Signs, Symptoms and Treatment of Myxomatous Valvular Degeneration (MVD) in Dogs

Summary:

Myxomatous valvular degeneration (MVD) is a slowly progressive condition that affects heart valve anatomy and function in middle-aged to older dogs. It is rarely noted in cats. Its exact cause is unknown, but it is more common in small breed dogs suggesting some genetic predisposition. Animals frequently develop a heart murmur but may remain asymptomatic for several years. Complications of late stages of the disease include congestive heart failure, arrhythmias, and eventual death of severely affected patients. Medications are available to help slow the progression of the disease (later stages) and treat symptoms as they arise to help maintain a good quality of life.

Description: 

Myxomatous valvular degeneration (MVD) is the most common heart disease identified in dogs. It is rarely identified in cats. The condition may be referred to by a variety of names, such as degenerative valve disease or valvular endocardiosis. The condition most frequently affects the mitral valve, which separates the filling and pumping chambers (atrium and ventricle) on the left side of the heart, leading some individuals to refer to it as mitral valve disease. All of these terms describe an age-related degeneration of the structural components of the heart valves. This degeneration results in thickening and elongation of the valve leaflets, which affects the ability of the valves to close properly. This may lead to leaks (regurgitation) in one or more of the heart valves causing an audible heart murmur. The degeneration and severity of the leaks progress with time, resulting in enlargement (dilation) of the heart chambers on either side of the leaky valve (Figures 1B, 2). Other complications such as irregular heart rhythms (arrhythmias) may develop. If the leaks become large enough, congestive heart failure and other life threatening complications can develop as well.

Cause:

Although myxomatous valvular degeneration (MVD) is a common problem in the dog, its exact cause is unknown. It occurs in some breeds more frequently than others, suggesting a genetic or inherited cause. It is also seen more commonly in small breed dogs with other disorders of cartilage formation and growth, suggesting that the mechanism may involve abnormal growth or degeneration of the connective tissue components of the valve leaflets. Currently research is underway to identify hormonal factors that may also play a role in valvular degeneration.

Symptoms:
The symptoms of MVD vary depending on the severity of degeneration of the valve leaflets. Usually, affected dogs are identified with a heart murmur before any symptoms arise. As valvular leakage becomes more severe and the heart enlarges, symptoms may include signs of congestive heart failure (exercise intolerance, weakness, difficulty or labored breathing, coughing) or fainting with exertion. Rarely, patients with advanced disease may die suddenly from rupture of a severely enlarged heart chamber or tearing of the supporting structures of the valve.

Diagnosis:
MVD may be suspected in any dog with a new heart murmur, but particularly in older small breed dogs. Diagnostics to confirm the condition include a thorough physical examination and an ultrasound evaluation of the heart (echocardiogram). In patients that are symptomatic, chest X-rays may be recommended. An electrocardiogram (EKG) may be necessary in patients with an irregular heart rhythm. There are no current blood or genetic tests to definitively diagnose the disease.

Treatment:
There are no effective preventative agents or drugs that reverse the progression of MVD. In patients with a heart murmur and minimal heart enlargement, no therapy may be recommended and the patient may simply be monitored regularly. In later stages of the disease, medications are usually recommended in attempt to delay the onset of symptoms caused by progressive heart enlargement. If congestive heart failure develops, additional medications may be indicated to rid the body of retained fluid, improve heart muscle function, treat arrhythmias, and make it easier for the heart to pump blood forward into the circulation. Different combinations of drugs are often necessary to keep patients free from symptoms depending on the severity of their condition, presence of other diseases (particularly kidney or liver dysfunction), and tolerance of the medications.

Prognosis:
The prognosis for patients with MVD varies with the stage of disease at the time of diagnosis and the rate of progression. Some breeds develop the condition sooner in life (Cavalier King Charles Spaniels, Maltese), and others may progress more rapidly. Generally, the condition progresses slowly over the course of several years so that patients may remain asymptomatic long after development of a heart murmur. Once congestive heart failure develops, patients may live for 12-18 months with a good quality of life if appropriately medicated.

Recommendations:
If your dog is showing symptoms that may be consistent with MVD or develops a new heart murmur, discuss these with your primary care veterinarian. They may recommend additional diagnostics or referral to a veterinary cardiologist for confirmation of the diagnosis and discussion of prognosis and treatment options.

Upstate Veterinary Specialties

Upstate Veterinary Specialties