Today we will discuss about mitral stenosis. More specifically, we will be discussing about the basic concepts regarding heart valves, structure of mitral valve, causes of mitral stenosis and clinical features of mitral stenosis. In the next article we will discuss in details about the investigations, treatment, complications of mitral stenosis and many more topics
The heart consists of four chambers, two atria (upper chambers) and two ventricles (lower chambers). There is a valve through which blood passes before leaving each chamber of the heart.
There are two pairs of valves in the heart, a pair of atrioventricular valves and a pair of semilunar valves.
The right atrioventricular valve is known as the tricuspid valve because it has three cusps.
The left atrioventricular valve is known as the bicuspid valve because it has two cusps. It is also called the mitral valve.
The semilunar valves include the aortic and pulmonary valves, each having three semilunar cusps. The cusps are folds of endocardium, strengthened by an intervening layer of fibrous tissue.
Valvular stenosis and regurgitation can be present alone or coexist, and may involve only a single valve, or more than one valve.
The clinical consequences of valve dysfunction vary depending on the valve involved, the degree of impairment, the tempo of disease onset, and the rate and quality of compensatory mechanisms. For example, sudden destruction of an aortic valve cusp by infection (infective endocarditis; see later) can cause acute, massive, and rapidly fatal regurgitation. In contrast, rheumatic mitral stenosis typically develops indolently over years, and its clinical effects can be well tolerated for extended periods.
Both mitral and tricuspid valves are made up of the following components:
Narrowing of the mitral valve and its failure to open completely in order to allow unidirectional blood flow from the left atrium to the left ventricle is called mitral stenosis.
The mitral valve orifice is normally about 4-6 cm2 in diastole and may be reduced to 1 cm2 in severe mitral stenosis. Patients usually remain asymptomatic until the stenosis is less than 2 cm2.
The incidence and mortality rate of rheumatic fever and rheumatic heart disease have declined remarkably in many parts of the world over the past century because of improved sanitation, and rapid diagnosis and treatment of streptococcal pharyngitis. Nevertheless, in developing countries, and in many crowded, economically depressed urban areas, rheumatic heart disease remains an important public health problem, affecting an estimated 15 million people. In Europe, this does not usually occur until several decades after the first attack of rheumatic fever, but in developing countries, children of 10-20years of age may have severe mitral stenosis.
Progressively severe dyspnoea develops from the elevation in left atrial pressure, vascular congestion and interstitial pulmonary oedema. Exercise tolerance typically diminishes very slowly over many years and patients often do not appreciate the extent of their disability. Eventually, symptoms occur at rest.
A cough productive of blood-tinged, frothy sputum or frank haemoptysis may occur.
The development of pulmonary hypertension eventually leads to right heart failure and its symptoms of weakness, fatigue, and abdominal or lower limb swelling.
The large left atrium predisposes to atrial fibrillation, giving rise to symptoms such as palpitations. Atrial fibrillation may result in systemic emboli, most commonly to the cerebral vessels, producing neurological sequelae, but mesenteric, renal and peripheral emboli are also seen. Prior to the advent of anticoagulant therapy, emboli caused one-quarter of all deaths.
Severe mitral stenosis with pulmonary hypertension is associated with the so-called mitral facies or malar flush. This is a bilateral, cyanotic or dusky pink discoloration over the upper cheeks, which is due to arteriovenous anastomoses and vascular stasis.
Murmer in mitral stenosis
The opening snap is followed by a low-pitched, 'rumbling', mid-diastolic murmur (due to turbulent blood flow), best heard with the bell of the stethoscope held lightly at the apex and the patient lying on the left side in expiration. The murmur is sometimes associated with a thrill. If the patient is in sinus rhythm, the murmur becomes louder or accentuated during exercise and at the end of diastole as a result of atrial contraction (pre-systolic accentuation). Early in the disease, a pre-systolic murmur may be the only auscultatory abnormality but, in patients with symptoms, the murmur extends from the opening snap to the first heart sound. Coexisting mitral regurgitation causes a pansystolic murmur that radiates towards the axilla.
When pulmonary hypertension develops, an early diastolic murmur due to pulmonary valvular regurgitation and a systolic murmur due to tricuspid regurgitation are also heard. These murmur are explained better in the following segment.
Basic concepts of heart valve
What is a heart valve?
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| The Heart Chambers and Valves |
There are two pairs of valves in the heart, a pair of atrioventricular valves and a pair of semilunar valves.
The right atrioventricular valve is known as the tricuspid valve because it has three cusps.
The left atrioventricular valve is known as the bicuspid valve because it has two cusps. It is also called the mitral valve.
