Measuring Ejection Fraction from the Parasternal Long-Axis View
The parasternal long-axis (PLAX) view is not the recommended primary view for measuring left ventricular ejection fraction—you should use the apical four-chamber and two-chamber views with the biplane Simpson's method instead. 1, 2
Why PLAX is Not Recommended for Standard EF Measurement
The current guidelines from the American Society of Echocardiography and European Association of Cardiovascular Imaging explicitly state that LV volumes and ejection fraction should be measured from apical four-chamber and two-chamber views using the biplane method of discs (modified Simpson's rule), not from the PLAX view. 1, 2 This is because:
Geometric assumptions fail: Methods that calculate volumes from linear PLAX measurements (like the Teichholz or Quinones formulas) are no longer recommended because they assume the left ventricle is a fixed geometric shape (prolate ellipsoid), which is inaccurate in patients with wall motion abnormalities or ventricular remodeling. 1, 2
PLAX provides linear dimensions, not volumes: The PLAX view is recommended for measuring linear internal dimensions of the LV and wall thickness at end-diastole and end-systole, but these linear measurements should not be used to calculate ejection fraction. 1
What PLAX View Actually Measures
In the PLAX view, you should measure: 1
- LV internal dimensions at end-diastole and end-systole (perpendicular to the LV long axis, at or immediately below the mitral valve leaflet tips)
- Wall thickness (septal and posterior wall)
- Fractional shortening (which reflects regional function but is not equivalent to ejection fraction)
The Correct Method: Biplane Simpson's Rule
To properly measure ejection fraction, follow this protocol: 2
- Obtain apical four-chamber view: Maximize LV area while avoiding foreshortening 1, 2
- Obtain apical two-chamber view: Again, maximize LV area 1, 2
- Trace endocardial borders at end-diastole (largest cavity) in both views 2
- Trace endocardial borders at end-systole (smallest cavity) in both views 2
- Machine calculates volumes using the biplane method of discs, which divides the LV into multiple cylindrical segments 2
This method is particularly reliable in abnormally shaped ventricles where geometric assumptions would fail. 2
When PLAX Can Provide Supportive Information
While PLAX cannot be used as the primary method for EF calculation, recent research suggests it can provide complementary assessment: 3, 4
Artificial intelligence tools have shown that PLAX views can estimate EF with reasonable accuracy (correlation 0.89, RMSE 7.29%) and 91% accuracy for detecting low EF (<50%), particularly useful in ICU settings where obtaining apical views is difficult. 3
Simplified wall motion scoring combining mid-parasternal short-axis and apical four-chamber views (MID-4CH method) showed excellent correlation (r² = 0.90) with standard methods, useful for point-of-care ultrasound by non-cardiologists. 4
Visual Estimation Alternative
If formal measurements are not feasible, visual estimation (eyeballing) from multiple views including PLAX correlates well with formal methods (R = 0.898 with biplane Simpson's), though this requires experience: 5
Critical Pitfalls to Avoid
- Never use linear dimension formulas from PLAX to calculate EF—they are outdated and inaccurate 1, 2
- Avoid foreshortening when obtaining apical views, as this underestimates volumes 1
- Don't rely on single measurements for borderline values (41-49%), as inter-study variability can be 5-7% 6
- Remember load dependency: EF cannot distinguish between preload, afterload, and intrinsic contractility 2
Special Populations
In arrhythmogenic cardiomyopathy, PLAX is used to measure the RV outflow tract diameter (normal <32 mm), not LV ejection fraction. 1 This is a completely different measurement with different clinical implications.