C  2008, the Authors Journal compilation C  2008, Blackwell Publishing, Inc. DOI: 10.1111/j.1540-8175.2008.00674.x Evaluation of Right Atrial Size in Patients with Atrial Arrhythmias: Comparison of 2D versus Real Time 3D Echocardiography Hajo M ¨ uller, M.D., Haran Burri, M.D., and Ren´ e Lerch, M.D. Division of Cardiology, University Hospitals of Geneva, Switzerland Aim: This study compares different parameters of right atrial size evaluated by two-dimensional (2D) echocardiography with right atrial volume measured using three-dimensional echocardiogra- phy (3DE). Methods and Results: One hundred sixty-three consecutive patients with a history of atrial arrhythmias were studied by standard two-dimensional and by real time 3DE. Of these 142 (87%) recordings were of sufficient quality for interpretation of the right atrium by both imaging techniques. The following parameters of right atrial size were measured: apical four-chamber short- axis diameter (4CH short axis), apical four-chamber long axis diameter (4CH long axis), and apical four-chamber planimetry area. The 2D-derived right atrial volume was calculated by using the sin- gle plane area-length method (4CH area-length). The 2D parameters were then correlated with right atrial volume measured by real time 3DE. Linear regression analysis showed moderate correlation for four-chamber planimetry area (r = 0.72, P < 0.001) and 2D-derived volume calculation (r of 4CH single plane area-length RA volume = 0.70, P < 0.001). Diameters correlated clearly less well with 3DE volume (r of 4CH short axis = 0.61, 4CH long axis = 0.59, P < 0.001 respectively). Conclusion: Real time 3DE is highly feasible for right atrial volume determination. The results demonstrate that measurements of dimensions using 2D echocardiography may not accurately assess right atrial size. If 3DE is not available, apical 4CH planimetry area is a simple alternative that may be used for evaluating right atrial size in clinical practice. The 2D-derived right atrial volume by single plane area-length method was not better correlated with 3DE volume than four-chamber planimetry area. (ECHOCARDIOGRAPHY, Volume 25, July 2008) atrial fibrillation, right atrial volume, three-dimensional echocardiography Measurement of right atrial size is clinically relevant and useful for the management of ar- rhythmias, pulmonary hypertension, valvular and congenital heart disease, 1–5 but few re- search and clinical data are available on quan- tification of right atrial size by echocardiog- raphy. Right atrial size can be assessed from many different views but is most commonly performed from the apical four-chamber view. 6 It has been evaluated in several small stud- ies using standard echocardiography by api- cal long- and short- (minor) axis diameters, 2,7,8 four- chamber planimetry area, 7,8 and by single plane two-dimensional (2D) volume determina- tion methods (area length method or method Address for correspondence and reprint requests: Hajo M¨ uller, M.D., Division of Cardiology, University Hospitals of Geneva, 24, rue Micheli-du-Crest, 1211 Geneva 14, Switzer- land. Fax: 41-22-3727229; E-mail: hajo.muller@hcuge.ch of discs). 9–11 As there are no standard orthog- onal right atrial views biplane volume calcula- tion has not been used. Assessment of volumes would be a robust and accurate way for the de- termination of right atrial size, as stated by the recently revised ASE guidelines. 6 However to date no normal limits have been defined using echocardiography. Magnetic resonance imaging is considered to be the gold standard for volume measurements and showed excellent correlation with right atrial cadaveric casts (r = 0.99, P < 0.001). 12 However, this imaging modality has limited availability, is time-consuming, relatively ex- pensive, and not feasible in all patients (e.g., in patients with pacemakers or with claus- trophobia). The 2D echocardiography remains therefore the most frequently used technique, but may not be the optimal one as it may not correctly indicate size in nonspherical atria. Furthermore, it is often difficult to reproduce Vol. 25, No. 6, 2008 ECHOCARDIOGRAPHY: A Jrnl. of CV Ultrasound & Allied Tech. 617