Mitral stenosis is a narrowing of the mitral valve in the heart. This restricts the flow of blood through the valve. Back pressure which builds up behind the narrowed valve can cause various problems and symptoms. The more severe the narrowing, the more serious the problems. Medication can help to ease symptoms. Surgery to stretch, repair or replace the valve may be needed.
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 squeeze (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. The valve has two flaps (cusps). The valve allows blood to flow into the left ventricle when the left atrium squeezes (contracts). When the left ventricle contracts, the valve closes and the blood flows out through the aortic valve into the aorta. (The aorta is the main artery which takes blood to the body.)
The cusps are stopped 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 get damaged or scarred which can prevent the valve from working properly. This can lead to disorders called mitral stenosis, mitral regurgitation, or both.
What is mitral stenosis?
Mitral stenosis means that when the mitral valve opens, it does not open fully. It is narrowed (stenosed) when it is open. So, there is some restriction of blood flow from the left atrium to the left ventricle. This in turn means there is a reduced amount of blood that is pumped out into the body from the left ventricle. In general, the more narrowed the valve, the less blood that can get through, the more severe the problem is likely to be.
What are the causes of mitral stenosis?
Rheumatic heart disease
This is the cause in most cases. 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 germ (bacterium) 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.
Other causes include:
- Deposits of calcium (calcification) in parts of the valve. This sometimes occurs in older people.
- Some heart problems present from birth (congenital). It is then usually part of a complex heart deformity.
- Infection of the valve (endocarditis).
- A complication of various uncommon diseases.
What effects does mitral stenosis have?
If the valve is only mildly narrowed (stenosed) you may have no symptoms or problems. If the stenosis is more severe, it takes more effort for the left atrium to pump the blood through the narrowed valve to the left ventricle. This causes a rise in pressure in the left atrium. The walls of the left atrium then become thickened (hypertrophied) and the atrium enlarges (dilates).
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). In severe stenosis the back pressure can extend right back through all the blood vessels in the lungs to the right ventricle of the heart (pulmonary hypertension).
What are the symptoms of mitral stenosis?
Symptoms can include:
- Shortness of breath. This tends to occur on exercise at first but occurs at rest if the stenosis becomes worse. This symptom is due to the congestion of blood and fluid in the lungs.
- Fainting, dizziness or tiredness. If the amount of blood getting through to the ventricle is reduced, the output of blood from the left ventricle to the body is then reduced.
- Chest pains (angina). This may develop if there is a reduced blood flow to the arteries that take blood to the heart muscle (the coronary arteries).
- Chest infections. These are common.
- Coughing up bloodstained sputum. This may occur due to the congestion of blood and fluid in the lungs.
If rheumatic fever is the cause then, typically, symptoms start between the ages of 20 and 50. (That is, 10-20 years after having have had an episode of rheumatic fever as a child.)
What complications may occur with mitral stenosis?
The main possible complications that may develop include the following:
- Atrial fibrillation develops in about 4 in 10 cases. In this condition, the heart beats in a fast and irregular way. This occurs because the electrical signals in the enlarged atrium become faulty. The irregular heart rhythm can cause the sensation of a 'thumping heart' (palpitations) and make you even more breathless. See separate leaflet called Atrial Fibrillation for more details.
- 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 for more details.
- A blood clot may form within the enlarged left atrium, which does not fully empty into the ventricle with each heartbeat. A blood clot is more likely to occur if you also develop 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 for more details.
- 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 Infective Endocarditis for more details.
How is mitral stenosis diagnosed?
- People with mitral stenosis may get flushed cheeks.
- A doctor may hear a heart murmur or other abnormal noises when listening with a stethoscope.
- The pressure in the jugular vein that runs along the side of the neck may be raised. A doctor may be able to detect that the level of blood in this vein is higher than normal.
- The tip of the heart lies next to the chest wall and can normally be felt beating against it (the apex beat). This can be found further to the left in mitral stenosis if the heart is larger than normal.
- The liver may be swollen and you may develop a swollen stomach due to fluid.
- Murmurs and noises are due to blood passing through abnormal valves, or to abnormal movement of valves. There are typical murmurs and noises which occur with mitral stenosis. A scan of the heart, called a heart echo (an echocardiogram), can confirm the diagnosis.
- Other heart tests, including CT scans and MRI scans can help to assess the severity of the condition.
What are the treatments for mitral stenosis?
Mild cases may not require any regular medication. Although medicines cannot correct a narrowed (stenosed) mitral valve, some medicines may be prescribed to help ease symptoms, or to help prevent complications. For example:
- Angiotensin-converting enzyme (ACE) inhibitors are medicines which help to reduce the amount of work the heart does. One may be prescribed to ease symptoms of heart failure.
- 'Water' tablets (diuretics) 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.
- If you develop atrial fibrillation, several medicines can be used to slow the heart rate down. They include beta-blockers, calcium-channel blockers and digoxin.
- Anticoagulation medication 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.
Surgical treatment is needed in more severe cases. There are various options, depending of the exact site and severity of the stenosis.
- Stretching the stenosed valve. This is a procedure that does not involve open heart surgery. It is called percutaneous balloon commissurotomy or balloon valvuloplasty. (It is called a commissurotomy, as the area where the valve flaps (cusps) come into contact with each other are known as the commissures.) This is possible in many cases. It is done by inserting a thin tube called a catheter through the skin (percutaneous) into the main blood vessel in the top of the leg. The catheter is passed up to the heart. The tip of the catheter is placed in the mitral valve opening. A balloon at the tip of the catheter is then inflated to stretch the narrowed valve. This is often successful in widening the narrowed valve.
- Valve repair is possible in some cases. This is called mitral commissurotomy or mitral valvotomy. This is usually done by open heart surgery. Basically, the edges (commissures) of valve cusps that have become scarred and fused are shaved back to widen the narrowed valve opening.
- 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 (for example, those made from titanium), although they can produce a noise which can be heard outside the body. Tissue valves are made from treated animal tissue (for example, 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 stenosis used to be given antibiotics before some dental treatments and some surgical operations. However, the National Institute for Health and Care 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 outlook (prognosis) for people with mitral stenosis?
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. It often takes years for symptoms to become serious. Medication can ease symptoms but cannot reverse a stenosed (narrowed) valve. Surgical treatments have greatly improved the outlook for most people with more severe stenosis. Surgery has a very good success rate. However, as with all surgical procedures and operations, there is some risk involved when you have surgery. Complications due to surgery occur in a small number of cases.
Further help & information
Dr Tim Kenny
Dr Colin Tidy
Dr Adrian Bonsall