Underestimation of Left Atrial Size Measured With Transthoracic Echocardiography Compared With 3D MDCT

OBJECTIVE. High-resolution 64-MDCT images of the beating heart can be used for measurement of left atrial volume with 3D chamber reconstruction. The purpose of this study was to correlate measurements of left atrial volume obtained with clinical transthoracic echocardiography (TTE) and measurements obtained with 64-MDCT 3D reconstructions of the left atrium. MATERIALS AND METHODS. Patients who underwent TTE and MDCT within 3 days were identified. TTE images were graded as excellent, good, or suboptimal. Two independent observers calculated estimates of left atrial volume from TTE and 64-MDCT images using 3D chamber reconstructions and conventional geometric assumptions on MDCT echocardiographic views. RESULTS. MDCT estimates of phantom volume on 3D chamber reconstructions agreed with actual volumes within 1.5%. The TTE images of 37 of the 52 patients were judged to be of good or excellent quality and were included in the analysis. Mean left atrial volume measured on 3D chamber reconstructions was 61 +/- 14 mL/m(2). Estimates of left atrial volume obtained with TTE were significantly lower (28 +/- 12 mL/m(2)) than similar estimates obtained with MDCT echocardiographic views (53 +/- 15 mL/m(2)) (p < 0.001). TTE left atrial volume and 3D chamber reconstruction left atrial volume exhibited moderate correlation (r = 0.60-0.70), but the correlation improved when analysis was limited to the 26 studies with excellent-quality TTE images (r = 0.71). MDCT echocardiographic estimates of left atrial volume with the area-length method had excellent correlation (r = 0.89) with and were closest to estimates made on 3D chamber reconstructions. CONCLUSION. Left atrial volume is significantly underestimated on TTE images, and TTE estimates have moderate correlation with left atrial volume measured with MDCT. Measured and estimated left atrial volumes at MDCT can provide important additive prognostic information in the care of patients undergoing MDCT for other reasons. Future studies are needed to obtain normative MDCT measurements of left atrial volume.