Mitral Valve Prolapse

Description

• Mitral valve prolapse (MVP) is a systolic billowing of one or both mitral leaflets into the left atrium (LA) during systole ± mitral regurgitation (MR).
• More specifically, MVP is a single or bileaflet prolapse of at least 2 mm superior displacement into the LA during systole on the parasternal long-axis annular plane of the valve on echocardiogram ± leaflet thickening.
  • Classic: prolapse with >5 mm of leaflet thickening
  • Nonclassic: prolapse with <5 mm of leaflet thickening
• Synonym(s): systolic click-murmur syndrome; billowing mitral cusp syndrome; myxomatous mitral valve; floppy valve syndrome; redundant cusp syndrome; Barlow syndrome

Epidemiology

• Predominant age: MVP has been described in all age groups.
• Initial descriptions based on clinical examinations suggested a 2:1 female predominance. Using modern echocardiogram criteria, men and women are affected equally (1).
• The most serious consequences of hemodynamically significant MR occur in patients age >50 years (1).

Prevalence
MVP is the most common valvular abnormality, affecting 2–3% of the general population (1).

Etiology and Pathophysiology

• The pathology causing MVP is multifactorial and includes the following:
  • Abnormal valve tissue
    • Myxomatous degeneration: redundant layers of leaflet “hooding” the cords, chordal elongation, and annular dilatation
    • Myxoid leaflets are more elastic and less stiff than normal valves.
    • Chordal rupture is more common.
  • Disparity in size between the mitral valve and the left ventricle (LV)
  • Connective tissue disorders
• MVP is often associated with variable degrees of MR which occurs in 9% of patients.
• The degree of MR depends on the degree of leaflet thickening and amount of flail or partially flail segments (2). When this occurs, 10-year mortality is 37% (2).
• Frequently, there is enlargement of the LA and LV.
• Mitral annulus is often dilated.
• Involvement of other valves may occur (tricuspid valve prolapse 40%, pulmonic prolapse and aortic prolapse 2–10%).
• Possible increased vagal tone
• Possible increased urine epinephrine and norepinephrine
• MVP patients often have orthostatic hypotension and tachycardia.
• Genetics causes proliferation of the spongiosa layer of the leaflets and fibrosis on the surface of them (1).
• Thinning and elongation of chordae tendineae
• The mitral valve differentiates during days 35 to 42 of fetal development, the same time as differentiation of the vertebrae and ribs.

• Familial MVP is inherited as an autosomal dominant trait but with variable expressivity and incomplete penetrance.
• Two genetic loci identified
  • MMVP1 on chromosome 16p11.2–p12.1
  • MMVP2 on chromosome 11p15.4

Risk Factors

• MVP is a primary cardiovascular disorder.
• MVP is more likely to occur in patients with connective tissue disorders (see “Commonly Associated Conditions”).
• Physical characteristics associated with MVP
  • Straight thoracic spine
  • Pectus excavatum
  • Asthenic body habitus
  • Low body mass index (BMI)
  • Scoliosis or kyphosis
  • Hypermobility of the joints
  • Arm span > height
  • Narrow anteroposterior (AP) diameter of the chest

Commonly Associated Conditions

• Marfan syndrome (91% of Marfan syndrome patients have MVP, although large majority of MVP patients do not meet criteria for Marfan.)
• Ehlers-Danlos syndrome
• Hypertrophic cardiomyopathy
• Pseudoxanthoma elasticum
• Osteogenesis imperfecta
• von Willebrand disease
• Primary hypomastia
• Graves disease
• Rheumatic heart disease