PISA Calculator
The PISA calculator uses the flow-convergence principle from Doppler echocardiography to quantify mitral regurgitation. Enter the PISA radius, aliasing velocity, peak MR jet velocity, and VTI to compute the effective regurgitant orifice area (EROA), regurgitant volume (RVol), and volume flow rate. Switch to mitral stenosis mode to derive mitral valve area (MVA) using the angle-corrected formula. Results are graded against American Society of Echocardiography (ASE) thresholds.
Formula
Worked example
With r = 0.8 cm, Vr = 40 cm/s, Vmax = 500 cm/s, VTI = 150 cm: PISA = 2π × 0.8² ≈ 4.02 cm². VFR = 4.02 × 40 = 160.8 mL/s. EROA = 160.8 ÷ 500 ≈ 0.32 cm² (32 mm², moderate-severe). RVol = 0.32 × 150 = 48 mL/beat.
What the PISA method measures
Proximal Isovelocity Surface Area (PISA) is an echocardiographic technique that applies the principle of conservation of mass to quantify valve regurgitation and stenosis. As blood accelerates toward a regurgitant orifice, it forms concentric hemispherical shells of equal velocity. Because all the blood crossing any shell must pass through the orifice, the flow rate at the shell equals the flow rate at the orifice. The PISA method exploits colour Doppler aliasing to identify the radius of one such shell, then calculates the surface area of that hemisphere (2pi x r squared) and multiplies by the known aliasing velocity to get the volume flow rate. Dividing by peak orifice velocity gives the effective regurgitant orifice area (EROA), and multiplying EROA by the VTI of the jet gives the regurgitant volume per beat.
How to acquire PISA measurements
Optimise the apical four-chamber or two-chamber view to display the mitral valve and left atrium. Activate colour Doppler and zoom in on the valve. Shift the colour baseline downward (for MR) by 20-40 cm/s until a clear hemispheric aliasing boundary appears on the atrial side of the valve. Freeze the image at mid-systole, when the MR jet peaks, and measure the radius from the aliasing boundary to the coaptation point. Record a continuous-wave Doppler trace of the full MR envelope from the same beat and measure peak velocity and VTI by planimetry. For mitral stenosis, measure the PISA on the left ventricular side of the valve at the peak of diastole and determine the angle between the leaflets at the PISA level. The angle correction factor (alpha/180) accounts for the fact that the convergence zone is a sector of a hemisphere rather than a full hemisphere when the leaflets are not fully open.
Interpreting EROA and regurgitant volume
The American Society of Echocardiography (ASE) and European Association of Cardiovascular Imaging (EACVI) define four severity grades. Mild MR has EROA below 20 mm squared and RVol below 30 mL per beat. Moderate MR spans 20-39 mm squared and 30-59 mL per beat. Severe MR is defined by EROA at or above 40 mm squared or RVol at or above 60 mL per beat. These thresholds are well validated for primary (degenerative) MR. For functional (secondary) MR, some evidence suggests that lower thresholds (EROA 20 mm squared, RVol 30 mL) may indicate hemodynamically significant regurgitation because of the adverse left ventricular loading state. Always integrate PISA results with vena contracta width, quantitative Doppler, pulmonary vein flow patterns, and chamber size before grading severity.
Angle correction and mitral valve area
For mitral stenosis, the standard PISA formula assumes a full hemisphere, which overestimates flow because the open leaflets restrict the convergence zone. The angle correction multiplies PISA by alpha/180, where alpha is the angle in degrees between the two leaflets at the PISA radius level. A normal open mitral valve has an angle near 180 degrees, so the correction approaches 1. In moderate stenosis the angle is typically 90-130 degrees. The corrected formula for mitral valve area is MVA = (2pi x r squared x Vr x alpha/180) / Vmax. Normal MVA is 4.0-5.0 cm squared. The ASE grades mitral stenosis as mild above 1.5 cm squared, moderate at 1.0-1.5 cm squared, and severe below 1.0 cm squared.
