Left Atrial Volume Index Thresholds: ACC/AHA vs. ASE Criteria
The American Society of Echocardiography (ASE) defines the upper normal limit for left atrial volume index (LAVI) as 34 mL/m² for both genders, while the ACC/AHA guidelines historically referenced 28 mL/m² as the normal threshold, though more recent ACC/AHA documents have aligned with the ASE cutoff of 34 mL/m². 1
ASE/EACVI Standardized Thresholds
The 2015 ASE/European Association of Cardiovascular Imaging (EACVI) guidelines established the current standard reference values for LAVI: 1
- Normal LAVI: ≤34 mL/m² (both genders)
- Mild enlargement: 35-41 mL/m²
- Moderate enlargement: 42-48 mL/m²
- Severe enlargement: ≥48 mL/m²
This represents an upward revision from the previous ASE threshold of 28 mL/m², based on data from 1,331 patients across five databases where the mean calculated LA volume was 25 mL/m². 1 The revised 34 mL/m² cutoff was chosen because it fits well with a risk-based approach for determining the boundary between normal and enlarged left atrium and is consistent with diastolic function evaluation guidelines. 1
Historical ACC/AHA Reference Values
Earlier ACC/AHA documents and related research referenced 28 mL/m² as the normal upper limit, with values categorized as: 2, 3, 4
- Normal: ≤28 mL/m²
- Mild: 29-33 mL/m²
- Moderate: 34-39 mL/m²
- Severe: ≥40 mL/m²
However, the 2020 ACC/AHA Valvular Heart Disease guidelines do not specify distinct LAVI thresholds but instead reference "enlarged" left atrium as a qualitative criterion for severe mitral regurgitation without providing numeric cutoffs. 1 The 2008 ACC/AHA guidelines similarly described left atrial enlargement qualitatively rather than with specific indexed volume thresholds. 1
Key Methodological Differences
The ASE guidelines prioritize the biplane disk summation technique (modified Simpson's method) over the area-length method because it incorporates fewer geometric assumptions and is theoretically more accurate. 1 Both methods require:
- Measurement at end-ventricular systole (frame just prior to mitral valve opening)
- Exclusion of the left atrial appendage and pulmonary veins from endocardial tracing
- Use of apical four-chamber and two-chamber views
- Indexing to body surface area (BSA)
The ACC/AHA documents have not provided the same level of technical detail regarding measurement methodology, instead deferring to ASE standards for chamber quantification. 1
Clinical Implications of the Threshold Difference
The difference between 28 mL/m² and 34 mL/m² has substantial prognostic significance: 2, 3
- Patients with LAVI >28 mL/m² have significantly higher rates of abnormal stress echocardiograms (negative predictive value of normal LAVI ≤28 mL/m² was 94.3% for normal stress testing). 3
- LAVI ≥40 mL/m² (severe by older criteria) confers a 42% increased mortality risk compared to normal LAVI, independent of left ventricular geometry. 2
- The prevalence of left atrial enlargement differs substantially depending on which threshold is applied: 18% (men) and 12% (women) using the older criteria versus 16% using LAVI/BSA with the 34 mL/m² cutoff. 4
Common Pitfalls to Avoid
Do not rely on anteroposterior diameter alone (traditional M-mode or 2D linear measurement), as a diameter ≤4.7 cm does not correlate well with LAVI and can miss significant left atrial enlargement. 5 A diameter >4.7 cm is predictive of LAVI >32 mL/m² (OR 17.33), but normal diameter measurements have poor negative predictive value. 5
Do not assume agreement between the two measurement systems—the kappa statistic for agreement between LAD/BSA and LAV/BSA is only 0.53 (fair agreement), and LAVI/BSA is more strongly associated with cardiovascular disease burden than diameter-based measurements. 4
Use the current ASE standard of 34 mL/m² as the upper normal limit for clinical decision-making, as this represents the most recent consensus from the primary echocardiography professional society and has been validated in large contemporary cohorts. 1, 6, 7