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The mitral valve is a one-way valve comprised of two leaflets that conducts blood flow through the left side of the heart. When open, the mitral valve permits oxygenated blood from the lungs to fill the heart’s main pumping chamber, the left ventricle. When the left ventricle squeezes to deliver blood throughout the body, the mitral valve normally closes to prevent blood from flowing back toward the lungs.
Mitral regurgitation or insufficiency is a condition whereby the mitral valve permits blood from the left ventricle to leak back towards the lungs. Mitral regurgitation is most often caused by congenital malformation or damage due to trauma, infection, or heart failure. Depending on the severity of the leakage, this situation can lead to progressive lung congestion and heart failure. Symptoms commonly include shortness of breath, decreased exercise endurance, and swelling of the extremities.
The severity of mitral insufficiency can sometimes be reduced with medications, however the most definitive treatment involves surgical repair of the valve or replacement with a prosthetic valve.
In many cases, the mitral valve can be repaired by reconstructing the native valve tissues to restore normal valvular structure and function. In fact, the mitral valve is the most commonly repaired heart valve. Experimental and clinical research has shown that repair of the mitral valve is preferable to its replacement largely because native mitral valve is an intimately associated with the structure of the left ventricle. In cases when repair of the mitral valve cannot be performed successfully, Mitral valve replacement is another option. Mitral valve replacement involves removing much of the native mitral valve tissues and replacing it with an artificial valve consisting of animal and/or manufactured components.
Many mitral valve repair techniques have been developed. The method chosen for any particular valve depends largely on the anatomic abnormality that has caused the valve to leak. One of the most common disease of the mitral valve is known as mitral valve prolapse. In this condition one or both of the mitral valve leaflets swings too far backwards during each heartbeat such that the leaflets do not close properly, allowing blood to leak between them. Repair techniques for this condition attempt to reestablish proper closing of the mitral leaflets by cutting out extra leaflet tissue, fixating the two prolapsing leaflets together, replacing or adjusting the valve suspension mechanism, and placing a prosthetic strut around the valve. All repairs require the use of cardiopulmonary bypass, otherwise known as “the heart-lung machine.” This permits the surgeon to safely open the left atrium and access the mitral valve in a relatively bloodless field. In most cases, the heart is also stopped for 1 to 2 hours to facilitate the repair. Repairs range from relatively simple operations to very complex intricate procedures. The total duration of the operation ranges from 3 to 5 hours.
Repair of the mitral valve is generally preferred over its replacement for several important reasons. Repairing the valve preserves the natural geometry and attachments of the left ventricle which permits it to function efficiently. This is most relevant in patients with abnormal heart function. Furthermore, patients with mechanical prosthetic valves must take a blood thinning drug known as coumadin or warfarin for the rest of their lives. Besides being somewhat of a nuisance, this confers a small risk of bleeding complications.
Although most mitral valves can be repaired with the properly selected techniques, some valves cannot and must therefore be replaced with a prosthetic valve. It is generally believed that mitral repairs are quite durable; approximately 10% to 15% of patients undergoing mitral repair require a reoperation for a failed repair later in life.
The most common surgical approach to the mitral valve requires the surgeon to saw open the breastbone and spread the edges apart to gain direct access to the heart. Although this approach provides excellent access to the heart, the resulting wound requires several months to heal completely, an extended recovery period with substantial activity restrictions, and can be subject to serious complications including infection, breakdown, and even death.
Currently at The Johns Hopkins Hospital, the most commonly employed minimally invasive approach to the mitral valve is a “mini-thoracotomy” which consists of a 3 inch incision made through the right side of the chest between the ribs. Heart-lung bypass is instituted with small tubes placed in the main artery and vein of the right leg through a 1 to 2 inch incision placed in the right groin crease. The heart is then stopped and the left atrium is opened to expose the mitral valve. At this point, specialized hand-held “chopstick” like instruments are inserted through this small incision by the surgeon to repair the valve. After the valve is repaired, it is tested. The heart is then closed and restarted. Finally, heart-lung bypass is discontinued and the incisions are closed.