Blase A. Carabello, MD, FACC

1. What is the usual cause of mitral stenosis (MS)?

    Most cases of MS stem from previous episodes of rheumatic fever. Most cases of rheumatic heart disease are seen in patients who emigrate from areas of the world where rheumatic fever is still common, including the Middle East, Asia, and South Africa. Although the rate of rheumatic fever is similar in men and women, MS is three times more common in women than in men. However, as the population ages, mitral annular calcification is increasing as an etiology for MS.

2. What is the pathophysiology of MS?

    MS inhibits the normal free flow of blood from left atrium (LA) to left ventricle (LV) in diastole. Normally, diastolic LA and LV pressures equalize shortly after mitral valve opening. In MS, the stenotic valve impedes LA emptying, inducing a diastolic gradient between LA and LV (Fig. 31-1). Elevated LA pressure is referred to the lungs, where it causes pulmonary congestion. Simultaneously, impaired LA emptying reduces LV filling, limiting cardiac output. Thus, the combination of increased LA pressure and decreased cardiac output produce the syndrome of heart failure. Because increased LA pressure increases pulmonary pressure, the right ventricle (RV) becomes pressure overloaded, eventually leading to RV failure.

3. What are the typical symptoms of MS?

    Patients with mild disease are likely to be asymptomatic. As MS worsens, dyspnea appears, as does orthopnea and paroxysmal nocturnal dyspnea. If RV failure ensues, it may be accompanied by edema and ascites. During exercise, sudden increases in LA pressure and pulmonary venous pressure may cause rupture of anastomoses between pulmonary and systemic veins, leading to hemoptysis.

4. What are the signs of MS at physical examination?

    The gradient across the mitral valve holds the valve open throughout diastole, so that when it closes, S1 may be quite loud. The murmur of MS is a soft diastolic rumble heard near the apex. The murmur is often preceded by an opening snap, caused by sudden opening of the stiffened mitral valve from higher than normal atrial pressure. If pulmonary hypertension has developed, P2 is increased in intensity. If RV failure has occurred, elevated neck veins, ascites, and edema are likely to be present.

5. How is the diagnosis of MS made?

    The chest radiograph used to be at the forefront of diagnosis and still can be helpful today. It demonstrates an enlarged LA, seen as a double shadow along the right-sided heart border. Thickened lymphatics from high pulmonary venous pressure are seen as Kerley lines. The pulmonary artery (PA) is usually enlarged.

    Today, however, the echocardiogram is key to the diagnosis because it images the mitral valve so well. The valve is thickened and there is impaired opening of the mitral leaflets (Fig. 31-2). The LA is almost always enlarged. Valve area can be determined from direct visualization and planimetry of the mitral orifice, from Doppler assessment of the transvalvular gradient, and from measuring the delay in LA emptying. Pulmonary pressure, LV function, and RV function are also evaluated. In general, the main criteria for severe MS follow below. The severity of MS is estimated using the criteria given in Table 31-1.

6. Is there effective medical management for MS?

    Yes. Patients with mild symptoms and normal PA pressure can be treated with diuretics to reduce LA pressure and relieve pulmonary congestion. The combination of LA enlargement and continued inflammation from a smoldering rheumatic process predisposes patients with MS to develop atrial fibrillation (AF). AF with rapid heart rate affects the MS patient gravely because it diminishes transit time for blood flow from LA to LV, further increasing LA pressure and diminishing cardiac output. Rate control with beta-adrenergic blocking agents (β-blockers), calcium channel blockers, or digoxin is imperative. If these agents fail to control heart rate, cardioversion is indicated. Once AF has developed in the MS patient, the risk of stroke approaches 10% per year. Thus, anticoagulation to an international normalized ratio (INR) of 2.5 to 3.5 is mandatory unless a grave contraindication exists.

7. What is the definitive management for severe MS?

    If symptoms cannot be controlled easily medically or if asymptomatic pulmonary hypertension develops, this mechanical lesion must be treated by mechanical relief of the stenosis, because either condition worsens MS prognosis. In most cases, mitral balloon valvotomy is the preferred therapy. In this procedure, a balloon is passed percutaneously from the femoral vein across the atrial septum (by needle puncture) through the mitral valve, where it is inflated (Fig. 31-3). Balloon inflation ruptures the adhesions at the commissures caused by the rheumatic process, allowing as much as doubling of the mitral valve area and normalizing cardiac output, LA pressure, and PA pressure, in turn, relieving symptoms.

    Criteria have been established to determine whether balloon valvotomy should be performed or the patient referred for surgery. These four criteria are valve mobility, subvalvular thickening, leaflet thickening, and degree of valvular calcification. In addition to these characteristics, the degree of mitral regurgitation (MR) is assessed, because balloon valvotomy can worsen the degree of mitral regurgitation. Balloon valvotomy is ineffective when mitral annular calcification is the cause of MS.

    Class I indications for percutaneous mitral balloon valvotomy include the following:

8. What are the causes of MR?

    There are two broad categories of MR, primary and secondary. In primary MR, disease of the mitral valve causes it to leak, imparting a volume overload on the LV. In secondary MR, disease of the LV causes wall motion abnormalities, ventricular dilation, and annular dilation, rendering the mitral valve incompetent. The most common causes of primary MR include myxomatous degeneration and mitral valve prolapse, infective endocarditis, rheumatic heart disease, and collagen vascular disease. Causes of secondary MR include coronary artery disease and subsequent myocardial infarction, and dilated cardiomyopathy.

