Mitral Regurgitation – leakage of the valve between the left atrium and left ventricle

Mitral Regurgitation – leakage of the valve between the left atrium and left ventricle

Mitral valve is the valve between the left atrium (upper chamber) and left ventricle (lower muscular chamber) and it should prevent backflow of blood from the left ventricle to the left atrium when the former contracts to pump out blood into the aorta (the largest blood vessel in the body carrying oxygenated blood). Mitral regurgitation (leak) can occur as a result of damage to the valve leaflets or due to papillary muscle dysfunction. Papillary muscles are the nipple shaped muscles which hold down the leaflets of the mitral valve when the left ventricle contracts and prevent them from billowing back into the left atrium. It can also occur when the left ventricular cavity is dilated.

In developing countries rheumatic fever is an important cause of mitral regurgitation (MR) as a result of mitral valvulitis (inflammation of the valve). In developed countries rheumatic fever is rare and mitral regurgitation is seldom of rheumatic etiology (cause). More common would be mitral valve prolapse (billowing back of the mitral valve while the ventricle contracts) and degenerative mitral valve disease. The severity of MR is quantified by the regurgitant fraction.

The fraction of the end diastolic volume (volume of the ventricle when the relaxation is complete) which regurgitates into the left atrium is known as the regurgitant fraction. It can be estimated by Doppler echocardiography (ultrasound imaging of the heart) as well as angiocardiography (imaging the heart by injecting a radiocontrast dye and using x-ray cine fluoroscopy).

Left ventricle and left atrium dilates (enlarges) gradually with increasing mitral regurgitation. As the left ventricle dilates, the mitral annulus (the fibrous ring to which the mitral valve is attached) enlarges and allows more regurgitation. This is why it is often mentioned that “mitral regurgitation begets mitral regurgitation”. Left ventricular end diastolic pressure may increase when the left ventricle fails in severe MR. This is more likely in acute (sudden onset) mitral regurgitation than in chronic (long standing) mitral regurgitation.

Rise in left ventricular end diastolic pressure also leads to elevation of left atrial pressure and pulmonary venous (vessels draining blood from the lungs to the left atrium) pressure. This in turn can lead to elevated pulmonary capillary (small blood vessels connecting the arteries and veins) pressures and pulmonary edema (collection of fluid within the small air passages of the lung). Reactive pulmonary arterial hypertension (increased pressure in the pulmonary arteries, which carry deoxygenated blood to the lungs for oxygenation) can also occur in chronic severe mitral regurgitation.

Severe mitral regurgitation can be surgically treated by mitral valve repair as well as mitral valve replacement. The scarred mitral valve of rheumatic MR is often not suitable for repair and requires replacement. Percutaneous (through the skin, without an open procedure) techniques for mitral valve repair are also becoming more common. Once the mitral valve is replaced by a mechanical prosthesis (artificial valve), life long anticoagulation (medicines to prevent clotting of blood) is mandatory, with its attendant problems. These patients need regular monitoring of blood clotting function with a test known as prothrombin time with an international normalized ratio (INR).