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MITRAL/TRICUSPID REGURGITATION DUE TO MYXOMATOUS HEART VALVE DISEASE


About the Diagnosis

This disorder is a problem affecting the hearts of older dogs. In the dog, as in humans, the mitral valve separates the two chambers (left atrium and left ventricle) of the left side of the heart; the tricuspid valve separates the chambers of the right side of the heart (right atrium and right ventricle). These one-way valves prevent backflow of blood each time the heart contracts, and properly-functioning mitral and tricuspid valves ensure that blood moves correctly through the heat and into the circulation.

"Endocardiosis" and "myxomatous valve degeneration" are the synonymous terms used to describe the thickening and distortion of these valves that occurs in some older dogs. It can be thought of as a form of premature aging of the heart valve tissue. Small breed dogs are most commonly affected by this condition, although it can sometimes occur in larger dogs. In about two-thirds of the cases, the mitral valve alone is affected; in about one-third, both the mitral and tricuspid valves are affected; and rarely is the tricuspid valve alone involved. As the condition progresses, the valves become leaky. The leakage of a heart valve means that with every heartbeat, a small amount of blood seeps back to the heart chamber where it just came from, rather than moving forward into the circulation. This inefficiency has two drawbacks: it compromises the amount of blood moving forward and into the body's circulation to nourish the organs and it increases the pressure inside the atria (the chambers feeding into the ventricles, which receive the leaked blood). Overall, valve leakage in the heart is such that the heart has to work harder than normal to keep up the normal circulation. If the leakage becomes worse over time, as it can from further thickening and distortion of endocarditis over a period of months to years, the heart may eventually not be able to keep up, and symptoms such as shortness of breath, exercise intolerance (loss of stamina), and cough start to become apparent. When this is the case, congestive heart failure is said to exist (see below). Treatment is then indispensable, since it can restore a good quality of life, and without treatment, the situation may quickly become life-threatening.

In the early stages of endocardiosis, the only symptom is the presence of a heart murmur. The turbulence created by blood leaking through the distorted valve creates the sound heard as a murmur, which is a coarse, hissing sound heard with every heartbeat (using a stethoscope) as opposed to the normal, thumping "lub-dub" sound of the healthy heart. This is often the only sign that endocardiosis is present, and it generally remains the only sign for years. However, endocardiosis tends to very gradually get worse, with a larger amount of blood leakage developing over time. If this progresses to the point that the body's compensatory mechanisms are exceeded, then fluid retention within the lungs (pulmonary edema) occurs, causing labored breathing, coughing, and intolerance of exercise. This is called "congestive heart failure." It is a somewhat misleading term because it does not mean that the heart has "failed" in the sense of stopping. Rather, it means the heart is failing to meet the body's circulatory requirements, and as a result, the circulation is disturbed in such as way as to cause fluid pooling, typically in the lungs.
With myxomatous mitral or tricuspid valve disease, congestive heart failure most often develops after a heart murmur has been known to be present for a long time-at least several months and usually a few years. If it is not detected and treated promptly, congestive heart failure may cause a dog to have trouble breathing, and the gums may take on a bluish or grey color due to lack of oxygen. The belly may become distended with fluid, and the pet often will be very inactive. Episodes of fainting can even occur. These are very advanced symptoms, and a dog should be brought to the veterinarian prior to these symptoms, when labored breathing or loss of stamina is first noticed. Fortunately, many dogs with endocardiosis never even develop congestive heart failure and have just a heart murmur and no other symptoms for their natural, normal life spans.

The condition is usually first diagnosed by the detection of a heart murmur during a routine health examination. For pets showing no symptoms, no treatment is needed because no medication exists that delays or repairs the process of endocardiosis. At this "asymptomatic" stage when only a heart murmur is present to indicate endocardiosis, x-rays or an echocardiogram (cardiac ultrasound) may be recommended to confirm the diagnosis and evaluate the extent of secondary enlargement or distortion of parts of the heart. Repeating these tests periodically will allow your veterinarian to assess how rapidly the problem is progressing. An electrocardiogram (ECG) may be used to check for irregular heartbeats, which may develop in the later stages of disease.

