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Aortic valve replacement is a procedure in which a person’s failing aortic valve is replaced usually with an artificial heart valve. An aortic valve can fail due to a range of diseases causing the valve to become leaky (aortic insufficiency/regurgitation) or narrowed (aortic stenosis). Until the end of the twentieth century, open-heart surgery was the only method of replacing an aortic valve and this remains the standard procedure. However, in the last decade transcatheter aortic valve implantation/replacement (TAVI in the EU or TAVR in the US) has become possible via a ‘key-hole’ approach in patients judged unsuitable for the standard procedure.

Types of heart valves
Approximately 300,000 people worldwide receive an aortic valve transplant each year. The vast majority of these have severe symptoms, such as severe aortic stenosis.There are two basic types of artificial heart valve: tissue valves and mechanical valves. A choice between the two is usually made based upon the person’s age, life expectancy, preference and comorbidities.



Tissue valves
Tissue heart valves are usually made from animal tissue (‘xenografts’), either animal heart valve tissue or animal pericardial tissue. The tissue is treated to prevent rejection and calcification. There are two main types: stented or stentless. Stented valves mimic the anatomy of the native valve and are mounted onto a metallic or polymer supporting stent. Stentless valves are manufactured from whole animal valves in an effort to remove the need for a stent. Tissue valves typically last 10–15 years in less active (e.g. elderly) people, but wear out faster in those who are younger. However, some valves, such as the Carpentier-Edwards and Medtronic valves, have reported a greater than 90% chance of lasting 20 years.

The main advantage of all biological valves is that anticoagulation is not required unless there is another reason for this e.g. atrial fibrillation.

In some cases a homograft—a human aortic valve—can be implanted. Homograft valves are donated from previously healthy people who have died often after a car crash or cerebral bleeding. The advantage of homografts is that they have potentially greater durability than xenografts depending on the state of preservation at harvest. They are particularly useful in infective endocarditis since they can be used to replace an infected aortic root and have a piece of mitral valve attached which can be used to repair a perforation in the base of the mitral valve which may implicate endocarditis.

In a Ross procedure the patient’s own pulmonary valve is autotransplanted to the left side and replaced with a homograft. The advantage is that the autograft is more durable, relatively speaking, than any xenograft or homograft. It is also more resistant to infection than xenografts and may grow, a major advantage in children since it may avoid the need for repeat operations.

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 on the valve that obstruct the leaflets. 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.

Valve selection
Tissue valves tend to wear out faster with increased flow demands – such as with a more active (typically younger) person. When a tissue valve wears out and needs replacement, the person must undergo another valve replacement surgery.

Open-heart surgery
Aortic valve replacement is most frequently done through open-heart surgery, where an incision is made by cutting through the sternum. Once the pericardium has been opened, the patient is put on a cardiopulmonary bypass machine (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 with a probe placed within the esophagus) can be used to verify that the new valve is functioning properly. Pacing wires may be put in place, so that the heart can be artificially 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.

Examples of tissue aortic valves used in open-heart surgery are the Carpentier-Edwards PERIMOUNT, the most widely used implanted tissue valve and the St Jude Trifecta. Mechanical valves include On-X and St Jude Medical Master series.

Outcomes
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 and technical consideration. 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 or be inoperable.

Hospital stay, recovery and complications
After open-heart surgery, the patient will frequently stay in an intensive care unit for 12–36 hours. The patient is often able to go home, in a further five to seven days, unless complications arise. Recovery from aortic valve replacement takes 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).

Common complications include heart block, which typically requires the insertion of a permanent cardiac pacemaker.

Minimally invasive valve surgery
Minimally invasive valve surgery (MIVS), or keyhole surgery, is where the surgeon replaces the valve through small incisions between two to four inches in length using specialised surgical instruments.

Outcomes
The main advantage with MIVS is an improved cosmetic appearance, the risk of death or serious complication during MIVS is approximately 0.8–4%, similar to open-heart surgery. However, as with open-heart surgery, this risk is raised in those people who are frail or have multiple comorbidities.

Hospital stay, recovery and complications
The small incisions of MIVS mean it typically involves smaller scars and faster recovery times than open-heart surgery. The average hospital stay post-surgery is 3–5 days, with the average recovery time at 1–4 weeks. Heavy lifting can normally be resumed within 5–8 weeks. Overall, post-operative pain scores are reported to be lower with MIVS than open-heart surgery. Complications include bleeding, infection and stroke occur, although the risks are reduced compared with open-heart surgery.

Transcatheter aortic valve implantation
TAVI/TAVR implants the valve using a catheter, removing the need for invasive open-heart surgery. The new valve is moved into position through an artery and once attached in place, the catheter is removed. Since the first TAVI procedure was performed in 2002, this technique has been used in more than 60 countries in people who are at extreme or high risk of serious complications if they undergo open-heart surgery.

There are two types of TAVI devices: balloon expanding and self-expanding. The leading balloon expanding devices are the Edwards SAPIEN valves by Edwards Lifesciences. and the Medtronic CoreValve system is the leading self-expanding device. Newer designs include the Lotus Valve (Boston Scientific), JenaValve (GmbH), Accurate (Symetis) and Portico (St Jude).



Outcomes
The effectiveness and safety of the TAVI procedure in people with severe aortic stenosis was tested between 2007 and 2009 in the PARTNER I trial, which compared the Edwards SAPIEN device to standard open-heart surgery. The results showed that the catheter implanted Edwards SAPIEN valve was as safe and effective as open-heart surgery and had similar rates of survival at 1 year. Additionally, there was a significant increase in survival in those people unsuitable for open-heart surgery. Inoperable patient mortality was reduced by 205% (absolute reduction) compared with a non-replacement alternative (lifestyle alterations and medication).

Hospital stay, recovery and complications
In the PARTNER trial, those receiving TAVI had a shorter recovery time. The length of stay in intensive care (3 vs. 5 days), length of stay in hospital (8 vs.12 days) and the risk of rehospitalisation due to complications were significantly reduced with TAVI versus open-heart surgery. Since this trial in 2009, recovery times have been further decreasing as the valve and delivery device design, as well as surgeon skills, have improved.

There are important differences between TAVI and open-heart surgery when understanding the risks. TAVI had an increased risk of stroke and complications to the vascular system (e.g. artery perforation) in the first 30 days, but more strokes occurred in the surgical group during the follow- up period. Open-heart surgery had an increased risk of bleeding and irregular heart beat.