There are numerous types of heart disease that can affect dogs. Degenerative valve disease is one of the most common forms of canine heart disease and is also known as endocardiosis, valvular insufficiency, valvular regurgitation or chronic valve disease.
Canine Degenerative Valve Disease and the Effect on the Canine Heart
The valve most commonly affected by degenerative valve disease in the dog is the mitral valve, the valve located between the left atrium and the left ventricle (the chambers of the heart). Less commonly, the tricuspid valve may be involved. The tricuspid valve is located between the right atrium and right ventricle. In both cases, the valves function to allow the flow of blood from the atrium into the ventricle and, in dogs with normal valves, block the flow of blood in the opposite direction.
When degenerative valve disease occurs, the affected valve becomes thickened and may assume a nodular appearance or undergo other structural changes. These degenerative changes to the valves cause the valves to become leaky, allowing a regurgitation of blood backwards into the respective atrium. This regurgitation results in the formation of a heart murmur, an abnormal sound associated with the heartbeat. Often, the first sign of degenerative valve disease will be the detection of a heart murmur during a routine veterinary examination.
Canine Congestive Heart Failure as a Consequence of Degenerative Valve Disease in the Dog
As the disease progresses, the regurgitation of blood from the ventricle back into the atrium causes an increased volume of blood within the respective atrium and ventricle, resulting in an increase in the size of both chambers. Eventually, the increase in size of the atrium and ventricle will result in increased pressure within both of these chambers. In the case of mitral valve degeneration, this increased pressure may affect the lungs, causing fluid to leak out of the blood vessels inside of the lungs and leading to pulmonary edema (fluid within the lungs) and congestive heart failure.
If the tricuspid valve is affected rather than the mitral valve, the increased pressure within the heart chambers may cause fluid to leak out into the chest and the abdominal cavity rather than into the lungs. This is known as right-sided heart failure and results in ascites (a fluid-filled abdominal cavity that appears as a bloated abdomen).
Symptoms of Degenerative Valve Disease in Dogs
Dogs most commonly affected by degenerative valve disease are older, small breed dogs. Males are more commonly affected than females but both sexes may suffer from degenerative valve disease. Breeds predisposed to degenerative valve disease include:
- Miniature Poodles
- Cocker Spaniels
- Miniature Schnauzers
- Dachshunds
- various terrier breeds
- Cavalier King Charles Spaniels - this breed may develop heart disease at a younger age than other breeds.
Less often, larger breed dogs have also been known to suffer degenerative valve disease, including German Shepherds, Doberman Pinschers and Weimeraners.
In the early stages of degenerative valve disease, there may be no visible symptoms, though a heart murmur may be audible. In more advanced disease, the most common symptoms of degenerative valve disease are those associated with congestive heart failure and include coughing, shortness of breath and an increased respiratory rate. Other symptoms may include depression, lack of appetite, weight loss and exercise intolerance. Dogs experiencing ascites as a result of right-sided heart failure may find lying down uncomfortable as well as frequently being short of breath. Syncope (fainting) may be seen in some cases. In advanced cases, arrhythmias and cardiac muscle disease may also occur.
Treatment of Dogs with Heart Failure Associated with Degenerative Valve Disease
In most cases, treatment is geared toward relieving the symptoms of congestive heart failure and may involve the following medications:
- diuretics, such as furosemide, hydrochlorothiazide or spironolactone
- angiotensin converting enzyme (ACE) inhibitors, such as enalapril or benazepril
- afterload reducers, such as amlodipine or hydralazine
- digoxin
- pimobendan
In cases of ascites or fluid accumulation within the chest cavity, removing the free fluid from the abdomen or chest may need to be performed through abdominocentesis or thoracocentesis.
Degenerative valve disease is the most common cause of heart disease and heart failure, including congestive heart failure, in dogs and is particularly common in older, small breed dogs. Treatment, when necessary, is usually aimed at relieving clinical signs and is very rarely curative.
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