MITRAL STENOSIS

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.
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 (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 valve or chordae (thin strands of tissue that anchor the cusps) 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.
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.
The incidence of rheumatic fever has significantly reduced since the introduction of antibiotics. It is however still quite common in some developing countries including Pakistan.
Other causes
Other causes include:
• Deposits of calcium (calcification) in parts of the valve. This sometimes occurs in older people.
• Some congenital (present from birth) 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 there may be 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 coronary arteries (the arteries that take blood to the heart muscle).
• Chest infections. These are common.
• Coughing up blood-stained 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. 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 Atrial Fibrillation page xx).
• 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 (Heart Failure page xx).
• A blood clot may form within the enlarged left atrium. 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.
• Endocarditissometimes 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.
How is mitral stenosis diagnosed?
• Clinical examination
• ECG
• Echocardiography
• Chest X-ray
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.
• 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.
• Stretchingthe stenosed valve. This is a procedure that does not involve open heart surgery. 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 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.
• 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 (This procedure is not usually available in Pakistan).
If surgery is needed, a surgeon will advise on which is the best option for the situation.
What is the prognosis (outlook) for people with mitral stenosis?
In some cases, the disorder is mild and causes no symptoms. If a patient develops 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.

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