What is the PISA Method?
The Proximal Isovelocity Surface Area (PISA) method is a quantitative Doppler echocardiographic technique used to assess the severity of valvular regurgitation, most commonly mitral regurgitation (MR). It is based on the hydrodynamic principle that as blood converges toward a regurgitant orifice, it accelerates and forms concentric hemispheric shells of equal velocity (isovelocity surfaces).
By measuring the radius of the PISA hemisphere at a known aliasing velocity on color Doppler, the instantaneous flow rate through the regurgitant orifice can be calculated. This allows derivation of the Effective Regurgitant Orifice Area (EROA) and the total Regurgitant Volume (RVol), which are the primary quantitative measures of MR severity recommended by the American Society of Echocardiography (ASE) and the European Association of Cardiovascular Imaging (EACVI).
PISA Formulas
The PISA method involves three sequential calculations:
Where r is the PISA radius (cm) and Valiasing is the aliasing velocity (cm/s). The 2πr² term represents the surface area of a hemisphere.
Where Vpeak MR is the peak velocity of the mitral regurgitant jet measured by continuous-wave Doppler (cm/s).
Where VTIMR is the velocity-time integral of the MR jet by continuous-wave Doppler (cm).
MR Severity Classification
| Parameter | Mild | Moderate | Severe |
|---|---|---|---|
| EROA (cm²) | < 0.20 | 0.20 – 0.39 | ≥ 0.40 |
| Regurgitant Volume (mL) | < 30 | 30 – 59 | ≥ 60 |
| Regurgitant Fraction (%) | < 30 | 30 – 49 | ≥ 50 |
| PISA Radius at Nyquist 40 cm/s (cm) | < 0.4 | 0.4 – 0.9 | ≥ 1.0 |
| Vena Contracta Width (cm) | < 0.3 | 0.3 – 0.69 | ≥ 0.7 |
PISA Concept Diagram
Measurement Technique
Step-by-Step PISA Measurement
- Obtain apical 4-chamber view: Optimize the image to clearly visualize the mitral valve and the MR jet origin
- Zoom in: Zoom on the mitral valve area to improve spatial resolution for PISA measurement
- Adjust aliasing velocity: Lower the Nyquist limit (color Doppler scale) to 30–40 cm/s to enlarge the PISA hemisphere and make it easier to measure. Shift the color baseline toward the direction of the regurgitant flow
- Measure PISA radius: Measure from the aliasing boundary (where the color changes from blue to red or vice versa) to the regurgitant orifice, perpendicular to the valve plane
- Record CW Doppler of MR jet: Place the continuous-wave Doppler cursor through the MR jet to obtain the peak velocity (Vmax) and velocity-time integral (VTI)
Pitfalls and Limitations
- Non-hemispheric PISA: The 2πr² formula assumes a perfect hemisphere. If the PISA shape is constrained by the valve or wall geometry, an angle correction factor (α/180°) may be needed
- Eccentric jets: Wall-hugging eccentric MR jets may have distorted PISA shapes, leading to underestimation of severity
- Dynamic MR: In conditions like mitral valve prolapse, MR severity can change throughout systole; the PISA measurement captures a single point in time
- Multiple jets: If multiple MR jets are present, PISA from each jet should ideally be calculated separately
- Atrial fibrillation: Beat-to-beat variability requires averaging measurements over multiple cardiac cycles
Understanding Mitral Regurgitation
Mitral regurgitation (MR) is the backward leakage of blood from the left ventricle to the left atrium through an incompetent mitral valve during systole. It is the most common valvular heart disease, affecting approximately 2% of the general population and increasing in prevalence with age.
Types of Mitral Regurgitation
- Primary (Organic/Degenerative) MR: Caused by structural abnormalities of the mitral valve apparatus itself — leaflets, chordae tendineae, papillary muscles, or annulus. Common causes include mitral valve prolapse, rheumatic heart disease, endocarditis, and connective tissue disorders
- Secondary (Functional) MR: The mitral valve structure is normal, but MR occurs due to left ventricular dilation or dysfunction that displaces the papillary muscles and prevents proper leaflet coaptation. Common in ischemic cardiomyopathy and dilated cardiomyopathy
Symptoms
- Dyspnea (shortness of breath), especially with exertion or lying flat
- Fatigue and exercise intolerance
- Palpitations (often due to atrial fibrillation)
- Peripheral edema (swelling of legs/ankles) in advanced cases
- Many patients with chronic MR are asymptomatic for years as the heart compensates
Indications for Surgery
According to the 2020/2021 ACC/AHA and ESC guidelines, surgery for primary severe MR is recommended in the following situations:
| Indication | Class | Details |
|---|---|---|
| Symptomatic severe MR | Class I | Surgery recommended if LVEF > 30%; repair preferred over replacement when feasible |
| Asymptomatic severe MR with LV dysfunction | Class I | LVEF ≤ 60% or LVESD ≥ 40 mm (trigger for surgery even without symptoms) |
| Asymptomatic severe MR with preserved LV function | Class IIa | May consider if high likelihood of durable repair (>95% success rate) at an experienced center |
| Asymptomatic severe MR with new-onset atrial fibrillation or pulmonary hypertension | Class IIa | PA systolic pressure > 50 mmHg at rest |
| Secondary severe MR with persistent symptoms despite GDMT | Class IIa | Transcatheter edge-to-edge repair (MitraClip) may be considered |
Worked Example
A patient has the following echocardiographic measurements:
- PISA radius: 0.9 cm at aliasing velocity 40 cm/s
- Peak MR velocity: 500 cm/s
- MR VTI: 150 cm
With an EROA of 0.41 cm² (≥ 0.40) and a regurgitant volume of 61.1 mL (≥ 60), this patient has severe mitral regurgitation by both quantitative criteria.
Frequently Asked Questions
What does PISA stand for?
PISA stands for Proximal Isovelocity Surface Area. It refers to the hemispheric surface area formed by blood flowing at the same velocity as it converges toward a regurgitant orifice. The concept is based on the continuity principle of fluid dynamics: flow through the PISA surface must equal flow through the regurgitant orifice.
Can PISA be used for other valve lesions?
Yes. While most commonly applied to mitral regurgitation, the PISA method can also be used to quantify tricuspid regurgitation, aortic regurgitation, and even mitral stenosis (by measuring flow convergence on the atrial side). The same fundamental principles apply, though measurement technique and reference values differ.
What is a normal EROA?
A normal mitral valve has no regurgitation and therefore no meaningful EROA. Trace or trivial MR is considered physiologically normal and is detected in up to 70–80% of healthy individuals on echocardiography. Clinically significant MR begins when EROA exceeds approximately 0.20 cm².
Why is aliasing velocity important?
The aliasing velocity (Nyquist limit) determines the size of the visible PISA hemisphere on color Doppler. A lower aliasing velocity makes the PISA radius larger and easier to measure accurately. The standard recommendation is to set the Nyquist limit to 30–40 cm/s for MR PISA measurement. The measured radius must be paired with the exact aliasing velocity used in the calculation.
How does PISA compare to other methods of MR quantification?
Other quantitative methods include the volumetric method (comparing LV stroke volume to aortic stroke volume), vena contracta width measurement, and 3D echocardiographic planimetry of the vena contracta area. The PISA method is the most widely used quantitative technique because it is relatively easy to perform and has been extensively validated. ASE/EACVI guidelines recommend an integrative approach using multiple parameters rather than relying on any single measurement.