Disclosure
Background: Mitral stenosis is characterized by restriction of blood flow from left atrium (LA) to the left ventricle (LV) due to a narrowed mitral passage. It is an acquired valvular defect, usually a consequence of rheumatic heart disease, though cases of mitral stenosis due to congenital etiology are occasionally encountered. Extensive mitral annular calcification (MAC) can also result in mitral stenosis, particularly in the aged. Mitral stenosis is seen more often in women than in men, and it generally develops at an earlier age in the developing countries than the Western societies. In the latter, the incidence of rheumatic fever has declined precipitously over the past 4 decades. Patients with mitral stenosis usually remain symptom-free for years. After the mitral orifice is reduced to one third of its normal size, symptoms typical of left-sided heart failure, such as dyspnea on exertion, orthopnea, and paroxysmal nocturnal dyspnea, develop. Right ventricular (RV) failure gradually ensues, causing ascites and edema. Multiple imaging modalities can be used to diagnose mitral stenosis. Echocardiography has become the most important diagnostic tool for confirming the diagnosis and for quantifying the severity of mitral stenosis and determining the optimal timing for intervention. Asymptomatic individuals with sinus rhythm on ECG need no treatment. After atrial fibrillation develops, pharmacologic agents can be administered to control the ventricular rate and for anticoagulation to prevent thromboembolism. Symptoms of dyspnea and orthopnea improve with diuretics. As symptoms worsen, and pulmonary hypertension occurs, mechanical correction of the stenosis rather than medical therapy becomes necessary. These mechanical options, which include valvuloplasty and mitral valve replacement, have changed the natural history of mitral stenosis, and terminally bedridden patients with mitral facies, cardiac cachexia, and end-stage congestive heart failure (CHF) are no longer encountered in everyday clinical practice. Nonetheless, mitral stenosis is still endemic, and it continues to be a substantial problem in many countries. Pathophysiology: Normal and stenotic mitral valves In a normal heart, an initial pressure gradient between the LA and LV exists at the onset of diastole that starts the LV filling. At a certain point in the diastolic filling period, as LV continues to receive blood, LA and LV pressures become equal, terminating LV filling. At the end of diastole in patients with sinus rhythm, atrial contraction causes additional (presystolic) filling. In contrast, when mitral stenosis is present, obstruction at the LV inlet increases LA pressure. As a result, a constant pressure gradient between the LA and the LV exists, and filling continues throughout diastole. Pulmonary venous pressure also rises because of the backup of pressure from the LA into the pulmonary vasculature. In addition, the restriction of flow into the LV reduces overall forward cardiac output. Cardiac performance In patients with mitral stenosis, the myocardium itself is usually normal. In one third of patients, however, the LV ejection fraction is low despite normal muscle function. This condition usually results from reduced preload due to LV inflow obstruction, along with augmented afterload as a consequence of reflex vasoconstriction that occurs to compensate for the reduced forward cardiac output. RV pressure overload The RV is responsible for generating most of the contractile force that pushes blood across the pulmonary circulation and through the mitral valve. The back pressure from mitral stenosis that causes pulmonary venous hypertension leads to backward pressure overload all the way back to the RV. Initially reversible pulmonary vasoconstriction develops, increasing the pulmonary arterial pressure and adding to the burden on the RV that begins to dilate, along with enlargement of the central pulmonary artery. Finally, as mitral stenosis worsens, pulmonary vascular changes become fixed, RV failure sets in, and signs of CHF begin to develop. Frequency:
Mortality/Morbidity: The prognosis for patients with untreated congenital mitral stenosis is poor. Among the patients with rheumatic mitral stenosis treated medically, the 10-year survival rate is approximately 80% in mildly symptomatic patients with New York Heart Association (NYHA) class II disease and 38% in patients with NYHA class III disease. The 5-year survival rate among patients with class IV disease may be as low as 15%. Race: The progression of mitral stenosis is most rapid in tropical and subtropical areas and in patients of Polynesian or Alaskan Inuit descent. In India, critical mitral stenosis tends to occur at an early age, such as in children as young as 6-12 years. Sex: Rheumatic mitral stenosis occurs more frequently in women than in men, with a female-to-male ratio of 3:1. Age:
