What parameters should be measured by echocardiography (American Society of Echocardiography - ASE) to assess the severity of mitral regurgitation?

Echocardiographic Assessment of Mitral Regurgitation Severity

To assess mitral regurgitation severity by echocardiography, measure effective regurgitant orifice area (EROA), regurgitant volume (RVol), regurgitant fraction (RF), vena contracta width, and evaluate left ventricular and left atrial dimensions—using these parameters together in an integrated approach rather than relying on any single measurement. 1

Quantitative Parameters for Severity Assessment

Primary Quantitative Measurements

The most critical quantitative parameters include: 1

• Effective Regurgitant Orifice Area (EROA): Severe MR is defined as EROA ≥40 mm² (≥0.40 cm²) 1
• Regurgitant Volume (RVol): Represents the actual volume of blood regurgitating back through the valve 1
• Regurgitant Fraction (RF): The percentage of MR volume relative to total LV stroke volume 1
• Vena Contracta Width: Severe MR is indicated by vena contracta width >7 mm (>0.7 cm) 1

Measurement Methods

Use the proximal isovelocity surface area (PISA) method as the primary quantitative approach: 1

• The PISA method calculates EROA and RVol by measuring the flow convergence zone proximal to the regurgitant orifice 1, 2
• PISA-derived EROA and PISA-derived RVol are the strongest predictors of actual regurgitant volume when validated against cardiac MRI 2
• PISA radius itself correlates strongly with MRI-derived regurgitant volume (r=0.65) 2

Measure vena contracta width directly: 1

• The vena contracta represents the smallest flow diameter at the level of the valve, immediately below the flow convergence region 1
• Use a Nyquist limit of 50-60 cm/s for optimal visualization 1
• Vena contracta width <3 mm indicates mild MR, while >7 mm indicates severe MR 1

Qualitative and Supportive Parameters

Structural Assessment

Evaluate valve morphology and mechanism: 1

• Presence of flail leaflet is specific for severe regurgitation and independently predicts regurgitant volume 1, 2
• Identify whether MR is primary (organic) or secondary (functional), as this affects interpretation of quantitative values 1
• Assess for leaflet prolapse, perforation, or restriction 1

Cardiac Chamber Assessment

Measure left ventricular and left atrial dimensions: 1

• Left ventricular end-diastolic volume (LVEDV) independently predicts regurgitant volume and should be weighted heavily 2
• In chronic severe MR, expect LV and LA dilation 1
• In acute severe MR, LV and LA dimensions may be normal or only mildly increased 1
• Assess LV ejection fraction (LVEF), as it affects interpretation of regurgitant volume 1, 3

Pulmonary Venous Flow

Assess pulmonary venous flow patterns by pulsed-wave Doppler: 1, 4

• Systolic flow reversal in pulmonary veins indicates severe MR 1, 4
• Place the sample volume in the pulmonary vein approximately 1 cm from the junction with the left atrium 1

Critical Pitfalls and Caveats

Color Doppler Jet Area Limitations

Do not use color flow jet area as a single parameter to quantify MR severity: 1

• Color Doppler jet area is influenced by technical factors (gain, Nyquist limit, machine settings) and hemodynamic factors (blood pressure, loading conditions) 1
• Eccentric jets adhering to the atrial wall (Coanda effect) significantly underestimate severity 1
• In very severe regurgitation, color Doppler may paradoxically underestimate severity 1

Non-Holosystolic MR

Recognize that MR is often not holosystolic, which affects quantification: 1

• Late systolic MR (as in mitral valve prolapse) or biphasic MR patterns require careful interpretation 1
• PISA calculations may overestimate severity in late systolic MR if applied throughout systole 1
• The duration of MR affects regurgitant volume even with the same EROA 1

Functional vs. Organic MR Differences

Interpret quantitative values differently based on MR mechanism: 1, 3

• Similar EROA values produce lower regurgitant volumes in functional MR compared to organic MR 3
• In secondary MR, a given EROA or RVol can be disproportionately severe depending on LV end-diastolic volume and LVEF 1
• Elevated systolic pulmonary artery pressure (>40 mmHg) accentuates the difference between functional and organic MR 3

Hemodynamic Influences

Account for loading conditions and clinical context: 1

• Positive pressure ventilation and sedation/analgesia significantly reduce MR severity 1
• Blood pressure, heart rate, and afterload all affect the degree of regurgitation 1
• A modest regurgitant volume developing acutely into a non-compliant LA can cause severe symptoms despite seemingly moderate quantitative values 1

Integrated Approach Algorithm

Follow this systematic approach: 1, 2

1. Measure PISA-derived EROA and RVol as your primary quantitative parameters 2
2. Measure vena contracta width as a complementary quantitative parameter 1
3. Assess LV end-diastolic volume as it independently predicts regurgitant volume 2
4. Identify flail leaflet if present, as this is highly specific for severe MR 2
5. Evaluate pulmonary venous flow for systolic flow reversal 1, 4
6. Assess LA and LV size relative to chronicity of MR 1
7. Ensure internal consistency among all parameters 1

Weight these parameters in order of importance: PISA-derived EROA > PISA-derived RVol > LV end-diastolic volume > presence of flail leaflet > vena contracta width 2

When Initial Assessment is Inadequate

Proceed to advanced imaging when transthoracic echocardiography data are internally inconsistent or conflict with clinical presentation: 1

• Transesophageal echocardiography (TEE) provides superior definition of valve morphology and mechanism, though it may underestimate severity due to sedation effects 1
• Cardiac magnetic resonance (CMR) provides the most reproducible quantitative measurements of RVol, RF, LV volumes, and LVEF when echocardiographic assessment is uncertain 1
• 3D echocardiography can directly measure vena contracta area and PISA, overcoming geometric assumptions of 2D methods 5, 6