Mitral Stenosis

Stenosis of the mitral valve is always the aftereffect of acute rheumatic fever. It affects primarily women (60–75 percent of all cases). It takes years for the gradual scarring process following the initial lesions of rheumatic fever to produce mitral stenosis. The interval between the attack (usually in childhood) and the development of symptoms varies widely. One factor is the severity of the attack of rheumatic fever. Furthermore, recurrent attacks lead to more-rapid

scarring of the valve. On average, mitral stenosis can first be detected 10 years after the initial attack; significant symptoms may not develop for another 10 to 30 years.

As described in chapter 1, the mitral valve consists of two leaflets separated by two commissures. The initial, rather minor damage to the valve during acute rheumatic fever consists of small lesions located usually at the edges of the leaflet. The healing and scarring process leads to the formation of adhesions between the leaflets, sealing the outer parts of the commissures, so that only the center part of the valve can open during diastole (see fig. 31, p. 129). The normal opening of the mitral orifice during diastole measures 4–6 cm² . Only when the sealing process reduces the size of the orifice to less than 2 cm² does the first effect of stenosis develop: the smooth flow of blood through the orifice becomes turbulent, giving rise to a murmur, which the examining physician can detect as evidence of mitral stenosis. However, at this point there is not enough resistance to flow to produce any effect on the circulation. Only further progression of the sealing process leads to the damming up of the orifice, raising the pressure in the left atrium. Usually when the opening is reduced to about 1.5 cm² , the patient begins to experience shortness of breath with activity. At this stage (mild mitral stenosis) disability may be minimal, merely requiring the patient to curtail strenuous activities. Sometimes postrheumatic progression stops before symptoms develop, and the patient may go through life without any serious consequences of the disease, in some cases even remaining unaware of its existence. Further progression of mitral stenosis, leaving an orifice of 1 cm² (moderate mitral stenosis), may produce more-pronounced symptoms and disability; furthermore, complications often develop. Severe mitral stenosis (with an orifice of 0.5–0.7 cm² ) produces serious disability—congestive heart failure and, in some patients, severe pulmonary hypertension.

Mitral stenosis differs from the other valvular diseases in that the mechanical obstacle to flow occurs before the blood enters the left ventricle; hence that important cardiac chamber is spared increased workload. Yet the blood dammed in the left atrium produces an effect on the pulmonary circulation similar to failure of the left ventricle. Consequently, shortness of breath resulting in disability develops early, as soon as mitral stenosis becomes mild or moderate, whereas in the other diseases dyspnea develops late, only

when the hypertrophied left ventricle can no longer cope with the overload.

The health of patients with mitral stenosis is frequently affected by complications, which may produce new disabilities or aggravate existing ones:

Atrial fibrillation . Elevated pressure in the left atrium resulting in its dilatation is a powerful contributing factor to atrial fibrillation, present in the majority of patients older than 50 years of age. The onset of atrial fibrillation, as a rule associated with a fast heart rate, is likely to produce disabling dyspnea or heart failure. However, response to treatment is usually satisfactory: as soon as the heart rate is slowed, the patient's symptoms abate or disappear.

Left atrial thrombi with emboli . Atrial fibrillation in the presence of a dilated left atrium facilitates the formation of thrombi attached to the atrial wall. Some portions of the clot may break loose and travel in the bloodstream as emboli, the most serious consequence of which is stroke—a relatively common complication of mitral stenosis. Embolic strokes are often reversible; that is, muscle paralysis and speech disturbance may only be temporary. Some patients, however, may suffer permanently disabling or even fatal strokes in the course of mitral stenosis.

Respiratory infection . Mitral stenosis affects blood flow through the lungs. The resulting congestion facilitates upper respiratory infections. Mild infections are inconsequential, but more-severe infections may greatly increase disability and precipitate heart failure.

Pulmonary hemorrhage . Spitting up of blood occurs commonly in mitral stenosis and is of no significance. Serious hemorrhaging from the lungs, requiring blood transfusion, is rare.

Pulmonary edema . Some patients with mitral stenosis are prone to pulmonary edema, particularly after eating salty food. Though potentially dangerous, pulmonary edema is easily treated, and recurrences can be prevented by restricting dietary salt or administering diuretics.

Severe pulmonary hypertension . In most cases of mitral stenosis elevation of pulmonary arterial pressure is only moderate. But in some patients small pulmonary vessels may react abnormally to

elevated pressure in the left atrium by developing severe pulmonary hypertension. This condition seriously compounds disability and may cause intractable heart failure.

Mitral stenosis can generally be diagnosed by performing a physical examination, though evaluation of its severity requires further tests. Among noninvasive tests, electrocardiographic changes and the size and shape of the cardiac shadow in a chest X ray are usually the first indicators in the diagnostic evaluation; an echocardiogram provides further data for estimating the severity of the stenosis and its effect on the circulation. The size of the stenotic mitral orifice can be calculated by means of cardiac catheterization, usually combined with angiography. These two invasive tests are typically performed when surgical treatment is being considered, in which case the extent of pulmonary hypertension and the presence or absence of mitral regurgitation and, in older patients, coronary-artery disease need to be determined.

Surgical repair or replacement of a stenotic mitral valve can not only restore adequate blood flow but also reverse all the secondary effects of mitral stenosis, even in the late stages of the disease. However, several cautionary factors must be considered before deciding on surgery. First, none of the available interventions is capable of restoring fully normal valvular function. Second, early disability in mitral stenosis may be amenable to effective nonsurgical treatment. Third, mitral stenosis often remains stable for years or even permanently, and moderate disability can be controlled by adjustments in life-style. Thus the consensus is that prime candidates for surgery are patients in congestive heart failure or otherwise seriously disabled who are unresponsive to intensive medical treatment.

Several kinds of medical (nonsurgical) treatment are available to patients with mitral stenosis. Diuretics, reinforced by restrictions on salt in the diet, can control fluid retention and the early stages of heart failure. Atrial fibrillation can be treated either by reducing the excessive ventricular rate or by restoring sinus rhythm. To inhibit clot formation, anticoagulants may be administered to certain patients, particularly those experiencing atrial fibrillation. Modification of physical activities may also be recommended.

Surgical treatment of mitral stenosis includes various approaches. In closed mitral valvotomy (without the use of the heart-lung machine)

the surgeon introduces a finger (or sometimes a special instrument) into the left atrium of a beating heart to break the adhesions between the two leaflets. This method, the first used in treating mitral stenosis, was the only one available until pump-oxygenators were developed. Open mitral valvotomy (with the use of the heart-lung machine) permits other techniques for separating the leaflets under direct vision. Mitral valvotomy has the advantage of preserving the natal mitral valve and is particularly successful in younger patients in whom the leaflets have not yet stiffened or calcified. A third alternative is replacement of the natal valve with a prosthetic valve or transplanted biological valve. A recent development, invasive but nonsurgical dilatation of the mitral valve (percutaneous balloon mitral valvuloplasty), has been shown to produce satisfactory results in some patients. The long-term effects of this procedure are not yet known.

The dramatic decrease in the incidence of rheumatic fever since the 1940s has greatly reduced the number of cases of mitral stenosis in the Western countries. Most persons in the United States treated for mitral stenosis are over the age of 50; many return for treatment because of the recurrence of stenosis following mitral valvotomy in the distant past or because of malfunction of prosthetic valves. Younger patients with mitral stenosis are mainly immigrants from less-developed countries.