• Degenerative (overlap with MV prolapse syndrome)
  • Usually occurs as a primary condition (Barlow disease or fibroelastic deficiency) but has also been associated with heritable diseases affecting the connective tissue including Marfan syndrome, Ehlers-Danlos syndrome, osteogenesis imperfecta, etc.
  • May be familial or nonfamilial. Occurs in 1.0–2.5% of the population (based on stricter echocardiography criteria) in a female-to-male ratio of 2:1.
  • Most common reason for MV surgery.
  • Myxomatous proliferation and cartilage formation can occur in the leaflets, chordae tendineae, and/or annulus.
• Rheumatic
  • May be pure MR or combined MR/MS.
  • Caused by thickening and/or calcification of the leaflets and chords.
• Infective endocarditis: Usually caused by destruction of the leaflet tissue (i.e., perforation).

• Dilated cardiomyopathy
  • Mechanism of MR is due to both of the following:
  • Annular dilatation from ventricular enlargement.
  • Papillary muscle displacement due to ventricular enlargement and remodeling prevents adequate leaflet coaptation.
• Ischemic
  • Ischemic MR is mostly a misnomer, because this is primarily postinfarction MR, not MR caused by active ischemia.
  • Mechanism of MR usually involves one or both of the following:
    • Annular dilatation from ventricular enlargement.
    • Local LV remodeling with papillary muscle displacement (both the dilatation of the ventricle and the akinesis/dyskinesis of the wall to which the papillary muscle is attached can prevent adequate leaflet coaptation).
  • Rarely, MR may develop acutely from papillary muscle rupture (more commonly of the posteromedial papillary muscle).

Congenital, infiltrative diseases (i.e., amyloid), SLE (Libman-Sacks lesion), hypertrophic cardiomyopathy with obstruction, mitral annular calcification, paravalvular prosthetic leak, drug toxicity (e.g., Fen-phen)

• Ruptured papillary muscle, ruptured chordae tendineae, infective endocarditis