How do replacement heart valves work?
A replacement heart valve can give a new lease of life to people with heart valve disease. Dr Pablo Lamata explains the different valve types to Senior Cardiac Nurse Emily McGrath. Plus, watch our new animations to see how healthy and replacement heart valves work.
Why would you have a replacement heart valve?
Heart valves can become diseased or damaged, which means they either don’t open properly (stenosis) or don’t close properly (regurgitation). This can stop your heart from working as it should, so a replacement valve is used to do the valve’s job of opening and closing.
How do replacement heart valves work?
Replacement valves act like gates that let the blood go through your heart. This means opening at the right time, so that blood can flow into the next chamber of your heart, or flow out towards the rest of your body; and also closing at the right time, so that your heart can pump effectively and the blood doesn’t flow backwards.
You have four valves in your heart but there are two – the aortic and mitral valves – that tend to be the ones that may need replacing.
What is the difference between a tissue and mechanical heart valve?
Mechanical valves are made from carbon and metal. Tissue (biological or bioprosthetic) valves are usually made from pig or cow tissue, or sometimes from human tissue (in which case they may be called homograft valves), that has been treated to make sure it is not rejected by the body. They are built to create a valve’s exact mechanical properties.
What are the pros and cons of mechanical and tissue valves?
Mechanical valves usually last a lifetime, but your blood is more likely to build up and stick on the valve, causing a clot. If this breaks off, it could cause a heart attack or stroke. If you choose to have a mechanical valve, you’ll need to take warfarin, a blood-thinning medication (anticoagulant) every day for life to reduce the risk of clots. You’ll need regular blood tests at your GP surgery or anticoagulation clinic, or you can test your own blood at home if you purchase a home-testing kit.
With tissue valves, you don’t need to take a blood-thinning medicine for life – although you may have to for some months after surgery. However, this type of valve won’t last as long as a mechanical valve and may need to be replaced or repaired after 10 to 20 years.
What are the differences between different mechanical valves?
The main difference between the mechanical valves is how the companies decide to design the mechanism for opening and closing.
How big are mechanical valves?
They come in different sizes, depending on your size – and therefore the size of your heart – and which valve is being replaced. An aortic valve is typically 2 – 3cm (about an inch) in diameter, while a mitral valve is typically 2.7 – 3.5cm (1.1 – 1.4 inches). The surgeon will decide the best size for you.
How do I decide which type of replacement heart valve to have?
The final choice is reached differently for each patient as many factors (including your physical condition, any other medical conditions you may have and your age) are considered with the guidance of your doctor.
Tissue valves tend to be the preferred choice of:
- older people (older than 70) as they may not need another valve operation in their lifetime
- people who have a risk of bleeding and don’t want to take warfarin
- people who have other major surgery planned and don’t want to have blood-thinning drugs
- people who are planning to have children and avoid the risk of warfarin in pregnancy
Tissue valves have the same risk of infection as mechanical valves.
Mechanical valves tend to be the preferred choice of:
- younger people (younger than 65) as this will lessen the chance of needing another valve operation because the valve will last for a lifetime
- people at risk of a replacement tissue valve deteriorating quickly
- people who are already taking warfarin for other reasons
- people who would be at risk if another valve operation were needed
How are replacement heart valves inserted?
The traditional surgical approach involves opening the chest and cutting the breastbone to reach the area of the valve. The heart needs to be stopped while the valve is replaced, so a heart-lung bypass machine is used to circulate blood around your body during the operation. This is a very complex procedure. However, nowadays a transcatheter aortic valve implantation (TAVI) can replace all that for suitable patients.
It uses a thin tube that is inserted – usually through your groin or wrist – to reach the valve and deploy a folded valve that unfolds and sits on top of the natural valve. The heart doesn’t need to be stopped and the old valve is not removed.
Recently, transcatheter mitral valve repair or replacement is becoming an option for selected patients. The MitraClip has recently been NICE approved, and involves a small clip being attached to your mitral valve. This treats mitral regurgitation by helping your valve to close more completely.
During the MitraClip procedure, a surgeon will guide a thin tube (or catheter) through to the mitral valve via a vein in your groin.
Can your body “reject” a heart valve?
All valve replacements are "biocompatible," which means your new valve will not be rejected by your immune system.
What are the risks of replacement heart valve surgery?
As with any surgery, there are risks from the anaesthesia and the procedure. The level of risk will depend on your age, other medical conditions you have and how many procedures are done in a single operation. The main risks include infections, blood clots, strokes, a temporarily irregular heartbeat (arrhythmia) and reduced kidney function for a few days.
The risk of dying from an aortic valve replacement is around 1 to 2 per cent, which is much smaller than the risk of leaving severe aortic valve problems untreated. For mitral valve replacement surgery the risk of dying is around 2 to 6 per cent. Most people who survive surgery have a life expectancy close to normal.
What is the recovery like after heart valve surgery and how long does it take?
If all goes well, you will be helped to sit out of bed the day after the procedure and you can expect some discomfort after your operation and you will be given pain relief medication. Your pain level will be monitored to make sure you are as comfortable as possible.
You will have a structured daily programme to get you back on your feet. Many people return home within about a week of surgery. On average, it takes two to three months to fully recover, but this can vary greatly as it depends on your individual condition and the type of surgery you have had.
The traditional surgical approach may need a longer recovery period, while recovery may take less time with a transcatheter approach.
Following surgery, your quality of life should improve. In the short term after you go home, you will be advised by your surgical team on how to start exercising gradually.
It is important to attend cardiac rehabilitation, where you can be helped to exercise safely, get advice about your medications, your nutrition and any psychological support you may need.
What research is happening?
The British Heart Foundation is funding my research into the best time to replace a valve.
There are two main aspects that govern this: how much the faulty valve will cause extra problems for the heart, and the ability of the heart to cope with this without much difficulty. We are focusing on the first.
When the valve does not work properly, it causes a loss of pressure, so the heart can’t pump blood to the rest of the body as effectively. We are therefore working on better methods to measure this loss in pressure. We capture the speed of blood flow using medical images and estimate the actual pressures that drive the blood flow, using models of fluid physics.
By combining advanced imaging and computer modelling technologies, we can accurately understand how much inefficiency the faulty valve is causing, without introducing an invasive sensor into the heart.
Meet the expert
Dr Pablo Lamata is a Reader in Computational Cardiology and a Wellcome Trust Senior Research Fellow at King's College London.
His research focuses on the combination of imaging and computational modelling technologies to improve the management of heart and circulatory diseases.