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PISA Calculator

The PISA (proximal isovelocity surface area) method is a Doppler echocardiography technique that quantifies mitral valve pathology by measuring blood flow acceleration across stenotic or regurgitant orifices. Cardiologists and sonographers use PISA calculations to grade mitral regurgitation severity, estimate effective regurgitant orifice area (EROA), regurgitant volume, and mitral valve area (MVA). This calculator automates those computations from ultrasound measurements.

Last updated:

Creators Łucja Zaborowska, MD, PhD
6,236 people find this calculator helpful

Understanding PISA and the Venturi Effect

PISA stands for proximal isovelocity surface area, a quantitative approach to assessing mitral valve haemodynamics. The method relies on the Venturi principle: as blood accelerates through a narrowed orifice, its velocity increases predictably. By measuring the radius at which Doppler shift reaches the aliasing velocity threshold, clinicians can calculate the hemisphere-shaped acceleration zone upstream of the valve defect.

In echocardiography, this manifests as a colour-coded hemispheric shell on the atrial side of a regurgitant or stenotic valve. The PISA radius (r) represents the distance from the valve orifice to the edge of this acceleration zone, typically measured in centimetres. Combined with peak velocity (Vmax) and aliasing velocity (Vr), PISA enables non-invasive computation of regurgitant volume and valve area.

Unlike visual grading alone, PISA quantification reduces observer bias and provides reproducible severity assessment for mitral regurgitation and mitral stenosis.

PISA Formula Derivations

The calculator applies five core equations derived from haemodynamic principles. All measurements must be in consistent units: cm for distance, cm/s for velocity, and degrees for angular measurements.

PISA = 2π × r²

VFR = 2π × r² × Vr

ERO = (VFR × 100) ÷ Vmax

MVA = (2π × r² × Vr × (α ÷ 180)) ÷ Vmax

RVol = (ERO ÷ 100) × VTI

  • r — Radial distance (cm) from the mitral orifice to the aliasing velocity boundary
  • Vr — Aliasing velocity (cm/s), the Doppler shift limit where colour wraps
  • Vmax — Peak velocity (cm/s) across the stenotic or regurgitant jet
  • α — Angle (degrees) between mitral leaflets measured on the atrial side
  • VTI — Velocity time integral (cm) of the regurgitant jet traced across one cardiac cycle
  • VFR — Volume flow rate (mL/s) through the valve orifice
  • ERO — Effective regurgitant orifice area (mm²)
  • MVA — Mitral valve area (cm²) in stenosis
  • RVol — Regurgitant volume (mL/beat) per cardiac cycle

Clinical Interpretation of Results

PISA results must be interpreted against validated echocardiographic criteria to grade mitral pathology severity.

Mitral Regurgitation Assessment:

  • Mild: ERO <20 mm², RVol <30 mL/beat
  • Mild-to-Moderate: ERO 20–29 mm², RVol 30–44 mL/beat
  • Moderate-to-Severe: ERO 30–39 mm², RVol 45–59 mL/beat
  • Severe: ERO ≥40 mm², RVol ≥60 mL/beat

Mitral Stenosis Assessment:

  • Normal: MVA 4.0–5.0 cm²
  • Mild: MVA >1.5 cm²
  • Moderate: MVA 1.0–1.5 cm²
  • Severe: MVA <1.0 cm²

A single PISA measurement provides one data point; integration with continuous-wave Doppler gradients, 2D anatomy, and clinical presentation strengthens diagnostic confidence.

Common Measurement Pitfalls

Accurate PISA quantification hinges on meticulous ultrasound technique; these considerations help avoid systematic errors.

  1. Aliasing Velocity Standardisation — Set the aliasing velocity (Nyquist limit) to a consistent value, typically 50–60 cm/s, before acquiring the PISA image. Changing the colour scale mid-examination alters the apparent PISA radius and invalidates comparisons. Document the Vr you used for future reference.
  2. Radius Measurement Precision — The PISA radius must be measured perpendicular to the direction of flow, from the orifice to the outer edge of the acceleration shell. Minor errors in r are magnified (r²) in the PISA formula, so a 1 mm mistake can shift area calculations by 2–3%. Use zoom and calipers; eyeballing introduces bias.
  3. Angle Measurement and Leaflet Geometry — The mitral leaflet angle α is measured on the atrial side between the two leaflets in the plane orthogonal to the jet. Non-planar or funnel-shaped orifices distort this assumption. MVA calculations assume a hemispherical convergence zone; eccentric jets may require adjustment or additional imaging planes.
  4. Angle Between Leaflets Assumption — The calculation assumes axisymmetric flow at a known angle. Prolapsing leaflets, calcification, or anterior leaflet involvement can create irregular flow geometry. If leaflets subtend &lt;90 degrees, the hemispheric model may overestimate PISA; if &gt;180 degrees, a full hemisphere may underestimate.

