What is the mitral valve?
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.
What is mitral regurgitation or insufficiency?
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.
How is mitral regurgitation treated?
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.
How is the mitral valve repaired?
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.
What are minimally invasive approaches to the mitral valve?
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.
Robotic Mitral Repair
Another approach which is also sometimes used at our center utilizes a surgical robotic system instead of the hand-operated instruments to perform the repair. The surgical robot is designed to perform complex operations through incisions that are much smaller and less traumatic than those used with traditional surgical approaches.
The first robot-assisted cardiac operation at Johns Hopkins Hospital, performed in June 2003, consisted of successfully placing a biventricular pacemaker lead on a beating heart. The surgical robotic system is comprised of four principal components: a surgeon console, a computerized control system, two instrument "arms," and a fiberoptic camera. The surgeon sits at the console and views the heart in three-dimensions through the fiberoptic stereoscopic camera system while manipulating the instinctive operating controls.The surgeon's hand motions are relayed to a computer processor, which digitizes and relays them to the fine instrument tips placed into the chest cavity through small 1 cm port incisions. This computerized robotic system enhances the surgeon's ability to perform minimally invasive cardiac surgery in several ways. First, the computer interface permits the accurate translation of the surgeon's hand motions to a dexterous endoscopic "wrist" placed within the chest cavity, conferring much higher degrees of freedom and precision than could be achieved with traditional hand-operated instruments. Second, the advanced two-camera stereoscopic optics provides unprecedented magnified, high-definition, full-color images of the heart and its structures in three-dimensions. This visualization provides much greater detail of the heart than is generally possible with the surgeon's eye.