By Allison Heaney, Board Certified Cardiologist at Wheat Ridge Animal Hospital
Degeneration of the mitral valve leaflet is the most common heart disease in dogs. It is estimated that 75% of canine patients presented to a cardiologist have degeneration of their mitral valve. Correspondingly, 75% of dogs that develop congestive heart failure do so because of this disease process and up to 30% of all dogs will have a murmur consistent with Mitral Valve Disease as they age.
Mitral Valve disease develops over time as the mitral valve degrades and loses its structural integrity. Due to the fact that some breeds are overrepresented for the disease there is likely a genetic component.
The purpose of the mitral valve is to prevent blood leaking backwards as the heart pumps blood forward to the body. As the valve degenerates, blood begins to leak backwards through the valve. This leakage can be heard through a stethoscope as a sound referred to as a murmur. While the intensity of the murmur can often correlate with the severity of the disease, this does not always hold true. Further diagnostics, such as radiography (chest x-rays) or echocardiography (ultrasound of the heart), can help to assess the severity of the disease.
Chest radiographs allow us to see the outline of the heart in order to determine if it is enlarged. They also allow us to assess the blood vessels in the lungs to evaluate for blood “backing up” in the vessels of the lungs. They also are the best diagnostic tools for evaluating for the development of fluid in the lungs as a consequence of heart disease (referred to as congestive heart failure or cardiogenic pulmonary edema.) Unfortunately, radiographs are limited in that they neither allow us to evaluate the function of the heart nor to assess for other complicating issues with the heart — such as elevated blood pressure in the lungs. Echocardiography is the gold standard for evaluating heart pump function, enlargement of the heart chambers, evaluating for increased pressure in the lungs as well as getting an overall picture of the structure and function of the heart. It does not, however, allow us to evaluate the lung tissue directly for the presence of fluid.
Symptoms of valve disease include coughing, increased respiratory rate or effort, decreased energy level, fainting episodes, or fluid accumulation in the abdomen. Obviously many other diseases can explain all of these symptoms, but among dogs with a heart murmur, careful screening for heart disease should be performed if any of these symptoms develop. For dogs with a heart murmur consistent with mitral valve disease, I encourage owners to monitor a sleeping respiratory rate at home. This is done by counting the number of times your dog breathes in one minute. If, over time, you notice that this number has increased or if it is above 40 breaths per minute you should alert your veterinarian.
While there is currently not an effective surgical procedure for this condition, it is currently being studied and is hopefully in our future. At this time, we can medically manage patients that have developed symptoms due to degenerative valve disease. While a dog can have a murmur for years prior to developing symptoms, once congestive heart failure has developed the average survival time is 18 months with medical management. Typically dogs feel very good while being medically managed and enjoy a great quality of life.
Wheat Ridge Animal Hospital
3695 Kipling Street
Wheat Ridge, CO 80033