What is the normal left atrium (LA) size by American Society of Echocardiography (ASE) criteria?

Normal Left Atrial Size by ASE Criteria

According to the American Society of Echocardiography (ASE) guidelines, the upper normal limit for 2D echocardiographic left atrial volume is 34 mL/m² for both genders. 1

Preferred Measurement Method

• The biplane disk summation technique is recommended as the preferred method to measure LA volume in clinical practice, as it incorporates fewer geometric assumptions than other methods and is theoretically more accurate than the area-length method 1
• 2D volumetric measurements are based on tracings of the blood-tissue interface on apical four- and two-chamber views 1
• At the mitral valve level, the contour should be closed by connecting the two opposite sections of the mitral annulus with a straight line 1
• Endocardial tracing should exclude the atrial appendage and pulmonary veins 1

Normal Values and Classification

• The mean normal LA volume is approximately 25 mL/m² 1
• LA volume classification by severity 1:
  • Normal: ≤34 mL/m²
  • Mildly enlarged: 35-41 mL/m²
  • Moderately enlarged: 42-48 mL/m²
  • Severely enlarged: >48 mL/m²

Technical Considerations

• LA length is defined as the shortest of the two long axes measured in the apical two- and four-chamber views 1
• For reliable calculations, the two lengths should not differ by more than 5 mm 1
• Volumes can be computed using either:
  • Area-length approximation: 8(A₁·A₂)/(3π·L), where A₁ and A₂ are the corresponding LA areas 1
  • Disk summation technique: adding the volume of a stack of cylinders with height h and area calculated by orthogonal minor and major transverse axes 1

Alternative Measurement Methods

• While LA anteroposterior (AP) diameter was historically used, it is less accurate as it represents only a single dimension 1
• 3D echocardiography is promising for assessing LA volume and correlates well with cardiac CT and MRI 1
• 3D echocardiographic LA volumes are typically larger than 2D volumes, but standardized methodology and normative data are currently limited 1

Clinical Implications

• LA volume can be increased in elite athletes, which needs to be considered to avoid misinterpretation as abnormal 1
• LA enlargement is associated with significant cardiovascular morbidity and mortality, including heart failure and stroke 2
• LA volume is a more robust and accurate determination of LA size compared with linear dimensions 1
• Volumetric measurements detect LA enlargement in approximately 37% more patients than linear measurements alone, suggesting they are more sensitive for early detection 3

Common Pitfalls

• Using only LA AP diameter can significantly underestimate LA enlargement 3
• Failure to exclude the pulmonary veins and LA appendage can lead to overestimation of LA volume 1
• Foreshortening of the LA in apical views can lead to underestimation of LA volume 1
• Inconsistent measurement timing (LA should be measured at end-ventricular systole, on the frame just prior to mitral valve opening) 1