What is the most common cause of mitral regurgitation?

Most Common Cause of Mitral Regurgitation

Degenerative mitral valve disease (myxomatous degeneration) is the most common cause of mitral regurgitation in developed countries. 1

Etiology of Mitral Regurgitation

Mitral regurgitation (MR) can be classified into two main categories based on etiology:

Primary (Organic/Structural) MR

Caused by intrinsic valvular disease, with the most common causes being:

1. Degenerative disease - Most common in developed countries 1, 2

   • Myxomatous degeneration (mitral valve prolapse)
   • Fibroelastic degeneration
   • Barlow's disease
   • Marfan syndrome
   • Ehlers-Danlos syndrome
   • Annular calcification

2. Other causes of primary MR:

   • Rheumatic disease (most common in developing countries) 2
   • Infective endocarditis
   • Ruptured papillary muscle (acute, following myocardial infarction)
   • Toxic valvulopathy

Secondary (Functional/Non-structural) MR

Occurs despite a structurally normal valve due to:

1. Left ventricular dysfunction causing:

   • Reduced closing force on leaflets
   • Systolic tethering of leaflets
   • Papillary muscle displacement
   • Annular dilation 1

2. Other causes of secondary MR:

   • Atrial functional MR (pure annular dilation due to left atrial enlargement in chronic atrial fibrillation or restrictive cardiomyopathy) 1
   • LV dyssynchrony from bundle branch block or right ventricular pacing 1

Pathophysiologic Mechanisms

Myxomatous Degeneration (MVP)

• Characterized by expansion of mitral valve leaflet area
• Elongated chordae tendineae
• Potential for chordal rupture
• Mitral annular dilation 3
• Abnormal bulging of leaflets into the left atrium during systole 4
• Genetic etiology with complex inheritance patterns 4
• Molecular disorder involving connective tissue with altered extracellular matrix 4

Carpentier's Classification of Leaflet Motion

1. Type I: Normal leaflet motion (seen in endocarditis, perforation, clefts)
2. Type II: Excessive leaflet motion (prolapse or flail)
3. Type III: Restricted leaflet motion
   • IIIA: Restriction during both systole and diastole (rheumatic disease)
   • IIIB: Restriction during systole only (ischemic/non-ischemic cardiomyopathy) 1

Clinical Significance

• Severe MR leads to left ventricular overload and dysfunction if left untreated 2
• Annual mortality rates in patients ≥50 years old:
  • 3% for moderate organic MR
  • 6% for severe organic MR 2
• Outflow obstruction is a strong predictor of disease progression to heart failure and stroke 1
• Patients with redundant leaflets may be at higher risk for sudden death and infective endocarditis 5

Diagnostic Approach

Echocardiography is the primary diagnostic tool:

• Transthoracic echocardiography (TTE) for initial assessment
• Transesophageal echocardiography (TEE) for better definition of morphology and severity
• Cardiac MRI when echocardiographic assessment is uncertain 1

Management Considerations

• Surgery is the only treatment proven to improve symptoms and prevent heart failure 2
• Valve repair improves outcomes compared to valve replacement, reducing mortality by approximately 70% in severe organic MR 2
• Best results are obtained in asymptomatic patients operated on in advanced repair centers with low operative mortality (<1%) and high repair rates (≥80-90%) 2

Early detection and accurate assessment of mitral regurgitation are crucial for optimal management and improved outcomes.