Introduction
Background
Mitral stenosis is characterized by restriction of blood flow from the left atrium (LA) to the left ventricle (LV) as a result of a narrowed mitral passage. It is an acquired valvular defect; it is usually a consequence of rheumatic heart disease, though cases of congenital mitral stenosis are occasionally encountered. Extensive mitral annular calcification (MAC) may 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 developing countries than in 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 develop, such as dyspnea on exertion, orthopnea, and paroxysmal nocturnal dyspnea. Right ventricular (RV) failure gradually ensues, causing ascites and edema.
Multiple imaging modalities may be used to diagnose mitral stenosis. Echocardiography has become the most important diagnostic tool for confirming the diagnosis, for quantifying the severity of mitral stenosis, and for determining the optimal timing for intervention.
Asymptomatic individuals with sinus rhythm on ECG need no treatment. After atrial fibrillation develops, pharmacologic agents may be administered to control the ventricular rate; in addition, anticoagulation therapy may be initiated to prevent thromboembolism. Symptoms of dyspnea and orthopnea improve with the use of diuretics. As symptoms worsen and pulmonary hypertension occurs, mechanical correction of the stenosis, rather than medical therapy, becomes necessary. These surgical 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.1,2
Related eMedicine topics:
Mitral Stenosis (from Cardiology)
Mitral Stenosis (from Emergency Medicine)
Rheumatic Heart Disease
Related Medscape topics:
Specialty Site Radiology
Specialty Site Cardiology
Resource Center Heart Failure Resource Center
Resource Center Hemodynamic Monitoring Resource Center
CME/CE Hemodynamic Assessment of Pulmonary Hypertension: Echocardiography and Cardiac Catheterization
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 occurs continuously 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 caused by 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. This causes an increase in the pulmonary arterial pressure and further burdens the RV, which begins to dilate; in addition, the central pulmonary artery enlarges. As mitral stenosis worsens, pulmonary vascular changes become fixed, RV failure sets in, and signs of CHF begin to develop.
Frequency
United States
Because of widespread and effective use of antibiotics in the treatment of streptococcal infections, the incidence of rheumatic endocarditis with subsequent valvular heart disease, including mitral stenosis, has greatly decreased in the United States.
At present, most patients are elderly individuals who initially develop degenerative MAC and subsequent mitral stenosis.
Rheumatic mitral stenosis is still encountered, but it occurs at an older age, and it progresses more slowly than previously. Among immigrant populations, trends similar to the those seen in their native countries are seen.
International
Mitral stenosis is still prevalent in developing nations where rheumatic fever is common. Both economic and genetic conditions may play a role.
Mortality/Morbidity
The prognosis for patients with untreated congenital mitral stenosis is poor. With medical treatment, the 10-year survival rate is approximately 80% for mildly symptomatic patients with rheumatic mitral stenosis who have New York Heart Association (NYHA) class II disease. The 10-year survival rate is 38% for patients with NYHA class III disease. The 5-year survival rate for 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; it may occur in children as young as 6-12 years of age.
Sex
Rheumatic mitral stenosis occurs more frequently in women than in men; the female-to-male ratio is 3:1.
Age
- In developing countries, rheumatic mitral stenosis tends to occur in patients in their teens.
- In the Western world, mitral stenosis manifests itself in the fourth or fifth decade of life; a latent period of 15-20 years follows the occurrence of acute rheumatic fever. In most patients, the progression from mild disability (NYHA class II) to severe disability (NYHA class III or IV) occurs over 5-10 years; this rate of progression is slower than the rate observed in developing countries.
- Degenerative calcific mitral stenosis secondary to MAC tends to occur in relatively elderly patients.
