Mitral regurgitation: mechanisms and mitral valve prolapse
THE CONTEXT
Mitral regurgitation can arise from the valve apparatus or from ventricular disease that prevents leaflet coaptation. Its haemodynamic effects differ between acute and chronic disease.
Primary and secondary regurgitation
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Primary mitral regurgitation results from pathology of the valve or valve apparatus.
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Secondary, or functional, mitral regurgitation results from failure of leaflet coaptation due to left ventricular pathology, with or without dilatation of the mitral valve annulus.
Acute versus chronic effects
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Chronic mitral regurgitation gradually dilates the left atrium, initially with little pressure increase and relatively few symptoms.
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Chronic left ventricular volume overload causes slow ventricular dilatation and a gradual rise in left ventricular diastolic and left atrial pressures.
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Acute mitral regurgitation rapidly raises left atrial pressure because left atrial compliance is normal. Marked symptomatic deterioration and acute pulmonary oedema often follow.
Mitral valve prolapse
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Mitral valve prolapse, also called a floppy mitral valve, is a common cause of mild mitral regurgitation.
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Possible underlying changes include a developmental valve abnormality or degenerative myxomatous change. Association with Marfan syndrome is rare.
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In mild prolapse, the valve remains competent but bulges into the atrium during systole, producing a mid-systolic click without a murmur.
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When regurgitation is present, a late systolic murmur follows the click and lengthens as regurgitation becomes more severe. The click may be absent, and findings can vary with posture and respiration.
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Progressive chordal elongation increases regurgitation. Chordal rupture causes sudden severe regurgitation and is rare before the fifth or sixth decade.
Associated features and prognosis
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Mitral valve prolapse is associated with typically benign arrhythmias, although an association with malignant arrhythmias is emerging.
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Atypical chest pain and a very small risk of embolic stroke or transient ischaemic attack may occur. Overall long-term prognosis is good.