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Mitral/Tricuspid Regurgitation Due to Myxomatous Heart

Valve Disease
VetBooks.ir secondary to this disease, there is strong evidence that starting

ABOUT THE DIAGNOSIS
no evidence of congestive heart failure. Many types and brands of
This disorder affects the hearts of adult dogs. In the dog, as in pimobendan will slow the progression of disease, even if there is
humans, the mitral valve is a trapdoor type of structure inside specialty or prescription dog foods are marketed for heart disease
the heart that separates the two chambers (left atrium and left but none of these has any proven benefit when myxomatous valve
ventricle) of the left side of the heart; the tricuspid valve likewise disease exists in this asymptomatic, “heart murmur-only” state,
separates the chambers of the right side of the heart (right atrium and premature feeding of some cardiac diets has been linked to
and right ventricle). These one-way valves ensure that the heart acceleration, rather than slowing, of the disease process. Some
functions efficiently by preventing backflow of blood each time the common-sense guidelines for the general care of dogs that have
heart contracts. As a result, properly-functioning mitral and tricuspid myxomatous heart valve disease include:
valves ensure that all the blood that enters the heart moves through • Avoiding or reducing intense physical exercise, because the heart
correctly and into the circulation. is under the greatest strain when it is forced to beat quickly.
This heart valve disorder has many names: “endocardiosis,” • Preferring lower-intensity, on-leash walks for physical activity, as
“degenerative valvular disease,” and “myxomatous valve degenera- long as the dog does not show signs of exhaustion or difficulty
tion” are some of the more common synonyms. The different names keeping up that might indicate too much activity.
refer to the same process: an abnormal thickening and distortion of • Avoiding treats or foods that are rich in salt, which causes fluid
the heart valves that occurs in some adult or older dogs. It can be retention and favors the development of congestive heart failure.
thought of as a form of premature aging of the heart valve tissue. • Beginning a weight-loss diet if your dog is overweight, as 40%
Small-breed dogs are most commonly affected by this condition, of pet dogs in North America are. An excess of body weight
although it can sometimes occur in larger dogs. In about two-thirds means unnecessary extra work for the heart.
of the cases, the mitral valve alone is affected; in about one-third, Overall, worsening heart valve function with time can lead to
both the mitral and tricuspid valves are affected; and rarely is the congestive heart failure. When it occurs, congestive heart failure may
tricuspid valve alone involved. With time, affected valves fail to cause a dog to have trouble breathing. Dogs should be brought
seal well when they close, allowing a small amount of blood to to the veterinarian as soon as changes in the breathing pattern or
leak back to the heart chamber where it just came from (atrium), loss of stamina is first noticed. As the disease progresses, more
rather than moving forward into the circulation. This inefficiency advanced signs can develop. The gums may take on a bluish or
has two drawbacks: it compromises the amount of blood moving gray color due to lack of oxygen, the belly may become distended
forward and into the body’s circulation to nourish the organs, and with fluid, and the dog often will be very inactive, or seem unable to
it increases the pressure inside the atrium (the chamber emptying get comfortable. Episodes of fainting can even occur. Fortunately,
into the ventricles). Overall, a poorly functioning heart valve means many dogs with myxomatous heart valve disease never even develop
that the heart has to work harder than normal to keep up the congestive heart failure and have just a heart murmur and no other
normal circulation. symptoms for their natural, normal life spans.
In the early stages of myxomatous valve disease, the only
symptom is the presence of a heart murmur. The turbulence created LIVING WITH THE DIAGNOSIS
by blood leaking through the distorted valve creates the sound heard Myxomatous heart valve disease is a process that gets progressively
as a murmur, which is a coarse, hissing sound heard with every worse. However, it can be years after the detection of a heart
heartbeat (using a stethoscope) as opposed to the normal, thumping murmur before congestive heart failure occurs. Periodic screening
“lub-dub” sound of the healthy heart. This is often the only sign of systemic blood pressure, chest x-rays and/or echocardiography
that this condition is present. It is common for a heart murmur to (heart ultrasound) is usually recommended to follow disease progres-
be a surprising or unexpected finding because myxomatous heart sion and to identify diseases that may further impair heart function
valve disease is well-tolerated in its early and intermediate stages (high blood pressure). The recommended frequency of these tests
and in fact, in some dogs it never progresses to more advanced varies with the stage of valve disease and individual patient.
stages of disease. However, myxomatous heart valve disease tends If your dog with myxomatous heart valve disease shows symp-
to very gradually get worse, and over time, an increasingly greater toms of congestive heart failure (see above), a variety of medications
amount of blood is sent back to the atrium. If this process continues can be used to control the symptoms. As the disease progresses,
to the point that the body’s ability to adapt is exceeded, then the medical management can become more complex, using additional
circulation becomes disrupted, causing fluid retention within the lungs medications and higher dosages.
(pulmonary edema) and associated symptoms: labored breathing, The long-term outlook for dogs with myxomatous heart valve
coughing, and intolerance of exercise. This is called “congestive disease but no symptoms of congestive heart failure is good: many
heart failure.” It is a somewhat misleading term because it does dogs tolerate the myxomatous heart valve disease unknowingly for
not mean that the heart has “failed” in the sense of stopping. the rest of their lives, whereas some others develop congestive heart
Rather, it means the heart is failing to meet the body’s circulatory failure after several months or more. Overall, dogs with myxomatous
requirements, and as a result, the circulation is disturbed in such heart valve disease and no observable outward symptoms beyond
a way as to cause fluid pooling, typically in the lungs. the heart murmur live for years (average 3 to 5 years, with tremendous
When congestive heart failure develops as a result of myxomatous variation meaning that a large proportion of these dogs live a normal
mitral or tricuspid valve disease, a heart murmur usually has been life span).
known to be present for a long time—at least several months The long-term outlook once congestive heart failure has occurred
and often a few years. Once a dog develops heart enlargement in a dog with myxomatous heart valve disease is guarded to fair.

From Cohn and Côté: Clinical Veterinary Advisor, 4th edition. Copyright © 2020 by Elsevier Inc. All rights reserved.