Anatomy
Proper function of the mitral valve requires the orchestration of many different components. Adequate mitral leaflet function requires 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-size 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. The mitral valve is a bicuspid valve consisting of a large anterolateral cusp and a posteromedial cusp that is shortened by half. The area of the normal mitral orifice is approximately 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
- Rheumatic heart disease
- MAC, degenerative
- Congenital conditions
- Thickened chordae
- Single papillary muscle
- Miscellaneous conditions
- Carcinoid
- Lupus
- Rheumatoid arthritis
- Mucopolysaccharidosis (Hurler syndrome)
- Coxsackie infection
- Amyloidosis
- Methysergide
Differential diagnoses
- Atrial myxoma
- Ball-valve thrombus
- Cor triatriatum
- Submitral ring or web
Rheumatic fever and carditis
Approximately 60% of patients with isolated mitral stenosis have rheumatic fever; approximately 90% of patients with multivalvular disease have isolated mitral stenosis. One of the critical consequences of acute rheumatic fever is pancarditis, which occurs in 40-50% of patients; pancarditis progresses gradually, causing chronic abnormalities. The mitral valve is frequently involved; the free edges of the commissures become fused, giving the mitral valve a characteristic fish-mouth appearance. Subvalvular structures, such as the chordae tendineae, gradually thicken and become calcified, leading to further restriction of leaflet mobility. The mean latent period between the occurrence of acute rheumatic fever and mitral stenosis is usually 20 years. Another 7-10 years pass before patients become significantly disabled.
Atrial septal defect with mitral stenosis
In some patients, atrial septal defect (ASD) is associated with acquired mitral stenosis. In this syndrome, called Lutembacher syndrome, the RV workload is higher than that associated with an isolated ASD because of left-to-right shunting of blood with an increase in 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.
Presentation
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
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, with the symptoms associated with LV failure). Subsequently, RV failure manifests itself 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 may be seen in some patients (see Image 8).
Palpation of the precordium reveals a quiet apical impulse. In pulmonary hypertension and RV hypertrophy, an 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 becomes quiet.
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); 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 may be soft in patients with low cardiac output. In such patients, modest exercise, such as isometric handgrip, may cause an increase in the intensity of the murmur. A presystolic accentuation of the mitral stenosis murmur is also heard coincidentally with the atrial contraction. In the presence of pulmonary arterial hypertension, another diastolic murmur of blowing quality, associated with 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 congestive heart failure (CHF). The rapid ventricular rate shortens the diastolic filling time to a period insufficient to allow the LA to empty. As a consequence, the LA pressure rises and the forward cardiac output decreases.
Congenital mitral stenosis
Symptoms of mitral stenosis usually appear within the first 2 years of life. Infants have delayed development and breathlessness, caused by 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; in most of the patients, echocardiography may be adequate for the planning of therapeutic interventions.3,4,5,6,7,8
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. Typical 2-dimensional (2D) echocardiographic findings include thickening of the mitral valve cusps; enlargement of the LA, with a normal or small LV; and a reduction in the size of the mitral valve orifice in diastole. A diminished E-F slope is noted on M-mode images. Doppler studies demonstrate an increase in the mean pressure gradient across the mitral orifice; Doppler studies are also helpful in quantifying the severity of mitral stenosis.
Electrocardiography
If the patient is in sinus rhythm, the electrocardiogram shows abnormality of the LA. LA abnormality is manifested by prolongation of the P wave, with a double-saddleback contour (p mitrale) in limb lead II. This contour represents a right atrial p wave followed by delayed LA P wave associated with 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 in mitral stenosis.
Differential Diagnoses
Other Problems to Be Considered
Rheumatic mitral stenosis
Calcific mitral stenosis
Congenital mitral stenosis
MAC
Lutembacher syndrome
Atrial myxoma
Ball-valve thrombus
Cor triatriatum
More on Mitral Stenosis |
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Further Reading
ACC/AHA/ASE 2003 guideline update for the clinical application of echocardiography: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/ASE Committee to update the 1997 guidelines for the clinical application of echocardiography).
American College of Cardiology Foundation
American Heart Association
American Society of Echocardiography. 1997 Mar 18 (revised 2003 Aug). 99 pages. NGC:003138
Guidelines on the management of valvular heart disease.
European Society of Cardiology. 2007 Jan. 39 pages. NGC:005534
Keywords
mitral stenosis, MS, mitral valve stenosis, mitral valve, rheumatic mitral stenosis, mitral commissural stenosis, mitral annular calcification, MAC, Lutembacher syndrome, congenital mitral stenosis, atrioventricular valve, rheumatic heart disease, rheumatic fever, acute rheumatic fever, carditis, pancarditis, cor triatriatum, submitral ring
