What is the definition of mitral regurgitation?

Definition of Mitral Regurgitation

Mitral regurgitation is defined as the retrograde flow of blood from the left ventricle into the left atrium during systole due to incomplete closure or coaptation of the mitral valve leaflets. 1

Classification of Mitral Regurgitation

Mitral regurgitation can be classified into two main categories based on underlying pathophysiology:

1. Primary (Organic) Mitral Regurgitation

   • Caused by intrinsic abnormalities of the mitral valve apparatus including:
     • Mitral valve prolapse
     • Myxomatous degeneration
     • Flail leaflets
     • Mitral annular calcification
     • Congenital abnormalities 2

2. Secondary (Functional) Mitral Regurgitation

   • Results from left ventricular dysfunction rather than primary valve pathology
   • Occurs because LV enlargement and remodeling lead to reduced leaflet closing
   • Often seen in ischemic cardiomyopathy or dilated cardiomyopathy 1, 2

3. Mixed Mitral Regurgitation

   • Due to both primary and secondary causes (e.g., mitral valve prolapse with ischemic cardiomyopathy) 1

Pathophysiology

• In primary MR, the valve leaflets, chordae tendineae, papillary muscles, or annulus are directly affected by a pathological process
• In secondary MR, left ventricular dilation causes mitral annular dilatation, papillary muscle displacement, and altered left ventricular geometry affecting valve coaptation 2
• The regurgitant flow creates volume overload on both the left atrium and left ventricle
• In acute severe MR, the hemodynamic effects are profound as the left ventricle and left atrium have not had time to adapt to the additional volume 3

Anatomical Considerations

• In primary MR due to flail leaflets, an LV end-systolic diameter ≥40 mm is associated with increased mortality whether treated medically or surgically 1
• In secondary MR, the effective regurgitant orifice is often crescentic rather than circular in shape, which can lead to underestimation of severity when using certain measurement techniques 1
• The direction of the regurgitant jet can provide clues about the etiology:
  • Anteriorly directed jets suggest intrinsic mitral valve abnormality
  • Posteriorly directed jets are more common in functional MR 2

Diagnostic Assessment

Echocardiography is the primary diagnostic tool for assessing mitral regurgitation:

• Transthoracic echocardiography (TTE) is the most commonly used imaging test for initial evaluation 1
• Transesophageal echocardiography (TEE) is often needed to better define morphology and MR severity, especially when TTE is inconclusive 1
• Cardiac magnetic resonance (CMR) is recommended when the distinction between moderate and severe MR is indeterminate by echocardiography 1

The assessment of MR severity requires integration of multiple parameters, not a single measurement:

• Effective regurgitant orifice area (EROA)
• Regurgitant volume (RVol)
• Regurgitant fraction (RF)
• Color Doppler jet characteristics
• Left atrial and ventricular dimensions 1

Clinical Significance

• Untreated severe mitral regurgitation results in high mortality and frequent hospitalization for heart failure 4
• Yearly mortality rates with medical treatment in patients aged 50 years or older are approximately:
  • 3% for moderate organic regurgitation
  • 6% for severe organic regurgitation 5
• The differentiation between primary and secondary MR is crucial as it affects treatment decisions and outcomes 1

Common Pitfalls in Assessment

• PISA Method Limitations: The proximal isovelocity surface area (PISA) method has significant limitations in measuring MR severity, particularly in secondary MR where the regurgitant orifice is often crescentic rather than circular 1
• Underestimation of Severity: In secondary MR, standard echocardiographic methods may underestimate the true effective regurgitant orifice area due to the non-circular shape of the orifice 1
• Overreliance on Single Parameters: Guidelines emphasize that assessment of MR severity requires integration of multiple parameters, not just a single measurement 1

Understanding the definition and classification of mitral regurgitation is essential for proper diagnosis, risk stratification, and treatment planning. The distinction between primary and secondary MR is particularly important as it guides therapeutic approaches and influences prognosis.