Mitral valve prolapse

For patient information click here


 * Associate Editor-In-Chief:

Overview
Mitral valve prolapse (MVP) is a valvular heart disease characterized by the displacement of an abnormally thickened mitral valve leaflet into the left atrium during systole. In its nonclassic form, MVP carries a low risk of complications. In severe cases of classic MVP, complications include mitral regurgitation and infective endocarditis.

The mitral valve, so named because of its resemblance to a bishop's miter, is the heart valve that prevents the backflow of blood from the left ventricle into the left atrium. It is composed of two leaflets (one anterior, one posterior) that close when the left ventricle contracts.

Each leaflet is composed of three layers of tissue: the atrialis, fibrosa, and spongiosa. Patients with classic mitral valve prolapse have excess connective tissue that thickens the spongiosa and separates collagen bundles in the fibrosa. This is due to an excess of dermatan sulfate, a glycosaminoglycan. This weakens the leaflets and adjacent tissue, resulting in increased leaflet area and elongation of the chordae tendineae. Elongation of the chordae may be associated with chordae rupture, and is commonly found in the chordae tendineae attached to the posterior leaflet. Advanced lesions — also commonly involving the posterior leaflet — lead to leaflet folding, inversion, and displacement toward the left atrium.

History
The term mitral valve prolapse was coined by J. Michael Criley in 1966 and gained acceptance over the other descriptor of "billowing" of the mitral valve, as originally described by JB Barlow. . Barlow had postulated that mitral valve prolapse was due to an aneurysm of the mitral leaflet and Criley demonstrated that it was instead due to displacement of the leaflet that led to the condition.

For many years, mitral valve prolapse was a poorly understood anomaly associated with a wide variety of both related and seemingly unrelated signs and symptoms, including late systolic murmurs, inexplicable panic attacks, and polythelia (extra nipples). Recent studies suggest that these symptoms were incorrectly linked to MVP because the disorder was simply over-diagnosed at the time. Continuously-evolving criteria for diagnosis of MVP with echocardiography have made the diagnosis more rigorous and specific. As a result, there may have been many patients who would not currently be classified as having MVP who were included in original studies of the disorder and its prevalence. In fact, some modern studies report that as many as 55% of the population would be diagnosed with MVP if older, less specific criteria for the diagnosis of MVP, such as M-mode echocardiography—were applied today.

In recent years, new objective diagnostic criteria for MVP have been proposed based upon two- and three-dimensional echocardiography. The disorder has also been classified into a number of subtypes with respect to these echocardiographic criteria.

Subtypes
Prolapsed mitral valves are classified into several subtypes, based on leaflet thickness, concavity, and type of connection to the mitral annulus. Subtypes can be described as classic, nonclassic, symmetric, asymmetric, flail, or non-flail.

Note: all measurements below refer to adult patients and applying them to children may be misleading.

Classic versus nonclassic
Prolapse occurs when the mitral valve leaflets are displaced more than 2 mm above the mitral annulus high points. The condition can be further divided into classic and nonclassic subtypes based on the thickness of the mitral valve leaflets: up to 5 mm is considered nonclassic, while anything beyond 5 mm is considered classic MVP.

Symmetric versus asymmetric
Classic MVP may be subdivided into symmetric and asymmetric, referring to the point at which leaflet tips join the mitral annulus. In symmetric coaptation, leaflet tips meet at a common point on the annulus. Asymmetric coaptation is characterized by one leaflet being displaced toward the atrium with respect to the other. Patients with asymmetric prolapse are susceptible to severe deterioration of the mitral valve, with the possible rupture of the chordae tendineae and the development of a flail leaflet.

Flail versus non-flail
Asymmetric prolapse is further subdivided into flail and non-flail prolapse. Flail prolapse occurs when a leaflet tip turns outward, becoming concave toward the left atrium, causing the deterioration of the mitral valve. The severity of flail leaflet varies, ranging from tip eversion to chordal rupture. Dissociation of leaflet and chordae tendineae provides for unrestricted motion of the leaflet (hence "flail leaflet"). Thus patients with flail leaflets have a higher prevalence of mitral regurgitation than those with the non-flail subtype.

Diagnosis
Two- and three-dimensional echocardiography are valuable in the diagnosis of MVP as they allow visualization of the mitral leaflets relative to the mitral annulus. This allows measurement of the leaflet thickness and their displacement relative to the annulus. Thickening of the mitral leaflets >5 mm and leaflet displacement >2 mm indicates classic mitral valve prolapse.

Differential Diagnosis of Underlying Causes

 * Acquired
 * Congenital
 * Marfan's Syndrome
 * Myxomatous generation of the mitral valve
 * Papillary muscle infarction
 * Papillary muscle trauma

Prevalence
Prior to the development of rigorous criteria for the diagnosis and classification of mitral valve prolapse, as described above, the incidence of mitral valve prolapse in the general population varied significantly. Studies estimated the incidence of mitral valve prolapse at 5 to 15 percent or even higher.

