Mitral Stenosis
L. Leonardo Rodriguez
I. INTRODUCTION. Rheumatic disease remains the predominant cause of mitral stenosis (MS). However, this etiology is declining in the United States, and other causes of MS should also be considered (Table 4.1).
In general, MS progresses slowly, and once symptoms begin to develop, there follows a period of about 7 years before they become severe. Once debilitating symptoms develop, the 10-year survival rate without intervention is <15%.
II. CLINICAL PRESENTATION
A. Signs and symptoms
1. There is a long asymptomatic course in patients with MS. Most patients tend to develop symptoms in the fourth or fifth decade of life.
2. Predominant symptoms are exertional dyspnea, followed by paroxysmal nocturnal dyspnea and orthopnea. In general, patients with chronic MS are able to tolerate higher left atrial (LA) pressures. Patients with very high pulmonary vascular resistance may never experience paroxysmal dyspnea.
3. Precipitating factors, such as exercise, pregnancy, infection, emotional stress, or atrial fibrillation with a rapid ventricular response, worsen symptoms by increasing transvalvular gradients and LA pressure. Atrial fibrillation with rapid ventricular response is a typical exacerbating factor and can lead to pulmonary edema, even in those with moderate MS.
4. Hemoptysis can occur and likely represents rupture of small bronchial veins from elevated LA pressure. Hemoptysis is now relatively uncommon, but it can present as sudden unexpected profuse hemorrhage, blood-stained sputum associated with acute pulmonary venous congestion, pink frothy sputum accompanying acute pulmonary edema, and frank hemoptysis due to pulmonary infarction (rare). Acute bronchitis in the winter months is also a common finding.
5. LA dilation and stasis, particularly in the context of atrial fibrillation (persistent or paroxysmal), predispose to thrombus formation and embolic events. Sometimes, embolic events are the presenting symptoms in patients with MS. Embolic events can involve cerebral (most common), coronary, or peripheral circulation. The thickened and deformed valve is predisposed to the development of endocarditis. Ortner syndrome refers to hoarseness caused by the dilated LA impinging on the recurrent laryngeal nerve.
6. With long-standing MS with pulmonary hypertension, symptoms of right ventricular (RV) failure may develop. Anginal chest pain can be present in patients with tight MS and may reflect low cardiac output. Fatigue is a common expression of reduced cardiac output. In patients with pulmonary hypertension, it may be secondary to increased RV oxygen demand.
B. Physical findings
1. Inspection and palpation: Patients may have a malar facial flush, which is nowadays uncommon. The jugular venous pulse can demonstrate a prominent a-wave if there is elevated pulmonary vascular resistance and the patient is still in sinus
rhythm. Jugular venous pressure is elevated in RV failure. In advanced cases with low cardiac output, peripheral cyanosis occurs. The carotid upstrokes are of low amplitude when there is low cardiac output. The apex beat is not displaced, and the impulse and first heart sound can be palpable. An apical diastolic thrill may be felt in the lateral decubitus position in a third of patients. If there is pulmonary hypertension, a parasternal RV lift with a palpable P2 is present. A RV lift is seen in about 60% of the patients.
rhythm. Jugular venous pressure is elevated in RV failure. In advanced cases with low cardiac output, peripheral cyanosis occurs. The carotid upstrokes are of low amplitude when there is low cardiac output. The apex beat is not displaced, and the impulse and first heart sound can be palpable. An apical diastolic thrill may be felt in the lateral decubitus position in a third of patients. If there is pulmonary hypertension, a parasternal RV lift with a palpable P2 is present. A RV lift is seen in about 60% of the patients.
TABLE 4.1 Etiologies of Mitral Stenosis | ||||||||||||||
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2. Auscultation: The main auscultatory findings are shown in Figure 4.1.
a. S1 is usually loud except in patients with associated significant mitral regurgitation (MR). The diastolic opening snap (OS) is the most characteristic auscultatory hallmark of MS. However, as the mitral valve becomes more calcified and immobile, the OS may no longer be present. It may also be absent in patients with associated moderate to severe MR. An OS should be differentiated from an S3 gallop (Table 4.2).
b. The murmur of MS is typically a low-pitched rumbling mid-diastolic murmur, heard best with the bell of the stethoscope with the patient in the left lateral decubitus position. Presystolic accentuation is more often present in sinus rhythm (although it can be occasionally heard in patients with atrial fibrillation) and is not related to the severity of MS. Auscultation after a brief period of exercise may accentuate the murmur of MS as the increased output and heart rate increase the transvalvular gradient. The length of the murmur correlates better with the severity of MS than its loudness. The longer the murmur and the shorter the time interval from S2 to the OS, the more severe the MS.
c. Diminished flow across the mitral valve in cases of congestive heart failure, pulmonary hypertension, and aortic stenosis may reduce the diastolic murmur. The presence of a loud S1 may be the only clue to the presence of MS in these cases.
d. Other conditions that may simulate the clinical presentation of MS include LA myxoma and cor triatriatum. The tumor plop of a myxoma may be mistaken for an OS, and tumor obstruction of the valve leads to a diastolic murmur. In this condition, the physical findings will vary with changes in position.
