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Mitral Stenosis - Surgical Options

In last week’s article, we discussed the Atrio-Ventricular Valves. I will be detailing treatment options for one of the commonest diseases of the atrio-ventricular valves - MITRAL STENOSIS.

The mitral valve is a bi-cuspid valve - one with two leaflets - situated between the left atrium and left ventricle. It’s constant exposure to the high stress to which the left sided heart structures are subject causes a greater incidence of disease than other valves.

Stenosis - or narrowing - of the mitral valve causes a block of the smooth flow of blood from the left atrium into the left ventricle, and an ensuing build-up of blood in the lungs, resulting in symptoms of the disease. I will describe here the surgical strategies available to deal with this potentially fatal illness.

While medical treatment using drugs is helpful in relieving symptoms of mitral stenosis, definitive cure can only be provided by widening the orifice of the mitral valve which is narrowed in this disease. Although it is now possible to do this non-surgically by a Balloon Mitral Valvuloplasty (BMV), this procedure is not feasible for all patients, and surgery is still the mainstay of treating mitral stenosis when the disease process is sufficiently advanced.

When is surgery necessary in Mitral Stenosis ?

Severity of symptoms is one of the major deciding factors about whether to operate or not for Mitral Stenosis. Symptoms of patients with heart disease are usually graded by a method called the New York Heart Association (NYHA) classification. When a patient with Mitral Stenosis develops NYHA Class 3 or 4 symptoms (that is, if there is severe breathlessness or other symptoms even on mild exertion or at rest), surgery is indicated.

Another reason to operate on these patients is the development of a rhythm disturbance of the heart called Atrial Fibrillation, which is not controlled with drug treatment. In these patients, surgery may be needed even with milder symptoms.

The severity of the narrowing of the mitral valve itself is a factor. Normally, the valve measures 4.5 to 6 sq.cm. in area. When the area is reduced to below 1.5 sq.cm per sq.meter of body surface area, surgery may be required.

Yet another indication for surgery is the phenomenon of systemic embolism. In Mitral Stenosis, especially when associated with atrial fibrillation, there is a high risk of blood remaining stagnant inside the left atrium, and blood clots forming inside the left atrium. These blood clots may fragment, and enter the blood stream and pass into the blood vessels leading to the brain. This is called embolism. When clots block blood flow to a portion of the brain, a stroke occurs resulting in paralysis or other neurological phenomena. A series of embolisms can cause irreversible injury and is a definite indication for relief of mitral stenosis surgically.

In addition to these classical indications, there may be certain special situations where surgery may be opted for. While early surgery would be needed for an physically active person who needs a greater blood flow and cardiac output, a sedentary lifestyle would allow maintenance with medical treatment for a longer time.

What are the surgical options available ?

Broadly, three categories of operations are available for mitral stenosis - Closed Mitral Valvotomy or Commissurotomy, Open Mitral Valvotomy or Mitral Valve Repair, and Mitral Valve Replacement. I will discuss each of these briefly.

Closed Mitral Valvotomy/Commissurotomy (CMV or CMC)

Although used very infrequently in the Western world, this simple operation is still widely performed for mitral stenosis in countries like India (where I live). The operation itself is elegant in its simplicity. It is performed through an incision in the side of the chest (a anterior-lateral thoracotomy). The surgeon places a finger inside the left atrium. Using this finger as a guide, he/she then passes an instrument called a Tubb’s dilator into the left ventricle through a small opening in it’s wall, and thenacross the orifice of the mitral valve. When the Tubb’s dilator is opened by pressing on a handle, its blades widen, and tear or split open the narrow mitral valve, thus relieving mitral stenosis.

The operation has its own pros and cons. It is performed “blindly” with only the surgeon’s fingers for guidance. There is a risk of “over-splitting” which may result in the valve tearing too much and becoming leaky, a complication that can be life-threatening and that will require immediate valve replacement surgery.

On the other hand, it is simple, quick and in expert hands gives excellent relief of mitral stenosis. Since it does not require the heart to be stopped or opened, CMV does not require the use of the Heart and Lung Machine, an apparatus used in open heart operations. This greatly decreases the incidence of ill effects (and of course, the cost) related to the use of this apparatus and results in a very low incidence of complications.

The operation has its limitations. It cannot be used when the valve is calcified, when there is a blood clot in the left atrium, or in very severe disease where the mitral valve is badly scarred and distorted. But in developing nations like India, the operation is still the one of first choice for mitral stenosis.

Open Mitral Valvotomy or Mitral Valve Repair

This is an open heart operation to treat mitral stenosis. An open heart operation is one where the heart is stopped temporarily, while the circulation of blood is maintained artificially using an apparatus called the Heart-Lung machine. (I will describe this in a separate article later). The heart is then opened, the mitral valve visualised and its narrowing relieved.