Anatomy: Proper function of the mitral valve requires the orchestration of many different components. Adequate mitral leaflet function depends on a mobile mitral annulus, intact chordae tendineae, normal-size atria that do not displace the orientation of the leaflets, well-functioning papillary muscles to maintain chordal tension as LV volume shrinks in systole, and a normal-sized ventricle that does not disorient the mitral leaflets or papillary muscles. The circumference of the normal ring of the mitral valve is generally 10 cm. It is a bicuspid valve consisting of a large anterolateral cusp and a posteromedial cusp shortened by half. The area of a normal mitral orifice is about 5-6 cm2. Mitral stenosis is generally classified as mild if the area is less than 4 cm2, moderate if it is less than 2 cm2, and severe if it is less than 1 cm2. Causes of mitral stenosis
Differential diagnoses
Rheumatic fever and carditis Approximately 60% of patients with isolated mitral stenosis had rheumatic fever, as have almost 90% of those with multivalvular disease. One of the critical consequences of acute rheumatic fever is pancarditis, which occurs in 40-50% of patients and which gradually progresses to chronic abnormalities. The mitral valve is frequently involved, with development of the characteristic fish-mouth appearance due to fusion of the commissures at the free edges. Subvalvular structures, such as chordae tendineae, gradually thicken and become calcified, leading to further restriction of leaflet mobility. The mean latent period between the acute rheumatic fever and mitral stenosis is usually 20 years. Another 7-10 years passes before patients become significantly disabled. Atrial septal defect with mitral stenosis In some patients, atrial septal defect (ASD) is associated with acquired mitral stenosis. This syndrome, called Lutembacher syndrome, is characterized an RV workload higher than that of an isolated ASD because of left-to-right shunting of blood with increased LA pressure. An enlarged pulmonary artery is the characteristic feature on chest radiographs. Congenital anomalies of the mitral valve Congenital mitral stenosis is rare. Some patients may have a single mitral papillary muscle in which all chordae attach to 1 spot, making the valve functionally stenotic (parachute mitral valve). The clinical presentation is similar to that of rheumatic mitral stenosis. Some patients who have cor triatriatum present with features similar to those of mitral stenosis. Such patients have a submitral membrane in the LA that may obstruct blood flow. Transthoracic echocardiography may show the membrane; however, in most instances, transesophageal echocardiography (TEE) is needed. Clinical Details: History Patients with mitral stenosis usually remain asymptomatic until the area of the valve is reduced to about one third of its normal size of 4 cm2. After the area is decreased to less than 4 cm2, symptoms may begin to develop. Symptoms The symptoms include dyspnea on exertion and fatigue. As mitral stenosis worsens, dyspnea on exertion (NYHA class II), progresses to orthopnea and paroxysmal nocturnal dyspnea (NYHA class III and IV due to LV failure). Subsequently, RV failure sets in that manifests as ascites and dependent edema. Physical examination Although mitral stenosis produces characteristic findings on physical examination, the diagnosis is frequently missed because the auscultatory findings may be subtle on inspection. Mitral facies can be seen in some patients. Palpation of the precordium reveals a quiet apical impulse. In pulmonary hypertension and RV hypertrophy, a RV parasternal lift may be encountered. On auscultation, a loud S1 is present because the transmitral gradient holds the mitral valve open throughout diastole until ventricular systole closes the fully opened valve with a loud closing sound (S1). In advanced mitral stenosis, as the mitral leaflets become so damaged that they neither open nor close well, S1 eventually quiets. S2 is physiologically split with a loud pulmonic component (P2) in the presence of pulmonary hypertension. S2 is usually followed by another early diastolic sound, called the opening snap (OS). The interval between S2 and the OS provides a good estimate of LA pressure and thus the severity of the mitral stenosis. When LA pressure is high, the OS closely follows S2 (0.06 s), but when it is normal, the OS occurs later (0.12 s), and it may mimic the S3 gallop. As mitral stenosis worsens, the S2-OS interval shortens. The OS is followed by the characteristic low-pitched early-diastolic murmur. This murmur can be soft in patients with low cardiac output. In such patients, modest exercise, such as isometric handgrip, may increase the intensity of the murmur. A presystolic accentuation of the mitral stenosis murmur is also heard coincident with the atrial contraction. In the presence of pulmonary arterial hypertension, another diastolic murmur of blowing quality due to resultant pulmonary regurgitation (Graham Steell murmur) often becomes audible. Mitral stenosis with atrial fibrillation Patients with mitral stenosis and atrial fibrillation frequently present with decompensated CHF. The rapid ventricular rate shortened the diastolic filling time to an insufficient period for the LA to empty. As a