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Purpose: With the advent of 3D echocardiography, novel interest has emerged to combine functional assessment with cardiac chamber shape quantitation, particularly to evaluate cardiac remodelling following therapy or intervention. However, studies in this field are limited to the left ventricle (LV). Our aim was to extend a recently proposed technique for 3D shape indexes to the analysis of the left atrium (LA), and to describe its changes during the cardiac cycle in normal subjects.Methods: Full-volume 3D data sets (Vivid E9, GE Healthcare, Horten, N) were acquired in 62 healthy subjects (age 18-65). LA endocardial surfaces were obtained with commercial software (4D AutoLVQ, EchoPac BT 11, GE Healthcare, Horten, N). The method was based on 3D LA shape description using 1D signal by sampling the LA endocardial surface through a helical pattern, and on its comparison with the signal obtained from a reference shape. Four dimensionless indexes (range 0-1) were defined: sphericity (S), ellipticity (E), cylindricity (Cl) and conicity (Cn). LA shape values in the frames with maximal (M) and minimal (m) LA volumes were compared using Wilcoxon-signed rank test.Results: All LA shape indexes (median, 25%-75%) showed a significant (p<0.03 for all) cyclic behaviour (Figure), but with different amplitude changes, which were maximal for S (12%) and minimal for E (3%). At M, it corresponded to max E (.94,.92-.94) and max S (.7,.67-.74), with min Cn (.73,.71-.74) and Cl (.82,.78-.84), while at m lower E (.92,.9-.93) and S (.65,.6-.67) and higher Cn (.76,.75-.78) and Cl (.85,.81-.88) were observed.Conclusions: LA 3D shape analysis is feasible, showing cyclic changes in all shape indexes. This approach could be used, together with LV analysis, to assess the effects of remodelling on LA-LV functional coupling.