, turbulent sound, called a murmur, which tends to get progressively louder as the valve leak worsens. In severe cases, the murmur may be felt as an odd “buzzing” sensation on the dog’s chest wall, usually lower down on the left side. In the later stages you begin to notice the dog tiring with exercise, breathing more rapidly, and sometimes coughing: a cough which is usually soft, but occasionally harsh and more evident at night or early morning, and possibly there may be collapsing or fainting. If the right side of the heart is affected more, you may notice a pot-bellied appearance as fluid accumulates. If one of the earlier-mentioned “disasters” occurs, your dog will be found dead, or collapsed in a desperate condition, coughing up pink or blood-tinged froth. However, this is uncommon: most cases progress slowly over a period of months to years.

How is it diagnosed?

Often the characteristic murmur is detected incidentally by your vet at a routine health check or vaccination examination. In other cases you may become aware of the signs mentioned above. Your vet may use a combination of physical examination, blood tests, xrays, ECG and ultrasound (echocardiography) to gain a better understanding of the disease severity. At present there is no way of detecting whether your individual animal is going to develop the disease later in life, or of accurately predicting the rate of progress. This means that finding no evidence of abnormality at an examination this year is not a guarantee that it will not have developed by next year.

How is it treated?

Unfortunately, there is currently no practical way of curing the disease: replacement of the degenerating valves is simply not practical. Treatment is aimed at ameliorating the existing signs. Recent research indicates there is nothing to be gained by beginning therapy before the dog begins to show signs of heart insufficiency. Once signs do begin, your vet will use a combination of diuretics, antihypertensives and cardiotonic drugs to control the signs and hopefully slow down progress. S/he may also recommend exercise restriction and dietary salt restriction. However, the grim fact still remains that most dogs who begin to show signs of heart failure will be dead within 2 years, despite the best of veterinary care. Thus it would be much better if we could prevent the disease from starting rather than trying to control its signs.

What is known about the genetics?

We have suspected a genetic tendency to mitral valve disease in the Cavalier King Charles Spaniel for some time, and recent work in Scandinavia and the Netherlands has confirmed this. Mitral valve disease is more prevalent in males, and the Scandinavian studies have clearly shown that if you breed with dogs having a higher grade of mitral valve disease you will produce more offspring with more severe grades. Unfortunately, quite a lot of dogs that will eventually develop mitral valve disease have no evidence of the disease until they are well into their breeding careers. There is currently no way of detecting early in life the tendency to develop mitral valve disease. All that the concerned breeder can do at present is to keep track of what happens with the offspring that s/he has bred, and to have all intended breeding stock regularly examined by their veterinarian. By doing this, s/he may be able to “breed away” from known affected bloodlines. The disease does not appear to be controlled by a single gene, and currently the proposed mode of inheritance is referred to as a “polygenic threshold trait”.

Can the Cavalier Club do more?

Awareness of the condition and the alarming numbers of Cavaliers affected is the first step, and I hope that this article helps to raise awareness. Conducting a “heart clinic” at a club show also helps raise awareness. It may also help if the club develops a recording system of bloodlines affected. However, this requires a high level of trust, honesty and discretion amongst members. Past experience with various genetic problems in other breeds has taught me that this is not easy to do! I have been keeping records of all dogs that I have examined, and currently I have data on several hundred dogs. I anticipate it will be possible to look at pedigree data in a few more years, and hopefully we can see if there is any useful trend there. However, until a better testing system (such as DNA analysis) can be developed, progress is likely to be very slow. I commend owners and breeders who are participating in our clinics for their progressive attitude.