consequence, the LA pressure rises along with a decrease in forward cardiac output. Congenital mitral stenosis Symptoms usually appear within the first 2 years of life. Infants have delayed development and breathlessness due to heart failure. Cyanosis and pallor may be noted. The heart is enlarged as a result of dilatation and hypertrophy of the RV and LA. Rumbling apical diastolic murmur is usually audible followed by a loud first sound. The OS is usually absent. Preferred Examination: Echocardiography, especially Doppler echocardiography, is the procedure of choice for evaluating the degree of mitral stenosis and in most of the patients this may be adequate for the planning of therapeutic interventions. Echocardiography Echocardiography generally provides sufficiently detailed images of the mitral valve and is the most important diagnostic tool in establishing the diagnosis. Doppler echocardiography is used to accurately depict the severity of mitral stenosis. Usual 2-dimensional (2D) echocardiographic findings include thickened mitral valve cusps, an enlarged LA with a normal or small LV, and reduced size of the mitral valve orifice in diastole. A diminished E-F slope is noted on M-mode images. Doppler studies demonstrate an increased mean pressure gradient across the mitral orifice and help in quantifying the severity of mitral stenosis. Electrocardiography If the patient is in sinus rhythm, LA abnormality is usually present on the electrocardiogram. LA abnormality is manifested by prolongation of the P wave that has a double-saddleback contour (p mitrale) in limb lead II. This contour represents right atrial p wave followed by delayed LA P wave due to an enlarged left atrium. LA abnormality is seen as a terminal negative deflection following the initial upright p wave in the chest lead V1. The main rhythm is usually sinus in the beginning. However, atrial fibrillation increases in frequency as mitral stenosis advances. If pulmonary arterial hypertension has developed, electrocardiography may show signs of RV hypertrophy. Limitations of Techniques: False findings on echocardiography are uncommon.
Rheumatic mitral stenosis
Findings: Chest radiograph in mitral stenosis may exhibit certain specific and non-specific findings that are generally a consequence of left atrial enlargement, mitral calcification, pulmonary hypertension, and CHF. Left atrial enlargement The characteristic radiologic finding of mitral stenosis is selective left atrial enlargement. An enlarged left atrial appendage, as shown by convexity at the left upper cardiac border just below the left main bronchus, suggests a rheumatic etiology. Generalized left atrial enlargement, particularly on the anteroposterior chest radiograph, alters the left border of the cardiac silhouette so that it becomes straight in contrast to its usual mild concavity beneath the pulmonary artery shadow. A double contour or double convexity may be discernible along the right cardiac border. On the lateral chest radiograph, an enlarged LA is seen as posterior displacement of the upper cardiac border inferior to the tracheal bifurcation. In fact, a lateral chest radiograph obtained during barium swallow study may show a large left atrium impinging on the esophagus and displacing it backward and to the left instead of its usual rightward displacement. Severe LA dilatation may cause aneurysmal enlargement, and the left atrium approaches within a few centimeters of the chest wall on 1 or both sides, as seen in long-standing mitral regurgitation with atrial fibrillation. LV is usually not enlarged in isolated mitral stenosis unless it is associated with clinically significant mitral regurgitation. Calcification Calcification may be detectable on the plain radiograph. It may be either in the wall of the left atrium or in a blood clot lining the atrial wall. This kind of calcification shows as a curvilinear structure and lies fairly high on the cardiac silhouette. Fluoroscopy can be used to identify dystrophic calcification in the mitral valve cusps in long-standing rheumatic heart disease. MAC may be seen in the shape of an ellipse, usually open medially in a J, U, or horseshoe shape. In addition to causing mitral stenosis, the dense calcification may interfere with valve closure and cause mitral regurgitation. Pulmonary hypertension In the presence of pulmonary arterial hypertension, the main pulmonary artery and central pulmonary vessels appear enlarged, with pruning of the peripheral vessels. Pulmonary congestion Mitral stenosis causes pulmonary venous hypertension that appears as increased vascularity on chest radiographs. Selective blood diversion to the upper lobes distends upper-lobe veins and constricts lower-lobe veins. Kerley septal costophrenic B lines represent interstitial edema. Pulmonary alveolar edema may appear as confluent pulmonary shadows present mainly in the perihilar region. The edematous interlobular septa of the lungs can be identified on the chest radiograph as opaque lines of different lengths, depending on their location. Kerley first described these lines, designated