Mitral stenosis overview

# Overview
Mitral stenosis is a valvular heart disease characterized by narrowing of the orifice of the mitral valve of the heart. In normal cardiac physiology, the mitral valve opens during  left ventricular diastole, to allow blood to flow from the left atrium to the left ventricle. Blood flows in the proper direction because during this phase of the cardiac cycle, the pressure in the left ventricle is lower than the pressure in the left atrium, and the blood flows down the pressure gradient. In the case of mitral stenosis, the valve does not open completely, and to transport the same amount of blood, the left atrium needs a higher pressure than normal to overcome the increased gradient. Mitral stenosis typically progresses slowly (over decades) from the initial signs of mitral stenosis to NYHA functional class II symptoms to the development of atrial fibrillation to the development of NYHA functional class III or IV symptoms. Once an individual develops NYHA class III or IV symptoms, the progression of the disease accelerates and the patient's condition deteriorates. Severe mitral stenosis (MS) is eventually lethal disease unless treated with vulvotomy or valve replacement, it may progress to serious complications like pulmonary hypertension, heart failure and death. Most of the cases are due to rheumatic heart disease.

# Pathophysiology
Mitral stenosis (MS) is most commonly secondary to acute rheumatic fever. Generally, the initial valvulitis is associated with valvular regurgitation but over a period of 2 or more years, the commissures fuse and the valves thicken and calcify. The chordal supporting structure also calcifies and retracts. The result is the typical fish mouth deformity. 70% of the time; the mitral valve is involved in isolation, and 25% of the time; the aortic valve is involved as well. The tricuspid and pulmonic valves are involved less commonly. Patients develop symptoms when the mitral vavle area is 2 to 2.5 cm2.

# Causes
The majority of cases of mitral stenosis result from rheumatic heart disease, which occurs as a complication of group A streptococcal infection in genetically susceptible individuals. Some cases may be congenital.

# Differentiating Miral stenosis from on Other Diseases
The possible causes, and other conditions that may present similarly, should be evaluated for when there is suspicion of mitral stenosis.

# Epidemiology and Demographics
In developed countries, the prevalence of mitral stenosis continues to decline as the prevalence of rheumatic fever declines. Currently, the estimated incidence in the United States is 1:100,000. The incidence in higher in developing countries.

# Natural History, Complications and Prognosis
After the initial episode of rheumatic fever, there is a latent period of 20 years before the onset of symptoms in mitral stenosis. Complications of mitral stenosis are left and right heart failure, endocarditis and embolization (stroke) and pulmonary embolism.  Survival in asymptomatic patients is 80% at 10 years.  Once symptoms develop, if mitral stenosis is left untreated, survival at 10 years is only 15%. The majority of patients die due to complications of pulmonary hypertension (which is associated with a mean survival of 3 years after its onset) and right heart failure.

# Diagnosis

## Stages
Staging of mitral stenosis (MS) is of utmost importance because it dictates the appropriate management plan for the affected patients.  The stages of MS are determined based on the valve morphology, the valve hemodynamics characteristics, the consequences of MS on the left atrium and the pulmonary arterial system, and on the presence or absence of symptoms.

## History and Symptoms
After the initial episode of rheumatic fever, there is an approximate 20 year latent period before symptoms develop in mitral stenosis.  Approximately half the patients will not have a recollection of having rheumatic fever.  In the developed world, most patients develop symptoms between the age of 20 and 50. Initial symptoms are worsened by exercise or tachycardia.  Symptoms may begin with an episode of atrial fibrillation, or may be triggered by pregnancy or other metabolic stress, such as an infection.  The symptoms are initially those of left heart failure, and subsequently are those of right heart failure.

## Physical Examination
Mitral stenosis is associated with a rumbling mid-diastolic murmur that is associated with an opening snap, best heard at the cardiac apex, and radiating to the axilla.  While the murmur increases when lying down, raising the legs, and with exercise, it decreases upon performing the valsalva maneuver.  The pulse pressure might be decreased among patients with mitral stenosis.  Later in the course of the disease there may be signs of right heart failure such as pedal edema, ascites, and congestive hepatopathy.

## Electrocardiogram
The electrocardiogram (ECG) in mitral stenosis might have no significant abnormalities. Findings suggestive of left atrial enlargement and hypertrophy might be present, such as a broad, bifid P wave in lead II (referred to as P mitral) and an enlarged terminal negative portion of the P wave in V1. The ECG might demonstrate findings of pulmonary hypertension and right ventricular hypertrophy.  Atrial fibrillation is not an uncommon finding among patients with mitral stenosis.

