What is the formula to calculate Mitral Regurgitation (MR) regurgitant flow?

Formula for Calculating Mitral Regurgitation Regurgitant Flow

The formula to calculate mitral regurgitation (MR) regurgitant volume (RVol) using the Proximal Isovelocity Surface Area (PISA) method is: RVol = EROA × VTI, where EROA (Effective Regurgitant Orifice Area) = 2πr² × aliasing velocity ÷ peak MR velocity, and VTI is the velocity time integral of the MR jet. 1

Understanding the Components of the Formula

• EROA (Effective Regurgitant Orifice Area): Calculated as 2πr² × (aliasing velocity ÷ peak MR velocity), where r is the PISA radius measured from the first color alias to the mitral valve orifice 1, 2
• VTI (Velocity Time Integral): Measured from the continuous-wave Doppler of the MR jet 1
• Regurgitant Volume (RVol): The product of EROA and VTI of the MR jet by continuous-wave Doppler 1

Important Considerations and Limitations

Technical Limitations of PISA Method

• PISA assumes a hemispheric flow convergence geometry, which is rarely the case in secondary MR 1
• The EROA shape in secondary MR is usually crescentic rather than round, leading to underestimation 1
• Errors in radius measurement are squared, resulting in large variance in calculated EROA 1
• Single-frame measurements can significantly over or underestimate MR severity, especially in non-holosystolic MR 1

Timing Considerations

• MR is often dynamic during systole, especially in secondary MR which typically has a biphasic pattern 1
• Using a single time point (early, mid, or late systole) can lead to significant errors:
  • Early systolic measurement may overestimate severity 1
  • Mid-systolic measurement may underestimate severity 1
  • Late systolic measurement may be inaccurate in prolapse cases 1

Alternative and Complementary Approaches

• 3D Echocardiography: Allows direct measurement of EROA and can avoid underestimation issues inherent to 2D PISA 1
• Volumetric Method: Calculate RVol as the difference between total LV stroke volume and forward stroke volume (LVOT stroke volume) 1
• Angle Correction: For eccentric jets, multiply the calculated RVol by the convergence angle/180° to reduce overestimation 3

Practical Application Algorithm

1. Measure PISA radius (r):

   • Set appropriate aliasing velocity (typically around 30-40 cm/s) 1
   • Measure the radius from the first color alias to the mitral valve orifice 2

2. Calculate EROA:

   • Apply formula: EROA = 2πr² × (aliasing velocity ÷ peak MR velocity) 1, 2
   • For eccentric jets, consider angle correction 3

3. Measure VTI:

   • Obtain continuous-wave Doppler of MR jet 1
   • Trace the dense portion of the spectral display 1

4. Calculate Regurgitant Volume:

   • RVol = EROA × VTI 1

5. Validate with complementary methods:

   • Compare with volumetric methods 1
   • Check for consistency with other echocardiographic parameters 1

Common Pitfalls to Avoid

• Single-frame measurement errors: In non-holosystolic MR, using a single frame can significantly overestimate severity 1
• Assuming hemispheric flow convergence: The actual shape is often asymmetrical, especially in secondary MR 1
• Neglecting the effect of driving velocity: High-velocity jets (>6 m/s) can appear larger on color Doppler despite mild MR 1
• Relying solely on PISA: Guidelines recommend using multiple parameters to determine MR severity 1
• Measurement errors: Small errors in radius measurement (e.g., 7mm vs. 8mm) can change classification from mild to severe MR 1

By understanding these limitations and applying appropriate corrections, the PISA method can provide valuable quantitative assessment of MR severity when used as part of a comprehensive evaluation 1.