Chapter 19. Mitral Stenosis

• Exertional dyspnea and fatigue.
• Opening snap, diastolic rumble murmur, loud S1, presystolic accentuated murmur.
• Right ventricular heave and loud P2 if pulmonary hypertension and right heart failure are present.
• A2-OS interval ≤ 80 ms in severe mitral stenosis.
• Sinus rhythm or atrial fibrillation, notched P wave or P mitrale in leads II and III and/or biphasic P wave in V1, right axis deviation, high amplitude of P wave in lead II, and large R wave in V1 on electrocardiography.
• Flattening of left atrial border and/or double density, elevated left main bronchus, enlarged pulmonary arteries, and Kerley B lines on chest radiography.
• Thickened and/or calcified mitral leaflets and subvalvular apparatus resulting in “hockey-stick” motion of the anterior leaflet and fusion of commissures resulting in fish-mouth appearance of the mitral valve on two- and three-dimensional echocardiography.
• Increased transmitral valve gradient and reduced mitral valve area by planimetry, pressure half-time, continuity equation, or proximal isovelocity surface area method of quantification on Doppler echocardiography.

Mitral stenosis is a condition where the mitral valve area is reduced, causing obstruction of blood flow from the left atrium into the left ventricle during left ventricular diastole, which can lead to elevated left atrial pressure resulting in pulmonary hypertension, pulmonary edema, and right heart failure. The condition becomes clinically evident when the mitral valve area is reduced to approximately 2 cm2. Mitral stenosis occurs predominantly in adults and is one of the sequelae of rheumatic fever in about 90% of cases. Only about 50–70% patients recall having had antecedent group A β-hemolytic streptococcal tonsillopharyngitis. It has an indolent course, and the latent period can be as long as 40 years after the initial episode of rheumatic fever.

Rheumatic fever is a major public health problem in developing countries. The prevalence in developing countries is 2.2 to 2.3 per 1000 using clinical screening compared to 0.5 per 1000 in developed countries. If echocardiography is used to screen, the prevalence increases to 21.5 to 30.4 per 1000 in underdeveloped countries. Despite this fourfold difference, the prevalence in Western countries has not decreased substantially because of the increased rate of immigration from developing countries. Mitral stenosis still accounts for 10% of native valve pathology. The pattern of valvular involvement is associated with the rate of recurrent or reactivation of streptococcal infection and thus varies geographically. Individuals in developing countries are more likely to suffer from multiple episodes of rheumatic fever and thus become symptomatic at an earlier age compared to individuals in industrialized countries, who often do not present until they are ≥ 45 years old. Patients from developing countries tend to have more severe stenosis but less leaflet calcification and less atrial fibrillation. Due to the shorter latent period, younger patients tend to have more commissural thickening and pliable valves, whereas older patients with a longer latent period tend to have more calcified valves. A subgroup of patients, pregnant women, often present during the second trimester of pregnancy because increases in intravascular blood volume, cardiac output, and heart rate can make the impediment to flow more pronounced.

Anatomy

The mitral valve has two leaflets, anterior and posterior, which come together at the anterior and posterior commissures. The anterior leaflet occupies one-third of the saddle-shaped annular circumference, and the posterior occupies two-thirds of the circumference. Primary, secondary, and tertiary chordae tendineae originate from both the anterolateral and posteromedial papillary muscles of the left ventricle and insert into margin and base of both the anterior and posterior leaflets. A competent mitral valve requires precise and concerted motion of the leaflets, chordae, and left ventricular and atrial contraction. Alteration of any components of this complex geometry can result in stenosis, insufficiency, or both (Figure 19–1).

