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Heart Valves
Written by Tim Sheppard MBBS BSc. Last updated 19/6/09

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What are heart valves?

Valves are put into a system to make sure that things are flowing in the right direction. If you want things to keep moving forward, then you need to put valves in to stop them turning round and going backwards. They're a bit like one-way doors, which let things through one way but not back again. Valves are often present in veins to stop blood going backwards, and you can also find them in man-made water pumps. Just like the heart, valves are put in a pump to make sure that the pumping action causes the contents to travel in the right direction.

So, when the heart is trying to pump blood around the body, it needs to try and make sure that it comes into one part of the heart and leaves through another. The way that it makes sure the blood is only going one way through the heart is to have valves directing the flow.

Inevitably, these valves are very important. If they weren't around, the blood wouldn't flow efficiently through the heart because some would keep slipping through the wrong way. Inefficient blood flow would mean that the body wouldn't get it's blood - and that's bad news for day-to-day living! If valves don't work, they can often make people very unwell. They are the mechanism by which the heart is able to ensure correct flow.

The heart valves are on the exit of each chamber. There are four chambers, so of course there are four valves. The most important (and loudest!) are on the left side of the heart because the blood is being sent from here to the whole body - so the pressure is higher. You need particularly strong valves, especially between the ventricle and atrium, because if it's not strong then the blood will slip back through the valve when the ventricle contracts.


What is the mitral valve?

The mitral valve is the valve which separates the left atrium and the left ventricle. It is sometimes known as the bicuspid valve because it has two flaps or cusps; and occasionally it is known as the left atrioventricular valve because it comes between the atrium and ventricle on the left hand side.

The reason it is called the mitral valve is because when the two cusps are together they were supposed to look a bit like a bishop's mitre (which is a hat that bishops wear). It takes quite a lot of imagination to persuade yourself that they really look like a bishop's mitre, but at least there is some kind of reasoning behind it.

The mitral valve is extremely important in making sure that the heart works properly. The left ventricle is the part of the heart which pumps blood to the whole body, and getting blood to important organs like the brain or the kidneys relies on the left ventricle working. If the mitral valve is too tight, then it may be that the left ventricle doesn't fill up so much. Alternatively, if the mitral valve leaks, some of the blood which is pumped by the left ventricle will leak back into the left atrium. If the heart is so inefficient, it can quickly cause issues. Furthermore, it can lead to lung problems. These two problems are called mitral stenosis and mitral regurgitation, and are considered below.


What is the aortic valve?

The aortic valve is really helpfully named because it is the valve which separates the left ventricle from the aorta. Because it has this position, it's actually an incredibly important valve. All the blood going out to the body has to come through the valve, so it needs to be flexible enough to let blood through. However, when the heart has finished pumping the blood out, the arteries are really stretched and they want to squeeze the blood back into the heart. The aortic valve is the only thing stopping all the blood from leaking back into the heart and therefore it is incredibly important for making sure that the heart works at all!!

The aortic valve is normally made up of three cusps. In some cases it is just made up of two, in which case it is referred to as a bicuspid aortic valve; although this isn't a problem on its own, people with a bicuspid aortic valve can go on to develop aortic stenosis, which isn't so good.

The cusps in the aortic valve are very interesting. When the heart is in systole, they are flattened against the side of the aorta. However, when the heart relaxes (in diastole), they open out to form three bowl-shaped cusps that block off the valve and prevent blood from flowing back. Because the blood will flow back as far as the valve, it will collect in these three little bowl-shapes, which is useful because two of them have holes leading to blood vessels out of them. These holes are leading to the arteries which supply the heart - the coronary arteries. So when the aortic valve is closed (when the heart is in diastole), blood is able to get to the heart's own vessels to supply it's own needs by going through these holes in the sides of the valves.


What is the tricuspid valve?

The tricuspid valve is the valve which separates the right atrium and the right ventricle. It is known as the tricuspid valve because it has three flaps or cusps; and occasionally it is known as the right atrioventricular valve because it comes between the atrium and ventricle on the right hand side.