## Chest X Ray
Chest X-ray in a patient with mitral stenosis might reveal left atrial enlargement.  Chest X-ray findings include double right heart border, a prominent pulmonary artery (suggestive of an elevation in the pulmonary artery pressure), and kerley lines (suggestive of interstial pulmonary edema).

## Echocardiography
Transthoracic echocardiography (TTE) should be performed among patients with suspected mitral stenosis to confirm the diagnosis and to establish the baseline severity of disease. It should then be performed to monitor the course of disease over time.  Echocardiography findings of mitral stenosis include decreased opening of the mitral valve leaflets and increased blood flow velocity during diastole. The trans-mitral gradient as measured by Doppler echocardiography is the gold standard in the evaluation of the severity of mitral stenosis.  TEE should also be performed prior to percutaneous mitral balloon commissurotomy for the evaluation of the presence of left atrial thrombus.

## Cardiac MRI
Cardiac magnetic resonance (CMR) may be beneficial to evaluate the structure and function of the left atrium and left ventricle as well as the severity of the mitral stenosis when echocardiography findings are inconclusive. It may help in identifying changes in left ventricular volume and masses in patients with valvular dysfunction.

## Cardiac Catheterization
While echocardiography remains the diagnostic imaging modality of choice, cardiac catheterization is useful to evaluate mitral stenosis when the results of the non-invasive testing are insufficient.  Simultaneous left and right heart catheterization demonstrate a pressure gradient such that the pulmonary capillary wedge pressure (a surrogate of the left atrial pressure) exceeds the left ventricular end diastolic pressure.

# Treatment

## Treatment Overview
Medical therapy for mitral stenosis includes anticoagulation and rate control (to increase diastolic filling time) in those patients with atrial fibrillation. Medical therapy can relieve symptoms, but the patient may need surgery to relieve the blood flow obstruction by mitral stenosis.  Surgical treatment in the symptomatic patient reduces the mortality rate of mitral stenosis compared to medical treatment. The interventional and surgical treatments for mitral stenosis include Percutaneous mitral balloon valvotomy (PMBV), Closed commissurotomy, Open commissurotomy (valve repair) and Mitral valve replacement.

## Medical Therapy
Medical treatment for mitral stenosis includes anticoagulation and rate control in patients with atrial fibrillation. Medical therapy can relieve symptoms, but the patient may need surgery to relieve the blood flow obstruction by mitral stenosis.  Surgical treatment in the symptomatic patient reduces the mortality rate of mitral stenosis compared to medical treatment. The interventional and surgical treatments for mitral stenosis include: percutaneous mitral balloon valvotomy (PMBV), closed commissurotomy, open commissurotomy (valve repair), and mitral valve replacement.

## Percutaneous Mitral Balloon Valvotomy (PMBV)
The development of this approach was done by Inoue in 1984 and Lock in 1985 for the treatment of mitral stenosis. For a long time, surgical commissurotomy and open valve replacement were the only methods by which mitral stenosis could be corrected. PMBV can be performed in chronically symptomatic patients, patients who present emergently with cardiac arrest or pulmonary edema and in asymptomatic patients who plan on childbearing or major noncardiac surgery. There is improvement in the mortality rates for mitral stenosis by intervention by percutaneous mitral balloon valvotomy or surgery.

## Surgery
The mainstay of treatment for mitral stenosis is not medical therapy. Mitral valve surgery is usually reserved for patients with either  a repair for the mitral valve or totally replace it in the heart. Beside percutaneous mitral balloon valvotomy (PMBV), surgical treatments for mitral stenosis include closed commissurotomy, open commissurotomy (valve repair) and mitral valve replacement. In open surgery, the surgeon makes a large cut in the sternum to reach the heart. Minimally invasive mitral valve surgery is done through much smaller surgical cuts than the large cuts needed for open surgery.

## Follow Up
Regular follow up is recommended among patients with asymptomatic mitral stenosis (MS) and preserved left ventricular ejection fraction.

## Prevention
Prevention of rheumatic fever (the most common cause of mitral stenosis) is the best way to prevent development of this valvular heart disease.  Any child who has a sore throat should see a doctor to treat any case of strep throat infections (by antibiotics) before it progresses to rheumatic fever. Any child who has a sore throat should see a doctor to treat any case of strep throat infections (by antibiotics) before it progresses to rheumatic fever.