Aortic valve replacement
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|Aortic valve replacement|
Aortic valve replacement is a procedure in which a patient's failing aortic valve is replaced with an artificial heart valve. The aortic valve can be affected by a range of diseases; the valve can either become leaky (aortic insufficiency) or partially blocked (aortic stenosis). Current aortic valve replacement approaches include open heart surgery via a sternotomy, minimally invasive cardiac surgery (MICS) and transcatheter aortic valve replacement (TAVR).
As risk of aortic valve surgery has decreased and long term data on the survival and quality of life of people after valve replacement has become available, evidence-based guidelines for aortic valve replacement have been developed. The American Heart Association and American College of Cardiology Guidelines for the Management of Patients with Valvular Heart Disease are a widely accepted source of information for cardiologists and surgeons.
Patients with severe aortic stenosis, where the aortic valve is narrowed and blood flow from the heart is obstructed are candidates for surgery when they develop symptoms or when the heart function is impacted. Certain asymptomatic patients may also be candidates for surgery, especially if exercise stress testing is positive.
Patients with leaky aortic valves (aortic insufficiency) often tolerate even severe degrees of insufficiency for a relatively long time before symptoms develop. Surgery is indicated for symptoms such as shortness of breath, and in cases where the heart has begun to enlarge (dilate) from pumping the increased volume of blood that leaks back through the valve.
Types of valves
There are two basic types of artificial heart valve: mechanical valves and tissue valves.
Tissue heart valves are usually made from animal tissue, 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 recovered 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, as the procedure allows the patient's own pulmonary valve (now in the aortic position) to grow with the child.
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 present a one-surgery solution, there is an increased risk of blood clots forming with mechanical valves. As a result, mechanical valve recipients must take anticoagulant (blood thinning) drugs such as warfarin for the rest of their lives, making the patient more prone to bleeding. The sound of mechanical valves may be heard and decrease the quality of life.
Tissue valves tend to wear out faster with increased flow demands - such as with a more active (typically younger) person. Tissue valves are increasing lasting longer - now typically approximately 20 years, but they might wear out faster in younger people. When a tissue valve wears out and needs replacement, the person must undergo another valve replacement surgery. For this reason, younger patients often receive mechanical valves to prevent the increased risk (and inconvenience) of another valve replacement.
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 put on a cardiopulmonary bypass machine, also known 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, a cut 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
After aortic valve replacement, the patient will frequently stay in an intensive care unit for 12–36 hours. The patient is often able to go home after this, in about four 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 about three months, if the patient is in good health. Patients are advised not to do any heavy lifting for 4–6 months after surgery, to avoid damage to the sternum (the breast bone).
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. Older patients, as well as those who are frail and/or have multiple comorbidities (i.e. other health problems), may face significantly higher surgical risk.
Minimally invasive surgery
More recently, some cardiac surgeons have been performing aortic valve replacement procedures using an approach referred to as minimally invasive cardiac surgery (MICS), in which the surgeon replaces the valve through small incisions between two and four inches in length using specialized surgical instruments rather than by cutting a six to ten-inch incision down the center of the sternum. MICS typically involves shorter recovery time and more attractive cosmetic results.
Another promising alternative for many high risk and older patients is transcatheter aortic valve replacement (TAVR), which delivers a new valve to the site of the diseased valve through a catheter. The replacement valve is collapsed and packaged in a way similar to a stent. Once in place it is expanded, pushing the old valve’s leaflets out of the way, and functions in place of the old valve. The catheter may be inserted through the femoral artery or through a small incision in the chest and then through a large artery or the tip of the left ventricle.
Guidelines suggest TAVR for most patients over 75 and surgical replacement for most patients less than 75. Ultimately, the best treatment choice is a decision based on many individual factors.
Early surgical approaches to aortic valve disease were limited by the necessity of operating with the heart beating. In the 1950s the Hufnagel valve was implanted in the descending thoracic aorta in patients with aortic insufficiency. The first successful replacement of the aortic valve was reported in 1960 by Harken, and early adoption of this technique proceeded slowly based on the limitations of available replacement valves and relatively primitive techniques for protecting the heart during surgery which were available at the time. With the evolution of mechanical heart valves and gradual developments in cardiopulmonary bypass (the heart lung machine) and cardioplegia which allow the heart to be stopped safely during surgery, aortic valve replacement became accepted therapy for patients with severe aortic insufficiency or regurgitation.
- Aortic valve repair
- Artificial heart valve
- Valvular heart disease
- Minimally invasive cardiac surgery
- Pericardial heart valves
- Open aortic surgery
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