Valves on the right hand side of the heart tend to be less important than the left hand side of the heart. However, the tricuspid valve is still important. If there is a problem with the valve, it can lead to problems with the heart, and changes to the tricuspid valve can often show up on clinical examination.

If the tricuspid valve becomes tight or stenosed then you obviously have tricuspid stenosis. This is a problem because it makes it harder to get blood into the right ventricle, and consequently increases the pressure behind the valve. It will show up on clinical examination because you will get a dominant A-wave in the JVP.

If the tricuspid valve gets a leak, you get tricuspid regurgitation. This is a problem because it means that even though the heart is trying to pump blood through, some of it will leak back. An inefficient heart will be a problem, although unless it is really bad, tricuspid regurgitation is not as big a problem as, say, mitral regurgitation. It will show up on clinical examination because you will get a dominant V-wave in the JVP. Because the blood is leaking back into the veins, it may leak back as far as the liver. If it does this, it may cause the liver to swell up with extra blood in it. The blood will transmit the beating of the heart, and so on examination you may also be able to feel an enlarged, pulsatile liver.


What is the pulmonary valve?

Because pulmonary refers to anything to do with the lungs, it makes sense that the valve which separates the heart from the lungs is the pulmonary valve. It comes between the right ventricle and the lungs, and it is important for making sure blood doesn't leak back into the heart when it's trying to get pushed through to pick up oxygen. Just like in the aorta, the pressure in the pulmonary arteries is high, and so the blood will be trying to leak back into the right ventricle. Only the pulmonary valve stands in the way.

As with other valves, the pulmonary valve can become too tight or it can leak. If it becomes too tight (pulmonary stenosis) then it makes it more difficult for blood to get into the lungs. The right side of the heart has to work harder to get blood through the valve, causing right ventricular hypertrophy, and blood might get backed up causing a raised JVP or dominant A-wave. It'll also be more difficult to get oxygen in the blood because the blood is finding it harder to get to the lungs; this can cause cyanosis and breathlessness, especially after exercise when the need for oxygen is greatest.

Pulmonary regurgitation, where there is a leak in the valve or the valve is just missing, is rarely a problem on its own because the heart can cope with a little bit of a leak. Unfortunately, anything more than a little bit of regurgitation suggests there is something else going on, and so it's a good idea to dig a bit deeper. It could be caused by high blood pressure in the lungs, or by an infection in the heart, both of which would need further treatment. It's also important to try and avoid it getting worse, because if it goes on too long, pulmonary regurgitation can make the right side of the heart work too hard. This leads to right ventricular hypertrophy and, eventually, right heart failure.


What is a (heart) murmur?

When something goes wrong with a heart valve, it doesn't stay silent. Because the heart valves make heart sounds, a change in the heart valve will make a change in the heart sound. This is a heart murmur.

One of the most important things to remember is that sounds come from vibrations. The heart valves closing cause vibrations which are picked up as sound through a stethoscope. If there is a tightening of the valve, then the blood is disrupted as it squeezes through the valve, and this disruption or turbulence produces vibrations which wouldn't normally be there. Heart sounds are brief because they are caused simply by the closing of the valve. Murmurs last longer because they are caused by the flow of blood through a valve, so you can tell that a murmur is different from a heart sound.

Murmurs caused by a leaky valve (or regurgitation) occur when the blood is leaking through, because there will be turbulence again. There will be disruption to normal blood flow because blood shouldn't be leaking through the valve, and so when it does, you get vibrations that can be picked up as sound.

Importantly, a murmur doesn't always mean something's wrong. Remember, a murmur is just sound, which is just caused by vibrations. A murmur means there's some kind of turbulence or disruption to blood flow. So in children, you can sometimes get murmurs that are totally innocent - it doesn't mean there's anything wrong, it's just one of those things which happens because there's a bit of disruption to blood flow. The thing to remember is that it can mean a valve is too tight there is a leak somewhere, which is why if a murmur is heard, you should be confident nothing is wrong before it is ignored.


What is mitral stenosis?

When the mitral valve becomes tight or narrow, it is called mitral stenosis. It can be caused by a number of things, but an infection is the most common: rheumatic fever is an infection that can sometimes lead to rheumatic heart disease and mitral stenosis, and an infection of the lining of the heart (infective endocarditis) can also sometimes cause stenosis of the mitral valve.

