What is PISA in Echocardiography?
The Proximal Isovelocity Surface Area (PISA) method is a well-established echocardiographic technique used to quantify valvular regurgitation and stenosis severity. Based on the principle of flow convergence, PISA exploits the aliasing artifact seen on color Doppler imaging to estimate the volume of blood flowing through a narrowed or leaking heart valve.
This calculator supports two clinical scenarios:
- Mitral Regurgitation (MR): Calculates the Effective Regurgitant Orifice Area (EROA) and Regurgitant Volume (RVol) to grade severity as mild, moderate, or severe.
- Mitral Stenosis (MS): Calculates the Mitral Valve Area (MVA) using the PISA continuity equation to assess stenosis severity.
How the PISA Method Works
When blood accelerates toward a small orifice, it forms concentric, hemispheric shells of equal velocity (isovelocity surfaces). On color Doppler, the point where blood velocity exceeds the Nyquist limit appears as an aliasing boundary — this is the PISA surface.
By measuring the radius of this hemisphere and the aliasing velocity, we can calculate the instantaneous volume flow rate using the formula:
Q = 2π × r² × Va
Where r is the PISA radius in centimetres and Va is the aliasing (Nyquist) velocity in cm/s.
Formulas Used
Mitral Regurgitation
- Flow Rate (Q) = 2π × r² × Va (mL/s)
- EROA = Q / Vmax (cm²) — where Vmax is the peak regurgitant velocity in cm/s
- Regurgitant Volume (RVol) = EROA × VTI (mL)
Mitral Stenosis
- Flow Rate (Q) = 2π × r² × Va × CF (mL/s) — where CF is the angle correction factor (default 1.0)
- Mitral Valve Area (MVA) = Q / (Vmax × 0.88) (cm²)
Severity Grading
Mitral Regurgitation (ASE/ESC Guidelines)
| Grade | EROA (cm²) | RVol (mL) |
|---|---|---|
| Mild | < 0.20 | < 30 |
| Moderate | 0.20 – 0.39 | 30 – 59 |
| Severe | ≥ 0.40 | ≥ 60 |
Mitral Stenosis (MVA)
| Grade | MVA (cm²) |
|---|---|
| Mild | > 1.5 |
| Moderate | 1.01 – 1.5 |
| Severe | ≤ 1.0 |
How to Use This Calculator
- Select the calculation mode: Mitral Regurgitation or Mitral Stenosis.
- Choose your unit system: Metric (radius in cm) or Imperial (radius in mm — automatically converted).
- Enter the PISA radius measured at the aliasing boundary on color Doppler.
- Enter the aliasing velocity (Nyquist limit) set on the color Doppler scale, typically 20–40 cm/s for MR and MS.
- Enter the peak velocity of the regurgitant or transmitral jet in m/s, measured by continuous-wave (CW) Doppler.
- Enter the VTI (velocity-time integral) of the jet in cm.
- For Mitral Stenosis, optionally adjust the correction factor (default 1.0).
- Click Calculate to see your results.
Tips for Accurate Measurement
- Reduce the Nyquist limit to 20–40 cm/s to obtain a well-defined PISA hemisphere.
- Measure the PISA radius at peak systole (for MR) or peak diastole (for MS).
- Ensure the aliasing boundary is hemispheric; irregular shapes may reduce accuracy.
- Use multiple views to confirm findings and reduce measurement variability.
- The PISA method assumes a flat orifice and hemispheric flow convergence zone.
Limitations
The PISA method has several known limitations:
- Assumes a circular, flat orifice — non-circular orifices may lead to underestimation.
- Angle correction may be needed when the regurgitant jet is not perpendicular to the orifice plane.
- Dynamic EROA changes throughout systole are not captured by a single measurement.
- Technical quality of the echocardiographic image significantly affects accuracy.
Medical Disclaimer
This calculator is intended for educational and informational purposes only. It is not a substitute for professional medical judgment, diagnosis, or treatment. All echocardiographic measurements and clinical decisions must be made by qualified healthcare professionals in the context of a complete clinical assessment. The developers of this tool accept no responsibility for clinical decisions made based on its output.