What is a myxomatous mitral valve?

Myxomatous Mitral Valve: Pathophysiology and Clinical Implications

A myxomatous mitral valve is characterized by abnormal thickening and redundancy of the valve leaflets due to proliferation of spongiosa tissue and accumulation of mucopolysaccharides, causing systolic billowing of the leaflets into the left atrium, which may lead to mitral regurgitation. 1

Pathophysiology

Myxomatous mitral valve degeneration involves specific structural changes:

• Histological features:

  • Marked proliferation of the spongiosa (the delicate myxomatous connective tissue layer)
  • Acid mucopolysaccharide accumulation
  • Focal interruption of the fibrosa (dense collagen layer that provides structural support)
  • Disruption of the stratified structure of the leaflets 1, 2

• Microscopic changes:

  • Extracellular matrix remodeling
  • Decreased cell numbers in myxomatous areas
  • Reduced connective tissue density
  • Increased glycosaminoglycan expression 3

• Molecular mechanisms:

  • Altered activity of matrix metalloproteinases
  • Transforming growth factor-β superfamily involvement
  • Weakened protection against oxidative stress 2

Clinical Spectrum

Myxomatous mitral valve disease presents along a spectrum:

1. Fibroelastic deficiency: Focal prolapse with otherwise normal valve anatomy
2. Forme fruste: Intermediate pathoanatomical variant
3. Barlow's syndrome: Diffuse process with excess, redundant, billowing tissue 1

Diagnostic Criteria

Echocardiographic diagnosis requires:

• Valve prolapse of 2 mm or more above the mitral annulus in the long-axis parasternal view
• With or without leaflet thickening (≥5 mm, measured during diastasis)
• With or without mitral regurgitation 1

Epidemiology and Risk Factors

• Prevalence: 1% to 2.5% of the general population 1
• Genetics:
  • Autosomal dominant inheritance with incomplete penetrance
  • Multiple chromosomal loci identified 4
  • Increased incidence in connective tissue disorders (Marfan syndrome)
• Associated conditions:
  • Von Willebrand's disease and other coagulopathies
  • Primary hypomastia
  • Thoracic skeletal abnormalities (straight thoracic spine, pectus excavatum) 1

Clinical Implications and Complications

Myxomatous mitral valve can lead to several complications:

• Mitral regurgitation: Ranges from absent to severe; the most frequent predictor of cardiovascular mortality 1
• Endocarditis: Leading predisposing cardiovascular diagnosis for infective endocarditis 1
• Arrhythmias: Increased incidence of complex ventricular ectopy and supraventricular arrhythmias 1
• Cerebrovascular events: Increased risk of stroke, particularly in patients under 45 years 1
• Sudden death: Rare complication (<2% of cases), highest incidence in familial forms 1

Risk Stratification

Echocardiographic features associated with higher risk:

• Leaflet thickness ≥5 mm
• Moderate to severe mitral regurgitation
• Left atrial enlargement
• Left ventricular dysfunction 1

Management Considerations

For patients with significant mitral regurgitation due to myxomatous degeneration:

• Surgical repair techniques:

  • Nonresection techniques using PTFE neochord reconstruction
  • Focal triangular resection with annuloplasty ring
  • Sliding leaflet valvuloplasty with annuloplasty ring 1

• Repair complexity factors:

  • Posterior leaflet prolapse has highest repair success rates
  • Complex cases (anterior leaflet, bileaflet, or Barlow's disease) should be referred to experienced mitral valve surgeons 1

Important Caveats

• Myxomatous mitral valve should not be confused with rheumatic mitral valve disease, which involves commissural fusion and leaflet thickening due to inflammatory processes
• The natural history is heterogeneous, ranging from benign with normal life expectancy to progressive with significant morbidity
• Regular echocardiographic follow-up is essential for patients with myxomatous mitral valve to monitor for progression of regurgitation and ventricular function