Aug 22 2016

Heart murmur – Mitral Valve Disease

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I’ve been told that my dog, a 6 year-old Cavalier King Charles Spaniel, has a heart murmur. I am a bit confused about what the murmur means and what to do!

A heart murmur is an abnormal heart sound that can be heard when listening to the heart with a stethoscope. It occurs when there is turbulence in the flow of blood through the heart. There are a variety of diseases that can produce a murmur in the heart. However, the Cavalier King Charles Spaniel breed is predisposed to the development of mitral valve disease. To better understand mitral valve disease, a little anatomy lesson is needed. The heart has four chambers: two upper chambers called atria (a right and a left atrium) and two lower chambers called ventricles (also divided into right and left). In between each chamber is a valve that allows the blood to move forward through the heart, while preventing the blood from going in a backward direction.

The heart valve located between the left atrium and left ventricle is known as the mitral valve. When blood exits the lungs it enters the left atrium, where it is briefly held. The blood then travels through the mitral valve into the left ventricle. The muscle of this chamber contracts and produces high pressure, allowing blood to be effectively pushed out of the heart to the rest of the body.

With mitral valve disease, this normally one-way valve between the left heart chambers becomes leaky. The contraction of the left ventricle then causes some of the blood to flow backwards into the left atrium, instead of pushing all of the blood forward to the body. Since blood is now flowing in the wrong direction, turbulence is created in the heart. It is this turbulence that produces the abnormal sound of a heart murmur.

Although not true for every type of murmur, in mitral valve disease there is a correlation between the loudness of the murmur and the severity of the disease. Therefore, a loud murmur indicates a leakier valve, more turbulence in blood flow, and more significant mitral valve disease.

Over time the left atrium stretches to accommodate the extra blood. But eventually there is more blood than the chamber can handle, so blood backs up into the lungs causing fluid to leak into the air spaces of the lung. This condition is known as congestive heart failure. Clinical signs that can be seen with heart failure include coughing, exercise intolerance, lack of stamina, increased breathing rate and respiratory distress.

When a murmur is detected, further work-up is needed to determine if there are any changes in the heart which would require medical intervention. Baseline blood work and urine tests help determine the overall health of the pet. If medications are started, these values are also important when monitoring how the body is responding to those medications. Cardiac enzymes that are released in higher levels when a heart is damaged can also be measured in the blood.

A chest x-ray is used to determine the heart size and shape. It will also show if there is fluid building up in the lungs or enlargement of the vessels. The heart’s electrical activity, rate and rhythm can be evaluated by an electrocardiogram (ECG). An abnormal rhythm may require specific intervention and can affect your pet’s prognosis.

The best test to determine the overall function of the heart is an ultrasound, also known as an echocardiogram. Sound waves are used to observe the heart’s motion as it contracts and relaxes. The amount of blood pumped by the heart can also be measured. This test often requires referral to a specialist with advanced training.

Not every murmur requires treatment. If there is no enlargement of the heart or signs of congestive heart failure, starting medication early does not slow the progression of heart disease or improve survival. Once these changes are evident, however, there are a number of drugs that can be used to help heart function and reduce clinical signs.

In order to determine the significance of your dog’s murmur, you should have further cardiac work-up performed. Early diagnosis, regular monitoring, and appropriately-timed initiation of cardiac medications are key factors in the successful management of mitral valve disease. There is no cure, but appropriate testing and treatment can provide your dog with the best chance for a good quality life for hopefully years to come.

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