A, B, and C, which are known as Kerley lines. A lines are 5- to 10-cm long and nonbranching; they fan radially upward and outward from pulmonary hilum. B lines are best seen in the lower lung zones, perpendicular to the pleural surface; these are shorter than 2 cm. The combination of A and B lines creates a reticular pattern, called C lines, that are transient and difficult to visualize. All of the Kerley lines represent edematous interlobular septa. The pulmonary lobules tend to be large and oriented obliquely to the pleura in the upper lobes, whereas in the lower lobes, they are shortened and perpendicular to the pleural surface. This feature results in the characteristic appearance of the B lines, which are the ones most readily identified on the chest radiograph. Miscellaneous findings Pulmonary hemosiderosis develops in long-standing mitral stenosis and pulmonary hypertension. It is seen on the chest image as fine punctuate opacities throughout the lungs. They may also occur as recurrent hemorrhages seen as iron-containing deposits in the pulmonary tissue. Pulmonary ossified nodules, defined as multiple discrete calcified opacities of up to 10 mm in diameter, may be seen at the bases of the lungs as well. Degree of Confidence: The degree of confidence is reasonably good. False Positives/Negatives: Findings are sometimes nonspecific. |
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Findings: CT scans occasionally depict calcification in the enlarged left atrium in patients with mitral stenosis. It may be seen to occupy the wall of the atrium, or it may be within a thrombus attached to the wall. Whenever calcification is observed in the atrial appendage, it generally indicates associated mitral stenosis. Calcification in the wall of the atrium or in the appendage is usually considered an unfavorable prognostic sign. Degree of Confidence: When calcification in the atrium is suspected but not positively identified on the chest radiograph, fluoroscopy or CT can be used to confirm the diagnosis. In the current era, CT scanning is rarely performed because echocardiography has gained widespread usage because of its portability and an absence of the risk of radiation. False Positives/Negatives: False findings are rare.
Findings: In patients with mitral stenosis, MRI can be helpful in cases if Doppler echocardiographic findings are insufficient or inconsistent with clinical data. Pulse sequences With recent technologic advances in magnetic resonance (MR) computer technologies, many pulse sequences can now be used for cardiac MRI. The 2 main pulse sequences can be described as dark-blood and bright-blood techniques. With dark-blood techniques such as spin-echo (SE) and fast SE (FSE), fast flowing blood appears black and hypointense, and it is principally useful for delineating the structure of cardiac chambers and the lumina of blood vessels. In contrast, the bright-blood techniques, such as gradient-recalled echo sequences (GRE), depict flowing blood as white and hyperintense. This appearance can be used to determine gradients and flows. Imaging planes Imaging planes for MRI of the thorax are the 3 orthogonal planes: transverse, sagittal, and coronal. Because the cardiac axes are not parallel to the axes of the body, planes parallel and orthogonal to cardiac axes (short and long axes of the heart) are used for cardiac imaging. For the mitral valve in particular, a long-axis view of the mitral valve is obtained through the LV apex and the outflow tract for a 5-chamber view. SE MRI ECG-gated multisection SE and FSE MRI usually demonstrates thickening and bulging of the leaflets of the mitral valve. It may also show the sizes of the chamber, particularly an enlarged left atrium and a normally sized left ventricle. Cine GRE MRI Cine MRI is performed by using GRE pulse sequences at multiple phases of the cardiac cycle. These can be used to determine the degree of mitral stenosis on the basis of the size and extent of the abnormal flow jet during diastole. The best planes for obtaining the signal void representative of the abnormal flow jet include the 4-chamber view and the coronal oblique plane displaying the left atrium and the left ventricle. Velocity-encoded cine MRI With the help of velocity-encoded cine MRI, the maximum velocity of the mitral stenotic jet can be calculated on planes perpendicular and parallel to the direction of the flow. This velocity can then be plugged into the modified Bernoulli equation (gradient = 4 X velocity2) to determine the gradient across the stenotic mitral valve. Degree of Confidence: MRI may be used if echocardiographic visualization is inadequate. This problem occurs in approximately 10% of patients because of air-tissue attenuation of ultrasound. MRI is often used in associated complex congenital heart disease because of its 3-dimensional (3D) capabilities and high resolution. MRI is of limited use in patients with atrial fibrillation, a common finding in mitral stenosis. Irregular rhythm can be a potential source of error in the measurements. False Positives/Negatives: False findings are rare.
