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September 2001
Vol. 4, No. 9, p 76.
diseases and disorders

The murmuring heart:
Mitral valve prolapse

opening art
Imagine a double gate that fits neatly together to keep things where they are supposed to be. If the hinges of the gate break, the sagging pieces will not close, letting the dog out and other things in. The broken gate scenario is analogous to mitral valve prolapse (MVP).

The mitral valve has a set of “gates” that swing open to permit blood to flow from the upper left chamber to the lower ventricle. The parts fit firmly together to keep blood from reentering that chamber. In MVP, the two flaps, or cusps, do not close properly and blood leaks back into the upperchamber (mitral regurgitation). The leakage occurs during the systolic pumping of the left ventricle, and the cusps billow into the atrium, producing a click and a murmur during regurgitation.

The mitral valve apparatus is composed of the mitral annulus, valve leaflets, chordae tendineae (cord structures that fasten the valves to the lower chamber), papillary muscles, and supporting left ventricular, left atrial, and aortic walls. A disturbance in any of these parts can result in dysfunction of the valve apparatus and prolapse of the mitral leaflets during systole. The valve leaflets are delicate; degeneration of the middle or spongiosa layer leads to an excess of mucopolysaccharide tissue that makes the layer—like the sagging gate—fit improperly. The small cords that operate the valve lengthen, and deposits of fibrin can form at the mitral–left atrialangle.

figureA controversial history
Traced to the 1600s, MVP has had a variety of names: irritable heart, soldier’s heart, Barlow’s syndrome, and DaCosta’s syndrome. William Osler, an eminent 19th-century physician, noted similarities between the condition and certain symptomssuch as panic attacks, depression, and insomnia, especially in women.

Current studies using echocardiographic diagnosis have revealed that the assumptions linking MVP to the array of symptoms were flawed(Pleva, M. C.; et al. eMedicine Journal, May 25, 2001; www.emedicine.com/emerg/topic316.htm). It is now generally agreed that symptoms other than palpitations are rare. The symptoms of MVP syndrome may occur in a particular patient as a result of chance rather than cause and effect.

In most studies, MVP is associated with benign symptoms. In fact, the Framingham Heart Study of 3491 participants (Freed, L.A.; et al.N. Engl. J. Med. 1999, 341, 1–7) found that MVP affected about 2.4% rather than the 5–35% reported in earlier studies.Previous studies used M-mode technology, a form of echocardiography, but newer color Doppler equipment has minimized false positive and false negative diagnoses. The study also questioned the assumption that women have the condition in the proportion of 3:1.

Although serious complications of MVP are rare, they include

  • Endocarditis. The absolute incidence of endocarditis is extremely low for the MVP population (Dajani, A.; et al. J. Am. Med. Assoc. 1997, 277, 1794–1801).However, a single dose of a prophylactic antibiotic is recommended for patients undergoing dental procedures associated with bleeding from soft or hard tissues.
  • Patients with longstanding MVP may experience progressive mitral regurgitation that could cause visual and cardiovascular problems.
  • Sudden death.

A genetic connection?
The primary form of MVP may be carried by an autosomal dominant gene on chromosome 3. Because the condition is frequently found in people with Marfan’s syndrome, some scientistsspeculate that MVP is a generalized disease of the connective tissue. The relationship to other connective tissue diseases may support the idea that MVP results from defective embryogenesis of cell lines of mesenchymal origin.

Hungarian scientists studying angiotensin II type 1 receptor (AT1) in 76 white subjects with MVP found several associations between adenosine–cytosine1166 polymorphism of the AT1 gene (Szombathy, T.; et al. Am. Heart J. 2000, 139, 101–105). The A-C transversion is located in an unregulated region of the gene and is a possible marker linking MVP with adjacent unknown genes. The location of the AT1 gene on chromosome 3 makes the site a candidate region for the MVP gene.

Further information

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