Mitral stenosis presents many years following an attack of acute rheumatic fever and usually present during the third or fourth decade of life. In the early stages of the disease, patients at rest are usually asymptomatic. However, factors such as severe anemia, fever, thyrotoxicosis, exercise, pregnancy or excitement may trigger an attack of dyspnea. Pregnant women with mild stenosis develop symptoms in their second trimester due to increase cardiac output and blood volume. 

The presentation depends on the severity of the disease. Patients may be totally asymptomatic in mild cases. As the stenosis worsens, symptoms of orthopnea, paroxysmal nocturnal dyspnea or dyspnea on exertion develops. However, despite of very high atrial pressure, some patients may still remain asymptomatic. It happens due to lymphatic hyperfunction that avoids the development of pulmonary congestion and other associated symptoms [6].

More severe symptoms occur as the stenosis worsens and left atrial pressure and size increase. Cough may occur due to bronchial compression by the enlarged left atrium. Rupture of the bronchial veins may result in hemoptysis. An occasional occurrence is hoarseness of voice which occurs due to impingement of the left recurrent laryngeal nerve by enlarged left atrium. This is called as Ortner's syndrome.

On physical examination, a characteristic mitral facies may be seen which appears as pinkish-purple patches on the cheeks. It is indicative of decreased cardiac output and vasoconstriction occurring due to chronic severe mitral stenosis.

Other characteristic findings on physical examination, include jugular vein distension, a prominent 'a' wave on pressure studies indicating increased right atrial pressure occurring due to pulmonary hypertension and right ventricular failure. On auscultation, there is a loud first heart sound, a diastolic murmur and an opening snap. The loudness of the first heart sound is caused by the accentuated closure of the thickened and calcified mitral valve leaflets. Furthermore, the second heart sound is usually split with the pulmonic component being louder in the presence of pulmonary hypertension. 

Baseline laboratory blood investigations include complete blood count, electrolyte levels, liver and renal function tests.

Echocardiography is the most sensitive and specific and is the main diagnostic tool in diagnosing mitral stenosis   It also helps in identifying the severity of the stenosis [7] [8]. Transesophageal echocardiogrphy (TEE) is preferred than transthoracic echocardiography as it provides better images and more accurate in assessing the valve anatomy and presence of thrombus in the left atrial appendage.

On echocardiogram, there is a characteristic "hockey stick" or "rheumatic" appearance of the valve in mitral stenosis.

Cardiac catheterization may be required to determine the severity of stenosis in cases where clinical presentation and noninvasive data doesn't correlate well.

An echocardiogram demonstrates the thickening of the mitral valve leaflets, dome shape of the anterior leaflet, fusion of leaflets at the commissures, and restriction of valvular opening. In more severe cases, an echocardiogram may help to demonstrate left atrial enlargement. It shows atrial fibrillation, and right ventricular hypertrophy in the presence of pulmonary hypertension.

A transthoracic echocardiography is recommended for all patients with suspected mitral valve stenosis to confirm the diagnosis, quantify the severity of the disease, identify any associated valve lesion and determine the suitability of the patient for surgery. 

Chest X-rays and electrocardiography (ECG) are adjunctive diagnostic tools for mitral stenosis. ECG is indicated to rule out associated atrial fibrillation. Typical features on Chest X ray in mitral stenosis include double shadow in the cardiac silhouette indicating left atrial enlargement, prominent pulmonary congestion from engorged pulmonary vessels, pulmonary vascular redistributed to the uppe lobes, mitral valve calcifications, and Kerley A and B lines indicating interstitial edema. The left border of the cardiac silhouette also appears straightened, attributable to the enlarged left atrial appendage and the upward push of the main bronchi.

Treatment of mitral stenosis depends on the presence and severity of symptoms. Treatment is limited to prophylaxis against recurrence of rheumatic fever in asymptomatic patients. However, mild exercises are recommended for all patients with mitral stenosis.

Generally, medical treatment aims at alleviating pulmonary congestion, preventing infective endocarditis and rheumatic fever recurrence, controlling the ventricular rate in case of atrial fibrillation and preventing thromboembolism [9]. Medical treatment is indicated in mild mitral stenosis. Generally prophylactic antibiotic against group A beta-hemolytic streptococcus is recommended to prevent the development of rheumatic fever [10].

