Mitral Valve Prolapse

Our understanding of mitral valve prolapse (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 much more investigation with a non-invasive technique that is free of radiation.¹ It is defined as prolapse of one or both mitral leaflets into the left atrium during (late) systole by >2mm beyond the long axis annular plane on echocardiography.²

The functioning of the heart valves is a dynamic process and should not be seen like a rigid piece of machinery. It is said that mitral valve prolapse occurs in 2-3% of the population and there is an equal sex incidence.³ The Framingham study gave an incidence of 2.4% in the general population⁴ and this is widely accepted as the correct order of magnitude. Many other studies have been too lax with their diagnostic criteria and have given figures that are unacceptably high. No test is perfect but strict criteria for diagnosis are important.¹

The cause is often multifactorial. Floppy mitral valve or mitral valve prolapse is often considered a genetic disorder of connective tissue.⁵ There may be anterior chest deformity, scoliosis, kyphosis, rheumatic fever, and joint hypermobility. There may be histological changes in the valve that are usually myxomatous degeneration due to accumulation of proteoglycans. (Proteoglycans are glycoproteins of high molecular weight in the extracellular matrix of connective tissue. They are polysaccharide side chains linked to a protein, and resemble polysaccharides rather than proteins in their properties.) Anatomical distortion of the normal relationship between the mitral valve and the left ventricle may result from a connective tissue disorder such as Marfan's syndrome, Ehlers-Danlos syndrome, osteogenesis imperfecta, adult polycystic kidney disease and pseudoxanthoma elasticum. More than half of patients with Marfan's syndrome may have the condition with significant mitral regurgitation developing in the 20s in 1 in 8.⁶ Mitral valve prolapse can be associated with panic disorder.⁷ An inherited autosomal dominant form has been identified, and mapped to loci on chromosome 16.⁸ More recently a second inherited type has been described with locus on chromosome 11 and it is called myxomatous mitral valve prolapse 2.⁹

It usually presents as an incidental finding on clinical examination or echocardiogram. Classically, MVP gives a dynamic mid-to-late systolic click, often followed by a late systolic mitral regurgitant murmur. It is best heard at the apex. This murmur is dynamic in that it moves within systole as the loading conditions change. For example, there is an earlier click with a Valsalva manoeuvre.

Patients may present with non-specific complaints such as easy fatigue, dizziness and vague chest pain. With such vague symptoms, MVP may be a diagnosis of desperation.

2D Echocardiography shows the prolapse, and thus distinguishes it from other documented causes of systolic clicks such as bicuspid aortic valves, atrial myxoma and pericarditis.² As mentioned above, strict diagnostic criteria are imperative to prevent excessive diagnosis.

ECG and chest x-ray are usually normal unless there has been progression to significant mitral regurgitation. If there is doubt about exercise tolerance, a treadmill test may be useful.

The timing of the murmur is unusual. Other possible causes include:

• Bicuspid aortic valves
• Atrial myxoma
• Pericarditis.

Mitral regurgitation is early systolic. Aortic stenosis and flow murmurs have a typical crescendo-decrescendo sound.

A possible connective tissue disorder such as Marfan's syndrome should be considered.

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

• If there are no symptoms, thin leaflets on the valves and minimal regurgitation, the patient should be reassured and repeat echocardiography in 3 to 5 years.
• Those with vague symptoms but little haemodynamic abnormality, may try a beta blocker and a 24 hour heart monitor may be employed to ascertain if there are significant ventricular ectopics or abnormal rhythms.
• Patients with symptomatic mitral regurgitation, left ventricular enlargement, or any reduction in systolic function should be referred for mitral valve repair. Where possible this is preferable to replacement. Severe mitral regurgitation with either atrial fibrillation or pulmonary hypertension also requires prompt referral.
• Management of asymptomatic patients is controversial, but those with severe mitral regurgitation ± flail valve segment appear to benefit from early surgical repair.
• Antibiotic prophylaxis is recommended for patients with a systolic murmur following the "click", or other patients at "high risk" such as those with ventricular dilatation, left atrial enlargement, thickened or myxomatous leaflets or redundant chordae.
• Patients with a normal appearance of the valves and without regurgitation do not need prophylaxis whether or not a "click" is present.²

• Infective endocarditis is 3-8 times the baseline risk at 0.02%/year. The risk is higher if male, aged >45, there is a systolic murmur, thickened or redundant leaflets.
• Mitral regurgitation may suddenly worsen because of rupture of chordal tendinae.
• Sudden cardiac death occurs in 4 per 10,000/year. The mechanism is not known, but some cases might be caused by arrhythmias.
• Cerebrovascular ischaemic events may be slightly more common with MVP, possibly due to systemic emboli but only in older patients with mitral regurgitation and abnormal valves, ± atrial fibrillation. Consider aspirin and/or anticoagulation in such high risk patients. Attributing the mitral valve prolapse as the cause of emboli in these patients with other stroke risk factors is highly dubious.
• Thromboembolic events may result from nonbacterial thrombotic lesions on the prolapsing mitral valve or they may originate from arrhythmias. However, modern wisdom appears to be that MVP is not a risk factor for stroke.¹⁰

Patients with mitral valve prolapse have an excellent prognosis although this does depends on the stringency of the criteria used for diagnosis. Only a minority may have infective endocarditis, severe mitral regurgitation requiring valve replacement, sudden cardiac death or potentially dangerous arrhythmias. There is a suggestion that even clinically benign cases may occassionally result in sudden death¹¹ but this is very difficult to prove.

Some recommend screening first degree relatives of affected individuals.¹²