What is degenerative mitral valve disease?
Canine degenerative mitral valve disease (MVD) is a common heart condition that affects small to medium size dogs as they age. The mitral valve undergoes degenerative changes such as thickening and prolapse. These changes prevent the valve from closing properly which causes the valve to leak (mitral regurgitation). Mitral regurgitation can lead to enlargement of the heart and congestive heart failure (CHF), which is usually manifested as difficulty breathing and coughing. Additionally, heart enlargement can lead to arrhythmias (irregular rhythms), which can cause weakness and collapse. Other names for the disease include myxomatous mitral valve disease (MMVD) and chronic valve degeneration (CVD).
Although certain breeds are predisposed (for example, Cavalier King Charles Spaniels and Dachshunds), any dog can be affected. Mitral valve disease is the most common heart disease in dogs, affecting millions in the United States. The disease usually progresses slowly over years, but in a small proportion of dogs it can progress rapidly. Although MVD leads to CHF in only 25-30% of affected dogs, this still translates to over a million dogs in the United States, making it a very important disease in veterinary medicine. Although a genetic basis is being investigated, the disease is very common in all types of dogs as they age.
How is mitral valve disease diagnosed?
Mitral valve disease is characterized by a left-sided heart murmur that is heard with a stethoscope. An echocardiogram (ultrasound of the heart) can be performed to confirm the diagnosis, determine if other valves are affected, assess heart muscle pumping function, and determine if the heart is enlarged. Chest x-rays show the degree of heart enlargement and are important to determine if CHF is present, especially if affected dogs have cough or difficulty breathing.
How is mitral valve disease treated?
Medical management: Treatment of MVD depends on the severity. Mild disease without heart enlargement (Stage B1) is typically monitored regularly without treatment. Dogs with heart enlargement but without symptoms (Stage B2) benefit from treatment with pimobendan to slow disease progression. Dogs that experience CHF (Stages C and D) require diuretics, ACE-inhibitors, and spironolactone in addition to pimobendan to control signs of congestion. Some dogs with CHF need to be hospitalized for initial heart failure treatment.
Interventional management: The V-Clamp is a device that brings the center of the mitral valve leaflets together to reduce the amount of mitral regurgitation (also called trans-catheter edge-to-edge repair). It is placed during open-chest surgery, which allows a catheter to be introduced into the beating heart (without cardiopulmonary bypass), through which the device is delivered. The V-Clamp is in the early phases of clinical use at several institutions in the United States.
Surgical management: Because medications only control the signs of CHF and do not treat the primary valve problem, there is great interest in surgical methods to repair the valve abnormalities associated with MVD. Surgical repair of the mitral valve is done through open-heart surgery facilitated by cardiopulmonary bypass, but access to this procedure is limited. The University of Florida College of Veterinary Medicine recently launched an open heart surgery program for dogs.
How is mitral valve disease monitored by my veterinarian and my cardiologist?
Signs of MVD in dogs can range from no signs, to difficulty breathing, coughing, collapse, and abdominal enlargement. Dogs that are not symptomatic for their heart disease are often monitored with chest x-rays at regular intervals to monitor for disease progression after the initial diagnosis. Dogs that have experienced CHF are monitored more closely with chest x-rays, blood pressure and bloodwork, typically every 3-6 months or after medication changes. Monitoring of home breathing rates at rest or sleep is a sensitive way to detect onset or recurrence of CHF. Most normal dogs and most dogs with controlled CHF breathe less than 30 times per minute. Therefore, an increase in resting or sleeping breathing rates above 30 is a reason to call a veterinarian and might prompt a recheck visit.
What is the prognosis with mitral valve disease?
Many dogs have MVD but do not experience CHF or other symptoms. However, for dogs who progress to develop CHF, the average survival time with medical therapy is approximately one year. This time can vary depending on patient factors and other concurrent diseases. Close monitoring and communication with both the primary care veterinarian and the cardiologist provide the best chance possible for dogs to feel good during this time. Surgical mitral valve repair offers a more definitive treatment for this important disease with significantly longer survival times than medical therapy.