Aortic valve replacement
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Aortic valve replacement is a cardiac surgery procedure in which a patient's failing aortic valve is substituted for an alternate healthy valve. The aortic valve can be affected by a range of diseases; the valve can either become leaky (aortic insufficiency / regurgitation) or partially blocked (aortic stenosis). Aortic valve replacement is open heart surgery. A new catheter-based approach (percutaneous aortic valve replacement or PAVR), which obviates the need for open heart surgery, is being used in some places of the world and is being tested in clinical trials in the United States and Europe.
Contents
Types of heart valves
There are two basic types of artificial heart valve: mechanical valves and tissue valves.
Tissue valves
Tissue heart valves are usually made from animal tissues, either animal heart valve tissue or animal pericardial tissue. The tissue is treated to prevent rejection and calcification.
There are alternatives to animal tissue valves. In some cases a homograft - a human aortic valve -- can be implanted. Homograft valves are donated by patients and harvested after the patient dies. The durability of homograft valves is comparable to porcine and bovine tissue valves. Another procedure for aortic valve replacement is the Ross procedure (or pulmonary autograft). In a Ross procedure, the aortic valve is removed and replaced with the patient's own pulmonary valve. A pulmonary homograft (pulmonary valve taken from a cadaver) is then used to replace the patient's own pulmonary valve. This procedure was first used in 1967 and is used primarily in children, because the procedure allows the patient's own pulmonary valve (now in the aortic position) to grow with the child.
Mechanical valves
Mechanical valves are designed to outlast the patient, and have typically been stress-tested to last several hundred years. Although mechanical valves are long-lasting and generally only one surgery is needed, there is an increased risk of blood clots forming with mechanical valves. As a result, mechanical valve recipients must generally take anti-coagulant (blood thinning) drugs such as warfarin for the rest of their lives, which makes the patient more prone to bleeding.
Valve selection
Tissue valves tend to wear out faster with increased flow demands - such as with a more active (typically younger) person. Tissue valves typically last 10-15 years in less active (typically elderly) patients, but wear out faster in younger patients. When a tissue valve wears out and needs replacement, the person must undergo another valve replacement surgery. For this reason, younger patients are often recommended mechanical valves to prevent the increased risk (and inconvenience) of another valve replacement.
Surgical procedure
Aortic valve replacement is most frequently done through a median sternotomy, meaning the incision is made by cutting through the sternum. Once the pericardium has been opened, the patient is placed on cardiopulmonary bypass machine, also referred to as the heart-lung machine. This machine takes over the task of breathing for the patient and pumping their blood around while the surgeon replaces the heart valve.
Once the patient is on bypass, an incision is made in the aorta and a crossclamp applied. The surgeon then removes the patient's diseased aortic valve and a mechanical or tissue valve is put in its place. Once the valve is in place and the aorta has been closed, the patient is taken off the heart-lung machine. Transesophageal echocardiogram (TEE, an ultra-sound of the heart done through the esophagus) can be used to verify that the new valve is functioning properly. Pacing wires are usually put in place, so that the heart can be manually paced should any complications arise after surgery. Drainage tubes are also inserted to drain fluids from the chest and pericardium following surgery. These are usually removed within 36 hours while the pacing wires are generally left in place until right before the patient is discharged from the hospital.
Hospital stay and recovery time
Immediately after aortic valve replacement, the patient will frequently stay in a cardiac surgery intensive care unit for 12-36 hours. After this, the patient is often moved to a lower-dependency unit and then to a cardiac surgery ward. Total time spent in hospital following surgery is usually between 4 and 10 days, unless complications arise. Common complications include heart block which typically requires the permanent insertion of a cardiac pacemaker.
Recovery from aortic valve replacement will take 1-3 months if the patient is in good health. Patients are advised not to do any heavy lifting for 6-8 weeks following surgery to avoid damaging the sternum (breast bone) while it heals.
Surgical outcome and risk of procedure
The risk of death or serious complications from aortic valve replacement is typically quoted as being between 1-3%, depending on the health and age of the patient, as well as the skill of the surgeon. Older patients, as well as more fragile ones, are sometimes ineligible for surgery because of elevated risks.
Percutaneous aortic valve replacement
Percutaneous aortic valve replacement allows the implantation of valves using a catheter without open heart surgery. It is routinely being used in Europe and other regions in patients who are at high risk to undergo open heart surgery, but is still in clinical trials in North America. The Edwards SAPIEN valve, commercially approved in Europe since 1997, is being evaluated in a multi-center clinical trial in the United States, with Cedars-Sinai Medical Center being the leading test site.
