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 / regurgitation) or partially blocked (aortic stenosis). Current aortic valve replacement approaches include open heart surgery, minimally invasive cardiac surgery (MICS) and minimally invasive, catheter-based (percutaneous) aortic valve replacement.

A catheter-based approach (percutaneous aortic valve replacement or PAVR) may eliminate the need for open heart surgery in select groups of patients. As of October 2012, in the USA there is an FDA-approved percutaneously implantable aortic valve system for high surgical risk and inoperable patients with symptomatic aortic stenosis with other catheter-based devices on trial use.

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 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
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.

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 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).

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 those who are frail and/or have multiple comorbidities (i.e. other health problems), may face significantly higher surgical risk.

Minimally invasive cardiac 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 to 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.

Percutaneous aortic valve replacement
Percutaneous aortic valve replacement implants the valve using a catheter, without open heart surgery. It is used in more than 50 countries in patients who are at extreme or high risk to undergo open heart surgery. The SAPIEN valve is made by Edwards Lifesciences. The Medtronic CoreValve system is another device used for this procedure, undergoing clinical trials in the United States.

In high-risk patients with severe aortic stenosis, transcatheter and surgical procedures for aortic-valve replacement had similar rates of survival at 1 year, although there were important differences in risks associated with the procedure. In the PARTNER trial, there was an early increased hazard of stroke in the first 30 days associated with TAVR (4.6% with TAVR vs. 2.4% with surgical replacement, P=0.12), but more strokes occurred in the surgical group during the followup period. Hemodynamic valve improvement, quality of life outcomes and the composite outcome of death from any cause or stroke did not differ significantly between the two treatment groups. Patients treated with the percutaneous procedure enjoyed a shorter recovery time with faster improvements in quality of life measures, although the two groups were equal in quality of life outcomes by 1 year.