Etiology

Mitral stenosis is predominantly due to organic valve pathology and less commonly due to functional valve pathology where the mitral leaflets are anatomically normal but their movement is altered. Approximately 90% of organic native valve mitral stenosis cases are associated with rheumatic fever or rheumatic heart disease, where the autoimmune response to group A streptococcal infection results in commissural thickening and fusion, valve and subvalvular apparatus thickening, calcification, and fusion, and consequently, restricted motion of the valve leaflets (Figure 19–2). Infective endocarditis and severe mitral annular calcification account for about 3% of cases. Other conditions that have been associated with valve fibrosis are systemic lupus erythematous, rheumatoid arthritis, malignant carcinoid, and exposure to medications with direct serotonin receptors activation (ergotamine and methysergide for migraine headaches, fenfluramine and chlorphentermine for weight reduction, and pergolide and cabergoline for Parkinson disease). In < 1% of cases, mitral stenosis is due to congenital abnormalities and thus will present during infancy or childhood. These rare entities include supravalvar mitral ring, which is an abnormal connective tissue band located above the annulus or is adherent to the annulus and valve, hypoplasia of the mitral annulus, fusion of the commissures, a double orifice mitral valve, and a parachute mitral valve, where chordae from both the anterior and posterior leaflets insert into one papillary muscle. Another rare anomaly, cor triatriatum, can result in stenotic physiology without valve involvement. In this condition, a membrane or a fibromuscular band separates the left atrium into two compartments. This abnormal tissue may vary in size and shape, may have fenestrations, or can be funnel-shaped, which restricts blood flow from the left atrium into the left ventricle.

Functional native mitral valve stenosis is rare and can result from a mass, such as a left atrial myxoma or a large left atrial thrombus, advancing across the mitral annulus and occupying a portion of the mitral orifice during left ventricular diastole. Acquired mitral stenosis can also be iatrogenic where a portion of the mitral leaflet is inadvertently sutured to annular tissue during aortic or mitral valve surgery. Impingement of the anterior leaflet of the mitral valve with the CoreValve during percutaneous intervention to treat severe aortic stenosis resulting in stenosis has been reported.

Mitral stenosis can also involve prosthetic valves, where a bioprosthetic mitral valve can calcify over time with or without pannus overgrowth and cause similar pathophysiology seen in native valves. Mechanical mitral valves can also exhibit stenotic physiology when leaflet or poppet motion is impeded by thrombus, vegetation, or pannus.

Pathophysiology

The normal mitral valve area is 4–6 cm2. Mild mitral stenosis occurs when the mitral valve area is reduced to 2 cm2 and becomes severe when the area is ≤ 1 cm2. In normal conditions, during early left ventricular diastole, blood flow from the left atrium into the left ventricle occurs from passive filling, is rapid, and peaks early, followed by diastasis, until active filling occurs from atrial contraction. Equalization of left atrial and left ventricular pressure occurs during mid-diastole. In the presence of mitral stenosis, the rate of passive filling is reduced and sustained throughout diastole, such that at end-diastole, left atrial pressure is higher than left ventricular pressure (Figure 19–3).

Within a cardiac cycle, the diastolic filling period (seconds per cycle) is the time between mitral valve opening and closure. The diastolic filling time is determined using the following formula:

Mitral flow is a function of both the cardiac output and diastolic filling time and is calculated using the following equation:

During each minute, the diastolic filling period averages about 30–32 seconds. As heart rate increases, more time of the 1 minute is devoted to systolic ejection and isovolumetric contraction and relaxation, thus leading to a reduction in the diastolic filling period (Table 19–1). At rest, the diastolic flow across the mitral valve is about 200 mL/s. During exercise, cardiac output can triple, and along with tachycardia and the compensatory reduction in diastolic filling, transmitral flow and gradient will increase. Assuming no change in left atrial and left ventricular compliance, as the mitral valve area decreases, left atrial pressure and transmitral gradient will increase disproportionately with mitral flow (Figure 19–4). Chronically elevated left atrial pressure results in left atrial enlargement, which can lead to paroxysmal or permanent atrial fibrillation. Rapid atrial fibrillation reduces the diastolic filling time and cardiac output, which in turn, perpetuates the vicious circle by further increasing left atrial pressure. Chronic elevation of left atrial pressure causes a rise in pulmonary venous pressure and eventually pulmonary arterial pressure. When left atrial pressure exceeds 25 mm Hg, pulmonary edema develops. Consequently, chronic pulmonary arterial hypertension leads to right ventricular pressure overload and then volume overload when the right heart fails. Over time, the pulmonary vasculature becomes permanently damaged, leading to fixed pulmonary hypertension and elevation of pulmonary vascular resistance.