The semilunar valves include the aortic and pulmonary valves, each having three semilunar cusps. The cusps are folds of endocardium, strengthened by an intervening layer of fibrous tissue.
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| Heart in Diastole and Systole |
What is the function of a heart valve?
The valves of the heart maintain unidirectional flow of the blood and prevent its regurgitation in the opposite direction.What is valvular stenosis?
Stenosis is the failure of a heart valve to open completely, which impedes forward flow of blood.What is valvular regurgitation?
Insufficiency results from failure of a heart valve to close completely, thereby allowing reversed flow of blood. Regurgitation is also known as insufficiency or incompetence.Valvular stenosis and regurgitation can be present alone or coexist, and may involve only a single valve, or more than one valve.
The clinical consequences of valve dysfunction vary depending on the valve involved, the degree of impairment, the tempo of disease onset, and the rate and quality of compensatory mechanisms. For example, sudden destruction of an aortic valve cusp by infection (infective endocarditis; see later) can cause acute, massive, and rapidly fatal regurgitation. In contrast, rheumatic mitral stenosis typically develops indolently over years, and its clinical effects can be well tolerated for extended periods.
Structure of the atrioventricular valves (mitral and tricuspid valves)
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| The Atrioventricular Valves (Mitral and Tricuspid Valves) |
- A fibrous ring to which the cusps are attached.
- The cusps are flat and project into the ventricular cavity. Each cusp has an attached and a free margin, and an atrial and a ventricular surface. The atrial surface is smooth. The free margins and ventricular surfaces are rough and irregular due to the attachment of chordae tendinae. The valves are closed during ventricular systole by apposition of the atrial surfaces near the serrated margins.
- The chordae tendinae connect the free margins and ventricular surfaces of the cusps to the apices of the papillary muscles. They prevent eversion of the free margins and limit the amount of ballooning of the cusps towards the cavity of the atrium.
- The atrioventricular valves are kept competent by active contraction of the papillary muscles, which pull on the chordae tendinae during ventricular systole. Each papillary muscle is connected to the contiguous halves of two cusps.
- Blood vessels are present only in the fibrous ring and in the basal one-third of the cusps. Nutrition to the central two-thirds of the cusps is derived directly from the blood in the cavity of the heart.
- The tricuspid valve has three cusps and can admit the tips of three fingers. The three cusps, the anterior, posterior or inferior, and septal lie against the three walls of the ventricle. Of the three papillary muscles, the anterior is the largest, the inferior is smaller and irregular, and the septal is represented by a number of small muscular elevations.
- The mitral or bicuspid valve has two cusps, a large anterior or aortic cusp, and a small posterior cusp. It admits the tips of two fingers. The anterior cusp lies between the mitral and aortic orifices. The mitral cusps are smaller and thicker than those of the tricuspid valve.
What is Mitral Stenosis?
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| Normal Mitral Valve vs Stenosed Mitral Valve |
Causes of mitral stenosis
Mitral stenosis is almost always rheumatic in origin, although in older people it can be caused by heavy calcification of the mitral valve apparatus. There is also a rare form of congenital mitral stenosis.Chronic rheumatic heart disease is the most common cause of mitral stenosis
Rheumatic heart disease occurs secondary to previous rheumatic fever due to infection with group A β-haemolytic streptococcus. The condition is more common in women than men (F:M = 2:1). Inflammation leads to commissural fusion and a reduction in mitral valve orifice area, causing the characteristic doming pattern seen on echocardiography. Over many years, the condition progresses to valve thickening, cusp fusion, calcium deposition, a severely narrowed (stenotic) valve orifice and progressive immobility of the valve cusps. Rheumatic heart disease is virtually the only cause of mitral stenosis.The incidence and mortality rate of rheumatic fever and rheumatic heart disease have declined remarkably in many parts of the world over the past century because of improved sanitation, and rapid diagnosis and treatment of streptococcal pharyngitis. Nevertheless, in developing countries, and in many crowded, economically depressed urban areas, rheumatic heart disease remains an important public health problem, affecting an estimated 15 million people. In Europe, this does not usually occur until several decades after the first attack of rheumatic fever, but in developing countries, children of 10-20years of age may have severe mitral stenosis.
Other causes of mitral stenosis
All other causes of mitral stenosis are extremely rare:- Congenital mitral stenosis.
- Lutembacher syndrome: the combination of acquired mitral stenosis and an atrial septal defect. This occurs in about 4% of ASD.
- Mitral annular calcification: This may lead to mitral stenosis if extensive, particularly in elderly patients and those with end-stage renal disease.
- Carcinoid tumours metastasizing to the lung, or primary bronchial carcinoid.
