The heart consists of 4 chambers, 2 atria and 2 ventricles, with the atrioventricular valves ensuring that blood flows from the atria to the ventricles when the heart is beating. Blood is supposed to flow one way with the valves working to ensure this ….
Chronic Valve Disease (CVD) is the leading cause of heart failure in dogs. CVD affects up to 40% of dogs and is seen more frequently in toy sized or small dogs, both purebred and of mixed origins. Some of the breeds affected with a higher incidence of this condition are the Cavalier King Charles Spaniel, Cairn Terrier, all 3 sizes of Poodles, Bull Terrier, Miniature Pinschers, Whippets, Chihuahua, Pekinese, Dachshund, Beagle, Papillion, Dobermans, Great Dane and German Shepherd.
CVD is most often a result of degenerative changes of the heart valves as the dog ages. In 2/3 of cases it is the mitral valve which is faulty perhaps because of the higher pressure in the left ventricle; only 1/3 of the time is it the bicuspid valve.
Mitral Valve Disease (MVD) can be referred to by different names: mitral valve insufficiency, endocardiosis, mitral valve prolapsed, myxomatous valvular degeneration, myxomatous mitral valve disease, mitral valve regurgitation.
The leaflets of the valves as the dog ages develop nodules along the edges of the valves and become thickened. This results in less of a seal along the edges of the valves allowing for blood to leak between the ventricles (known as regurgitation). As the blood leaks back into the left atrium it increases the pressure on the atrium which makes it harder for the blood to flow from the lungs into the heart.
As the disease progresses other symptoms may appear such as an enlarged heart (seen on x-ray), exercise intolerance and eventually congestive heart failure (CHF). During the early stages of the disease, though a systolic murmur of grade 1-2 is heard there are usually no clinical signs. As the disease progresses, the murmur will become more audible, the dog may become intolerant of exercise, respiratory rate will increase and finally as fluid begins to accumulate in the lungs coughing and labored breathing develops.
In certain breeds such as the Cavalier King Charles Spaniel, a form of mitral valve disease can develop at a younger than normal age (<5 years) with a fairly rapid rate of progression, due to an inherited predisposition for the disorder. This does not occur with all Cavaliers, though most will eventually develop the first symptom of the disease (heart murmur), often between 7-11 years of age.
Having a heart murmur is not a death sentence! The rate of progression varies greatly from dog to dog. A low-grade heart murmur may be heard on a dog at age 2 but not progress further until the dog is much older (10-12 years). In other cases, the rate of progress can be rapid and may develop into more serious symptoms such as CHF within a couple of years.
While there is no cure for mitral valve disease treatment has progressed considerably through the use of medications and can extend an affected dog’s life allowing them to live reasonably comfortably for years. Different vets have various opinions about when treatment should begin; some feel that medications should be given as soon as a heart murmur is heard, while others wait until further symptoms such as coughing appear. Here is a discussion paper by two canine cardiologists on the two different views.
Treatments are individualized per the dog’s situation. Diets, weight and exercise schedules may be adjusted. Different medications may be given depending upon the symptoms. Some of the medications used in the treatment of MVD are:
- Angiotensin Converting Enzyme (ACE) inhibitors – these work to lower the blood pressure and reduce the afterload of blood flowing out of the heart.
- Diuretics – these are used to clear excess fluids from the lungs and body.
- Vasodilators – they dilate the veins and arteries to allow for better blood flow.
- Pimobendan (dual-acting indication) – this is a positive inotrope which works to strengthen cardiac muscle contractility and also acts as a vasodilator to dilate blood vessels.
Current testing for the disease is usually done using a stethoscope to listen for the regurgitation in the valve (systolic murmur) which is the earliest symptom of mitral valve disease.