Recommended Method for Left Atrial Strain Calculation
The recommended method for left atrial (LA) strain calculation is to use speckle-tracking echocardiography with R-R gating (QRS onset as reference point), utilizing dedicated LA strain analysis software with optimized atrial-focused views and proper region of interest placement. 1
Technical Requirements and Acquisition
Image Acquisition
- Obtain dedicated, focused image acquisitions to optimize lateral and temporal resolution
- Use apical 4-chamber and 2-chamber views (same views used for LA volume calculation)
- Ensure adequate frame rate for accurate speckle tracking
Software and Analysis
- Use dedicated software with automated LA wall detection algorithm for improved measurement reproducibility
- The region of interest (ROI) should:
- Fit within the thin LA wall
- Accurately track the motion of the mitral annulus
- Avoid the strong signals of adjacent stationary pericardial tissue (which can underestimate strain values) 1
Reference Timing
- Set zero strain reference timing at end-diastole (R-R gating)
- While P-P gating (using P-wave onset as reference) is an alternative method, R-R gating:
- Is less prone to errors than P-P gating
- Can be used during atrial fibrillation
- Is the recommended approach by current guidelines 1
LA Strain Parameters to Calculate
LA function parameters are computed as time-strain curves over the cardiac cycle:
- Reservoir function (LASr): Represents LA filling during ventricular systole
- Conduit function: Reflects passive emptying during early and mid-diastole
- Contraction strain: Measures active LA pumping during late diastole 1
Strain rate parameters can also be calculated:
- Systolic strain rate: Rate of LA expansion (reservoir function)
- Early diastolic strain rate: Rate of LA compression by LV relaxation (conduit function)
- Late diastolic strain rate: Rate of active LA contraction 1
Normal Reference Values
According to the HUNT study (using GE EchoPAC system), bi-plane mean ±2SD reference values are:
For females:
- LASr: 33.2% (17.2–49.2%)
- LA conduit strain: -17.0% (-30.8 to -3.3%)
- LA contraction strain: -16.2% (-25.4 to -7.0%)
For males:
- LASr: 32.7% (16.0–49.3%)
- LA conduit strain: -15.7% (-29.1 to -2.3%)
- LA contraction strain: -17.0% (-26.9 to -7.0%) 1
Common Pitfalls and How to Avoid Them
Incorrect ROI placement
- Ensure ROI fits within the thin LA wall
- Avoid including pericardial tissue which can underestimate strain values
Reference timing inconsistency
- Consistently use R-R gating, especially for longitudinal follow-up
- Using different reference points (P-wave vs. QRS) leads to discrepant values 1
Software variability
- Use dedicated LA strain software rather than LV software repurposed for LA analysis
- Dedicated LA tracking software significantly improves reproducibility for LA strain during reservoir and atrial contraction phases 2
Load dependency
- Be aware that LA load impacts volume and strain measurements regardless of method used
- Consider combining early diastolic mitral inflow (E) and annulus (e′) velocities with LASr to estimate LA stiffness: E/e′/LASr 1
Vendor differences
- Use the same vendor's software for serial measurements to ensure comparability
- Be aware of potential differences in normal values between different software platforms
3D vs. 2D Strain Analysis
While 2D strain analysis is more commonly used, 3D strain analysis offers several advantages:
- Allows tracking of speckles in all longitudinal dimensions
- Prevents speckles from moving out of the imaging plane
- Provides LA volumes without geometric assumptions
- Enables more reproducible tracking 1
However, 3D strain analysis has limitations including lower spatial resolution and the need for dedicated equipment and training 1.
By following these recommendations for LA strain calculation, clinicians can obtain reliable measurements that provide valuable insights into LA function and potential pathologies.