Heart disease is a terrifying diagnosis for most dog owners. One of the most common types of heart disease seen in dogs is degenerative valvular disease.
Degenerative valvular disease is most common in small breed dogs but can affect large breed dogs as well. It is most common in middle-aged and senior dogs but can be seen less often in younger dogs also.
It is estimated that degenerative valve disease accounts for approximately 75% of all heart disease in dogs.
How the Normal Canine Heart Works
The heart of the dog is divided into four chambers. Unoxygenated blood flows into the right atrium and then through the tricuspid valve into the right ventricle. It then leaves the right ventricle through the pulmonic valve into the pulmonary artery to travel to the lungs. It returns to the left side of the heart after it has been oxygenated. It enters the left side of the heart through the left atrium. From the left atrium, the blood flows through the mitral valve into the left ventricle. It leaves the ventricle through through the aortic valve to enter the aorta and then flows to the rest of the body.
The valves that are present in the heart are shaped like leaves that cover the openings which they guard. Their function is to open to let blood flow through the opening and then to close off the opening to prevent the blood from flowing backwards and re-entering the chamber which it has just left.
What Happens to Dogs with Valvular Heart Disease
In degenerative valvular heart disease, the valves of the heart become deformed and misshapen. Most often the affected valve becomes thicker than normal. It may start to look more like a knob than a leaf. When the valve becomes deformed, it no longer adequately closes the opening of the heart which it guards when it is closed. When this happens, blood can begin to flow backwards through the valve when the heart contracts instead of moving forward as it should. This is referred to as valvular regurgitation.
The most common valve involved is the mitral valve. Less often, the tricuspid valve is involved. Some dogs can have both mitral valve and tricuspid valve disease. Very infrequently, the pulmonic valve or the aortic valve becomes diseased.
Signs of Degenerative Heart Valve Disease in Dogs
The signs of degenerative valve disease are similar to those seen with many other forms of heart disease.
A heart murmur will be present in almost all dogs with mitral valve disease or tricuspid valve disease. This is often the first sign of a problem. The heart murmur is audible with a stethoscope and may be noticed by your veterinarian during a routine physical examination.
Many dogs with heart murmurs resulting from degenerative heart valve disease show no other signs of heart disease. These dogs may have disease that is progressive and they should be observed and monitored closely for signs of heart disease. However, many dogs with valvular heart disease develop only mild symptoms which do not affect their quality of life.
More specific signs of heart disease depend on which valve is diseased.
Signs of Mitral Valve Disease in Dogs
When the mitral valve is the diseased heart valve, left-sided heart failure will occur because of changes which occur in the left side of the heart.
Left-sided heart failure will cause fluid to build up in the lungs, causing coughing, shortness of breath and an increased respiratory rate as well as more general symptoms such as not eating well, tiring easily and acting depressed.
Signs of Tricuspid Valve Disease in Dogs
When the tricuspid valve becomes diseased, it is the right side of the heart that is affected, leading to right-sided heart failure. Right-sided-heart failure causes fluid to accumulate in the abdominal cavity, causing the belly to have a bloated appearance. It may also cause fluid to build up in the chest cavity outside of the lungs. Your pet's legs may become swollen also.
When both mitral and tricuspid valve disease is present, you may see a combination of both left- and right-sided heart failure.