Findings: Echocardiography is the most widely used imaging modality in the evaluation of mitral stenosis. A full echocardiographic examination includes 2D transthoracic or TEE, Doppler echocardiography, and color flow Doppler imaging. In most patients, echocardiography can provide adequate information to formulate a therapeutic strategy without the need for cardiac catheterization. General findings In patients with mitral stenosis, characteristic findings on 2D echocardiography include thickening and reduced mobility of anterior and posterior mitral leaflets, with predominant involvement of the commissures, especially in rheumatic mitral stenosis. In advanced mitral stenosis, substantial calcification occurs within the leaflet and the subvalvular tissues, including the chordae tendineae and the papillary muscles. Leaflet motion at the tips is decreased in the beginning, sparing the body and leading to the characteristic doming of the mitral valve seen on 2D echocardiograms. The anterior leaflet assumes a hockey-stick appearance. The actual restrictive orifice of the mitral valve can be planimetrically measured in a parasternal short-axis view. In the M-mode, the thickened leaflets can be seen. Because of their limited mobility, flattening of the E-F slope is observed, which can be used to calculate the severity of mitral stenosis. Assessment of the severity of mitral stenosis Both continuous-wave and pulsed Doppler echocardiography can be performed at rest and with exercise to quantitate the transmitral gradient. Pressure half-time method for calculating the area of the mitral valve The pressure half-time (T1/2) is the time in milliseconds required for the peak pressure gradient to decline to one half of its original value. T1/2 can be calculated as follows: Mitral valve area = T1/2 ÷ 220 milliseconds. This relationship may be somewhat inaccurate in patients who just underwent balloon mitral valvotomy or in the patients with concomitant mitral regurgitation, aortic insufficiency, or decreased LV diastolic function. Continuity equation for calculating the area of the mitral valve The continuity equation for calculating the area of the mitral valve involves the determination of quantitative mitral valve flow and is applied as follows: A1(V1) = A2(V2), where A1 is area 1, A2 is area 2, V1 is velocity 1, and V2 is velocity 2. Flow and dimensions at the level of the mitral valve annulus or forward flow in the LV outflow tract can be used in this equation. Regurgitation or multivalve disease may make the calculations inaccurate. Assessment of other cardiac structures LA dilatation is seen in mitral stenosis. With stasis of blood flow especially in the presence of atrial fibrillation, intramural or intra-appendage thrombus formation may be seen as echogenic mass. These findings are best delineated with TEE. The most common clinically significant sequela of mitral stenosis is secondary pulmonary hypertension with subsequent right-sided heart dysfunction and tricuspid regurgitation. The tricuspid regurgitation jet can be measured to determine the PA systolic pressure, by using the Bernoulli formula. The pressure gradient is calculated as 4V2, where V is the velocity jet measured in centimeters on the Doppler echocardiograph. Degree of Confidence: The degree of confidence is high. However, echocardiography has specific limitations. Because ultrasound is not transmitted well through calcified structures or bone, an appropriate acoustic window is necessary for optimal visualization. In adults, a noncalcified window must be obtained; this is typically in the intercostal spaces or from the subxiphoid positions. In patients with narrow intercostal spaces, imaging can be suboptimal. A greater limitation is the degree to which the air-filled structures reflect ultrasound. Intervening lung tissue in patients with obstructive lung disease can result in suboptimal or inadequate imaging as well. False Positives/Negatives: False findings are uncommon.