In patients with mild symptoms respond well to diuretics. Beta- blockers or Ca channel blockers are effective in controlling ventricular rate in those with AF or sinus tachycardia. At risk patients, such as those with a history of embolism, AF or left atrial clot should be given anticoagulants. These should also be considered in those with enlarged left atrium on echo. A low salt diet is recommended as an adjunctive measure to reduce the pulmonary congestion. Low level of physical exercise is encouraged in all the patients. Antibiotics are not routinely indicated in mild mitral stenosis except the patient who had undergone surgical valve replacement, to avoid the risk of endocarditis.

Intervention is required in symptomatic patients with moderate stenosis of the mitral valve if more than one below criteria are present:

• A coexisting disease or complication requiring surgery
• Exercise-induced mean transmitral gradient > 15mmHg in symptomatic patients
• Pulmonary capillary occlusion pressure > 25mmHg.

In patients with severe mitral stenosis intervention is required if more than one below criteria are present:

• Any coexisting or complicating cardiac pathologies which require surgery
• Valve suitable for percutaneous balloon commissurotomy

Those with very severe MS, intervention is indicated in all those who are suitable for percutaneous balloon commissurotomy

Surgical options for mitral stenosis include mitral valvotomy or mitral valve replacement. Mitral valvotomy may be performed via surgery or percutaneous intervention. Surgery could be done via open or closed techniques. Open technique is hardly used these days except in developing countries and is largely replaced by percutaneous balloon commissurotomy [11].

Percutaneous balloon commissurotomy is indicated in moderate to severe asymptomatic cases of mitral stenosis with pulmonary capillary wedge pressure of at least 25mmHg while exercising and a pulmonary arterial systolic pressure of at least 50mmHg at rest and 60mmHg during exercise [12]. Those patients with symptomatic moderate or severe MS with suitable valve are also candidate for percutaneous balloon commissurotomy. 

The course of mitral stenosis varies between patients. However, severe complications take around 7 to 9 years to develop following the onset of symptoms.

The prognostic factors in mitral stenosis include age, degree of mitral valve stenosis, presence of pulmonary hypertension, and the clinical status of the patient. Pulmonary hypertension and atrial fibrillation are associated with high risk of death. Cardiac failure and cerebrovascular or pulmonary embolism  are the major causes of death in these patients.

In patients with non-calcified valves, results of surgical or balloon commissurotomy are the same. However, valve replacement becomes necessary as restenosis occurs in most patients, causing functional deterioration after a variable period

Before recent advances in surgical practice, the prognosis was poor in patients with mitral stenosis. Those having NYHA class III has had a 5-year survival rate of 62%, whereas in class IV it was only 15%. Data from the surgical era shows that those patients who didn't opt for surgical correction had a survival rate of 44% [5].

Generally, the prognosis is good in patients who undergo surgical repair of the valve. However, the life expectancy of such patients is still low as expected for the age due to the related complications of the disease.

The common cause of mitral stenosis is rheumatic fever. Mitral stenosis often occurs years after the initial episode of acute rheumatic fever, which is caused by group A beta-hemolytic streptococcus (GABHS).

Less common causes of MS include systemic lupus erythematosus, whipple disease, fabry disease, rheumatoid arthritis, carcinoid tumors, hunter-hurler syndrome, and methysergide treatment. Mitral stenosis may also occur as a congenital defect in the structure of the valve. Certain conditions may mimic the presentation of mitral stenosis, these include: infective endocarditis having large vegetation, ball valve thrombosis, mitral annular calcification, severe non-rheumatic mitral annular calcification, left atrial myxoma, and cor tritriatum.

The M protein antigen is a cross reacting antigen common in both group A hemolytic Streptococcus and heart. During streptococcal infection, autoimmune attack may occur against heart, which further leads to mitral stenosis [1] [2] [3].

Rheumatic heart disease is estimated to occur in 15.6 million people worldwide currently with over 280,000 new cases and 230,000 deaths occurring each year.

The prevalence of rheumatic heart disease open link and mitral stenosis is quite low in developed nations at 0.001% as compared to the developing nations [4]. For example, in India, the prevalence rate of rheumatic heart disease is 100 to 150 cases per 100,000. In Africa, this is rate is about 35 cases per 100,000.

Rheumatic mitral stenosis is found more frequently in females with a ratio of 2 or 3:1. The condition usually presents between the third and fourth decade of life. 

Mitral stenosis is characterized by thickening and immobility of the mitral valve leaflets. The presence of thickened, shortened and matted chordae along with fusion of the commissures narrowing of the mitral orifice. Rheumatic fever is the commonest cause of mitral stenosis. However, many patients do not remember the onset of the fever.

