Best method in clinical practice and in research studies to determine leftatrial size

Although the anteroposterior dimension of the left atrium is universally us ed in clinical practice and research, we hypothesized that it may be an ina ccurate surrogate for volume because its use is based on the unlikely assum ption that there is a constant relation among atrial dimensions, The follow ing measurements of the left atrium were made at end ventricular systole: ( 1) M-mode-derived anteroposterior linear dimension from the parasternal lon g-axis view; (2) digitized planimetry of the left atrial (LA) cavity from t he apical 4-chamber view; and (3) digitized planimetry of the LA cavity fro m the apical 2-chamber view. The following volume calculations were obtaine d from these digital measurements: (1) volume derived from the M-mode dimen sion assuming a spherical shape; (2) volume derived from the single plane a rea-length of apical 4-chamber view, which assumes that LA geometry can be generalized from a single 2-dimensional plane; and (3) volume derived from the biplane method of discs. The correlation coefficient between the M-mode and biplane methods of determining LA volume was r = 0.76. The mean differ ence (+/-2 SDs) between these methods is -25 +/- 33 ml. The correlation coe fficient between the single plane apical 4-chamber and biplane methods of d etermining LA volume is r = 0.97, The mean difference (+/-2 SDs) between th ese methods was -5.0 +/- 12 mi, indicating good agreement. The M-mode measu re of the left atrium is an inaccurate representation of its size. Two-dime nsional-derived LA volumes provide a more accurate measure of the true size of the left atrium and are more sensitive to changes in LA size. When an e chocardiographic measure of LA size is made either in an individual patient or as a variable in a research study, the M-mode measure should be avoided , (C)1999 by Excerpta Medico, Inc.