The reason that mitral stenosis is a problem is that it makes it harder for blood to get through the heart. It will get as far as the left atrium without problem, but from there, the heart is trying to squeeze a normal amount of blood through an abnormally tight opening. This means that the left atrium is working extremely hard, and the pressure will rise. This pressure can back up through the lungs, causing pulmonary hypertension. When the left atrium is too stressed out, it can also start to become chaotic in the way that it contracts, leading to atrial fibrillation. If the problem becomes too severe for too long, it leads to heart failure, so it needs to be sorted out.

Mitral stenosis may be detected on clinical examination. The best signs to look out for are a tapping apex and a murmur. The first heart sound is caused by the mitral valve closing after the blood has been pushed through. The turbulence causing a murmur in mitral stenosis comes from blood being pushed through the tight (or 'stenotic') valve, so the murmur will be heard before the first heart sound (i.e. between S2 and S1). This is known as a diastolic murmur - in this case, a mid-diastolic murmur, and it should be heard over the apex. It will probably be quite quiet unless the stenosis is really bad, but may be heard better if the patient is rolled onto their left, or if the bell of the stethoscope is used to listen. Unlike mitral regurgitation, the murmur from mitral stenosis should stay where it is - that is, you won't find that you can hear it under the armpit or somewhere else ('radiation').

There are other signs to look out for. If the problem has been going for a while, the stenosis may have caused atrial fibrillation. It may also have lead to pulmonary hypertension, which will cause a malar flush (redness across the face). This can go on to lead to growth of the right ventricle (right ventricular hypertrophy) which will be felt as a left parasternal heave. If it progresses to right heart failure, you will start to get a back up of pressure in the veins, which will lead to a high pressure in the capillaries, which will lead to pushing fluid out of the vessels, and the development of oedema or swelling in the feet or at the bottom of the back.

When you're thinking about treating the problem, medications may be enough to keep symptoms at bay, but ideally you need to do something with the valve. A surgeon could cut the patient open and change the valve with some kind of replacement. The alternative is something called a balloon valvuloplasty, which avoids open surgery, and just involves a small wire being fed through a blood vessel to the heart, where a balloon is inflated in the middle of the valve to open it.


What is mitral regurgitation?

When the mitral valve becomes loose or leaky, it is called mitral regurgitation or mitral incompetence. Because the valve is set up to stop blood from leaking, mitral regurgitation happens when part of the valve isn't working. This means not just the valve cusps, but also the ring that keeps the cusps in place (the annulus) and the papillary muscles and chordae tendineae that stop the cusps from prolapsing (that is, they stop the cusps from closing too far).

Regurgitation has a long list of causes. It may be because of an injury to the cusps, which can happen in infection of the heart lining (infective endocarditis) or when damage is done directly through trauma or a procedure such as balloon valvulotomy. It may also happen if inflammation and fibrosis stop the valve from working properly, which may happen with certain types of medication or after rheumatic fever. An atrial myxoma is a rare tumour of the atrium which can also cause the area around the mitral valve to fill with mucus, leading to the valve not working. Another very important cause is when the ring around the outside of the valve (the annulus, which keeps it in the right shape) is lax or weak, which can happen in connective tissues diseases such as Marfan's syndrome and systemic lupus erythematosus. Finally, if muscles that keep the cusps in place stop working or become disconnected, the cusps will not form a tight seal but will prolapse, causing serious mitral incompetence.

Obviously, this is a problem. If blood is not going forward through the heart, you're going ot find that the heart isn't doing it's job properly. In the short term, this can be massively problematic because unless the heart can try to make up for the leaky valve, you won't get enough blood out of the heart to the body. To try and make sure enough blood is pumping, the left ventricle will pump harder - and, hopefully, this will keep problems at bay. However, much like with mitral stenosis, you get back pressure on the lungs because the blood keeps leaking back, and the left atrium enlarges to try and reduce the pressure and help blood get from the lungs to the heart. The Left ventricle also grows (hypertrophy) in order to try to keep pumping the blood around the body, pumping harder to make up for all the blood leaking backwards. Eventually the heart just can't cope anymore, and you start to find a smaller amount of blood getting out of the heart to the body. The heart is failing.

