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Chronic Degenerative Valvular Disease in Dogs
The most common kind of heart disease in dogs involves degeneration of the valves in the heart. In a normal heart, blood flows in one direction from the right to the left side of the heart. Blood that has had the oxygen removed by the body travels back to the right side of the heart. From the right side of the heart, blood is pumped into vessels in the lungs, where the blood becomes oxygenated again. From the lungs, the blood with oxygen goes to the left side of the heart, which pumps to the rest of the body so the oxygen can be used. To keep blood moving in this pattern, there are valves in the heart that form tight seals to prevent backflow of blood.
In dogs with chronic valvular disease, also known as degenerative myxomatous valve disease or endocardiosis, the valves become irregular at the edges so they are unable to form an adequate seal. As a result, blood can whoosh backwards and stay in the heart longer than it is supposed to. The abnormal motion of blood, also called regurgitation, is what your veterinarian hears and calls a heart murmur when they listen to your dog. The most commonly affected heart valve is on the left side of the heart - the mitral valve. These dogs have a leaky mitral valve leading to mitral valve regurgitation.
What causes heart valves to degenerate in dogs?
We do not know exactly what causes degenerative valve disease in dogs. Certain breeds are predisposed, so it seems like there is a genetic component. For example, one of the most commonly affected breeds is the Cavalier King Charles spaniel. Other breeds include Chihuahuas, miniature and toy poodles, pomeranians, Yorkshire terriers, dachshunds, and pekingese. There are other theories as to the cause like alterations in a signaler called serotonin or abnormalities in the connective tissue that change the way the valve moves.
How do I know if my dog has valvular disease?
Most dogs with valvular disease have no symptoms. Most of the signs we think of with heart disease like difficulty breathing, coughing, a fast or irregular heart rate, pale gum color are signs of something more serious like heart failure.
The vast majority of dogs with valvular disease have a heart murmur that your veterinarian can hear with a stethoscope. The location and volume of the heart murmur along with the dog’s breed can raise suspicion for valvular disease. This is one reason an annual physical examination is so important - finding a heart murmur and possible heart disease as early as possible leads to better outcomes for your pet.
What do I do if my veterinarian thinks my dog has valvular disease?
If your veterinarian hears a heart murmur, generally the next steps are checking blood pressure and doing some imaging.
Chest radiographs or x-rays show the heart and lungs in 2 dimensions and can be helpful especially for baseline information or to diagnose heart failure. A general practitioner can perform chest radiographs.
Echocardiography (heart ultrasound) gives 3 dimensional images in real time and is very helpful especially in early disease to track changes in the heart over time. Often an electrocardiogram (ECG) is done at the same time as an echocardiogram to check the electrical rhythm of the heart. Echocardiograms are performed by board-certified cardiologists.
Following the recommendations of your veterinarians, whether they are general practitioners or cardiologists, will make managing your dog’s heart disease as successful as possible.
What happens to the heart with valvular disease?
When there is regurgitation of blood back through one or more of the valves in the heart, there is a larger volume of blood in the heart at any given moment. If you think about it for a moment, this makes a lot of sense - instead of the blood moving along its normal path, some of it whooshes backwards and stays behind in the heart rather than moving into the vessels in the lungs or the rest of the body. This extra volume causes the heart to work harder to try and push the blood out. It also means less blood with oxygen is reaching the rest of the body.
Since most dogs with valvular disease have an affected mitral valve, we’ll focus there. The heart chambers separated by the mitral valve (left atrium and ventricle) thicken with extra muscle over time to compensate for the increased blood volume. Over time, as the valve degenerates more and there is more regurgitation of blood, less blood is sent out to the body. Certain receptors notice there is less circulating blood, which activates responses in the body that try to increase blood volume. These changes ironically hasten the progression of heart disease and stretching out of the heart muscle.
Will my dog develop congestive heart failure (CHF)?
CHF occurs when there is severe mitral valve regurgitation. Stretching of the heart muscle, especially in the left atrium, leads to uncompensated regurgitation. This means the heart is no longer able to accommodate the extra blood volume in the heart and it backs up into the vessels in the lungs and the lung tissue itself - this is called pulmonary edema.
Are there treatments for valvular disease in dogs?
Many dogs with valvular disease do not need any treatment at all. This is because dogs with early valve disease compensate well. With monitoring over time, many dogs will have progression in the amount of blood regurgitated through the diseased valves with secondary changes as described above. In those cases, a drug called pimobendan is recommended.
Pimobendan is a long-term medication that increases the heart’s ability to contract and helps dilate blood vessels to reduce the pressure against a beating heart. Dogs with mitral valve disease advanced enough to start pimobendan live significantly longer and have more easily treated heart failure than those not on the medication.
Some dogs will benefit from special diets that have less sodium.
If your dog has been diagnosed with heart failure, they may need to be hospitalized or at least started on therapy to remove fluid from the lungs. There are medications used long-term to try and keep the heart in a compensated state and prevent another episode of heart failure.
Is there surgery to repair diseased heart valves in dogs?
While surgical therapy is possible, there are not many places to have this performed. Referral centers and specialty clinics may have surgical options.
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