Axial area and anteroposterior diameter as estimates of left atrial size using computed tomography of the chest: Comparison with 3-dimensional volume

BackgroundLeft atrial (LA) size has incremental value in risk stratification.ObjectivesWe aimed to assess feasibility and reproducibility of 2 quick measures of LA size by chest CT (axial LA area and LA anteroposterior [AP] diameter) by using contrast-enhanced and CT scans.MethodsWe measured LA size in 100 contrast-enhanced 64-slice multidetector CT (MDCT) scans (randomly selected from the ROMICAT collective) by (1) axial LA area at the level of the left ventricular outflow tract and the mitral valve leaflets, (2) AP diameter in 3-chamber view, and (3) 3-dimensional (3D) LA volume by Simpson's methods. We assessed interobserver and intraobserver intraclass correlation coefficient (ICC) for axial LA area and AP diameter as well as their correlation to 3D LA volume. For axial area, feasibility and reproducibility were also determined in 100 non–contrast MDCT scans, randomly selected from the Framingham Heart Offspring collective.ResultsIn contrast-enhanced CT, both LA axial area and AP diameter had excellent reproducibility (interobserver: axial area: ICC, 0.96, mean relative difference, 2.4% ± 7.4%; AP diameter: ICC, 0.91, 3.6% ± 7.2%; intraobserver: axial area: ICC, 0.99, 0.4% ± 5.2%; AP diameter: ICC, 0.94, 1.7% ± 5.5%). Correlations with 3D volume were better for axial area (r = 0.88) than for AP diameter (r = 0.67). In non–contrast images, axial area could be assessed with excellent reproducibility (interobserver: ICC, 0.96, 0.5% ± 8.3%; intraobserver: ICC, 0.99, 0.01% ± 4.4%).ConclusionBoth AP diameter and axial LA area permit quick and reproducible estimates of LA volume in contrast-enhanced and non–contrast electrocardiographic-gated chest CT. However, LA area should be used preferably over AP diameter because of its better agreement to 3D LA volume.