Echocardiographic evaluation of left atrial size and function: Current understanding, pathophysiologic correlates, and prognostic implications Dominic Y. Leung, MBBS, FRCP, FHKCP, FRACP, FACC, PhD, Anita Boyd, B Med Sc Hons, Arnold A. Ng, BSc(Med), MBBS, FRACP, DDU, Cecilia Chi, and Liza Thomas, MBBS, FRACP, PhD Sydney, New South Wales, Australia Left atrial (LA) volume has recently been identified as a potential biomarker for cardiac and cerebrovascular disease. However, evidence regarding the prognostic implications of LA volume still remains unclear. Evaluation of LA size and function using traditional and more recent echocardiographic parameters is potentially feasible in the routine clinical setting. This review article discusses the conventional and newer echocardiographic parameters used to evaluate LA size and function. Conventional parameters include the assessment of phasic atrial activity using atrial volume measurements, transmitral Doppler peak A velocity, atrial fraction, and the atrial ejection force. Newer parameters include Doppler tissue imaging (DTI) including segmental atrial function assessment using color DTI, strain, and strain rate. In addition, an overview of the implications and clinical relevance of the findings of an enlarged left atrium, from currently available literature, is presented. (Am Heart J 2008;156:1056-64.) The left atrium (LA) serves multiple functions, acting as (1) a reservoir during left ventricular (LV) systole; (2) a conduit for blood transiting from the pulmonary veins to the LV during early diastole; (3) an active contractile chamber that augments LV ventricular filling in late diastole; and (4) a suction source that refills itself in early systole. 1 Through these varying mechanical functions, the LA modulates LV filling. In addition, the LA also acts as a volume sensor with the atrial wall releasing natriuretic peptides in response to stretch, generating natriuresis, vasodilatation, and inhibition of the sympathetic nervous system and renin-angiotensin-aldosterone system. Con- tributing up to 30% of total LV stroke volume in normal individuals, this atrial contribution is of particular importance in the setting of LV dysfunction to maintain adequate LV stroke volume. 2 The loss of this atrial contribution to LV filling and stroke volume with atrial fibrillation can often lead to symptomatic deterioration. There is a growing body of evidence demonstrating that an enlarged LA is indicative of significant ventricu- lar, 3 atrial, 4 or valvular disease 5 and as a marker of adverse cardiovascular outcomes. 6 Among the various noninva- sive imaging modalities to assess LA size, 2-dimensional (2D) echocardiography is the most widely accepted. However, there is currently no accepted “gold standard,” and in contrast to the assessment of LV function, there is a paucity of literature regarding the evaluation of LA function. In this article, we review the current literature on echocardiographic evaluation of LA size and function, its physiologic and pathophysiologic correlates, methods of assessment, and prognostic implications. Left atrial size: methods of assessment Echocardiographic assessment of LA size is a measure- ment of its anteroposterior dimension on M-mode or 2D echocardiography in the parasternal long axis view. Although this measurement has been used extensively in clinical and research work, it is now recognized as an inaccurate representation of the true LA size. 7 Enlarge- ment of the LA is often asymmetrical and may occur in the medial-lateral as well as the superior-inferior axes because enlargement in the anteroposterior axis may be limited by the thoracic cavity. Therefore, LA anteroposterior dimen- sion is not an accurate reflector of LA volume, especially in those with an enlarged LA. 7 It is not surprising that the agreement between LA dimension and LA volume was only fair 8 and that the relationship between LA size and cardiovascular disease burden and outcome is stronger for LA volume than for LA dimension. 8,9 Although LA size can be represented as a 2D measure- ment of LA area from the apical 4 and 2 chamber views, LA volume is the preferred measurement. 10 The American Society of Echocardiography, in conjunction with the European Association of Echocardiography, recom- mended either an ellipsoid model or the Simpson's method. 10 Modifications of the ellipsoid model including From Liverpool Hospital, University of New South Wales, Sydney, New South Wales, Australia. Submitted April 26, 2008; accepted July 23, 2008. Reprint requests: Liza Thomas, MBBS, FRACP, PhD, Department of Cardiology, Liverpool Hospital, Locked Bag, 7103, Liverpool BC, NSW 1871, Australia. E-mail: ltho6412@bigpond.net.au 0002-8703/$ - see front matter © 2008, Mosby, Inc. All rights reserved. doi:10.1016/j.ahj.2008.07.021 Curriculum in Cardiology