Living with the Diagnosis

Endocardiosis is a process that gets progressively worse. However, it can be years after the detection of a heart murmur before congestive heart failure occurs. Until the symptoms of congestive heart failure are apparent, the main precautions to take are for the dog to not exercise excessively (not to exhaustion, nor excessively intensely), to avoid medications or other situations that can increase the heart rate unnecessarily, and to avoid treats or foods that are excessively high in salt. Your veterinarian can help you determine what to avoid and what to favor.

If your dog with endocardiosis shows signs of congestive heart failure (see above), a variety of medications can be used to control the symptoms. As the disease progresses, medical management will become more complex, using additional drugs and higher doses.

The long-term outlook for dogs with endocardiosis but no symptoms of congestive heart failure is good: many dogs tolerate the endocardiosis unknowingly for the rest of their lives, whereas some others develop congestive heart failure after several months or more. Overall, dogs with endocardiosis and no observable outward symptoms beyond the heart murmur live for years (average 3 to 5 years, with tremendous variation meaning that a large proportion of these dogs live a normal lifespan).

The long-term outlook once congestive heart failure has occurred in a dog with endocardiosis is guarded to fair. These dogs require medication (pills) daily and periodic checkups with the veterinarian. The life span after the onset of congestive heart failure is extremely variable and depends on the severity of the endocardiosis and the dog's response to medication. Dogs may live from days to years after developing congestive heart failure, with an average of 6 to 10 months.

Treatment

As mentioned above, there is no medication warranted before the onset of congestive heart failure.
Management of congestive heart failure includes the use of medications, low-salt diets, and exercise restriction. The first medication usually prescribed is a diuretic (water pill) to prevent fluid buildup. Fluid accumulation in the lungs is one of the factors that cause the labored breathing and cough associated with heart disease. Furthermore, vasodilator drugs can be used for helping to reduce the workload of the heart. As your pet's heart disease worsens, several other medications may be added to treat specific problems. Digoxin strengthens the heartbeat and helps control some types of irregular heartbeats. Several other medications can be prescribed for irregular heartbeats if needed. Severe heart failure may require hospitalization and oxygen therapy until your pet's condition can be stabilized. The goal of this treatment is to find a combination that makes your dog comfortable and enjoying a good quality of life.

DOs

• Give all medications exactly as directed.

• If congestive heart failure develops, restrict your pet's exercise to leash walks.

• If your pet is overweight, start a weight reduction program.

DON'Ts

• Do not feed salty treats.

• Do not overdo physical activity with your dog. Endocardiosis is not a type of heart disease that exercise will improve. Leash walks and mild to moderate degrees of activity, as tolerated by your dog, are ideal.

• Do not be alarmed if you notice your dog's heartbeat seems irregular when your dog otherwise seems to feel fine. Healthy dogs often have an irregular-sounding heart rhythm ("respiratory sinus arrhythmia") that is simply a normal variation related to their breathing.

When to Call Your Veterinarian

• If your pet is receiving digoxin and shows lack of appetite, depression, vomiting, or diarrhea (signs of intolerance to the medication), stop the digoxin and call your veterinarian.

• If your pet's symptoms become worse or reappear, an adjustment in medication dosage may be needed.

Signs to Watch For

• Coughing or difficulty breathing or exercise intolerance.

• In advanced disease:

o Bluish or grey gums or swollen belly.

o Fainting spells or severe weakness.

Routine Follow-Up

• The frequency of follow-up examinations depends upon the severity of your pet's disease. Pets with no symptoms or mild symptoms should be evaluated every 6 to 12 months. More severely affected pets should be examined after 2 to 3 weeks initially and then approximately every 2 to 4 months.