As part of the Framingham Heart Study, more modern estimates of the prevalence of mitral valve prolapse have been lower at 2.4%. There was a near-even split between classic and nonclassic MVP, with no significant age or sex discrimination. Based on data gathered in the United States, MVP is prevalent in 7% of autopsies.

Signs and symptoms
While mitral valve prolapse has been associated with a variety of symptoms it should be noted that the frequency of these symptoms does not differ significantly from that of the general population. Therefore the causal link between mitral valve prolapse and these associated symptoms is not clear. Some patients with MVP experience heart palpitations, atrial fibrillation, or syncope. Between 11% and 15% of patients experience moderate chest pain and shortness of breath. These symptoms may not be directly attributable to the prolapsing mitral valve, but rather by the mitral regurgitation that often results from prolapse. In addition, the American Heart Association has linked anxiety and panic attack disorders to Mitral Valve Prolapse, although the causal nature of this association is not clear.

For unknown reasons, MVP patients tend to have a low body mass index (BMI) and are typically leaner than individuals without MVP. MVP occurs more frequently among individuals with the Marfan syndrome.

Auscultation
Upon auscultation a mid-systolic click is present, followed by a late systolic murmur which is best heard at the apex.

2D Echo features
The leaflets and chordae are thick and reduntant. Reduced tensile strength leads to progressive elongation or rupture of chordae. Ruptured chordae appear as flail segments.

To diagnose mitral valve prolapse, the following criteria should be fulfilled - Movement of any part of either leaflet more than 2mm behind the annular plane in parasternal long axis view and movement of point of co-aptation behind the annular plane in apical 4 chamber view. Mitral regurgitation can result in enlarged LA size.

Doppler
Colour flow mapping and CW doppler shows predominantly late systolic mitral regurgitation.

Mitral valve prolapse syndrome
Mitral valve prolapse syndrome (MVP Syndrome), also referred to as mitral valve prolapse dysautonomia, is thought to represent an imbalance of the autonomic nervous system in association with mitral valve prolapse. The underlying etiology that causes both autonomic dysregulation and the structural abnormalities present in mitral valve prolapse is unknown. Most patients who suffer from mitral valve prolapse syndrome may have an underlying dysautonomia as the cause of their symptoms. In particular, supraventricular arrhythmias such as those observed with MVP syndrome are associated with increased parasympathetic tone.

Symptoms generally attributed to MVP syndrome include palpitations, shortness of breath, and syncope. Because of the low specificity of these symptoms, and the fact that there is significant overlap in the causes of these symptoms with sequelae of significant mitral regurgitation often seen with mitral valve prolapse, MVP syndrome is most likely over-diagnosed. The uncertainty regarding the frequency of this syndrome may in part be due to the fact that there is no consensus criteria to diagnose MVP syndrome.

Mitral regurgitation
Mitral valve prolapse is frequently associated with mild mitral regurgitation, where blood aberrantly flows from the left ventricle into the left atrium during systole. Occasionally MVP patients experience severe regurgitation, often due to chordae tendineae rupture.

Sudden death
Severe mitral valve prolapse is associated with arrhythmias and atrial fibrillation that may progress and lead to sudden death. As there is no evidence that a prolapsed valve itself contributes to such arrythmias, these complications are more likely due to mitral regurgitation and congestive heart failure.

Prognosis
The major predictors of mortality are the severity of mitral regurgitation and the ejection fraction. Generally, MVP is a benign disorder. However, MVP patients with a murmur, not just an isolated click, may have a poorer prognosis.

Treatment
Most patients only need reassurance. Those with mitral valve prolapse and symptoms of dysautonomia (palpitations, chest pain) may often benefit from beta-blockers (e.g., propranolol). Patients with prior stroke and/or atrial fibrillation may require anticoagulation is, such as aspirin or warfarin.

Mitral valve prolapse associated with severe mitral regurgitation can be treated with repair or surgical replacement of the mitral valve. Repair of the mitral valve is always preferable to replacement and should be performed by surgeons that are skilled in the procedure. Current ACC/AHA guidelines suggest that early repair of mitral valve, performed in centers of surgical excellence, should be considered even in patients without symptoms of heart failure. Symptomatic patients, those with evidence of diminished left ventricular function or left ventricular dilatation need urgent attention.

Prevention of infective endocarditis
People with mitral valve prolapse are at higher risk of infective endocarditis (bacterial infection of the heart tissue), as a result of certain non-sterile procedures such as teeth cleaning and biopsy during colonoscopy. However, an April 2007 study by the American Heart Association has determined that the risks of prescribing antibiotics outweigh the benefits of antibiotic prophylaxis before an invasive procedure (such as dental surgery). Therefore, MVP patients who have taken prophylactic antibiotics routinely in the past may no longer need them.