Other conditions in which a diastolic rumble may be present include large atrial septal defect or ventricular septal defect, the Austin-Flint murmur of aortic regurgitation, which is typically preceded by an S3, and tricuspid stenosis. (The murmur is heard at the left sternal border and typically increases with inspiration.) Patients with severe MR may have a short diastolic rumble also preceded by S3, but the loud holosystolic murmur is the predominant finding.
 FIGURE 4.1 Finding on auscultation in mitral stenosis. Increased first sound. Louder pulmonary component of the second sound in patients with pulmonary hypertension. OS followed by diastolic rumble with presystolic accentuation. In patients with mild MS, the rumble may be present only at the beginning of diastole and after atrial contraction (points of maximal diastolic gradients). D, diastole; OS, opening snap; S, systole. |
TABLE 4.2 Differences between Opening Snap and Third Heart Sound on Auscultation | ||||||||||||
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III. ETIOLOGY (TABLE 4.1)
A. It is important to remember that up to 50% of patients with rheumatic MS are not aware of a history of rheumatic fever. Although the incidence of rheumatic fever is roughly equal between men and women, rheumatic MS develops two to three times more frequently in women.
1. Thickening and fibrosis of leaflets with commissural fusion is the pathognomonic finding. Commissural and chordal fusion and chordal shortening contribute to the development of stenosis. Calcium deposition occurs on the leaflets, chordae, and annulus, decreasing valvular excursion. As a result of these changes, the mitral valve becomes funnel-shaped with a decreased orifice size.
B. Causes of nonrheumatic MS include extensive annular calcification in the elderly, congenital malformation, radiation heart disease, lupus, and restrictive mitral valve
repair for MR. In addition, valvular thickening may result in MS after healed endocarditis of the mitral valve.
repair for MR. In addition, valvular thickening may result in MS after healed endocarditis of the mitral valve.
Calcific MS is increasingly recognized in the aging population. Frequently, but not always, it is associated with chronic kidney disease, but is also seen in elderly patients with aortic stenosis. The morphology of the mitral valve in calcific MS differs from rheumatic disease. The commissures are spared and the obstruction is caused by severe calcification of the mitral annulus, reducing the mobility of the leaflets and reducing the annular area. Management of these patients is different from those with rheumatic MS. There is no role for balloon valvuloplasty, and surgery is technically more difficult.
IV. PATHOPHYSIOLOGY
A. The normal area of the mitral valve orifice is 4 to 6 cm2. A pressure gradient between the left atrium and the LV (LA) develops when the valve area is <2 cm2. As the orifice area decreases, both the LA pressure and the transmitral pressure gradient increase (Fig. 4.2). Although the transmitral pressure is a useful indicator of MS severity, it is critically affected by the cardiac output and duration of diastolic filling period (gradient increases as the square of flow). The cross-sectional area of the mitral valve orifice is basically independent of flow considerations and thus can be considered a more robust measure of the severity of MS. The severity of the stenosis needs to be assessed in terms of not only the valve area and gradients but also symptomatology and exercise capacity. Mixed MS and MR is often associated with greater symptomatic impairment than might be predicted from the severity of either lesion alone. The current American College of Cardiology/American Heart Association (ACC/AHA) guidelines in Valvular Heart Disease define four stages of MS (Table 4.3).
B. Increased LA pressure is transmitted to the pulmonary vasculature, resulting in symptoms of pulmonary congestion. The passive increase in pulmonary venous pressure may elevate pulmonary vascular resistance (reactive pulmonary hypertension). Patients with increased pulmonary vascular resistance are less prone to pulmonary edema. Pulmonary hypertension is usually reversible if the stenosis is relieved. However, in long-standing, severe MS, irreversible obliterative changes in pulmonary vasculature may occur. Severe pulmonary hypertension can cause RV dysfunction and right-sided heart failure.
 FIGURE 4.2 Simultaneous left atrial and left ventricular pressure showing elevated diastolic pressure gradient. This is the hemodynamic hallmark of mitral stenosis. D, diastole; LAP, left atrial pressure; LVP, left ventricular pressure; S, systole. |
TABLE 4.3 Stages of Mitral Stenosis as Proposed in the 2014 American College of Cardiology/American Heart Association Guidelines | ||||||||||||||||||||
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