Normal Left Atrial Size on Echocardiography
The upper normal limit for left atrial volume indexed to body surface area is ≤34 mL/m² for both men and women, with a mean normal value of approximately 25 mL/m². 1
Preferred Measurement Method
Volume measurement using the biplane disk summation technique is the recommended approach for assessing left atrial size, as it accounts for chamber remodeling in all directions and is more accurate than single-dimension measurements. 2, 1
Technical Requirements for Accurate Measurement
- Measure at end-ventricular systole (the frame just before mitral valve opening) when the LA is at its maximum size 2, 1
- Obtain dedicated apical four-chamber and two-chamber views with the LA maximized and not foreshortened 2
- Exclude the pulmonary vein confluences and left atrial appendage from endocardial tracings 2, 1
- Use the mitral annulus plane (not the leaflet tips) to define the atrioventricular interface 2
- Ensure the two long-axis lengths differ by no more than 5 mm for reliable calculations 1
Classification of Left Atrial Size
Left atrial volume index categories are defined as follows: 1
- Normal: ≤34 mL/m²
- Mildly enlarged: 35-41 mL/m²
- Moderately enlarged: 42-48 mL/m²
- Severely enlarged: >48 mL/m²
Alternative Linear Measurements (Less Preferred)
While the anteroposterior (AP) diameter measured from the parasternal long-axis view has been used historically, it is not recommended as the primary measurement because it represents only a single dimension and frequently underestimates LA enlargement during remodeling. 2, 1
- When AP diameter is used, normal values have remained consistent with prior recommendations, though specific cutoffs are gender-dependent 2
- LA-APD commonly underclassifies LA enlargement by ≥2 severity grades compared to volumetric assessment 3
Important Clinical Considerations
Indexing to Body Surface Area
Always report the indexed value (mL/m²) rather than absolute volume, as indexing to BSA accounts for gender differences in LA size and provides standardized reference values. 2
Prognostic Significance
LA volume is a powerful predictor of adverse cardiovascular outcomes including heart failure, stroke, and mortality, as it reflects the chronicity and burden of elevated left ventricular filling pressures. 2, 1
Common Pitfalls to Avoid
- Foreshortening the LA in apical views leads to underestimation of volume—ensure the base is at maximum width and length is maximized 2, 1
- Including pulmonary veins or LA appendage in tracings causes overestimation of LA volume 2, 1
- Using TEE to measure LA size is not recommended as the entire chamber often cannot fit in the image sector 2
- Relying solely on AP diameter misses significant LA enlargement that occurs asymmetrically 2, 1
- Measuring at the wrong phase of the cardiac cycle (must be at end-ventricular systole) produces inaccurate results 2, 1