What is mitral regurgitation?

What is mitral regurgitation?

Mitral regurgitation is a leak in the mitral valve between the left atrium and left ventricle. Normally mitral valve prevents backflow of blood from the left ventricle, the lower muscular chamber when it contracts. In mitral regurgitation, as the valve is leaky blood flows back into the left atrium, the upper chamber when the left ventricle contracts. This leads to enlargement of the left atrium. The blood which leaks into the left atrium returns back into the left ventricle when it relaxes after a contraction. This increases the load on the left ventricle as it has to contract more forcefully.

The volume overloaded left ventricle enlarges and its muscle becomes thickened gradually to cope up with the increased work load. The forceful contraction of the left ventricle is felt by the person as palpitation. In the long run the left ventricle starts failing due to the overload in case of severe mitral regurgitation. When the left ventricle fails, the pressure in the chamber when it relaxes increases and is transmitted back to the left atrium.

Increase in left atrial pressure is in turn passed on to the pulmonary veins, which bring oxygenated blood from the lungs to the left atrium. When the pressure in the pulmonary veins go above 25 mm Hg, fluid starts collecting in the small air cavities of the lungs known as alveoli. This causes breathlessness and decrease in oxygen levels in blood as it interferes with oxygenation of blood in the lungs. This situation occurs in heart failure and is known as pulmonary edema.

Mitral regurgitation can occur as a sequelae of rheumatic fever, a disease which affects the large joints of the body and heart valves. Mitral regurgitation can also occur secondary to enlargement of the left ventricle in heart failure due to other causes. Another cause is mitral valve prolapse (MVP), a condition in which redundant mitral leaflets bend back into the left atrium when the left ventricle contracts. Age related degenerative changes in the mitral valve can also produce mitral regurgitation. Rarely infections of the valve can increase the leak and need prolonged treatment for control.

Another important cause of mitral regurgitation is a heart attack. Heart attack weakens the region of the left ventricular muscle which holds the mitral leaflets taught when it contracts. Rarely heart attack can also cause a rupture of the muscle which holds back the mitral leaflets when the left ventricle contracts. This is a serious situation because it leads to sudden severe leak in the mitral valve.

Usual tests done in case of suspected mitral regurgitation are ECG, X-ray of the chest and echocardiogram (ultrasound imaging of the heart). Echocardiogram will give an estimate of the severity of the mitral regurgitation, pumping function of the heart and the status of other heart valves. When mitral regurgitation is due to a heart attack another important test is a coronary angiogram. Coronary angiogram is an X-ray imaging of blood vessels of the heart after injecting radiocontrast medications into them.

Mitral regurgitation can be treated with medications which reduce the load of the left ventricle by enlarging the peripheral blood vessels. When the peripheral blood vessels are enlarged, more blood is pumped out than what leaks back, reducing the load on the left ventricle. If the disease is progressive and medications do not bring relief, mitral valve can be either repaired or replaced.

Mitral valve repair is usually done by an open heart surgery. Recently devices which can be introduced through small holes in the groin have also been used to repair the mitral valve. This device places a clip on the mitral leaflets, reducing the leak. It is not necessary to open the chest for this procedure as it is done under the guidance of X-ray imaging in special procedure room known as cardiac catheterization laboratory.

Mitral valve which is too damaged to be repaired can be replaced surgically. Both biological bioprosthetic valves and mechanical valves are available. Mechanical valves have a high tendency for clotting and need life long medications to prevent clot formation. The clotting function has to be monitored on a regular basis to prevent bleeding and clotting complications. Bioprosthetic valves need clot preventing medications only for a short period after implantation.