Mitral stenosis is associated with increased levels of prothrombotic metabolites. This hypercoagulable milieu poses a high risk of left atrial and left atrial appendage thrombus formation. Other factors that independently predict thrombosis in mitral stenosis are ≥ 1 year duration of atrial fibrillation, left atrial size ≥ 4.5 cm, left atrial spontaneous echo contrast on echocardiography, and a prior thromboembolic event.

Symptoms & Signs

Dyspnea and Fatigue

The classic symptoms of mitral stenosis are dyspnea and fatigue during exercise or in the setting of any condition that results in sinus tachycardia such as hyperthyroidism, hypovolemia, anemia, fever/infection, emotional stress, pregnancy, or exposure to sympathomimetic agents. Those with more advanced disease can experience shortness of breath at rest. In addition, patients are predisposed to developing atrial fibrillation, and the loss of atrial contraction and synchronized contraction with the left ventricle during each cardiac cycle can exacerbate dyspnea on exertion or even produce shortness of breath at rest, especially in patients with left ventricular dysfunction. Chest pain is rare, but patients may have intermittent or sustained palpitations from paroxysmal or permanent atrial fibrillation. One of the most devastating morbidities associated with mitral stenosis is embolic cerebral vascular accident, which occasionally can be the presenting symptom.

Congestive Heart Failure

As mitral stenosis becomes more severe, elevated left atrial pressure causes pulmonary vascular congestion. Pulmonary edema usually is manifested by dyspnea. In the early stages, pulmonary edema may occur only during exertion, and as the disease progresses, pulmonary edema occurs at rest. Occasionally, acute pulmonary edema can occur with exercise. Other signs of left heart failure include weight gain, orthopnea, and paroxysmal nocturnal dyspnea. In the late stages of mitral stenosis, there is irreversible adverse remodeling of the pulmonary vasculature, which results in elevated pulmonary artery pressure and pulmonary vascular resistance. Subsequently, right heart failure ensues when right heart hypertrophy can no longer adapt to the high pulmonary and right ventricular pressures. Symptoms of right heart failure include exercise intolerance, dyspnea, abdominal fullness, and lower extremity edema.

Hemoptysis

When severe mitral stenosis leads to severe pulmonary hypertension, rarely the bronchial veins can rupture and cause hemoptysis.

Physical Examination

Arterial Pulses

In severe stenosis, when stroke volume is reduced, pulses are diminished.

Rhythm

In the early stages of mitral stenosis, patients have normal sinus rhythm. In moderate to severe mitral stenosis, elevated left atrial pressure and atrial tissue fibrosis can lead to atrial arrhythmia, predominantly in the form of atrial fibrillation, where heart sounds will be rapid and irregularly irregular.

Opening Snap

The opening snap (OS) is due to the abrupt opening of the mitral leaflets during left ventricular diastole, where the leaflets are still relatively mobile. It may not be detected if the valve is severely calcified and restricted. The OS is heard best at the base of the heart but can also be audible at the apex. The duration between aortic valve closure and OS, the A2-OS interval, can be used to determine stenosis severity. The astute clinician can estimate the duration of this interval on auscultation. An A2-OS duration of <80 ms is indicative of severe mitral stenosis with a corresponding left atrial pressure of at least 25 mm Hg. As left atrial pressure rises, the OS occurs earlier, leading to a shorter A2-OS interval (see Figure 19–3).

Diastolic Rumble Murmur

The diastolic murmur in mitral stenosis is due to turbulent flow across the mitral valve. This murmur is low-pitch and is heard best at the apex using the bell of the stethoscope when the patient lies in the left lateral decubitus position. The diastolic murmur can also be more prominent after exercise, although tachycardia results in a shorter diastolic filling time, which may make auscultation more challenging. Maneuvers that increase venous return accentuate the diastolic murmur and shorten the A2-OS interval, whereas maneuvers that decrease venous return decrease the murmur and lengthen the A2-OS interval. The duration of the murmur, and not the amplitude, correlates with stenosis severity. In mild stenosis, the diastolic murmur is audible during late ventricular diastole when atrial systole occurs and represents “presystolic accentuation.” As the valve becomes more stenotic, the diastolic murmur is present throughout diastole. In very severe stenosis, the amplitude may be diminished significantly due to extremely low flow across the valve and may be inaudible.

