We can do it after catheterisation as the LA is mapped (x,y,z) with a roving electrode at the tip of one catheter. If that is out of the question, then an interesting surrogate would be left ventricle stroke volume...

LA dimension in anterior - posterior (AP) plane is not used for assessing LA size. Its been warranted that the dilatation of LA dimension in the above plane alone underestimates it. ASE recommends LA volume measurements via area- length method. The LA volumes can be estimated( single plane or biplane method). ie area traced in apical four chamber view & two chamber view at the end systole when the volumes are at the largest/ long axis length of atrium ( measure the length from the center of the mitral annulus to the superior aspect of LA perpendicular). Volume ( ml) = 0.85 x (A1 x A2)/ L where A1 is the area in Ap4CV, A2 - area in Ap2CV and L - shortest length of atrium from both views ( cm). LA volume is always indexed to body surface area. This calculations are via Echocardiogram.

Thanks to Fernando Schlindwein and Meena Sumathy. The latter is usefull for me