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Left Atrium

title: Left Atrium author: J. Austin Straley, DO date: 2026-09-07 categories: - Cardiology - Echocardiography

Left atrial volume reflects the cumulative effect of LV filling pressure over time. LA enlargement is associated with diastolic dysfunction, atrial fibrillation, valvular disease, and adverse cardiovascular outcomes.

Acquisition

Measure maximal LA volume at end ventricular systole, immediately before mitral valve opening.

Use dedicated, nonforeshortened:

  • Apical four-chamber view
  • Apical two-chamber view

Trace the LA endocardial border while excluding:

  • Left atrial appendage
  • Pulmonary veins
  • Area beneath the mitral annular plane

The long axis should extend from the midpoint of the mitral annulus to the superior LA wall. Avoid foreshortening and use the longer measured LA length when calculating biplane volume.

LA Volume

The biplane method of disks is preferred over anteroposterior diameter because LA enlargement may occur asymmetrically.

\[ \text{LAVi} = \frac{\text{LA volume}} {\text{body surface area}} \]
LAVi LA size
≤34 mL/m² Normal
35–41 mL/m² Mildly enlarged
42–48 mL/m² Moderately enlarged
>48 mL/m² Severely enlarged

Three-dimensional echocardiography may provide more accurate volume assessment when image quality and dedicated software are available.

Linear Dimension

The LA anteroposterior diameter is measured from the parasternal long-axis view.

  • Normal diameter: approximately ≤4.0 cm
  • Measure perpendicular to the aortic root at end systole
  • Do not use AP diameter alone to classify LA size

AP diameter may underestimate enlargement because the LA expands in the superior–inferior and medial–lateral directions.

Interpretation

Common causes of LA enlargement include:

  • Chronic elevation in LV filling pressure
  • Mitral regurgitation
  • Mitral stenosis
  • Atrial fibrillation or flutter
  • Hypertension
  • Hypertrophic cardiomyopathy
  • Restrictive cardiomyopathy
  • High-output states
  • Athletic remodeling

LAVi is a marker of chronic, rather than instantaneous, filling pressure.

A normal LAVi does not exclude:

  • Acute elevation in LA pressure
  • Early diastolic dysfunction
  • Flash pulmonary edema
  • Acute mitral regurgitation

An enlarged LA does not prove currently elevated filling pressure, particularly with atrial fibrillation, significant mitral valve disease, or athletic remodeling.

LA Function and Strain

LA function consists of:

  1. Reservoir function: pulmonary venous return during ventricular systole
  2. Conduit function: passive LV filling during early diastole
  3. Booster-pump function: active atrial contraction

LA reservoir strain may supplement LAVi when assessing LV filling pressure, especially when standard diastolic parameters are indeterminate.

  • LA reservoir strain <18% supports increased LA pressure in appropriate clinical settings.1
  • Strain is affected by rhythm, image quality, software, loading conditions, and underlying atrial disease.
  • Booster-pump function is absent during atrial fibrillation.

LA strain should be integrated with conventional diastolic parameters rather than interpreted alone.

See Diastolic Function.

Reporting

The left atrium is normal in size.

The left atrium is mildly/moderately/severely dilated.

Left atrial volume index is ___ mL/m² by the biplane method
of disks.

The left atrium is visually enlarged; accurate volumetric
assessment was limited by foreshortening/poor endocardial definition.

Pitfalls

  • Measuring the LA from foreshortened apical views
  • Measuring at end diastole instead of end systole
  • Including pulmonary veins or the LAA in the trace
  • Using AP diameter instead of LAVi to grade LA size
  • Using a single-plane volume when both apical views are adequate
  • Assuming LA enlargement proves currently elevated filling pressure
  • Excluding acute elevated filling pressure because LAVi is normal
  • Applying LAVi without considering mitral valve disease or atrial fibrillation

Key Points

  • Measure maximal LA volume at end systole.
  • Use dedicated apical four- and two-chamber views.
  • Prefer biplane LAVi over AP diameter.
  • Normal LAVi is ≤34 mL/m².
  • LAVi reflects chronic exposure to elevated filling pressure.
  • LA strain may supplement, but does not replace, standard diastolic assessment.

References

  1. The 2025 ASE diastolic-function guideline uses LA reservoir strain <18% as a finding that can support elevated LA pressure in selected diagnostic pathways. ↩