Mitral regurgitation may be detected on clinical examination. The best signs to look out for are an apical thrill and a murmur. The apical thrill is when, on palpation, you can feel the vibrations almost as though you can feel the murmur over the apex beat. The first heart sound is caused by the mitral valve closing after the blood has been pushed through. The turbulence causing a murmur in mitral regurgitation comes from blood leaking back through the mitral valve when it should be closed, so the murmur will be heard all the time that the valve is shut (i.e. between S1 and S2). This is known as a systolic murmur - in this case, a pan-systolic murmur, and it should be heard over the apex. It may be quiet, but because it happens during systole, it should be easier to hear than mitral stenosis because the pressure is higher. It should 'radiate' round to the axilla - that is, you may be able to hear it round in the armpit.

When you're thinking about treating the problem, medications can actually be quite useful. The main thing to avoid is heart failure, when the left ventricle is having to work harder than it can. Because of blood leaking back, the ventricle has to pump harder in order to successfully get blood out to the body. However, if you give medications to reduce blood pressure, this decreases the pressure in the body that the ventricle is pumping against (the 'afterload'), and so it stops the heart having to work quite so hard.

Of course, if it starts to look like the left ventricle just isn't able to cope (i.e. it's not getting enough blood out), the valve will need surgery. The surgeons may decide to repair the leak, or to replace the valve altogether.


What is aortic stenosis?

As with the mitral valve, the aortic valve can become narrow and tight; and, as with mitral stenosis, aortic stenosis may be caused by a number of things including rheumatic fever. Stenosis is commonly due to the effect of stiffening over time, when the body leaves behind calcium on the valve (calcification) that makes it harder and harder to open until eventually it becomes the tight and narrow valve you see in aortic stenosis. It may also be due to an abnormality from birth called a bicuspid aortic valve, where the valve has two cusps instead of three, because this makes the valve more likely to get calcification.

It's not particularly helpful to have something getting in the way of blood travelling out of the heart. The pressure will build up behind this tight opening because the left ventricle is going to be desperately pushing to try and get the blood through. This build up of pressure causes the ventricle to change in shape, to hypertrophy - growing bigger but not in a good way. Instead of making a healthy heart, the growth makes the left ventricle work less well.

The tight opening means that not enough blood can get out especially when there is increased demand (e.g. during exercise). This leads to shortness of breath whenever you do exercise, because your body knows it's not getting enough oxygen around. The growth of the left ventricle combined with this problem with blood supply also leads to chest pain when the heart isn't getting enough oxygen (angina). Sometimes the heart is having so much trouble getting blood out that patients can faint (syncope). Over time, the build up of pressure behind the tight valve leads to heart failure, which is bad news for the patient.

Aortic stenosis may be detected on clinical examination. The best signs to look out for are a slow rising pulse, a thrusting or sustained apex and a murmur. A slow rising pulse is a lot like it sounds, with the tight valve slowing the speed at which the pulse can reach its peak. You may also be able to feel the apex beat thrusting beneath your hand when you feel for it during the examination.

The second heart sound is caused by the aortic valve closing after the blood has been pushed through. The turbulence causing a murmur in aortic stenosis comes from blood being pushed through a tight valve, so the murmur will be heard all the time that the valve is open (i.e. between S1 and S2). This is known as a systolic murmur - in this case, an ejection systolic murmur because the noise peaks in the middle. It should be heard over the aortic area - the sternal border of the second intercostal space on the right side. It should be one of the easiest murmurs to hear. It often 'radiates' up into the neck, so you can hear it on both sides when you put a stethoscope over the carotid arteries.

Of course, all this sounds terrible. In fact, a lot of people can have aortic stenosis and not every realise it. In a lot of people it causes no symptoms and causes no problem at all. The thing is, if a doctor finds it, it needs to be dealt with. Treatment of the symptoms (if there are any) is all well and good, but patients basically need a valve replacement. This can either be done with open surgery, or it can be done through a wire in an artery. The disadvantage over the wire in the artery is that it's a newer technique and you don't have so much control. Both techniques are good, and the surgeon needs to discuss with a patient what will be best for them. In children, it may be possible to use the wire technique simple to pass a balloon between the tight opening and inflate it to open the valve (a balloon valvuloplasty).


