By Eva Briggs
Last week I brought my dog to the vet for his annual checkup. Boomer is in great shape for a 12-year-old dog, so I was surprised to learn that he had a new heart murmur due to a disorder called mitral valve regurgitation.
I took out my stethoscope and was startled by how loud his murmur was. It’s a problem that occurs in people, too.
First, a reminder that the term heart murmur refers to an abnormal sound caused by turbulent blood flow. Often murmurs happen because the heart’s structure is abnormal. But some murmurs, especially in kids where the heart’s plumbing is smaller, are innocent. Innocent murmurs occur in a structurally normal heart and don’t indicate heart disease.
The mitral valve separates the left atrium of the heart from the left ventricle. During diastole, the relaxation phase of the heart, blood returning from the lungs fills the left atrium. When the heart contracts, the left atrium squeezes sending blood through the mitral valve to fill the larger left ventricle. Next the mitral valve closes and the left ventricle contracts, delivering blood to the body.
In mitral regurgitation, the mitral valve doesn’t close all the way. Blood leaks backwards into the left atrium. So the body receives less blood and the left ventricle has to work harder. It can stretch, enlarging the heart.
Often mitral regurgitation has no symptoms initially. It may take months or years to progress to symptoms.
When mitral regurgitation becomes symptomatic, it causes heart failure. The overworked weakened heart muscle can’t keep up. At first exercise becomes difficult. Exertion causes fatigue or shortness of breath. The shortness of breath can worsen, especially when lying down. Fluid in the lungs leads to cough, and fluid in the body causes leg swelling. The stretched heart muscle can develop abnormal rhythms, causing palpitations and sometimes atrial fibrillation.
What causes mitral regurgitation? In my dog’s case, and for many people, it arises from age-related degeneration.
Another cause is mitral valve prolapse. In this common disorder, the mitral valve bulges backward when the ventricle contracts. Most of the time there is no associated leak. Over time some people develop mitral regurgitation. Another cause is damage to the chordae tendinae, tendons that tether the two segments (leaflets) of the valve to prevent the leaflets from bulging backward.
Rheumatic fever, a complication of untreated strep throat, can damage the mitral valve. It’s now rare in the U.S. but not uncommon in developing countries. Infection of the heart valve, endocarditis, is another potential cause.
One way the heart valve can become infected in otherwise healthy young people is by injection of drugs under nonsterile conditions. Heart attacks that affect the heart muscle supporting the mitral valve can cause mitral regurgitation that is potentially sudden and severe.
Myocarditis, inflamed or damaged heart muscle, is another cause.
Chest trauma can damage the mitral valve, sometimes rupturing the chordae tendinae and producing sudden severe symptoms.
Other causes include congenital heart disease, atrial fibrillation, radiation therapy to the chest, and medicines containing ergotamine.
If your doctor suspects mitral regurgitation, a variety of tests help determine the diagnosis and severity. An echocardiogram uses sound waves to image the heart and the blood flow through the heart. An EKG evaluates the electrical system of the heart. A chest X-ray is another way to evaluate heart size and look for fluid in the lungs. Other tests that a cardiologist might order include a cardiac CT, cardiac MRI, exercise or other stress test, or cardiac catheterization.
Once the diagnosis is made, how is it treated? Patients with mild disease may need no treatment other than close monitoring.
As the disease progresses, medications might be needed. Diuretics, often called “water pills” relieve excess fluid in the lungs or legs. Blood thinners may be needed if there is associated atrial fibrillation. Since elevated blood pressure worsens mitral regurgitation, antihypertensive drugs are prescribed if blood pressure is high.
Many patients eventually require surgery to repair or replace the mitral valve. Some types of repair can even be done via a catheter inserted in the groin.
Lifestyle changes can also help. Exercise regularly (within any limits set by your doctor), eat a heart healthy diet, quit smoking, cut back on alcohol, prevent infective endocarditis, and follow up regularly with your doctor.
As for Boomer, he has no heart symptoms, so my vet is recommending watchful waiting. I like to hope he has several more years of romping through the woods with me.
Eva Briggs is a medical doctor who works at two urgent care centers (Central Square and Fulton) operated by Oswego Health.