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Purpose: The non-invasive evaluation of left atrial (LA) mechanical function is challenging, with no accepted gold-standard. Speckle-tracking measurement of LA deformation has theoretic advantages over other approaches, but validation studies are lacking. The aim of this study was therefore to compare speckle-tracking LA deformation indices with trans-oesophageal echocardiographic (TOE) measurement of left atrial appendage emptying velocity(LAAEV) and spontaneous echocardiographic contrast (SEC), which has been demonstrated to predict important clinical outcomes.Methods: Trans-thoracic echocardiography was undertaken in 51 patients (median age 59 years, 36 sinus rhythm) immediately prior to clinically indicated TOE. LA deformation was evaluated offline from grey-scale images using commercially available software (EchoPac BT 11) by averaging values from the apical 2- and 4-chamber views. Indices studied included global longitudinal left atrial strain (GLAS), and LA strain rate in systole, early and late diastole (SSR, ESR and ASR respectively), as well as peak A wave velocity on trans-mitral pulse-wave Doppler, and peak A' velocity from colour tissue Doppler imaging of the septal mitral annulus.Results: The closest correlation with LAAEV was observed with LA ASR (Table). Doppler echocardiographic measures of LA function displayed only weak association with LAAEV. LA ASR featured an area under the receiver-operating characteristic curve of 0.80 (0.64-0.95) for the identification of LAAEV <50cm/s. ASR differed significantly between those with and without spontaneous echo contrast (-0.59±0.48s-1 v. -1.1±0.57s-1,p=0.02).Conclusion: Our findings suggest that left atrial strain rate using speckle tracking transthoracic echocardiography may be the best non-invasive measure of LA mechanical function.