What is aortic regurgitation?

Again, like with the mitral valve, the aortic valve can become leaky, and it is referred to as aortic regurgitation. Instead of keeping the blood going in the right direction, blood leaks or regurgitates back into the heart. The valve can leak for a number of reasons, but the main things to think about are a problem with the valve itself, or a problem with the base of the valve (the aortic root, where it attaches to the heart). The most common cause is normal aging, when over a long period of time the valve is unfortunately more likely to leak. However, it's important to rule out a cause. The valve itself might be a different shape (e.g. a bicuspid aortic valve) or it might have been damaged (e.g. in infective endocarditis). If the problem is with the aortic root, then connective tissue diseases including Marfan's syndrome can lead to the root being too loose and allowing blood to leak back.

Obviously, this is a problem. If blood is not going forward through the heart, you're going ot find that the heart isn't doing it's job properly. In the short term, this can be massively problematic because unless the heart can try to make up for the leaky valve, the blood which is pumped out of the heart won't be getting very far before it leaks back in. To try and make sure enough blood is pumping, the left ventricle will pump harder - and, hopefully, this will keep problems at bay. However, much like with other valve problems, you get back pressure on the lungs because the blood keeps leaking back. Like with aortic stenosis, you'll get abnormal growth of the left ventricle (ventricular hypertrophy) in order to try to keep pumping the blood around the body, pumping harder to make up for all the blood leaking backwards. Eventually the heart just can't cope anymore, and you start to find a smaller amount of blood getting out of the heart to the body. The heart is failing.

Aortic regurgitation may be detected on clinical examination. Because the blood leaks back into the heart after the heart stops beating, the difference between the systolic and diastolic blood pressures will be high - i.e. a wide pulse pressure. Other signs to look out for are a collapsing pulse, capillary nailbed pulsation and a murmur. The second heart sound is caused by the aortic valve closing after the blood has been pushed through. The turbulence causing a murmur in aortic regurgitation comes from blood leaking back through the aortic valve when it is closed, so the murmur will be heard just after the valve has shut (i.e. at the beginning of diastole, between S2 and the next S1). This is known as a diastolic murmur - in this case, an early-diastolic murmur, and it should be heard over the aortic area (right sternal edge in the second intercostal space). It may be quiet because it happens during diastole (when the pressures around the heart are lower) but because it is to do with the aorta, it will often be possible to hear - especially if the regurgitation is severe.

In many patients, a little bit of aortic regurgitation won't be a problem. If there are no symptoms, it may be that it's not actually too dangerous and there's no need to do anything or worry about it for now. Over time, things may get worse, and certainly if there's symptoms you'll want to do something. Medications tend to focus on trying to lower the blood pressure so that the pumping heart doesn't have to pump too hard - it's already having to pump hard because the blood is leaking back, the last thing you want is for it to have to pump against really tight vessels. So medications like ACE-inhibitors may be useful at opening up the vessels to reduce the pressure a bit. However, surgical treatment is the only way of curing it, and that needs an open operation. This should be done as soon as possible in people whose aortic valves are causing a problem. Even if a patient has an infected heart valve, an operation should be carried out as soon as possible. Because man-made valves tend to be more likely to pick up any infection that's already there, a patient with infective endocarditis who is getting a replacement valve should get a homograft (i.e. a human valve) to replace theirs, rather than e.g. a metal one.


What is a valve cusp?

A valve cusp is one of the flaps of a particular valve which is used to stop the valve from letting blood come back through. So, when all the cusps meet in the middle, this stops blood from escaping back. Sometimes they are also known as leaflets. The mitral valve has two cusps, and all the others have three.

Of course, the cusp is not the only part of a valve - you have the annulus around the outside which keeps everything in place, and you need strings to secure the flaps, which in the heart are the chordae tendineae. However, the cusps are the most obvious and arguably the most important part of the valve - without them, all you've got is a hole!


Further Reading