Mitral valve disease (MVD) is the most common heart disease in dogs. About 75% of dogs are affected by the time they are 13 years old. The problem is an insufficient valve on the left side of the heart, sometimes on the right side. The insufficiency causes enlargement of the atrium and main chamber, which can lead to coughing and later fluid in the lungs (pulmonary edema). If the right side is severely affected, fluid may also accumulate in the abdomen and chest.
This article provides a brief overview of the disease. If you want to learn about the disease in more detail, I can recommend my book „Mitral Valve Disease in Dogs“. It is written specifically for dog owners and in the book you will find everything you want to know about this disease and much more.
What causes MVD in dogs?
MVD is a disease that the dog is not born with, but develops later in life. It is thought to be genetic, which has only been proven for Dachshunds and Cavalier King Charles Spaniels. There is nothing you can do to prevent your dog from developing MVD, but you should make sure your dog comes from a responsible breeder if it is a purebred dog. Other factors such as diet, activity or even obesity are not thought to play a role in the development of the disease.
Symptoms of mitral valve disease in dogs
At the beginning of the disease process, you will not notice any changes in your dog. As the disease progresses, the heart enlarges and small dogs in particular may begin to cough. This is a dry, hacking cough caused by the heart pressing on the large bronchial tubes and irritating cough receptors. The cough is not dangerous, but can be very bothersome to the animal and owner. However, some dogs do not develop a cough at all.
Not every dog reaches the stage where the heart can no longer continue to enlarge and fluid forms in the lungs (pulmonary edema). However, when this occurs, it is a life-threatening condition that will cause the dog to suffocate without treatment. Coughing may or may not be present, but rapid breathing to severe dyspnea is the main symptom of pulmonary edema. In some dogs with involvement of the right side of the heart, fluid may accumulate in the abdomen and an enlarged abdomen may be present.
Of course, other symptoms such as decreased appetite and weakness may be present, but this is usually only the case with severe disease.
Diagnosis of mitral valve disease in dogs
An insufficient heart valve always causes a heart murmur, which can be easily diagnosed with a stethoscope. A clinical examination with auscultation of the heart should be performed at each veterinary visit. Usually a heart murmur is detected before the owner notices any changes in the dog. Sometimes coughing is the main symptom and leads to the detection of a heart problem. However, the heart murmur does not tell much about how advanced the disease is and whether or not it needs treatment.
The final diagnosis is made by an ultrasound examination. A heart scan is a quick and painless procedure and provides an accurate assessment of the heart. The disease can be classified into different stages and the appropriate treatment can be initiated. Unfortunately, ultrasound waves cannot penetrate the lungs because the air reflects them completely. Therefore, we must rely on X-rays to assess the lungs and decide whether pulmonary edema is present in the case of severe disease and symptoms.
Treatment of mitral valve disease in dogs
There is a lot of research we can rely on for out treatment decisions. There are also guidelines available, that were put together from leading experts in animal cardiology all over the world and are updated regulary.
We categorise the disease in different stages and treatment differs in every stage.
Stage B1 is mild disease, with an insufficient valve but no chamber enlargement. The dogs should not show any symptoms yet. A heart murmur is usually present, but if it is very early in the disease progress, it might be difficult to heart the murmur.
Stage B2 is reached once the atrium and the main chamber are enlarged and treatment with pimobendan should be initiated. Research shows that pimobendan can prolong the progression into the next stage substantially.
Once the patient develops pulmonary edema (or fluid in the belly) for the first time, he or she is in stage C. This is when diuretics need to be started permanently and most cardiologist will also start ACE inhibitors and spironolacton. Pimobendan continued and stays an important component of the treatment plan.
If the dog is going into heart failure again, we call that stage D. Recurrent pulmonary edema might need more aggressive treatment, with higher doses of diuretics and pimobendan and might need other drugs added in. This however, is very individual and should be decided on a case to case bases.
Prognosis of mitral valve disease in dogs
Not all dogs with an insufficient mitral valve will develop heart failure. It is very different from dog to dog how fast the disease does progress. Some breeds – especially Cavalier King Charles Spaniels – often have a very fast progression and also develop the disease at a very young age. Others might be old already and the heart problem never reaches a stage where the owner notices any symptoms. Once the dog does develop heart failure and needs to be treated with diuretics, the average survival time is more or less a year. But again, this can vary greatly among dogs.
In humans the diseased valve is eventually replaced by an artificial or animal valve. There are a handful of veterinary clinics nowadays, that offer a valve repair procedure for dogs. But this very expensive surgery is far form routine in the veterinary world at the moment and a very experienced team is needed to have a successful outcome. At the moment there is one clinic in France, one in Austria, one in Japan and in London that offer mitral valve repair. But of course this is subject to change.
ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs
Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study-A Randomized Clinical Trial