Loud S1

Closure of minimally calcified and pliable mitral leaflets transmits as a loud S1. However, as calcification increases, the valve is less mobile and the S1 is soft.

Findings with Pulmonary Hypertension

A loud pulmonic valve closure (P2) can be audible in patients who have developed passive pulmonary hypertension. There may also be a systolic murmur from tricuspid regurgitation. If right ventricular hypertrophy is also present, a right ventricular heave may be palpable. Right heart systolic dysfunction can present as hepatomegaly, peripheral edema, and ascites.

Other Findings

If there is mixed valve disease, the holosystolic murmur of chronic mitral regurgitation is present. If there is concomitant aortic regurgitation or pulmonary insufficiency, a high-pitch blowing diastolic murmur can be appreciated. If a patient has left ventricular systolic failure, elevated jugular venous pressure, pulmonary rales, and lower extremity edema are seen.

Electrocardiography

The rhythm can be sinus or atrial fibrillation. A notched P wave or “P mitrale” in leads II and III and/or a biphasic P wave in lead V1 can be present, which reflect left atrial enlargement. If there is right ventricular enlargement and right ventricular failure, they manifest as right axis deviation, incomplete right bundle branch block, and tall R wave in V2 or deep S wave in V6. Right atrial enlargement is represented by high amplitude (≥ 2.5 mm) of the P wave in lead II (Figure 19–5).

Chest Radiography

Left atrial appendage enlargement on radiography results in straightening of the left superior cardiac border on the posteroanterior view, which is seen more commonly than the double density, where both the left and right atrial borders are seen when the left atrium enlarges to the right. Occasionally, the left main bronchus is also elevated due to left atrial enlargement. If there is enlargement of the pulmonary veins, an antler configuration is visible. In the frontal projection, when pulmonary hypertension coexists with mitral stenosis, the main pulmonary artery is enlarged and extends beyond the tangent line drawn from the aortic knob to the left ventricular apex (Figure 19–6). Chronically elevated pressure in the pulmonary veins can result in redistribution of blood flow to the upper lobes, seen as cephalization of the pulmonary vessels, and interlobular edema at the bases appearing as Kerley B lines. When pulmonary arterial hypertension ensues, pruning of the peripheral vessels is present. The left ventricular contour is usually normal, and if there is right heart failure, the right ventricle fills the retrosternal space in the lateral projection.

Echocardiography

M-Mode, Two-Dimensional, and Three-Dimensional Echo Imaging

Echocardiography is the imaging modality of choice to investigate the severity of mitral stenosis because it offers both anatomic and functional information. Due to commissural fusion, the anterior and posterior leaflets move anteriorly, and the E-F slope is reduced on M-mode images (Figure 19–7). Two-dimensional echo images show fusion of the commissures, thickened and calcified leaflets, and chordae tendineae. During diastole, the posterior leaflet is fixed and the anterior leaflet opens and appears like a hockey stick in the parasternal long axis view. In the parasternal short axis view, the mitral valve has a “fish-mouth” appearance in the open position (Figure 19–8). The left atrium is enlarged and could have visible thrombus. The Wilkins echocardiography score is used to determine suitability for successful balloon valvotomy, where 1 to 4 points are assigned in each of four categories: leaflet thickening, leaflet calcification, leaflet mobility, and subvalvular apparatus thickening. A score of ≤ 8 predicts a favorable outcome.

Over the past decade, the availability of real-time, three-dimensional (3D) echocardiographic imaging allows better visualization of the stenotic valve in 3D space and provides simultaneous acquisition of orthogonal views of the mitral valve, which improves the accuracy of planimetry. 3D imaging also provides additional information on the orientation of the subvalvular apparatus, which permits detailed planning prior to interventional procedures (Figure 19–9).

