Free PISA Calculator

Introducing the PISA Calculator for Mitral Valve Assessment

The free online Proximal Isovelocity Surface Area (PISA) calculator provides clinicians with a rapid, evidence‑based tool for quantifying mitral regurgitation and mitral stenosis. By leveraging the PISA method, the instrument determines the effective regurgitant orifice area (EROA or ERO), the regurgitant volume (RVol), the mitral valve area (MVA), and the volume flow rate. It functions equally well as a PISA MR calculator, an EROA calculator, and a dedicated mitral valve area calculator.

The Physical Principle Behind PISA

PISA is an echocardiographic technique grounded in fluid dynamics. According to the Venturi effect, blood accelerates as it approaches a narrowed orifice—the more severe the narrowing, the greater the velocity. This acceleration creates a series of concentric shells of equal velocity proximal to the orifice. The outermost shell that is clearly visible on color Doppler is the proximal isovelocity surface area (PISA). In reality, the flow begins to speed up before it reaches the orifice, so the flow convergence zone takes the shape of a hemisphere rather than a flat disk. Therefore the geometric model uses the surface area of a hemisphere, $2\pi r^{2}$, where $r$ is the measured radius.

How to Measure the PISA Radius on Echo

Obtaining a reliable PISA measurement requires attention to several technical details:

• Use color Doppler with an appropriate Nyquist limit (typically between 30–40 cm/s) so that the aliasing contour is easily distinguishable.
• Identify the vena contracta—the narrowest, fastest portion of the regurgitant jet—and measure the radial distance from this point to the farthest edge of the clearly aliased flow convergence.
• Perform the measurement at the moment of peak regurgitation (usually mid‑systole for mitral regurgitation or throughout diastole for stenosis).
• Capture multiple echocardiographic planes and select the view that demonstrates the largest, most well‑defined PISA radius.
• If possible, average the radius over two to three consecutive beats.

Key Input Parameters

The calculator requires several Doppler‑derived quantities:

Parameter	Symbol	Unit	Purpose
PISA radius	$r$	cm	Half‑hemisphere geometric input
Aliasing velocity at $r$	$V_r$	cm/s	Velocity at the color alias boundary
Peak mitral velocity	$V_{\max}$	cm/s	Continuous‑wave Doppler peak velocity
Leaflet angle	$\alpha$	degrees	Angle between mitral leaflets (stenosis only)
Velocity time integral	$VTI$	cm	Integral of the regurgitant jet velocity profile

Clinical Worked Example

Consider a 56‑year‑old man with suspected mitral stenosis. The following echo data were acquired:

• $V_{\max} = 30\ \text{cm/s}$
• $r = 0.5\ \text{cm}$
• $V_r = 10\ \text{cm/s}$
• $\alpha = 25^\circ$
• $VTI = 10\ \text{cm}$

The calculator can be used to answer three separate questions:

1. Mitral valve area (MVA) – Enter $V_{\max}$, $r$, $V_r$, and $\alpha$. The tool computes the MVA and classifies the stenosis severity. In this case the MVA fell below 1.0 cm², consistent with severe stenosis.
2. Mitral regurgitation grading – Input $r$, $V_r$, and $V_{\max}$ to obtain the ERO. Adding the VTI yields the RVol. Here the ERO indicated severe regurgitation while the RVol suggested only mild regurgitation—a discrepancy that underscores the value of evaluating multiple parameters together.
3. PISA itself – Enter only the radius to obtain the isovelocity surface area, which was 1.6 cm².

Interpreting the Calculator’s Output

The instrument automatically grades the results according to established echocardiographic cutoffs.

Mitral Regurgitation Severity by ERO and RVol

Grade	ERO (mm²)	RVol (mL/beat)
Mild	< 20	< 30
Mild–Moderate	20–29	30–44
Moderate–Severe	30–39	45–59
Severe	≥ 40	≥ 60

Mitral Stenosis Severity by MVA

Classification	MVA (cm²)
Normal	4.0–5.0
Mild stenosis	1.5
Moderate stenosis	1.0–1.5
Severe stenosis	< 1.0

Formulas Employed by the Calculator

The calculations follow directly from the PISA concept:

• Proximal isovelocity surface area $$\text{PISA} = 2\pi r^{2}$$
• Volume flow rate through the hemisphere $$\text{VFR} = 2\pi r^{2} \times V_r$$
• Effective regurgitant orifice area $$\text{ERO} = \dfrac{\text{VFR}}{V_{\max}}$$
• Regurgitant volume $$\text{RVol} = \text{ERO} \times \text{VTI}$$
• Mitral valve area (for stenosis) $$\text{MVA} = \dfrac{2\pi r^{2} \times V_r \times (\alpha / 180)}{V_{\max}}$$

All areas are expressed in cm², velocities in cm/s, and volumes in mL (1 mL = 1 cm³). The leaflet angle $\alpha$ appears only in the MVA formula because during stenosis the flow convergence is constrained by the valve leaflets, requiring an angular correction; for regurgitation the hemisphere is assumed to be a full 180° shell.

Limitations and Clinical Context

Although the PISA method offers a convenient and reproducible way to assess mitral valve disease, its results should always be interpreted in conjunction with the full echocardiographic examination and the patient’s clinical status. The calculator is intended for educational and reference purposes only and does not replace a formal evaluation by a qualified cardiologist. Moreover, while the PISA principle is general, this tool has been validated specifically for the mitral valve; extrapolation to other valves should be undertaken with caution.