The normal area of the mitral orifice is about 4-6 cm2. In mitral stenosis, this is significantly reduced, however, mitral stenosis remain asymptomatic till the valve area reduces to 2-2.5 cm2. At this point patient may start experiencing exertional dyspnea with moderate exercise due to the increased left atrial pressure and transmitral gradient. Severe symptoms occur when the area becomes less than 1 cm2.

As the mitral valve orifice narrows, the pressure gradient across the valve increases, leading to an increase in left atrial pressure and volume. This triggers a vicious cycle of increased pulmonary venous and capillary pressures which eventually causes pulmonary hypertension. Over time, pulmonary hypertension causes right heart failure, tricuspid incompetence and pulmonary regurgitation. Right heart failure leads to hepatic congestion, elevated jugular venous pressure, ascites, and bilateral pedal edema.

With the increase in left atrial pressure transudation of fluid occurs into the lung interstitium leading to dyspnea on rest and mild exertion. Rupture of the pulmonary veins from high hydrostatic pressure may result in hemoptysis. In addition, increased atrial left chamber size is a risk factor for atrial fibrillation, which in turn predisposes to thromboembolism and embolic complications such as stroke.

Although, left ventricular end-diastolic pressure and cardiac output may remain normal in the early stages of the disease, cardiac output falls over time eventually leading to left heart failure.

Since the most common cause of mitral stenosis is rheumatic fever, the prevention of the rheumatic fever is the most effective way to prevent mitral stenosis. Rheumatic fever develops due to untreated strep throat infection, which can be easily managed with appropriate antibiotics. They are effective in preventing rheumatic carditis and rheumatic fever when given even after 9 days following an attack of group A streptococcal tonsillo-pharyngitis. Antibiotics also decrease the spread of the infection to the contacts. Routine treatment of contacts of patients with group A streptococcal pharyngitis is neither necessary nor indicated.

Patients with mitral stenosis need regular yearly follow up. Those with progressive MS need echo every 3 to 5 years, while those with severe MS and MVA of 1.0 to 1.5 cm2 are advised to undergo echo every 1 to 2 years. 

Mitral stenosis is a structural abnormality of the mitral valve causing narrowing of its orifice and impeding the diastolic filling of the left ventricle. It most commonly occurs as a complication of rheumatic fever. Other causes of mitral stenosis include SLE, Carcinoid heart disease, rheumatic arthritis and infective endocarditis. It is more prevalent in developing countries and shows a predilection for females.

Pulmonary congestion and raised pulmonary venous and capillary pressure occurs over time. Pulmonary hypertension ensues which later presents with heart failure.

Clinical features include those of pulmonary hypertension and heart failure, such dyspnea, paroxysmal nocturnal dyspnea, orthopnea, and hemoptysis.

The diagnostic modality of choice for mitral stenosis is the echocardiography, which clearly demonstrates the valve stenosis. Chest X ray and ECG helps to demonstrate the valvular stenosis and the presence of complications.

Atrial fibrillation, pulmonary hypertension,and thromboembolism are well known complications of mitral stenosis.

Both medical and surgical treatment is available and the choice depends on the severity of symptoms and progression of the disease. Medical care is reserved for patients with mild stenosis, while surgery is preferred for moderate to severe cases. Antibiotic prophylaxis against group A beta-hemolytic streptococcus is recommended to avoid development of MS.

Overview.

The heart is divided into two halves: the left and right and each half has two chambers: the atria (singular: atrium) and the ventricles. While the ventricles pump blood away from the heart, the atria receive blood into the heart and pump to the ventricles. There are valves between the atria and the ventricles to regulate blood flow through both chambers during each heartbeat. The valve between the left atrium and ventricle is called the mitral valve and mitral stenosis is an abnormal narrowing of the valve, thereby, impeding flow of blood from the left atrium to the left ventricle.

Etiology.

The commonest cause of mitral stenosis is acute rheumatic fever, a condition caused by a bacterial agent called group A beta-haemolytic streptococcus (GABHS). Mitral stenosis occurs years after the patient must have recovered from the episode of rheumatic fever. What this narrowing does is to prevent the flow of blood from the left atrium to the left ventricle causing a back flow of blood out of the heart to where it was coming from: the lungs. In turn, the lungs would get congested with blood giving rise to so many symptoms, including difficulty breathing, rapid breathing at rest, exercise intolerance, and coughing up blood.