Quantification of Mitral Stenosis

The parameters used to diagnose and quantify mitral stenosis are depicted in Table 19–2. Continuous wave Doppler flow is used to measure the mean mitral gradient based on the Bernoulli equation where velocities across the mitral valve are measured and the mean pressure gradient is the Σ4v2/n, where v is the velocity and n is the number of individual velocities measured. The mean gradient is determined by tracing the velocity time integral (VTI), which then is automatically calculated by ultrasound software packages. This measurement is straightforward to obtain but is dependent on heart rate, heart rhythm, and global left ventricular systolic function. The mean gradient can be low in bradycardia or in low cardiac output states (Figure 19–10).

The mitral valve area (MVA) can be measured by planimetry of the mitral orifice in the parasternal short axis view. The area can be overestimated if the imaging plane is not at the level where the orifice is the smallest or underestimated when there is significant calcification. The availability of 3D echo images has improved the accuracy and reproducibility of this technique. The advantage of this method is that it is easy to obtain if image quality is excellent (Figure 19–11A).

Using Doppler measurements, estimating the MVA by pressure half-time (PHT) is the simplest Doppler method. The PHT is the time during diastole when the transmitral gradient falls to 50% of the initial peak gradient.

This method is invalid immediately after balloon valvotomy and in patients with severe aortic regurgitation or in conditions with high filling pressures or decreased left ventricular compliance. In atrial fibrillation, at least five measurements should be recorded and averaged (Figure 19–11B).

The second Doppler method used to calculate MVA is based on the principle of energy conservation. The continuity equation used to calculate the cross-sectional area of the mitral valve is:

where LVOT D is the diameter of the left ventricular outflow tract measured in the parasternal long axis view and VTI is the time velocity integral of the LVOT and mitral valve (MV), respectively. This method assumes that flow across the mitral valve is equivalent to flow across the aortic valve. It is inaccurate when there is significant concomitant mitral or aortic regurgitation. Mitral regurgitation can overestimate the severity of mitral stenosis, and aortic regurgitation can underestimate the severity mitral stenosis. In addition, poor visualization of the LVOT on two-dimensional imaging can significantly affect the MVA (Figure 19–11C).

The third Doppler method used in MVA calculation is the proximal isovelocity surface area (PISA) method, where

This method is the most complex and technically challenging because it requires measuring the radius of PISA in the left atrium and the angle between the two mitral leaflets in the left atrium. However, since it is uses only velocity measurements, it is unaffected by factors that alter flow conditions (Figure 19–11D).

Exercise-Stress Echocardiography

When symptoms are discordant with two-dimensional and Doppler findings, exercise-stress echocardiography can be used to assess mitral stenosis severity since exercise increases cardiac output and gradient without changing the MVA. The mean mitral gradient and pulmonary artery systolic pressure are measured during each stage of bicycle exercise and are correlated with the perception of dyspnea. Dobutamine stress can also be employed, and a dobutamine-induced mean transmitral gradient of ≥ 18 mm Hg has a 90% accuracy rate for predicting a high-risk subpopulation. The tricuspid annulus S-wave velocity reflects right ventricular function, and its response during exercise is an independent predictor of functional capacity. A reduced S-wave velocity is a marker of poor prognosis.

Cardiac Computed Tomography and Magnetic Resonance Imaging

Currently, computed tomography and magnetic resonance imaging are not routinely used to assess mitral valve morphology. However, due to high image resolution of anatomic features, the role of both imaging techniques is being investigated.

Cardiac Catheterization

When echocardiographic data are ambiguous and/or suboptimal, often in situations when left atrial and left ventricular compliance are altered, cardiac catheterization is used to simultaneously and directly measure the left atrial and left ventricular pressures during diastole. On the left atrial pressure tracing, the “a” wave is accentuated, due to elevated pressure during atrial contraction. The left atrial pressure tracing also records an enlarged V wave, but it is not exclusively seen in mitral stenosis (Figure 19–12). If direct left atrial access is not performed, then the pulmonary capillary wedge (PCW) pressure is used as the surrogate for left atrial pressure. When PCW pressure is used, the operator must be absolutely certain that the balloon right heart catheter is in the “wedged” position by evaluating the hemodynamic waveform and, ideally, by measuring the oxygen saturation distal to the catheter, which originates from the oxygenated blood of a pulmonary vein. The diagnostic finding of mitral stenosis is the presence of a diastolic gradient when the PCW pressure or left atrial pressure is measured simultaneously with the left ventricular pressure. The magnitude of difference in gradients at end-diastole reflects the severity of obstruction. Tachycardia will increase and bradycardia will decrease the transmitral gradients. The Gorlin formula is used to calculate the MVA, where

