How to Measure Ejection Fraction Using Ultrasound
The most accurate method to measure ejection fraction (EF) on ultrasound is the biplane method of discs (modified Simpson's rule) obtained from apical four-chamber and two-chamber views, which is particularly reliable in abnormally shaped ventricles. 1
Standard Measurement Technique
Equipment Setup
- Use a phased array cardiac transducer (optimal) or a 2-5 MHz curved array abdominal probe with a small footprint if cardiac probe unavailable 1
- Activate cardiac presets on the machine to optimize image quality 1
- Both portable and cart-based ultrasound machines are acceptable 1
Image Acquisition Views
Obtain the following standard views for EF calculation:
- Apical four-chamber view: Primary view for biplane Simpson's method 1
- Apical two-chamber view: Second view required for biplane Simpson's method 1
- Parasternal long-axis view: Provides complementary information 1
- Parasternal short-axis view: Additional assessment of ventricular function 1
Measurement Protocol
For quantitative EF measurement (preferred over visual estimation): 2, 3
- Trace the endocardial border at end-diastole (largest cavity size) in both apical four-chamber and two-chamber views 1
- Trace the endocardial border at end-systole (smallest cavity size) in the same views 1
- The machine calculates volumes using the biplane method of discs (modified Simpson's rule) by integrating segmental areas 1, 4
- EF is automatically calculated as: (EDV - ESV)/EDV × 100 2, 3
Visual Estimation Method (Alternative)
For rapid bedside assessment, emergency physicians with limited training can accurately estimate EF visually: 1
EF Classification Standards
According to current guidelines, classify EF as follows: 2
- Hyperdynamic: > 70%
- Normal: 50-70%
- Mildly reduced: 40-49%
- Moderately reduced: 30-39%
- Severely reduced: < 30%
Advanced Techniques
Three-Dimensional Echocardiography
- 3D measurements are more accurate than 2D when available, particularly validated against cardiac MRI 1, 5
- Provides better assessment in patients with good acoustic windows 1
- Reduces inter-study variability compared to 2D methods 1
Automated AI-Assisted Algorithms
- Novel handheld devices with AI algorithms can automatically calculate EF (autoEF) with good agreement to manual measurements 6
- Sensitivity of 90% and specificity of 87% for detecting abnormal LV function (EF < 50%) 6
- Analysis time significantly reduced (141 seconds vs 261 seconds for manual methods) 5
Important Caveats and Pitfalls
Technical Considerations
- Image quality is critical: Adequate endocardial border visualization is essential for accurate measurements 7
- Avoid geometric assumptions: Linear measurements (Teichholz or Quinones methods) are not recommended as they depend on geometric assumptions that fail in abnormally shaped ventricles 1
- Harmonic imaging improves reproducibility of 2D LV volumes but uses lower frequencies that may reduce spatial resolution 1
Clinical Context
- EF varies between imaging modalities and interpreters - a single measurement may not be adequate, particularly for borderline values (41-49%) 2
- Load dependency: EF cannot distinguish between preload, afterload, and intrinsic contractility in pressure overload conditions 1
- In critically ill patients on ventilatory support, normal EF values are not well established 1
- Atrial fibrillation and tachycardia make measurements more challenging - average multiple cardiac cycles 1
Alternative Functional Assessment
When EF appears preserved but dysfunction is suspected, consider: 1
- Global longitudinal strain (GLS): Values < -16% indicate mild depression, < -10% severe reduction
- GLS is highly feasible and reproducible, detecting subclinical LV dysfunction before EF impairment 1
Documentation Requirements
Document the following in the medical record: 1
- Indication for the examination
- Views obtained and image quality
- Quantitative EF measurement or qualitative assessment (normal/moderately/severely depressed)
- Store images as part of the medical record when feasible 1