Findings: Cardiac catheterization Cardiac catheterization is usually unnecessary for assessing the severity of mitral stenosis. Nonetheless, coronary arteriography is usually performed in many patients with mitral stenosis are in an age group likely to have coronary disease exists if heart surgery is anticipated or if the patient has coexistent angina. In such cases, left- and right-sided heart catheterizations are performed to evaluate the coronary arteries, to confirm the transmitral gradient, and to determine the valve area by using the Gorlin equation, as follows: Mitral valve area = [CO(DFP X HR)]/37.6 X h1/2), where CO is cardiac output (in milliliters per minute), DFP is the diastolic filling period, HR is the heart rate, and h is the mean gradient. Need for catheterization Careful clinical evaluation and noninvasive assessment, particularly with 2D and Doppler echocardiography, can provide sufficient information to permit an informed decision in majority of patients. Preoperative catheterization is recommended for the following patients with mitral stenosis: (1) patients who have a discrepancy between clinical and echocardiographic findings; (2) patients who have associated chronic obstructive pulmonary disease, in whom the contribution of mitral stenosis to the symptoms must be determined; (3) patients in whom LA myxoma should be excluded; (4) patients who have angina pectoris or angina-like chest pain in whom associated coronary artery disease must be excluded; and (5) men older than 40 years and women older than 50 years who have risk factors for coronary artery disease or a positive stress test result and in whom surgery is planned. Critical narrowing of 1 or more coronary vessels occurs in approximately 25% of all adults with severe mitral stenosis. This finding is most common in men older than 45 years who have angina and risk factors for coronary artery disease Angiocardiography in Lutembacher syndrome Angiocardiographic findings in Lutembacher syndrome are similar to those in ASD. Other signs that may aid in the diagnosis include the following: enlargement of the RA and RV along with the pulmonary artery, re-opacification of the right side of the heart after left-sided opacification, and dilution in the RA in the presence of a large shunt. Degree of Confidence: The degree of confidence is good. False Positives/Negatives: False findings are rare.
Intervention: The prophylaxis, evaluation, and treatment of mitral stenosis may involve the medical approaches and surgical or percutaneous approaches, such as balloon mitral valvotomy (balloon mitral valvuloplasty).
The prognosis for patients with untreated congenital mitral stenosis is poor. The results of surgical valve replacement are mixed; a mitral valve prosthesis is usually required, and this must be replaced as the child grows. Patients must undergo anticoagulation therapy with warfarin for the prevention of stroke and prosthetic valve thrombosis. Complications of overanticoagulation or underanticoagulation frequently occur. Balloon mitral valvuloplasty has been used as a palliative procedure; the results have been mixed and depend on the structure of the valve and the papillary muscles.
Prophylaxis
Patients with mitral stenosis due to rheumatic heart disease should receive penicillin prophylaxis for beta-hemolytic streptococcal infections and prophylaxis for infective endocarditis. In patients with valvular heart disease, concomitant conditions, such as anemia and infections, should be treated promptly and aggressively.
Adolescents and young adults with severe valvular heart disease should be advised to avoid entering occupations that require strenuous exertion. Asymptomatic patients with moderate mitral stenosis should be reevaluated yearly. Heavy exertion is contraindicated in symptomatic patients.
General drug treatment
In symptomatic patients with mitral valve disease, considerable improvement can be achieved with the use of oral diuretics and the restriction of their sodium intake.
Digoxin does not affect the hemodynamics and usually does not benefit patients with mitral stenosis and a sinus rhythm. However, it is useful in reducing the heart rate in those with atrial fibrillation with or without right-sided heart failure. Beta-blocking agents and rate-slowing calcium antagonists may increase the patient's exercise capacity by reducing heart rate in those with a sinus rhythm or atrial fibrillation.
Hemoptysis is managed by using measures designed to reduce pulmonary venous pressure. These include sedation, upright positioning, and aggressive diuresis.
Anticoagulant therapy is helpful in preventing venous thrombosis, stroke, and pulmonary embolism in patients who have had 1 or more episodes of pulmonary emboli. Such patients include those who are at high risk of systemic embolization (eg, those with persistent or transient atrial fibrillation, especially elderly patients >70 y) and those with previous systemic emboli. Treatment with warfarin is indicated to maintain an international normalized ratio (INR) of 2.5-3.5.
No firm evidence suggests that anticoagulation reduces the incidence of pulmonary or systemic emboli in patients with a sinus rhythm and no prior history of embolization.
Treatment of atrial fibrillation
As an overview, patients with mitral stenosis and atrial fibrillation usually become decompensated. This occurs because the rapid heart rate reduces the diastolic filling time and, in turn, increases LA pressure and decreases cardiac output. The heart rate must be controlled promptly preferably with an infusion of diltiazem or esmolol for acute atrial fibrillation or with oral digoxin, a beta-blocker, or a calcium channel blocker in chronic atrial fibrillation. Anticoagulation and conversion to sinus rhythm should be undertaken either pharmacologically or with synchronized direct-current (DC) countershock.
Premature atrial contractions frequently precede atrial fibrillation. After atrial fibrillation develops, antiarrhythmic drugs may be ineffective in restoring a sinus rhythm because of the pathologic changes that occur in the atrium secondary to increased pressure and the arrhythmia itself.