This formula accurately determines MVA only in patients with isolated mitral stenosis. In those who also have mitral regurgitation, the Gorlin formula overestimates the degree of mitral stenosis because it does not account for the increased regurgitant flow across the valve. Pulmonary arterial pressure is also measured and is usually elevated proportionally with left atrial hypertension in the absence of intrinsic pulmonary disease. Similar to noninvasive measurements, in the setting of atrial fibrillation, a minimum of five measurements should be collected and averaged since the mean gradient is dependent on the R-R interval.

Dyspnea on exertion and exercise intolerance are nonspecific symptoms that can be present in many other cardiac and noncardiac conditions. It is important to consider left and right heart cardiomyopathy; valvular pathology such as aortic stenosis, aortic insufficiency, and mitral regurgitation; pericardial disease such as chronic constrictive pericarditis; intracardiac shunting; and bradyarrhythmias and tachyarrhythmias. Obviously, numerous pulmonary processes can lead to dyspnea, including obstructive and restrictive lung disease and interstitial lung disease. Other etiologies of dyspnea and fatigue to consider are chronic anemia, hypothyroidism, thyrotoxicosis, and obesity. The likelihood of mitral stenosis should always be considered when evaluating pregnant patients with new-onset dyspnea.

Lifestyle Modifications

Patients with moderate or severe mitral stenosis should be counseled to avoid strenuous activities and thereby reduce risk of tachycardia. They should also be advised to consume a low-sodium diet in order to avoid fluid retention and to prevent development of pulmonary edema.

Pharmacologic Therapy

Secondary Prevention of Rheumatic Fever

Since recurrent rheumatic fever is associated with progression of mitral stenosis, secondary prevention with antimicrobial therapy is recommended and the duration of therapy is dependent on the individual's age, extent of initial cardiac involvement, and risk of recurrent infection. Intramuscular benzathine penicillin G (1.2 million units every 4 weeks) is recommended in most cases. In populations with a high incidence of rheumatic fever, a 3-week schedule is more effective. Patients with rheumatic fever with carditis and residual valvular disease should take antimicrobial therapy for 10 years or until age 40, whichever is longer. Those without residual cardiac disease should continue for 10 years or until age 21, whichever is longer. Individuals who had only rheumatic fever, without carditis, can take prophylactic therapy for 5 years or until age 21, whichever is longer. Alternatively, oral penicillin V 250 mg twice daily or sulfadiazine 0.5 g (< 27 kg) to 1.0 g (> 27 kg) daily can be used.

Atrial Fibrillation

Since tachycardia decreases the diastolic filling time, the ventricular rate should be aggressively treated with atrioventricular nodal blockers, including β-blockers, nondihydropyridine calcium channel blockers, and digoxin. When the tachycardia is refractory to atrioventricular nodal blockers, then pharmacologic cardioversion with antiarrhythmic medications or direct-current synchronized cardioversion is appropriate. In nonpregnant patients with atrial fibrillation, it is imperative that anticoagulation with warfarin be initiated with a therapeutic international normalized ratio goal of 2–3. The risk of systemic embolic events ranges from 1.5–4.7% per year without anticoagulation and decreases to about 0.7–0.8% per year on therapeutic warfarin. Successful valvotomy does not reduce the thrombotic risk, and thus patients still require indefinite anticoagulation. While tempting, there are no data to support empiric warfarin therapy in the absence of atrial fibrillation. Of note, the CHADS2 or CHA2DS2-Vasc used to estimate stroke risk associated with atrial fibrillation is not applicable in valvular or rheumatic mitral stenosis.

Congestive Heart Failure

Diuretics along with sodium restriction are used to treat pulmonary edema. In the setting of concomitant right ventricular failure, venodilators can be added.

Interventional Therapy

Mechanical therapy should be considered when the MVA is < 1.5 cm2 or when the mitral valve index is < 0.6 cm2/m2. In addition, when New York Heart Association Congestive Heart Failure (NYHA) Class III/IV symptoms become refractory to optimal medical, invasive intervention should be pursued. Currently percutaneous balloon valvotomy is the preferred method for enlarging the mitral orifice in a selected patient group.