When to Apply PISA Quantification

PISA is most reliable when ultrasound windows are adequate and the jet origin is clear. The method excels in symptomatic patients with moderate-to-severe regurgitation and in discordant cases where visual grading conflicts with clinical severity.

Ideal scenarios: Rheumatic mitral stenosis with restricted leaflet motion; primary (organic) mitral regurgitation from prolapse, endocarditis, or cleft leaflet; and functional regurgitation in dilated left ventricles.

Limitations: Multiple jets, eccentric regurgitation directed along the posterior atrial wall, very high Vmax (>500 cm/s), and poor acoustic windows reduce reliability. In atrial fibrillation, beat-to-beat variability may require averaging. Pulmonary hypertension and right ventricular dysfunction can alter tricuspid valve flow patterns that confound colour Doppler.

Always integrate PISA with left atrial size, left ventricular dimensions, transmitral gradients, and clinical symptoms when grading mitral disease severity.

Frequently Asked Questions

What is the difference between regurgitant volume and effective regurgitant orifice area?

Regurgitant volume (RVol, mL/beat) quantifies the total volume of blood leaking backward per heartbeat, derived from ERO and the velocity time integral. Effective regurgitant orifice area (EROA or ERO, mm²) represents the anatomical size of the pathological opening through which that blood flows. ERO is geometry-independent and more reproducible; RVol incorporates the duration of regurgitation. Both are needed for comprehensive severity grading, as a small orifice during a short diastole may leak less than a larger one open for longer.

Why do sonographers measure both Vmax and Vr in PISA calculations?

Vmax (peak mitral jet velocity) reflects the stenotic pressure gradient and drives the regurgitant volume calculation. Vr (aliasing velocity) marks the boundary of the proximal acceleration zone on the colour Doppler image, allowing radius measurement. Together they define the PISA geometry and flow rate. Vmax alone cannot locate the acceleration shell; Vr alone does not account for jet momentum. Both are essential for accurate ERO and MVA.

Can PISA be used in atrial fibrillation?

Yes, but with caveats. Atrial fibrillation causes beat-to-beat variation in cycle length, preload, and jet velocity. Mitral regurgitation severity may fluctuate with ventricular filling time. Sonographers should acquire PISA images in multiple beats (preferably 3–5) and average the radius and VTI measurements. Single-beat measurements in irregular rhythms risk misclassification. When atrial fibrillation is new or unstable, serial echocardiograms may be necessary to confirm true change in valve function.

How does the mitral leaflet angle affect MVA calculation in stenosis?

The angle (α) between the two leaflets on the atrial side accounts for the geometric shape of the stenotic orifice. Horizontal, parallel leaflets (180°) yield larger MVA estimates; leaflets closer together (acute angle) produce smaller estimates. If leaflets subtend 90°, the PISA forms a quarter-hemisphere rather than a full hemisphere. Incorrect angle measurement directly biases MVA. Severe rheumatic stenosis with doming often narrows this angle; precise measurement in the appropriate imaging plane is critical for accurate area assessment.

What ultrasound settings optimise PISA measurement accuracy?

Use a Nyquist limit (aliasing velocity) of 50–60 cm/s for regurgitation and adjust as needed for stenosis to visualise the proximal acceleration zone clearly. Optimize the colour gain to avoid excessive noise while maintaining edge definition. Measure the PISA radius in the plane perpendicular to jet flow, preferably from both apical four-chamber and two-chamber views if available. Zoom the PISA region to near full-screen size and use electronic calipers. Document all acquisition parameters and report them alongside results to enable comparison on follow-up studies.

Is PISA reliable in post-operative mitral valve repair?

PISA can assess residual regurgitation after repair, but interpretation requires caution. Annuloplasty rings, sutures, and altered leaflet geometry distort the hemispherical flow assumption. Eccentric jets, common after repair, reduce PISA accuracy. Intraoperative transoesophageal echocardiography (TOE) using PISA may overestimate post-repair regurgitation compared to transthoracic imaging weeks later as oedema resolves. Serial measurements are more informative than single post-operative values. When doubt exists, combine PISA with continuous-wave Doppler peak gradient, jet width ratio, and colour jet area for robust assessment.

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