Left atrium dimensions
From Echocardiography in ICU
The left atrium has three major roles:
-contractile pump that delivers 15% to 30% of the LV filling
-reservoir that collects pulmonary venous return during ventricular systole
-conduit for the passage of stored blood from the LA to the LV during early ventricular diastole.
LA size is important and has been related to adverse cardiovascular outcomes. LA dilatation reflects long-term increased filling pressure: diastolic dysfunction and/or mitral valve disease, stenosis or regurgitation.
LA size is measured at the end-systole, when the LA chamber is at its greatest dimension
LA antero-posterior diameter in parasternal long axis view
This method of measurement has been done extensively in clinical trials, but is no longer recommended.
LA diameter is measured in parasternal long axis, perpendicularly to the LA walls. You will measure the LA diameter in end-systole, from leading edge of the posterior aortic wall to the leading edge of the posterior LA wall.
It can be measured in 2D, or in Mmode if the ultrasound beam is perpendicular to the LA walls.
LA minor and major axis in apical 4 chamber view
You have to get a good apical 4 chamber view, with complete visualization of the atria, mitral and tricuspid valve, and both ventricles.
This method is not recommended, measurement of LA area and volumes are preferred.
LA area and volume in apical 4 chamber view
LA area and volume are the most reliable measurements for the determination of LA enlargement.
The measurement should be done at end-systole, on the frame just before the opening of the mitral valve. You need to get a good apical 4 chamber view. You will trace the inner border of the LA, excluding the area under the mitral valve annulus and the inlet of the pulmonary veins. The LA shape should be roughly square.
LA volume may be measured using Simpson’s rule, similar to its application for LV measurements, which states that the volume of a geometric figure can be calculated from the sum of the volumes of smaller figures of similar shape.
|LA dimensions||Normal||Mildly dilated||Moderately dilated||Severely dilated|
|Major axis (mm)||41-61||62-67||68-76||>77|
Lang RM, Bierig M, Devereux RB. Recommendations for chamber quantification. J Am Soc Echocardiogr. 2005 Dec;18(12):1440-63
Vasan R.S et al. Distribution and categorization of echocardiographic measurements in relation to reference limitsthe Framingham heart study; formulation of a height- and sex-specific classification and its prospective validation. Circulation (1997) 96 : pp 1863-1873