Clinical features (symptoms and sings) of mitral stenosis
| Clinical features (and their causes) in mitral stenosis |
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| Symptoms of mitral stenosis |
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| Signs of mitral stenosis |
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Symptoms of mitral stenosis
Usually, there are no symptoms until the valve orifice is moderately stenosed (area less than 2cm2).Progressively severe dyspnoea develops from the elevation in left atrial pressure, vascular congestion and interstitial pulmonary oedema. Exercise tolerance typically diminishes very slowly over many years and patients often do not appreciate the extent of their disability. Eventually, symptoms occur at rest.
A cough productive of blood-tinged, frothy sputum or frank haemoptysis may occur.
The development of pulmonary hypertension eventually leads to right heart failure and its symptoms of weakness, fatigue, and abdominal or lower limb swelling.
The large left atrium predisposes to atrial fibrillation, giving rise to symptoms such as palpitations. Atrial fibrillation may result in systemic emboli, most commonly to the cerebral vessels, producing neurological sequelae, but mesenteric, renal and peripheral emboli are also seen. Prior to the advent of anticoagulant therapy, emboli caused one-quarter of all deaths.
Signs of mitral stenosis
The physical signs of mitral stenosis are often found before symptoms develop and their recognition is of particular importance in pregnancy.Face
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| Mitral Facies |
Pulse
Mitral stenosis may be associated with a small-volume pulse, which is usually regular early on in the disease process, when most patients are in sinus rhythm. However, as the severity of the disease progresses, many patients develop atrial fibrillation, resulting in an 'irregularly irregular' pulse. The development of atrial fibrillation in these patients often causes a dramatic clinical deterioration.Jugular veins
If right heart failure develops, there is obvious distension of the jugular veins. If pulmonary hypertension or tricuspid stenosis is present, the 'a'-wave will be prominent, provided that atrial fibrillation has not supervened.Palpation
There is a tapping impulse felt parasternally on the left side. This is the result of a palpable first heart sound combined with left ventricular backward displacement produced by an enlarging right ventricle. A sustained parasternal impulse due to right ventricular hypertrophy may also be felt.Auscultation
The forces that open and close the mitral valve increase as left atrial pressure rises. Auscultation therefore reveals a loud first heart sound which can be palpable (tapping apex beat) if the mitral valve is pliable, but this will not occur in calcific mitral stenosis. As the valve suddenly opens with the force of the increased left atrial pressure, an 'opening snap' will be heard. The opening snap moves closer to the second sound (S2) as the stenosis becomes more severe and left atrial pressure rises. Just line the first heart sound, the opening snap may be inaudible if the mitral valve is heavily calcified. |
| Signs of Mitral Stenosis |
Murmer in mitral stenosis
The opening snap is followed by a low-pitched, 'rumbling', mid-diastolic murmur (due to turbulent blood flow), best heard with the bell of the stethoscope held lightly at the apex and the patient lying on the left side in expiration. The murmur is sometimes associated with a thrill. If the patient is in sinus rhythm, the murmur becomes louder or accentuated during exercise and at the end of diastole as a result of atrial contraction (pre-systolic accentuation). Early in the disease, a pre-systolic murmur may be the only auscultatory abnormality but, in patients with symptoms, the murmur extends from the opening snap to the first heart sound. Coexisting mitral regurgitation causes a pansystolic murmur that radiates towards the axilla.
When pulmonary hypertension develops, an early diastolic murmur due to pulmonary valvular regurgitation and a systolic murmur due to tricuspid regurgitation are also heard. These murmur are explained better in the following segment.
How to assess the severity of mitral stenosis clinically?
The severity of mitral stenosis is judged clinically on the basis of several criteria:- The presence of pulmonary hypertension implies that mitral stenosis is severe. Pulmonary hypertension is recognized by a right ventricular heave, a loud pulmonary component to the second heart sound and, eventually, signs of right-sided heart failure, such as oedema and hepatomegaly. Pulmonary hypertension results in pulmonary valvular regurgitation, which causes an early diastolic murmur in the pulmonary area, known as a Graham Steell murmur. Pulmonary hypertension ultimately also causes right ventricular hypertrophy and dilatation with secondary tricuspid regurgitation, which causes a systolic murmur and giant ‘v waves’ in the venous pulse.
- The time between the opening snap and second heart sound (S2-0S interval) shortens with more severe degrees of mitral stenosis.
- The length of the mid-diastolic murmur is proportional to the severity.
- As the valve cusps become immobile, the loud first heart sound softens and the opening snap disappears. When pulmonary hypertension occurs, the pulmonary component of the second sound is increased in intensity and the mitral diastolic murmur may become quieter because of the reduction of cardiac output.
That's all for today!
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