Mitral valve prolapse

The competence ofthe mitral valve depends on several features. Firstly, its structure must be normal. Secondly, there must be co-ordinated interaction of the mitral leaflets, annulus, chordae tendineae, papillary muscles, and left ventricular wall.1-3 Mitral regurgitation may result from any condition which deforms or immobilises these structures. Our increasing knowledge of mitral valve function has focused attention on a fascinating syndrome, recently reviewed by Devereux et al.4 Variously named Barlow's syndrome, the late systolic click syndrome, floppy mitral valve, and mitral leaflet prolapse syndrome, it is not uncommon though readily missed; not overtly rheumatic in origin though this has been suggested. Occasionally familial, usually benign, in some patients it is associated with ill-explained complications such as chest pain, ventricular ectopic beats, angiographic abnormalities in left ventricular contractile pattern, and electrocardiographic abnormalities. Gallevardin described the distinctive auscultatory features of mitral valve prolapse back in 1913, and he also observed the effects of posture on the timing of midsystolic clicks and the often associated late systolic murmurs. He mistakenly attributed these findings to pleuropericardial adhesions, and this was not refuted until 1961, when Reid suggested that the click was caused by abrupt tensing of the chordae and the late systolic murmur by late systolic mitral regurgitation.5 Barlow first showed angiographically that there was late systolic prolapse ofthe posterior mitral leaflet.6 In 1968 Engle drew attention to an abnormality of left ventricular contraction,7 and this has been extended8 9 to designate mitral valve prolapse as a segmental cardiomyopathy in which the altered shape of the ventricle in systole leads to slackening of the chordae and leaflets and consequent prolapse into the left atrium.10 The most recent theory suggests that the underlying abnormality is congenital or acquired dilatation of the mitral annulus" or defective systolic contraction of the annulus, possibly associated with defective contraction of the basal portion of the left ventricle.9 After a period of confusion and over-diagnosis echocardiography has greatly aided the recognition and understanding of mitral prolapse.'2 Prolapse of one or both leaflets into the left atrium can be directly visualised, and the click has been shown to occur at the moment of prolapse in late systole. Both the click and prolapse occur at a constant ventricular diameter, explaining the effect of posture and drugs on their timing.413 Prompt squatting or infusion of a pressor agent increases left ventricular volume and so reduces or abolishes prolapse, but they may induce chest pain.'4 In one individual clicks may be multiple or absent and move their position in systole." The murmur may vary from absent to a honk or whoop which can be heard across the room.'6 The auscultatory features are highly variable, and prolapse which is evident angiographically or echocardiographically may occasionally be clinically silent. Other inconstant clinical features are jerky pulses and a frankly bifid left ventricular impulse.'517 Electrocardiographic abnormalities are common.815 There is T wave inversion in inferior and sometimes also lateral leads in about one-third of cases. Ventricular premature beats have also been reportdd and supraventricular tachycardia is common. Abnormalities of rhythm are often provoked by effort. Most patients have no symptoms; in those who do these are often ill explained. Some patients are aware of an intermittent noise in the heart. Complaints of fatigue, faintness, shortness of breath, and decreased exercise tolerance may be due to exercise-induced dysrhythmias or to chest pain-which is common, often atypical, but sometimes highly suggestive of coronary origin. Wooley has recently suggested (in half fun, whole earnest) that a previously well-known but now extinct disease might in truth have been mitral valve prolapse syndrome'8: the non-entity emotively described as "soldier's heart" or "the effort syndrome," eponymously as Da Costa's syndrome, or simply as neurocirculatory asthenia or "disorderly action of the heart." In the era of "soldier's heart" diagnosis had to remain conjectural unless the outcome of a disease was frequently fatal. Who can ever find out whether Wooley is right? The incidence of mitral valve prolapse depends on how hard it is sought. The syndrome is uncommon in childhood, becomes more frequent in women than in men, but then gradually increases in frequency and in old age is probably equally common in either sex. Though mitral prolapse can result from ischaemic papillary muscle and segmental contraction abnormality, coronary artery disease is an uncommon association. Nearly all patients with Marfan's syndrome have echocardiographic or clinical evidence of mitral prolapse, and Marfan's syndrome has been recognised in about 4%0 of reported cases.4 Myxomatous degeneration leads to ballooning of leaflets and thinning and elongation of chordae. The mitral annulus may also become appreciably dilated. Abnormalities of the thoracic cage without Marfan's syndrome have also been described in mitral prolapse: a narrow anteroposterior diameter to the chest with a straight back (making the auscultatory features much easier to recognise). The frequency of angiographic mitral prolapse in secundum atrial septal defect has only recently been fully recognised; it has been reported in up to one-third of patients in whom it has been specifically sought. The prognosis is usually benign, but four major complications may supervene. Sudden chordal rupture may lead to the abrupt development of severe mitral regurgitation, and this medical emergency is now well recognised. Gradually progressive mitral regurgitation due to increasing prolapse accounts for about 10% of valve replacements for isolated mitral regurgitation in adults. Infective endocarditis is rare, though an undoubted hazard, and this too can be responsible for the advent of a serious leak. Sudden death is the least common complication; it may be related to ventricular dysrhythmias19 or to an associated re-entry pathway leading to a catastrophic rapid ventricular rate should atrial fibrillation develop.20