Left Atrial to Aortic root ratio
Description
The increase in effective pulmonary blood flow may be estimated by the left atrial to aortic ratio. The LA:Ao uses the relatively fixed diameter of the aorta to assess the degree of left atrial volume loading. This ratio correlates significantly with increased pulmonary flow attributable to excessive transductal flow; optimal threshold ratio > 1.5 has been is associated with a significant PDA.2D Image
Diagram
The cursor is placed at the plain of the aortic valve hinges to include the maximal diameter of the LA. LA:Ao can be measured using this view to obtain an M-mode tracing (yellow line). The cursor should be perpendicular to the aortic wall at the level of the aortic valve.
Diagram
LA:Ao in M-mode. A dilated LA is illustrated and is compared with the diameter of the Ao to obtain the ratio.