Percutaneous Balloon Valvotomy

Percutaneous balloon valvotomy is reserved for individuals with pliable valves with minimal calcification and mild or no mitral regurgitation and can be considered in those who are poor surgical candidates with the above valve morphology. It can also be performed safely in pregnant patients. All patients considered for valvotomy need to have an invasive assessment of mitral valve hemodynamic data prior to the procedure and immediately after completion of the procedure. Patient selection is absolutely essential for procedural success. The Wilkins echocardiographic score of ≤ 8 predicts a very favorable outcome. On average, the mitral gradient decreases by approximately 7–10 mm Hg, mitral orifice increases by approximately 0.7–1 cm2, and cardiac output increases by about 0.6 L/min. The immediate, short-, and long-term results are excellent. For those with a score of ≤ 8, the survival rate at 12 years was 82% versus 57% in those with higher scores, and event-free survival was 38% versus 22%. At 19 years, restenosis-free survival ranges from 22 to 30%, and event-free survival ranges from 21 to 35%. Successful valvotomy can last for decades in flexible, noncalcified valves and is comparable to surgical commissurotomy. In some patients, the stenotic mitral valve can undergo repeat balloon valvotomy. In addition, successful valvotomy can result in normalization of pulmonary artery systolic pressure, regression of tricuspid regurgitation, and improvement of left ventricular systolic function if it is reduced prior to intervention (Figure 19–13).

Even though the success rate ranges from 85 to 99% in appropriately selected patients, the procedure is associated with a 0–0.5% mortality rate, up to a 12% incidence of hemopericardium, and a 1–2% rate of systemic embolization. The most catastrophic complication of balloon valvotomy is severe mitral regurgitation, which occurs in 2–10% of cases when the heavily calcified leaflets, and not the commissures, are split. In 1.6–3% of cases, surgical treatment of mitral regurgitation is necessary. Use of transesophageal and intracardiac echocardiography during valvotomy assists in balloon placement, septal puncture guidance, and detection of complications.

Surgical Commissurotomy

Surgical commissurotomy can be performed either by the closed or open approach. The surgical mortality rate is 2–5% in isolated mitral valve repair or replacement. After surgical commissurotomy, the postoperation mean mitral gradient and MVA can be measured noninvasively. In countries where percutaneous balloon valvotomy is not available or is cost-prohibitive, surgical commissurotomy can be performed with similar results. In populations with a high Wilkins echocardiographic score or atrial fibrillation, compared with balloon valvotomy, surgical open mitral commissurotomy or mitral valve replacement is associated with a higher event-free survival rate of 94% versus 80% at 9 years. However, compared to the percutaneous approach, surgical commissurotomy is associated with greater morbidity, longer hospital stay, and longer recovery. Similar to the balloon valvotomy, a relatively larger mitral orifice does not reduce the risk of thrombosis.

Mitral Valve Replacement

If the valve is heavily calcified or commissurotomy does not increase the mitral orifice area sufficiently, then mitral valve replacement is indicated. A Wilkins echocardiographic score > 8 and at least moderate mitral regurgitation are independent risk factors for surgery after balloon valvotomy. The choice of a bioprosthetic valve versus a mechanical valve depends on the age of the patient, existing comorbid conditions, and ability to comply with oral anticoagulant therapy. A mechanical valve is preferable in young patients in order to avoid accelerated bioprosthetic valve calcification, especially in those who are hemodialysis dependent. In women of childbearing age who are interested in future pregnancies, a bioprosthetic valve is often selected to avoid warfarin-induced embryopathy.

Prognosis of uncorrected mitral stenosis is closely linked with NYHA congestive heart failure class at the time of diagnosis. The 10-year mortality rate for patients who are asymptomatic is < 20%. NYHA Class II and III patients have a mortality rate of 40%, and patients in Class IV approach a rate of 80–85%. Sixty to 70% of patients with severe mitral stenosis die from congestive heart failure, 20–30% from systemic thromboembolism, and 1–5% from infection (Figure 19–14).