Mitral Valve Prolapse

Mitral valve prolapse (MVP) is a relatively common heart valve abnormality. Our understanding of MVP is comparatively recent. The findings on auscultation were described in the mid 19th century but it was not until left ventricular angiography, about 50 years ago, that the mechanism was appreciated. Echocardiography has enabled more investigation.

MVP is defined on echocardiography as single or bileaflet prolapse of at least 2 mm beyond the long-axis annular plane, with or without leaflet thickening.¹

Note that in the 1980s, MVP was over-diagnosed, especially in young women, due to incomplete understanding of normal valve anatomy and echocardiographic appearances. Various non-specific symptoms were attributed to MVP, such as atypical chest pain, exertional dyspnoea, palpitations, syncope and anxiety. These were sometimes termed "mitral valve prolapse syndrome". However, data from the Framingham study and others does not support a link between these symptoms and MVP.^1,2

The prevalence of MVP is estimated as 2-3% of the population, with an equal sex ratio.¹

The cause is often multifactorial.

• A common occurence is leaflet thickening and redundancy, known as myxomatous degeneration - not related to hypothyroidism but involving the accumulation of proteoglycans on histology. The underlying mechanism is not known.
• MVP may also occur with histologically normal valves. Contributing/associated factors may be:
  • A disproportionately small left ventricular cavity.
  • Unrepaired secundum atrial defects.
  • Certain recognised syndromes:
    • Marfan's syndrome (recent research suggests 28% prevalence, lower than previously thought³)
    • Ehlers-Danlos syndrome (6% prevalence)
    • Osteogenesis imperfecta
    • Pseudoxanthoma elasticum
    • Adult polycystic kidney disease
• Genetic factors - there is probably a familial, autosomal dominant condition with variable penetrance and variable clinical presentation. There may be other genetic forms.^4,5

MVP is generally asymptomatic, unless there are complications such as significant mitral regurgitation. It usually presents as an incidental finding on clinical examination or echocardiogram.

Classical auscultation findings are:

• A dynamic mid-to-late systolic click, often followed by a late systolic mitral regurgitant murmur.
• The murmur is dynamic in that it moves within systole as the loading conditions change.
  • There is an earlier click with reduction of end-diastolic volume e.g. on standing or a Valsalva manoeuvre.
  • The click will be later in systole when the left ventricular afterload or end-diastolic volume is increased e.g. by squatting or hand-grips.

A careful physical examination is said to be highly sensitive for echocardiographic MVP, although it is not specific (see differential diagnosis). MVP may also be found on echocardiography when auscultation is normal.

Look for associated conditions e.g. Marfan's syndrome.

A click heard during auscultation may also be due to:

• Redundant leaflets or chordae, without echocardiographic prolapse
• Bicuspid aortic stenosis
• Atrial myxoma
• Pericarditis

• Patients with signs of MVP should have 2D echocardiography. This shows the prolapse and distinguishes it from other causes of systolic clicks.
• As mentioned above, strict criteria for echocardiographic diagnosis are important to avoid over-diagnosis.
• Transthoracic echocardiography can confirm MVP, but can miss prolapse of the lateral scallop of the valve; transoesophageal echocardiography may be more sensitive.
• ECG and chest x-ray are usually normal unless there has been progression to significant mitral regurgitation.
• If there is doubt about exercise tolerance, an exercise test may be useful.

The problem facing the doctor who has made the diagnosis in an asymptomatic patient is what, if anything, to do about it, bearing in mind the usual good prognosis.

Patients with MVP can be classified as high or low risk of developing severe mitral regurgitation.

Low risk

Those with no symptoms, only mild regurgitation and stable examination findings, do not need treatment. These patients can be followed up conservatively.

High risk

Factors which increase the risk of severe mitral regurgitation developing are:

• Age over 50, hypertension or obesity
• Moderate-severe mitral regurgitation
• Mitral regurgitation during exercise but not at rest
• Echocardiographic findings of mitral leaflet thickness >5mm, posterior leaflet prolapse or increased left ventricular dimensions
• Atrial fibrillation
• Reduced left ventricular systolic function
• Left atrial enlargement

Patients at high risk need follow-up to monitor for progressive mitral regurgitation. If this occurs, the surgical repair or replacement of the valve may be needed, and the optimal timing of surgery must be considered.

Prophylaxis

Anti-thrombotic treatment is not recommended for MVP alone.⁶

Endocarditis prophylaxis: patients with MVP are at increased risk of endocarditis if they have:

• A systolic click and murmur on examination.
• Myxomatous degeneration and mitral regurgitation on echocardiography.
• "High risk" features (above) such as left ventricular dilatation, left atrial enlargement, leaflet thickening, redundant chordae, or other high risk features as above.

Recent NICE guidelines state that:⁷

• Routine antibiotic prophylaxis is not required for most procedures.
• However, antibiotic cover for infective endocarditis should be given to patients who are receiving antibiotics for a gastrointestinal or genitourinary procedure to an infected site.
• Patients at risk of endocarditis should be aware of relevant symptoms.

Surgery

Valve surgery is indicated for patients with:

• Symptomatic severe mitral regurgitation.
• Patients who are asymptomatic but have left ventricular enlargement (end-systolic diameter >45 mm) or reduced systolic function (ejection fraction <60%).
• Severe mitral regurgitation with atrial fibrillation or pulmonary hypertension (AHA/ACC Class IIa recommendation for valve surgery).

The management of asymptomatic patients with severe mitral regurgitation but preserved left ventricular function is controversial. However, there is a trend towards earlier surgical valve repair for patients with severe mitral regurgitation. This is because:

• There is a high success rate and durability of surgical repair.
• Some research shows improved clinical outcomes with early intervention.
• Occult left ventricular dysfunction can precede symptoms.
• Those with severe mitral regurgitation and a flail valve leaflet may benefit from early surgical repair.

Surgical options are:

• Mitral valve repair, usually by leaflet resection, possibly with placement of an annuloplasty ring. This is generally the treatment of choice, if surgery is needed.
• A new technique for repair, using polytetrafluoroethylene neochordae (this is still under evaluation).⁸
• Mitral valve replacement.

The overall prognosis is excellent for most patients with MVP, with an expected lifespan similar to the general population.
A minority of patients may develop complications, which are:

• Progression to severe mitral regurgitation, which may may require surgery (as above).
• There is a small increased risk of:
  • Sudden cardiac death:
    • The absolute risk is very low, but in patients with myxomatous MVP it is twice that of the general population.
    • If there is severe mitral regurgitation with a flail leaflet, this carries a higher risk (up to 2% per year).
  • Infective endocarditis:
    • Without mitral regurgitation, the incidence of infective endocarditis is similar to that of the general population.
    • In patients with mitral valve prolapse and a systolic murmur, the risk increases to about 0.05% per year.
  • Possibly, an increased risk of stroke, but this has not been proved.

Results of mitral valve repair are usually good.

It is suggested that first degree relatives of those with MVP should have echocardiography to screen for the condition.⁹