Limitations and clinical integration
PISA assumes a perfectly hemispherical convergence zone and is derived from a single video frame at mid-systole. Eccentric or wall-hugging jets distort the hemisphere, causing underestimation. Non-holosystolic jets (e.g., mid-systolic prolapse) cause overestimation because the peak radius does not represent the average flow across the full systole. Colour gain, Nyquist limit setting, and image magnification all affect the measured radius, so small errors in radius have a squared effect on PISA and a downstream effect on EROA. Whenever PISA results seem inconsistent with other echo or clinical findings, supplement with vena contracta area, volumetric Doppler, or cardiac MRI for a definitive assessment.
ASE mitral regurgitation severity thresholds
| Severity | EROA (mm²) | RVol (mL/beat) | Regurgitant fraction |
|---|---|---|---|
| Mild | < 20 | < 30 | < 30% |
| Mild-Moderate | 20-29 | 30-44 | 30-39% |
| Moderate-Severe | 30-39 | 45-59 | 40-49% |
| Severe | ≥ 40 | ≥ 60 | ≥ 50% |
Based on the 2017 American Society of Echocardiography guidelines for grading valvular regurgitation.
Frequently asked questions
What is PISA in echocardiography?
PISA stands for Proximal Isovelocity Surface Area. It is a quantitative Doppler technique that uses the flow-convergence principle to estimate the volume of blood leaking through a defective heart valve each beat. By measuring the radius of a hemispherical colour-Doppler aliasing boundary and knowing the aliasing velocity, clinicians can derive the volume flow rate and the effective size of the regurgitant orifice without invasive catheterisation.
What EROA indicates severe mitral regurgitation?
The American Society of Echocardiography defines severe primary (degenerative) mitral regurgitation as an EROA at or above 40 mm squared and a regurgitant volume at or above 60 mL per beat. For functional (secondary) MR, some guidelines use a lower threshold of 20 mm squared and 30 mL per beat because the LV is already compromised. Always combine EROA with vena contracta, RVol, and chamber dimensions before making a severity determination.
Why does the PISA formula use 2pi r squared?
A sphere has a surface area of 4pi r squared. The PISA hemisphere is exactly half a sphere, so its surface area is 2pi r squared. Every point on this hemispherical shell is moving at the same velocity (the aliasing velocity Vr), so the flow rate through it is 2pi r squared times Vr in mL/s. Conservation of mass then requires that this equals the flow rate through the regurgitant orifice.
What is the aliasing velocity and how do I choose it?
The aliasing velocity (Nyquist limit) is the colour Doppler velocity at which colour wraps from red to blue (or vice versa). Shifting the baseline changes where aliasing occurs. The ASE recommends setting the aliasing velocity to 20-40 cm/s so that the hemispheric PISA shell appears clearly with a smooth, well-defined boundary. A shell that is too small (Nyquist too high) or too large and asymmetric (Nyquist too low) reduces accuracy.
How accurate is PISA compared with cardiac MRI?
PISA has moderate-to-good agreement with phase-contrast cardiac MRI for grading primary MR, with reported correlations of r = 0.75-0.90 in controlled studies. However, PISA tends to underestimate eccentric and multiple-jet regurgitation and can vary with acquisition technique. Cardiac MRI is considered the non-invasive gold standard for regurgitant volume quantification when echo results are inconclusive.
Can PISA be used for tricuspid or aortic regurgitation?
Yes, the same flow-convergence principle applies to any regurgitant valve. For tricuspid regurgitation the PISA hemisphere is measured on the right atrial side in the apical four-chamber view. For aortic regurgitation, flow convergence is imaged in the left ventricular outflow tract from a parasternal long-axis view. The same formulas apply, though severity thresholds differ: severe TR is defined by EROA above 40 mm squared and severe AR by EROA above 30 mm squared.