Mitral stenosis

What is mitral stenosis?

Mitral stenosis occurs when there is obstruction to flow through the mitral valve separating the left atrium and left ventricle of the heart.

• The obstruction occurs due to a structural abnormality of the valve. Mitral stenosis increases left atrial and pulmonary arterial pressure (especially in tachycardia).

• Pulmonary hypertension can lead to right ventricular dilation and tricuspid regurgitation. Right ventricular failure results in raised jugular venous pressure, liver congestion, ascites and peripheral oedema. Left ventricular function and cardiac output can be normal in isolated mitral stenosis.

• Static blood flow in the left atrium (worsened in atrial fibrillation) can cause thromboemboli.

Mitral stenosis may be associated with other heart valve lesions - eg, tricuspid regurgitation.¹

Causes of mitral stenosis (aetiology)²

Rheumatic mitral valve disease is considerably less common in North America and European countries than in developing countries, where rheumatic heart disease remains by far the leading cause of valvular disease.³ Causes of mitral stenosis include:

• Rheumatic fever (the most common cause).

• Degenerative calcification (can occur in the elderly).

• Congenital mitral stenosis (secondary to parachute mitral valve or Lutembacher's syndrome).

• Inborn errors of metabolism (eg, Hurler-Scheie syndrome, Anderson-Fabry disease).

• Systemic lupus erythematosus.

• Rheumatoid arthritis.

• Carcinoid syndrome.

• Infective endocarditis with large vegetations.

• Amyloid deposition in the mitral valve.

How common is mitral stenosis? (Epidemiology)⁴

• The prevalence of rheumatic disease has declined in developed countries, with a consequent decline in the prevalence of mitral stenosis.

• The estimated incidence is 1 in 100,000 in developed countries, but higher in developing nations - eg, 35 cases per 100,000 in Africa.

• The onset is usually between the third and fourth decades of life.

• Rheumatic mitral stenosis is more common in females.

Presentation⁵

See also the separate Heart Auscultation (Types of Heart Sounds and Murmurs) and Heart Murmurs in Children articles.

Patients with mitral stenosis may feel asymptomatic for years and then present with a gradual decrease in activity.

• Breathlessness: progressive breathlessness is the main symptom. This can include shortness of breath on exertion, orthopnoea and paroxysmal nocturnal dyspnoea. Pulmonary oedema can be triggered by the onset of atrial fibrillation.

• Atrial fibrillation: palpitations due to atrial fibrillation may be the presenting feature.

• Systemic emboli: are a rarer presentation. Stroke, renal failure and myocardial infarction can occur.

• Haemoptysis: this may occur secondary to rupture of the bronchial veins due to raised left atrial pressure.

• During pregnancy: the increase in blood volume may make a previously asymptomatic woman develop symptoms.

Signs of mitral stenosis

• Malar flush on the cheeks.

• Raised jugular venous pressure.

• Laterally displaced apex beat.

• Right ventricular heave.

• Loud first heart sound with an opening snap in early diastole.

• A mid-late diastolic murmur, best heard, with the patient in the left lateral position, with the bell of the stethoscope.

• Atrial fibrillation.

• Signs of right ventricular failure including hepatomegaly, ascites and peripheral oedema.

Investigations

• CXR: may show left atrial enlargement and interstitial oedema (Kerley A and B lines) if severe. Mitral valve calcification may be seen. There may be prominent pulmonary vessels with redistribution of pulmonary vasculature to the upper lobes.

• ECG: may reveal atrial fibrillation, left atrial enlargement and right ventricular hypertrophy. See the separate ECG A Methodical Approach article.

• Echocardiography:^{5 7} Is the main method used to assess the severity and consequences of mitral stenosis, as well as the extent of anatomical lesions.
  

  • Echocardiography also evaluates pulmonary artery pressures, associated mitral regurgitation, concomitant valve disease and left atrial size.

  • Due to the frequent association of mitral stenosis with other valve diseases, a comprehensive evaluation of the tricuspid and aortic valves is essential.

  • Transthoracic echocardiography (TTE) usually provides sufficient information for routine management.