The procedure is carried out through a vertical incision down the middle of the chest, and the breast-bone (sternum) is split using an electric saw. After the heart is stopped, the surgeon makes an incision in the left atrium. Using specially designed instruments, the valve is visualised. The severity of disease is assessed. If the valve is not too badly scarred, a repair is considered. Usually, in mitral stenosis, the two leaflets of the mitral valve are stuck to each other at the line of closure, called the “commissures”. Using a scalpel, the surgeon makes a cut at the commissures, and separates the stuck leaflets. If there are additional areas of narrowing below the leaflets - called “sub-valvar fusion” - those are also divided using a knife. Any areas of calcification are carefully removed. If in addition to mitral stenosis, there is a certain amount of “leakiness” of the mitral valve (mitral regurgitation) special techniques are required to correct it as well.

There are many advantages to performing a valve repair operation. Most important, by avoiding the replacement with an artificial valve, it obviates the need for life-long medication with blood-thinners (or anticoagulants). This is the major bug-bear of valve replacements, since excessive doses of anti-coagulants cause bleeding from minor injuries, while lesser doses may carry the risk of blood clots forming on the artificial valve with embolism and stroke. Frequent testing and monitoring of anticoagulant dosage is an absolute necessity and is inconvenient to the patient. Other advantages of valve repair are a suggestion of lesser complications and longer survival after surgery. There is also a reduced risk of infection of the valve (infective endocarditis) as compared to valve replacement.

The disadvantage of open mitral valvotomy for mitral stenosis (as well as for closed valvotomy) is the risk of recurrence of stenosis after 2 to 20 years. The actual risk differs from one patient to the other, but most operated patients will develop a second stenosis within 20 years of surgery.

Mitral Valve Replacement (MVR)

The third surgical option for mitral stenosis is to replace the native mitral valve with an artificial prosthesis. Artificial heart valves come in many different patterns, but all carry significant disadvantages. The ideal heart valve has not yet been discovered, but the present day prostheses are greatly superior to earlier models, and have much lesser risks than before. Considerable research is being made on further improving the design and structure of prosthetic valves.

Mitral valve replacement is an open heart operation. Similar to open mitral valvotomy, the surgeon opens the left atrium of the arrested heart, excises the mitral valve which is usually severely diseased, scarred or calcified, and inserts an appropriately sized artificial valve in its place. In recent years, a few surgeons have proved that when the native valve leaflets are retained (not excised), the heart functions more efficiently after replacement with a prosthesis. This “leaflet-preserving” mitral valve replacement is now more frequently performed.

Mitral valve replacement is usually reserved for severely diseased valves because of its greater morbidity. Lifelong medication with blood-thinners - or anticoagulants - is needed to prevent blood clots forming on the surface of the artificial valve. These drugs carry their own risks and limit the lifestyle of the patient. A small risk of infection of the artificial valve - infective endocarditis - exists, and this complication may be serious enough to warrant a repeat operation. So even minor infections need aggressive treatment in a patient who has had a prosthetic valve inserted. Any invasive tests or operative procedures, including tooth extractions and dental procedures, need “antibiotic cover” to prevent endocarditis. Valve replacement itself has its own procedure related complications like hemolysis (damage to blood cells due to injury by the foreign surface of the valve), peri-valvular leak (leak of blood around the valve due to sutures cutting out), prosthetic dehiscence (where the artificial valve may become loose and partly tear out from its bed) and prosthetic valve thrombosis (block of the valve by blood clot or fibrous tissue, which is more likely when anticoagulation is inadequate).

Associated Procedures

Maze Procedure for Atrial Fibrillation:
When atrial fibrillation unresponsive to medical treatment co-exists with mitral stenosis, it may or may not regress after correction of the mitral stenosis alone. Recently, Dr.James Cox devised a new operation called the Maze Procedure - named because it involves making multiple incisions into the left atrium, creating a “maze” through which electrical impulses wander and get lost ! The maze operation has had reasonably good success rates in controlling atrial fibrillation, but the outcome depends on the surgeon’s experience with the procedure.

Tricuspid Valve Repair:
In some cases of long standing mitral stenosis, the tricuspid valve is exposed to high back pressure and may become leaky - Tricuspid Regurgitation. When severe, this may need to be corrected. A De Vega annuloplasty is a commonly used method, where a purse-string suture taken around the circumference of the tricuspid valve is tightened just enough to reduce the leak across the valve.

Clot removal from left atrium:
When a blood clot is present in the left atrium, it is carefully removed and the left atrial appendage (a small sac like projection from the left atrium) is closed from within to reduce the risk of recurrent formation of blood clots.

Newer Trends in Mitral Valve Surgery

Minimal Invasive Valve Replacement:
The most recent innovation in mitral valve replacement surgery is to perform the entire operation with a small skin incision, and only partial division of the breast bone. Still in an experimental stage, this technique is projected to be more cosmetic and associated with less pain and discomfort post-operatively, allowing early discharge from hospital.

Homograft Mitral Valve Replacement:
With the more frequent performance of heart transplant operations, there has been a resurgence of interest in using mitral valves taken from human cadavers to replace diseased mitral valves. A group of surgeons from France have performed these operations successfully on a small subset of patients, but the long term results of the procedure are awaited. Benefits include the avoidance of anti-coagulants, and the lesser risk of artificial valve related complications.

I hope this answers most of your questions about mitral stenosis and its surgical treatment. If there are any areas that need further clarification, please let me know and I’ll try and explain them.

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