Mitral Stenosis

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. The valve has two flaps or 'cusps'. The valve allows blood to flow into the left ventricle when the left atrium 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 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

Other causes are rare and include:

• Deposits of calcium ('calcification') in parts of the valve. This sometimes occurs in older people.
• Some congenital heart problems. 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?

If you develop symptoms, they typically start between the ages of twenty and fifty. (That is, 10-20 years after having have had an episode of rheumatic fever as a child.) Symptoms 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) may develop if there is a reduced blood flow to the coronary arteries (the arteries that take blood to the heart muscle).
• Chest infections are common.
• Coughing up blood stained sputum may occur due to the congestion of blood and fluid in the lungs.

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. This is where 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 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 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.
• 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'.

How is mitral stenosis 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 which occur with mitral stenosis. An ultrasound scan of the heart called an echocardiogram (heart echo) can confirm the diagnosis.

Detailed ultrasound scans of the heart, and other heart tests, can assess the severity of the condition.

What are the treatments for mitral stenosis?

Medication

Mild cases may not require any regular medication. Although medicines cannot correct a stenosed mitral valve, some medicines may be prescribed to help ease symptoms, or to help prevent complications. For example:

• 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.
• 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.
• 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.

Surgical treatments

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 cusps come in 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, made from titanium. 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

You will normally be advised to take a short course of antibiotics if you have certain surgical procedures such as cystoscopy or colonoscopy. During these procedures, some bacteria may be 'pushed' into the bloodstream. The 'antibiotic cover' aims to kill any bacteria which may get into the bloodstream and helps to prevent endocarditis (described above). Most doctors who do these surgical procedures are aware of the need to recommend antibiotic cover to people with heart valve disease. The British Heart Foundation (contact details below) also lists a range of procedures that require antibiotic cover.

Dental treatments: until recently, it has also been advised that people with heart valve disease should take antibiotic cover when they have dental treatment. However, a guideline published in 2006 from the British Society for Antimicrobial Chemotherapy (BSAC) says that this is not needed in most situations. Their information aimed at patients says:

"A BSAC group of experts has spent a lot of time carefully looking at whether dental treatment procedures are a possible cause of infective endocarditis (IE) [sometimes called bacterial endocarditis (BE)], which is infection of the heart valve.

After a very detailed analysis of all the available evidence they have concluded that there is no evidence that dental treatment procedures increase the risk of these infections.

Therefore it is recommended that the current practice of giving patients antibiotics before dental treatment be stopped for all patients with cardiac abnormalities, except for those who have a history of healed IE, prosthetic heart valves and surgically constructed conduits.

The main reasons for this are the lack of any supporting evidence that dental treatment leads to IE and the increasing worry that administration of antibiotics may lead to other serious complications such as anaphylaxis (severe allergy) or antibiotic resistance.

The advice from the BSAC is that patients should concentrate on achieving and keeping a high standard of oral and dental health, as this does reduce the risk of endocarditis. Help for this will be provided by your Dental Professional."

However, this guideline is controversial. It has caused a lot of debate, especially from some cardiologists (heart doctors) and dentists who maintain that antibiotic cover is still needed for dental procedures. See references below for details of some articles that deal with this controversy. Your own doctor or dentist will advise for your own particular circumstance.

What is the prognosis (outlook) 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 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 and information

British Heart Foundation

14 Fitzhardinge Street, London, W1H 6DH
Tel - Heart Information Line: 08450 70 80 70 Web: www.bhf.org.uk