Understanding the heart
The heart has four chambers – two atria and two ventricles. The walls of these chambers are mainly made of special heart muscle. During each heartbeat both of the atria contract first to pump blood into the ventricles. Then both ventricles contract to pump blood out of the heart into the arteries. There are one-way valves between the atria and ventricles, and between the ventricles and the large arteries coming from the heart. The valves make sure that when the atria or ventricles contract, the blood flows in the correct direction.
What is the mitral valve?
The mitral valve lies between the left atrium and left ventricle. It allows blood to flow into the left ventricle when the left atrium contracts. However, when the left ventricle contracts, the mitral valve closes and the blood flows out through the aortic valve into the aorta (the main artery which takes blood to the body).
The mitral valve has two flaps (cusps). The cusps are prevented from turning inside out by thin strands of tissue called chordae. The chordae (not shown in the diagram) anchor the cusps to the inside wall of the ventricle. The valve or chordae may become damaged or scarred which can prevent the valve from working properly. This can lead to disorders called mitral stenosis, mitral regurgitation, or a combination of these two.
What is mitral regurgitation?
Mitral regurgitation is sometimes called mitral insufficiency or mitral incompetence. In mitral regurgitation the valve does not close properly. This causes blood to leak back (regurgitate) into the left atrium when the left ventricle contracts. Basically, the more open the valve remains, the more blood regurgitates, the more severe the problem.
What are the causes of mitral regurgitation?
Mitral regurgitation can occur if the valve is weakened or damaged. Causes include:
This is the most common cause. The tissues which connect the mitral valves to the heart wall can become weak and stretched over time, which results in the valves not shutting together properly.
Rheumatic heart disease
Rheumatic heart disease is a general term which means any heart problem which develops after having an episode of rheumatic fever.
Rheumatic fever is a condition which sometimes follows an infection with a bacterium (germ) called the streptococcus. Your body makes antibodies to the bacterium to clear the infection. But in some people the antibodies also attack various parts of the body, in particular the mitral valve.
Inflammation of the valve develops which can cause permanent damage and lead to thickening and scarring years later.
Rheumatic fever used to be common in the UK in the era before antibiotics, but is now rare. It is still quite common in some developing countries.
Mitral valve prolapse
This is also called floppy mitral valve. In this condition the valve is slightly deformed and bulges back into the let atrium when the ventricle contracts. This can let a small amount of blood leak back into the left atrium. As many as 1 in 20 people has some degree of mitral valve prolapse. It most commonly occurs in young women. It usually causes no symptoms as the amount of blood that leaks back is often slight.
The cause of most cases of floppy valve is unknown. It sometimes occurs with connective tissue disorders such as Marfan’s syndrome.
Other causes are less common and include:
- Hypertrophic cardiomyopathy – a disease where the heart muscle thickens and can distort the mitral valve.
- A heart attack (myocardial infarction), which can sometimes cause damage to the ventricle where the chordae are attached. This can cause rupture of the chordae, which distorts the mitral valve.
- Congenital heart problems. It is then usually part of a complex heart deformity.
- Infection of the valve (endocarditis).
- A complication of various other diseases.
What effects does mitral regurgitation have?
As the valve does not close properly, some blood is pumped back into the left atrium when the left ventricle contracts. Minor leaks do not matter much. However, with larger leaks, it causes an increase in the pressure in the atrium. Therefore, the wall of the atrium may become thicker (hypertrophy) and the atrium may enlarge (dilate). A ‘back pressure’ of blood may then cause congestion of blood in the blood vessels which bring blood to the left atrium (the pulmonary veins which bring blood from the lungs).
Also, if a lot of blood leaks into the left atrium when the left ventricle contracts, less blood is pumped into the body via the aorta. The heart compensates for this. The wall of the left ventricle may become thicker, the ventricle may enlarge, and the heart rate may increase.
What are the symptoms of mitral regurgitation?