After electrical cardioversion, a sinus rhythm can often be maintained with antiarrhythmic agents. This approach is especially effective in young patients with mild mitral stenosis but without marked LA enlargement who have been having atrial fibrillation for less than 6 months. In most adults, conversion to a sinus rhythm is rare.
Immediate treatment of atrial fibrillation should include anticoagulation and rate control. For anticoagulation, intravenous heparin should be started as a bridging therapy followed by oral warfarin to achieve an INR of 2.0-3.0.
For rate control, the ventricular rate should be slowed with intravenous digoxin and a beta-blocking agent or rate-slowing calcium antagonist. An effort should be made to reestablish a sinus rhythm by using a combination of pharmacologic treatment and cardioversion. If cardioversion is planned in a patient who has had atrial fibrillation for more than 24 hours before the procedure, anticoagulation with warfarin for more than 3 weeks is indicated. As an alternative, if a TEE shows no atrial thrombus, immediate cardioversion can be performed by using intravenous heparin.
Paroxysmal atrial fibrillation and repeated conversions, spontaneous or induced, pose a risk of embolization. In patients in whom the heart rhythm cannot be converted or in whom a sinus rhythm cannot be maintained, digitalis should be used to achieve a ventricular rate at rest at approximately 60 bpm. If this rate is not possible, small doses of a beta-blocking agent, such as atenolol 25 mg/d, may be added.
Multiple repeat cardioversions are not indicated if a sinus rhythm cannot be maintained while the patient is receiving adequate doses of an antiarrhythmic.
Patients with chronic atrial fibrillation who undergo open mitral valve repair or replacement may undergo the Cox maze procedure (atrial compartment operation). In more than 80% of patients undergoing this procedure, a sinus rhythm can be maintained postoperatively, and most patients can regain normal atrial function.
Latest trials have shown that the 2 strategies for atrial fibrillation—conversion to sinus rhythm and rate control with anticoagulation—are equivalent in terms of their outcomes.
The prognosis of patients with mitral stenosis worsens once their symptoms progress beyond early NYHA functional class II, unless the stenosis is relieved by intervention.
Balloon mitral valvotomy (balloon mitral valvuloplasty)
In most instances, an excellent result can be obtained with percutaneous balloon mitral valvotomy. Unlike aortic stenosis, mitral stenosis involves fusion of the valve commissures. Balloon dilatation produces a commissurotomy and a substantial increase in valve area that is maintained for 10 years or longer. A patient's suitability for balloon valvotomy is partially determined during echocardiography (by using the Wilkins criteria, see Patient selection by echocardiographic score). However, even when the valve anatomy is not ideal, valvotomy may be attempted in patients at an advanced age or in patients with severe comorbid risk factors.
Valvular procedural treatment must be individualized. For example, surgery might be deferred in a mildly symptomatic and sedentary elderly person with a mitral valve orifice of 0.8 cm2/m2 body surface area, whereas a 30-year-old laborer might be an excellent candidate for mechanical relief of obstruction, even if the mitral valve orifice size is 1.2 cm2/m2 body surface area.
The table below summarizes the advantages and disadvantages of some valvotomy procedures.
Advantages and Disadvantages of Some Valvotomy Procedures
Indications for balloon mitral valvotomy Symptomatic patients with moderate-to-severe mitral stenosis (ie, area of the mitral valve orifice < approximately 1.0 cm2/m2 body surface area <1.5-1.7 cm2 in normal-sized adults). Balloon mitral valvotomy is also indicated in patients with mild stenosis (orifice area of 1.0-1.5 cm2/m2) who are symptomatic during ordinary exertion, who have pulmonary arterial systolic pressures exceeding 60 mm Hg, or who have mean pulmonary capillary wedge pressures exceeding 25 mm Hg with exercise. LA thrombus must be excluded. Balloon mitral valvotomy also poses acceptable results in patients with accompanying mild or moderate aortic regurgitation and in those with mitral restenosis after surgical valvotomy. It may also be used in patients with unfavorable valves who are unsuitable for surgery because of high risks.
Patient selection by echocardiographic score
A widely adopted echocardiographic scoring system that Wilkins and colleagues developed helps in patient selection. In this system, 4 features of the mitral valve are identified, as follows:
Each of these 4 features is then graded on a scale of 1-4 representing minimal, mild, moderate, and severe, for a total possible score of 16. A score of 8 or less indicates high probability of successful balloon mitral valvuloplasty.
