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Minimally-Invasive Aortic Valve Replacement
What is the aortic valve?
The aortic valve is a one-way valve comprised of three leaflets that conducts blood flow from the main pumping chamber of your heart, the left ventricle, into the largest artery in your body, the aorta, which conducts blood throughout the rest of your body. When the left ventricle squeezes blood into the aorta, the aortic valve normally closes to prevent blood from flowing back into the left ventricle.
Diseases of the aortic valve are functionally classified into those that cause the valve to leak, known as aortic regurgitation or insufficiency, and those that narrow its opening, known as aortic stenosis. These processes are caused by congenital malformations or acquired diseases including infection, degeneration and calcification, aortic aneurysms, tumors, and radiation.
What is aortic regurgitation or insufficiency?
Aortic regurgitation or insufficiency is a condition whereby the aortic valve permits blood ejected from the left ventricle to leak back into the left ventricle. Aortic regurgitation is most often caused by damage to the aortic valve from a recent infection (e.g., dental abscess), dilation of the aorta, and rheumatic heart disease.
Depending on the severity of the leakage, this situation can lead to progressive lung congestion and congestive heart failure. Symptoms commonly include shortness of breath, decreased exercise endurance, and swelling of the extremities.
What is aortic stenosis?
Aortic stenosis is a condition whereby the leaflets of the aortic valve become abnormally rigid such that they do not open fully, causing narrowing of the valve. This narrowing presents significant resistance against the main pumping action of the left ventricle as it tries to eject blood throughout the body.
Aortic stenosis is most often caused by degeneration with age whereby calcium is deposited on the valve leaflets rendering them stiff. Congenital malformation of the valve where by two of the three leaflets are fused into one, known as a bicuspid aortic valve, predisposes the valve to early calcific degeneration.
Depending on the severity of the valve narrowing, this situation can lead to progressive lung congestion and heart failure. Signs and symptoms commonly include shortness of breath, chest pain/heaviness, fainting/lightheadedness, decreased exercise endurance, and swelling of the extremities.
How are aortic stenosis and regurgitation treated?
The severity of aortic insufficiency can sometimes be reduced with medications, but aortic stenosis has no effective medical therapy. For both conditions, the most definitive treatment involves surgical replacement of the valve with a prosthetic valve. Timely surgery is advised since significant delay can lead to irreversible congestive heart failure.
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 aortic valve replaced?
Aortic valve replacements require the use of cardiopulmonary bypass, otherwise known as ?the heart-lung machine.? This permits the surgeon to safely open the aorta and access the aortic valve in a bloodless field. In most cases, the heart is also stopped for about 1 hour to facilitate the replacement.
The operation involves opening of the aorta and removal of the diseased aortic valve leaflets. Commonly, calcifications around the valve must also be removed carefully. The resulting valve ring or annulus is then measured to select the size of the valve prosthetic. A series of sutures are then placed around the valve annulus and subsequently through the prosthetic valve. The valve is then lowered into the annulus and secured. The aorta is closed and the heart restarted. The total duration of the operation ranges from 2 to 3 hours.
There are two major types of aortic valve prostheses: mechanical and tissue.
Mechanical prosthetic valves have lifelong durability, however a blood thinning drug known as coumadin or warfarin must be taken for the rest of the patient's life to prevent blood clots from forming on the hinges of the valve. Besides being somewhat of a nuisance, this confers a small risk of bleeding complications.
Tissue or bioprosthetic valves are made of either cow (bovine) or pig (porcine) tissue. Because they are made of organic materials, no blood thinning drugs must be taken, however they have a finite lifespan ranging from 15 to 20 years.
Selection of the valve type depends on a variety of factors including the patient's age, occupation, lifestyle, medical history, and preferences. This decision is made in close consultation with the surgeon.
What are minimally invasive approaches to the aortic valve?
The most common surgical approach to the aortic 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 aortic valve is a mini-sternotomy which consists of a 4 to 5 inch incision made through the upper portion of the chest, dividing only the upper portion of the breastbone. The conduct of the rest of the operation proceeds in the standard way described above.