Eventually, the lungs get so congested that the right half of the heart in which the ventricles pump blood into the lungs, fails and unable to pump blood to the lungs to provide oxygen into. This is defined as right heart failure. In time, a total heart failure occurs.

Presentation.

The congestion of the lungs and heart failure are the main causes of symptoms and signs of mitral stenosis. Cough, fast breathing, difficulty breathing on lying flat are common symptoms of this disease. 

Workup.

When doctors suspect this disease, they send the patient for a test called echocardiography. This test uses high frequency sound waves similar to that of an ultrasound scan to create images of the whole heart. The image provides excellent view of the heart chambers and the structure of the valves. Chest X-rays and electrocardiogram (ECG) may also be recommended.

Treatment.

Treatment of this disease depends on the severity of the symptoms. In very mild cases, doctors may prescribe medications which reduce the congestion of the lungs, prevent blood clot formation, and recurrence of rheumatic fever. In moderate and severe cases, surgery is recommended if the patient is found suitable. Surgery may be by open or closed techniques or may involve the use of a small tube which is inflated into a balloon when it gets to the area of the mitral valve, this is referred to as a percutaneous balloon commissurotomy.

Antibiotics would also be prescribed to prevent infection by the bacterium which causes rheumatic fever.

1. Bessen D, Jones KF, Fischetti VA. Evidence for two distinct classes of streptococcal M protein and their relationship to rheumatic fever. J Exp Med.1989; 169: 269–283.
2. Smoot JC, Barbian KD, Van Gompel JJ, Smoot LM, Chaussee MS, Sylva GL, Sturdevant DE, Ricklefs SM, Porcella SF, Parkins LD, Beres SB, Campbell DS, Smith TM, Zhang Q, Kapur V, Daly JA, Veasy LG, Musser JM. Genome sequence and comparative microarray analysis of serotype M18 group A Streptococcus strains associated with acute rheumatic fever outbreaks. Proc Natl Acad Sci U S A. 2002 Apr 2;99(7):4668-73. Epub 2002 Mar 26.
3. Stollerman GH. Rheumatogenic streptococci and autoimmunity. Clin Immunol Immunopathol. 1991 Nov;61(2 Pt 1):131-42.
4. Marcus RH, Sareli P, Pocock WA, et al. The spectrum of severe rheumatic mitral valve disease in a developing country. Correlations among clinical presentation, surgical pathologic findings, and hemodynamic sequelae. Ann Intern Med. 1994 Feb 1. 120(3):177-83.
5. Horstkotte D, Niehues R, Strauer BE. Pathomorphological aspects, aetiology and natural history of acquired mitral valve stenosis. Eur Heart J. 1991 Jul. 12 Suppl B:55-60.
6. Runco V, Levin HS, Vahabzadeh H, Booth RW. Basal diastolic murmurs in rheumatic heart disease: intracardiac phonocardiography and cineangiography. Am Heart J. 1968 Feb;75(2):153-61.
7. Henri C, Pierard LA, Lancellotti P, Mongeon FP, Pibarot P, Basmadjian AJ. Exercise Testing and Stress Imaging in Valvular Heart Disease. Can J Cardiol. 2014 Sep. 30(9):1012-1026.
8. Wunderlich NC, Beigel R, Siegel RJ. Management of mitral stenosis using 2D and 3D echo-Doppler imaging. JACC Cardiovasc Imaging. 2013 Nov. 6(11):1191-205.
9. Nishimura RA, Otto CM, Bonow RO, et al. 2014 AHA/ACC guideline for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol. 2014 Jun 10. 63(22):e57-185.
10. Gerber MA, Baltimore RS, Eaton CB, Gewitz M, Rowley AH, Shulman ST, et al. Prevention of rheumatic fever and diagnosis and treatment of acute Streptococcal pharyngitis: a scientific statement from the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee of the Council on Cardiovascular Disease in the Young, the Interdisciplinary Council on Functional Genomics and Translational Biology, and the Interdisciplinary Council on Quality of Care and Outcomes Research: endorsed by the American Academy of Pediatrics. Circulation. 2009 Mar 24. 119(11):1541-51.
11. Bruce CJ, Nishimura RA. Newer advances in the diagnosis and treatment of mitral stenosis. Curr Probl Cardiol. 1998 Mar. 23(3):125-92.
12. Feldman T. Rheumatic Mitral Stenosis. Curr Treat Options Cardiovasc Med. 2000 Apr. 2(2):93-104.