The severity of symptoms can vary greatly depending on the underlying cause, how much blood leaks, and whether or not the left ventricle is diseased. Some people with mild regurgitation have no symptoms. If symptoms occur they can include:
- Shortness of breath. This tends to occur on exercise at first, but occurs at rest if the regurgitation becomes worse. This symptom is due to the congestion of blood and fluid in the blood vessels in the lungs.
- Fainting, dizziness or tiredness.
- Chest pains (angina) may develop if there is a reduced blood flow to the coronary arteries or if not enough blood gets to the thickened ventricle.
- The pulse may be faster than normal.
The symptoms often develop gradually over years. However, they can develop quickly if the damage to the valve occurs quickly (for example, following a heart attack).
What complications may occur with mitral regurgitation?
- Atrial fibrillation may develop in more severe cases. This is where the heart beats in a fast and irregular way. This occurs because the electrical signals in an enlarged atrium become faulty. The irregular heat rhythm can cause palpitations, and make you even more breathless. (See separate leaflet called ‘Atrial Fibrillation’.)
- Heart failure may develop and gradually become more severe. This causes worsening shortness of breath, tiredness, and fluid retention in various tissues of the body. (See separate leaflet called ‘Heart Failure’.)
- A blood clot may form within an enlarged left atrium. This is more likely if you have atrial fibrillation. A blood clot may travel through the heart, be carried in the bloodstream and get stuck and block a blood vessel in another part of the body. For example, it may get stuck in a blood vessel going to the brain and cause a stroke. (See separate leaflet called ‘Stroke’.)
- Endocarditis sometimes develops. This is an infection of the valve. (Damaged valves are more prone to infection than normal valves.) Unless promptly treated, endocarditis can cause serious illness. (See separate leaflet called ‘Endocarditis – Infective’.)
How is mitral regurgitation diagnosed?
A doctor may hear a heart murmur or other abnormal noises when listening with a stethoscope. Murmurs and noises are due to blood passing through abnormal valves, or to abnormal movement of valves. There are typical murmurs and noises that occur with mitral regurgitation. An ultrasound scan of the heart, called an echocardiogram (heart echo), can confirm the diagnosis.
What are the treatments for mitral regurgitation?
Mild cases may not require any regular medication. If you develop symptoms or complications, various medicines may be advised.
- Diuretics (water tablets) usually help if you are breathless. They make the kidneys produce more urine. This gets rid of excess blood and fluid which may build up in the lungs or other parts of the body with the back pressure from the heart.
- Angiotensin-converting enzyme (ACE) inhibitors are medicines which help to reduce the amount of work the heart does and to ease symptoms of heart failure.
- Anti-arrhythmic medication may be needed to control your heart rate if you develop atrial fibrillation.
- Warfarin (anticoagulation) is usually advised if you develop atrial fibrillation. This helps to prevent blood clots from forming.
Shocking the heart with an electrical current – this is also an option in some people who develop atrial fibrillation as a complication (described earlier).
Surgical treatment is needed in more severe cases:
- Valve repair may be an option in some cases.
- Valve replacement is needed in some cases. This may be with a mechanical or a tissue valve. Mechanical valves are made of materials which are not likely to react with your body, such as titanium. Tissue valves are made from treated animal tissue, such as valves from a pig.
If you need surgery, a surgeon will advise on which is the best option for your situation.
Antibiotics to prevent endocarditis
People with mitral regurgitation used to be given antibiotics before some dental treatments and some surgical operations. However, the National Institute for Health and Clinical Excellence (NICE) no longer recommends that they be taken routinely for any of these procedures. Antibiotics are now only offered to people who have an infection at the time of the operation.
What is the prognosis (outlook) for people with mitral regurgitation?
In some cases the disorder is mild and causes no symptoms. If you develop symptoms they tend to become gradually worse over the years. However, the speed of decline can vary. In many cases it can take years for symptoms to become serious. Medication can ease symptoms, but cannot reverse a damaged valve.
Surgical treatment has greatly improved the outlook in most people with more severe regurgitation. Surgery has a very good success rate.
Further help and information
British Heart Foundation
Greater London House, 180 Hampstead Road, London, NW1 7AW
Tel (Heart Help Line): 0300 330 3311 Web: www.bhf.org.uk
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