Determination of zero reference level for left atrial pressure by echocardiography

This study compares the anterior chest wall to mid-left atrial distance (D) determined by echocardiography with three standard cardiac zero reference levels (ZRL); 5 cm. from the sternal angle, (2) 10 cm. from the back, (3) midchest. Echocardiography was performed on 50 subjects (16 normal subjects and 34 subjects with heart disease). Chest wall, aortic root, and left atrial echoes were obtained to measure D. The AP diameter of the chest (L) was measured using calipers. Thus, ZRL (2) equals (L-10) cm. from the front of the chest and ARL (3) equals L/2, respectively. The difference between the mean of D and ZRL 1, ZRL 2, and ZRL 3 is ø8 c.m, -0.9 cm., and -0.5 cm., respectively.

(a) ZRL (1) is consistently in error; in 17 patients the difference was greater than 5.4 cm.; (b) there is no significant difference between D and ZRL (2) or ZRL (3), and hence they are valid reference systems, and (c) echocardiography can be used to accurately determine the zero reference level for left atrial pressure measurements.