9. How does primary MR affect the LV?

    MR imparts a volume overload on the LV because the LV must pump additional volume to compensate for that lost to regurgitation. In some way, MR causes sarcomeres to lengthen, increasing end-diastolic volume, enabling the LV to increase its total stroke volume.

10. What are the other effects of primary MR on the heart and lungs?

    MR also causes volume overload on the LA, increasing LA pressure. Increased LA pressure leads to pulmonary congestion and the symptoms of dyspnea, orthopnea, and paroxysmal nocturnal dyspnea. Eventually MR may also lead to pulmonary hypertension, RV pressure overload, and RV failure. LA enlargement also predisposes the patient to atrial fibrillation.

11. What are the clues to MR on physical examination?

    The typical murmur of MR is holosystolic, radiating to the axilla. It may be accompanied by a systolic apical thrill; the apical beat is displaced downward and to the left, indicating LV enlargement. In severe MR, an S3 is usually heard. Here the S3 may not indicate heart failure but rather is caused by the increased LA volume emptying into the LV at higher than normal pressure.

12. How is the diagnosis of MR confirmed?

    Although both the chest radiograph and the electrocardiogram (ECG) may indicate LV enlargement, as with other valvular heart diseases, echocardiography is the diagnostic modality of choice (Fig. 31-4). It demonstrates LA and LV size and volume, allows assessment of LV function and PA pressure, and can reliably quantify the amount of MR present.

    Echocardiographic findings suggestive of severe MR include enlarged LA or LV, the color Doppler MR jet occupying a large proportion (more than 40%) of the LA, a regurgitant volume 60 ml or more, a regurgitant fraction 50% or greater, a regurgitant orifice 0.40 cm² or greater, and a Doppler vena contracta width 0.7 cm or larger.

    Severity of MR is established using the criteria in Table 31-2. Magnetic resonance imaging may be used to establish or confirm the severity of MR and its attendant volume overload.

13. Are there effective medical therapies for chronic primary MR?

    No. The asymptomatic patient will not benefit from medical therapy, and once symptoms develop, MR should be treated surgically. It should be noted that some patients with MR also have systemic hypertension, which should be treated in the same manner in which hypertension is routinely treated.

14. What is the definitive therapy for primary MR, and when should it be employed?

    As with all primary valve disease, MR is a mechanical problem requiring a mechanical solution. Here, however, the therapy for MR departs from that of other valve lesions. Unlike the aortic valve, the mitral valve serves to do more than just direct forward cardiac flow. The mitral valve is also an integral part of the LV, coordinating LV contraction and maintaining LV shape. When the valve is destroyed at the time of surgery, there is a precipitous fall in LV function postoperatively, which does not occur when the valve apparatus is conserved. Further, operative mortality is lower with valve repair than with valve replacement. Thus, every attempt should be made to repair rather than replace the valve at the time of surgery.

    Because the onset of symptoms worsens prognosis for patients with MR, mitral valve repair should be performed at that time. However, some patients fail to develop symptoms even though LV dysfunction has ensued. To guard against permanent LV dysfunction, mitral surgery should be performed before ejection fraction falls to 60% or less, or before the LV can no longer contract to an end-systolic dimension of 40 mm. The onset of atrial fibrillation or pulmonary hypertension is also an indication for surgery. It should be noted that not all mitral valves can be repaired. In such cases, mitral valve replacement is performed.

    Class 1 indications for mitral valve repair or replacement include the following:

15. How is secondary MR managed?

    This area is one of substantial uncertainty. In virtually all cases of secondary MR, there is also severe LV dysfunction and heart failure. As such, standard therapy for heart failure is indicated. When mitral surgery should be undertaken is unclear, but it is usually reserved for those patients who have failed medical therapy for heart failure, including cardiac resynchronization therapy when appropriate. The last decade has produced substantial interest in percutaneous approaches to MR. While none are yet approved for general use in the US, a percutaneously deployed device that clips the two mitral leaflets together may be effective in treating functional MR and in inoperable patients with primary MR. Results from Europe, where the device is commercially available, are promising.

16. What is mitral valve prolapse?

    Mitral valve prolapse (MVP) is the condition in which there is systolic billowing of one or both mitral leaflets into the LA (Fig. 31-5), with or without resulting MR. It is usually diagnosed by echocardiography, according to established criteria (valve prolapse of 2 mm or more beyond the mitral annulus, as seen in the parasternal long-axis view). Its prevalence is 1% to 2.5%.

17. What is the classic auscultatory finding in MVP?

    The classic finding is a midsystolic click and late systolic murmur, although the click may actually vary somewhat within systole, depending on changes in LV dimension. There may actually be multiple clicks. The clicks are believed to result from the sudden tensing of the mitral valve apparatus as the leaflets prolapse into the LA during systole.

18. What is the natural history of asymptomatic MVP?

    The course of patients with MVP can range from benign, with a normal life expectancy, to worsening MR and progressive LA dilation and LV dysfunction and congestive heart failure.

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