Percutaneous balloon mitral valvotomy is the procedure of choice in patients who have symptomatic, hemodynamically severe stenosis with an echocardiographic score of 8 or less and without LA thrombus. A score of 8 or less is usually associated with excellent immediate and long-term results, whereas scores exceeding 8 are associated with less-impressive results, including the risk of mitral regurgitation.
The decreased cost and morbidity rates are obvious advantages of good patient selection.
Contraindications to balloon mitral valvotomy
Balloon mitral valvotomy is contraindicated in patients with severe mitral regurgitation, severe aortic regurgitation, or LA thrombus. In addition, balloon mitral valvotomy should not be performed in patients with stenotic bioprosthetic valves.
Fluoroscopically visible calcium and coexisting mitral regurgitation are additional important predictors of an adverse outcome. TEE enables accurate evaluation of mitral valve structure and function along with an assessment of concomitant mitral regurgitation and LA thrombus, a contraindication to balloon mitral valvotomy. 3D echocardiography is also useful in assessing indications for balloon mitral valvotomy. The findings on echocardiography predict the outcome of both open and closed surgical valvotomy equally.
Procedure for balloon mitral valvuloplasty
The percutaneous for balloon mitral valvuloplasty technique consists of advancing a small balloon flotation catheter across the interatrial septum through a transseptal puncture, enlarging the opening of the mitral valve, positioning a large (23-25 mm) hourglass-shaped balloon (Inoue balloon), and inflating it within the orifice of the mitral valve. Sometimes, 2 small (12-18 mm) balloons may be used for simultaneous inflation.
The mechanism includes commissural separation and fracture of the nodular calcium.
In terms of the hemodynamic results, the transmitral pressure gradient decreases from approximately 18 to 6 mm Hg, cardiac output increases by about 20%, and the area of calculated mitral valve doubles from 1.0 to 2.0 cm2 on average. An improvement in exercise tolerance occurs proportional to the favorable hemodynamic effects.
The mortality rate associated with balloon mitral valvuloplasty is 1-2%. Complications include cerebral emboli (1%) cardiac perforation (1%) mitral regurgitation severe enough to require surgery (another 2%, approximately 15% have a lesser degree of mitral regurgitation). Approximately 5% of patients have a small residual ASD due to the septotomy, but this closes or decreases in size in most.
In patients with favorable anatomic findings, the survival rate without functional disability or the need for surgery or repeat balloon mitral valvuloplasty is 70% at 7 years. Excellent results are also reported in children and adolescents in developing nations, where patients tend to be young. These young patients usually have pliable valves, which are ideal for balloon mitral valvuloplasty.
Valvulotome procedure
Because the cost of the balloon catheter is deemed high in developing countries with minimal financial resources, a reusable metallic valvulotome has been developed for use. Early results appear to be similar to those of balloon mitral valvuloplasty.
Mitral valve replacement
Mitral valve replacement is indicated in 2 groups of patients with mitral stenosis whose valves are not suitable for valvotomy: (1) those with a mitral valve area less than 1.5 cm2 in NYHA class III or IV disease and (2) those with severe mitral stenosis (mitral valve area <1.0 cm2), NYHA class II, and severe pulmonary hypertension (pulmonary artery systolic pressure >70 mm Hg).
This procedure is often required in patients with combined mitral stenosis and moderate or severe mitral regurgitation; in those with extensive commissural calcification, severe fibrosis, or subvalvular fusion; and those who have undergone previous valvotomy.
The surgical mortality rate after isolated mitral valve replacement is 3-8% in most centers, 6.4% of 13,936 such operations for patients with mitral stenosis and/or mitral regurgitation reported in the national database of the Society of Thoracic Surgeons.
Regarding morbidity, bioprosthetic valves mechanically deteriorate faster in the mitral position than in the aortic position because of the increased transvalvular gradient. Patients with mechanical prostheses have a lifelong hazard of anticoagulation.
Because the surgical mortality risk in patients in NYHA class IV disease may be high (10-20%), surgery should be contemplated before the disease reaches this stage. On the contrary, such patients should not be denied valve replacement surgery unless comorbid conditions preclude surgery or an acceptable outcome. Medical/Legal Pitfalls:
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
){kind=small}
