American Heart Journal
Volume 147, Issue 2 , Pages 195-196, February 2004

Left atrial size: renewed interest in an old echocardiographic measurement

  • John S Gottdiener, MD

      Affiliations

    • Division of Cardiology, St Francis Hospital, State University of New York School of Medicine at Stony Brook, St Francis Hospital, Roslyn, NY, USA
    • Corresponding Author InformationReprint requests: John S. Gottdiener, MD, Division of Cardiology, St Francis Hospital, State University of New York School of Medicine at Stony Brook, St Francis Hospital, Roslyn, NY 11576-1348, USA.

Article Outline

 

Left atrial dimension was one of the first available measurements of cardiac size by M-mode1 and subsequently 2-D2, 3echocardiography. More recently, 3-D techniques have allowed true volumetric reconstruction of the left atrium that have been validated by cardiac magnetic resonance imaging.4

At first, interest in echocardiographic assessment of left atrial size centered on its utility in assessing the significance of left ventricular (LV) volume overload such as mitral regurgitation and as a predictor of atrial fibrillation5 or successful electrical cardioversion of atrial fibrillation. Subsequent research has shown that left atrial size is associated with both diastolic and systolic heart failure6 and is a predictive value of subsequent heart failure with or without preserved LV function.7 Moreover, left atrial size has been shown to be an important prognosticator of outcome after acute myocardial infarction.8 Left atrial size, often increased in hypertension, will decrease with drug treatment,9 although not all drugs are equally effective and the magnitude of decrease in left atrial size may not parallel decreases in blood pressure or LV mass.

Left atrial size is closely associated with Doppler measurements of diastolic function10 and with the severity of diastolic dysfunction.11 It is likely but unproven that left atrial size integrates the effects of left atrial pressure (and hence LV filling pressure) over time. Doppler measurement of mitral inflow and pulmonary vein flow velocities, as well as of mitral anular velocities with tissue Doppler, reflect left ventricular filling dynamics at the time of recording. However, in the absence of atrial fibrillation, measurement of left atrial size supplements those measures by potentially recording the history of LV filling over a longer albeit unspecified interval of time. Much remains to be learned about how the left atrium enlarges in response to altered filling of the left ventricle, such as the time course of change in size in response to changes in pathophysiology or treatment of heart failure and hypertension.

However, the left atrium may not enlarge in a symmetrical fashion, and any or all three of its orthogonal axes may increase at rates greater than the other, resulting in variable shape of the left atrium. Hence, use of a single linear dimension may not accurately reflect either left atrial volume or its change. Moreover, utilization of 2-D echocardiography to extrapolate left atrial volumes by use of geometric assumptions may not always be valid if the geometric assumptions are not true. One way of comparing the utility of an echocardiographic measure of volume is to compare it with a gold standard such as MRI. Previous research has shown that left atrial volumes measured by 3-D echocardiography compare well with those measured by cardiac MRI.4 However, 3-D echocardiographic off-line reconstruction of cardiac volumes is complex and time-consuming, hence unwieldy in clinical practice. In this issue of the American Heart Journal, Khankirawatana et al12 report the use of commercially available 3-D echocardiographic reconstruction to evaluate several 2-D echocardiographic methods of measurement of left atrial size, including a triplane 2-D echocardiographic algorithm previously described.13 This method uses conventional 2-D echocardiographic equipment and imaging techniques to provide an approximation of true 3-D reconstruction by using 3 standard 2-D apical views (4-chamber, 2-chamber, and apical long-axis), with the assumption that the 4-chamber, 2-chamber, and long-axis views are separated by constant angles. The other methods evaluated were estimation of left atrial volume by cubing the anteroposterior linear dimension (the most commonly reported measure of left atrial size in clinical use), volume estimation from three orthogonal linear left atrial dimensions (ellipsoid formula), and biplane estimation of volume obtained from planimetry of left atrial areas in 4-chamber and 2-chamber apical views. Commendably, the authors also determined the interobserver and intraobserver variability of the echocardiographic methods but not the test-retest reliability, which is more germane to clinical practice and research studies in which measurement of interval change is important. Of the four methods, observer variability was least, and closeness of fit to the gold standard of true 3-D reconstruction greatest with the simplified 3-D reconstruction method. Notably, however, 2-D biplane volumes compared almost as well (r = 0.91; SEE, 9.0 mL) with true 3-D construction as the simplified 3-D reconstruction method (r = 0.95; SEE, 7.6 mL).

However, what should be done in clinical practice? The simplified 3-D reconstruction method is still likely to be difficult to apply in busy clinical echocardiographic laboratories, true 3-D dimensional echocardiographic methods are not widely available as well as time consuming, and biplane 2-D methods may problematic because of poor quality 2-chamber views that foreshorten the left atrium. However, it has been shown14 that left atrial volume estimated from planimetry of the left atrium in the apical 4-chamber view alone (not evaluated in the present study) corresponds very well with biplane volumes (r = 0.97; mean difference, −5 mL). Moreover, in the study reported by Rodevan et al,4 the simplified 3-D method of left atrial volume estimation underestimated minimum MRI left atrial volumes and had only marginally better accuracy than 4-chamber single-plane or biplane methods. Until proven otherwise, measurement of left atrial volume, or perhaps even more simply—area—in the apical 4-chamber view may be the best combination of simplicity, speed, and accuracy for daily clinical use. Further research will be necessary to determine what is the best method in clinical practice to measure left atrial size and its change.

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References 

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PII: S0002-8703(03)00599-4

doi:10.1016/j.ahj.2003.08.002

American Heart Journal
Volume 147, Issue 2 , Pages 195-196, February 2004

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