  • Trans-oesophageal echocardiography (TOE) should be performed to exclude left atrial thrombus before percutaneous mitral commissurotomy (PMC) or after an embolic episode, or if TTE provides insufficient information.

Management of mitral stenosis⁵

See also the separate Prevention of Infective Endocarditis, Rheumatic Fever and Atrial Fibrillation articles.

• Asymptomatic patients with clinically significant mitral stenosis, who have not undergone intervention, should be followed up by means of clinical and echocardiographic examinations.

• Commissurotomy (valvotomy) involves making one or more incisions at the edges of the commissure formed between the valves in order to relieve the constriction.

Medical therapy

• Diuretics or long-acting nitrates can be used to alleviate dyspnoea.

• Beta-blockers can improve exercise tolerance.

• Anticoagulant therapy is indicated in patients with either permanent or paroxysmal atrial fibrillation. In patients with sinus rhythm, anticoagulation is indicated when there has been prior embolism, or a thrombus is present in the left atrium.

• Heart rate control can be beneficial in patients with mitral stenosis and atrial fibrillation and fast ventricular response. Heart rate control may also be considered for patients with mitral stenosis in normal sinus rhythm but with symptoms associated with exercise.⁷

Surgery⁷

• Percutaneous mitral commissurotomy (PMC):
  

  • Symptomatic patients with severe mitral stenosis or those with pulmonary hypertension should be considered for PMC.²

  • Contra-indications to PMC include mitral valve area >1.5 cm², left atrial thrombus, greater than mild mitral regurgitation, severe or bicommissural calcification, absence of commissural fusion, severe concomitant aortic valve disease, severe combined tricuspid stenosis and regurgitation, and concomitant coronary artery disease requiring bypass surgery.

  • When PMC is not successful and symptoms persist, surgery should be considered early unless there are definite contra-indications.

  • Major complications include procedural mortality (0.5-4%), haemopericardium (0.5-10%), embolism (0.5-5%), and severe regurgitation (2-10%).

  • Event-free survival after PMC ranges from 30-70% after 10-20 years.

  • When functional deterioration occurs, it is late and mainly related to re-stenosis. Successful PMC also reduces embolic risk.

• Closed mitral commissurotomy is still performed in developing countries, but otherwise has largely been replaced by open mitral commissurotomy using cardiopulmonary bypass, which is also now seldom performed. In series from experienced centres, mostly including young patients, long-term results are good with ten-year survival rates of 81-90%.

• Surgical valve replacement should be considered for patients who are not candidates for percutaneous intervention.² Surgery for mitral stenosis is currently mostly valve replacement as a result of increasingly elderly presentation and unfavourable valve characteristics for valve repair.

• The addition of atrial fibrillation ablation to mitral valve surgery has been shown to significantly increase the rate of freedom from atrial fibrillation at one year among patients with persistent or long-standing persistent atrial fibrillation; however, the risk of implantation of a permanent pacemaker was also increased.⁸

• Mitral valve surgery and excision of the left atrial appendage may be considered for patients with severe MS who have had recurrent embolic events while receiving adequate anticoagulation.

Complications

Worldwide, untreated mitral stenosis continues to cause significant morbidity and mortality.⁹

• Pulmonary hypertension.

• Dilated left atrium.

• Atrial fibrillation.

• Thromboembolic events.

• Right heart failure.

• Rheumatic fever.

• Infective endocarditis.

Prognosis

• For patients with no symptoms or minimal symptoms, ten-year survival is very good.

• However, when limiting symptoms occur, ten-year survival is poor for patients with untreated mitral stenosis.

• When severe pulmonary hypertension develops, mean survival is less than three years.

• Most patients with severe untreated mitral stenosis die as a result of progressive heart failure but others may die from systemic embolism or pulmonary embolism, or infection.

• The prognosis is much improved in patients who undergo surgical or percutaneous relief of valve obstruction.¹ However, life expectancy is still shortened compared with that expected for age, largely because of the complications of mitral stenosis.

Prevention of mitral stenosis

• Prevention of rheumatic fever.

• Prevention of endocarditis.