Online Appendix for the following June 20 JACC article
TITLE: Left Atrial Size: Physiologic Determinants and Clinical Applications
AUTHORS: Walter P. Abhayaratna, MBBS, FRACP, Division of Cardiovascular
Diseases and Internal Medicine, Mayo Clinic, Rochester, Minnesota, James B. Seward,
MD, FACC, Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic,
Rochester, Minnesota, Christopher P. Appleton, MD, FACC, Division of Cardiovascular
Diseases, Mayo Clinic, Scottsdale, Arizona, Pamela S. Douglas, MD, FACC,
Cardiovascular Medicine Division, Duke University, Durham, North Carolina, Jae K. Oh,
MD, FACC, Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic,
Rochester, Minnesota, A. Jamil Tajik, MD, FACC, Division of Cardiovascular Diseases,
Mayo Clinic, Scottsdale, Arizona, Teresa S. M. Tsang, MD, FACC, Division of
Cardiovascular Diseases and Internal Medicine, Mayo Clinic, Rochester, Minnesota
APPENDIX
MEASUREMENT OF LA VOLUME BY ECHOCARDIOGRAPHY
Two-Dimensional Echocardiographic Methods for Estimating LA Volume. Various
echocardiographic techniques for the quantitation of LA volume are distinguished by the
number of planes employed for volumetric assessment and geometric assumptions
inherent to each method. Accuracy is increased with the use of more than one plane
because of asymmetry of the atrial cavity in health and asymmetric changes in LA size
with disease, which may be detectable from one plane but not others. Biplane area-length
method and biplane Simpson’s method of discs, using orthogonal views, have been wellvalidated against reference standards such as angiography, CT, MRI and 3D
echocardiography (1–8). Although 3D echocardiography may prove to be the preferred
method of LA volume assessment in the future, 2D assessment remains the current
standard for clinical practice.
Biplane Area-Length Method. This method involves the use of two orthogonal views of
the atria are obtained from an apical transducer position (Fig. 1).
It is important to obtain planes for measurement that do not foreshorten the long axis of
the left atrium (Fig. 2).
Since LA reference values have been established using apical four-chamber (A4CH) and
two-chamber (A2CH) views, it would be recommended that these views are used for the
calculation of LA volume. However, if the A2CH view is suboptimal, the apical long-axis
view has been used as its substitute. Left atrial volume can be estimated using the
following formula:
LA Volume
(AL)
 0.85 
A4CH  A2CH
L
The length (L) from the midpoint of the mitral annulus plane to the superior margin of the
left atrium in the orthogonal apical views should be nearly equal. A slight discrepancy
may exist because of the variability of chamber orientation and limitation of image
projections. However, a difference >5 mm should call attention to the possibility of
measurement error or a foreshortened LA in at least one view. The longer, the shorter,
and the average of the two lengths from the two views have all been used in different
studies for the calculation of volume. The use of the longer of the two lengths will yield a
slightly smaller volume, while the use of the shorter length will yield a slightly larger
volume calculation. The American Society of Echocardiography (9) has recommended
the use of the shorter of the two lengths for calculation of LA volume, which minimizes
the “underestimation” of LA volume by echocardiography when compared to CT or MRI
assessments. As we routinely ensure optimal visualization of the LA without
foreshortening, and check that the two lengths measured in the orthogonal views are
within 5 mm of each other; we have used the average of the two lengths for calculation of
LA volume in our previous research studies, since any small error in measuring the
length is equally likely for both views. With these criteria, the relative difference in LA
volume between that calculated with the use of the shorter versus the average of the two
lengths is less than 5%.
Method of Discs by Simpson’s Rule. The LA volume may also be measured using
Simpson’s rule, which states that the volume of a geometrical figure can be calculated
from the sum of the volumes of smaller figures of similar shape. Simpson’s algorithm is
based on the premise that a cavity, such as the LA, can be divided into a series of stacked
oval discs with a known height and orthogonal minor and major axes. The use of
Simpson’s method requires the input of biplane LA planimetry to derive the diameters.
Optimal contours should be obtained orthogonally around the long axis of the LA using
2D apical views (Fig. 3). This method provides very comparable LA volumes to the arealength method. Limitation to a more widespread use of this method stems from the lack
of a specific biplane atrial volume package in current commercial echocardiography
machines. Otherwise, this is a simple and highly efficient method.
Single-plane Simpson’s method could be used to estimate LA volume by assuming the
stacked discs are circular. However, this makes the assumption that the LA widths in the
apical two- and four-chamber are identical, which is often not the case. The correlation
between biplane Simpson’s method and area-length LA volume is excellent (r = 0.98)
(10). In our experience, both biplane methods are simple and accurate. The one distinct
advantage of the disc method is its reliance on the computerized summation of disc for
the total volume, and it does not require input of a specific length for volume calculation
in the area-length method. The latter has been a source of confusion since different
lengths have been used by different investigators.
Step-by-Step Guide for Biplane LA Volume Assessment
A. Optimize image quality in the apical four-chamber, two-chamber, and long-axis
views. The two planes chosen for the measurement of LA volume will be
determined by the quality of the images from the A2CH and apical long axis (i.e.,
A4CH and A2CH or A4CH and long axis).
B. Obtain maximal LA size. The transducer is angulated until the LA area is
maximized and the extent of foreshortening is reduced. Persistent foreshortening
may be reduced by imaging with the transducer at one intercostal space below the
A4CH view.
C. Timing of maximum LA volume. Maximal LA volume occurs after the end of
ventricular systole, and this can be gauged by using the end of T-wave on the
electrocardiogram for timing. The appropriate frame for measurement of
maximum LA volume is identified by scrolling to the LA image just prior to
mitral valve opening.
D. LA planimetry. The inferior LA border is defined as the plane of mitral annulus
and not the tips of leaflets. By convention, the atrial appendage, pulmonary veins
and recesses of the atrioventricular valves are excluded for the volume
measurement by drawing a straight line across these structures to the adjacent
atrial borders.
E. Measure the long-axis LA length. This is defined as the distance between the midpoint of the mitral annulus plane to the mid-posterior LA wall. The length is
measured from the A4CH and A2CH view (or long-axis view).
Other Methods for LA Volume Assessment
1. Method Using Three Axes and Assuming an Ellipsoid Formula
Another method uses three axes (length, width, and height) and assumes an ellipsoidal
shape of the atrium. The LA volume is calculated using the following formula:
LA Volume
(PE)
 4/3 (
LAD LA LAD SA1 LAD SA2)


2
2
2
LADLA is the long-axis dimension, measured as the maximum perpendicular distance
from the midpoint of the plane of the mitral annulus to the superior-posterior LA border
in the A4CH view; LADSA1 and LADSA2 are orthogonal short axis maximum diameters. To
the best of our knowledge, this echocardiographic method has not been validated against
reference methods. Because the measurement of only six points around the entire LA
endocardial surface, it is, in theory, more prone to error when compared to methods in
which the LA area is planimetered.
2. Methods Assuming a Spherical Geometry
The LA volume can be calculated with the “cube” formula, which, despite its name,
calculates the volume of a sphere using a single linear LA anteroposterior dimension.
LA Volume
(cube)
 4/3 (LAD AP 2)
3
The LADAP is the maximum LA anteroposterior diameter measured in the parasternal
long axis. This is the least accurate of 2D volumetric methods (4,6,11) as the assumption
of a spherical shape is usually the greatest departure from reality and should be avoided.
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