Assessment of cardiac chamber size using anatomic M-mode

Anatomic M-mode (AMM) is an echocardiographic technique that is capable of generating M-mode studies from two-dimensional (2D) cine loops. Unlike conventional M-mode (CMM) whose scan line must lie along the axis of the ultrasound signal, AMM produces M-mode studies independent of the orientation of the ultrasound beam. We sought to determine the ability of AMM to measure cardiac dimensions in normal dogs and to assess the accuracy and variability of AMM and CMM vs. 2D measurements. Thirty-eight healthy dogs underwent physical exam and 2D, CMM, and AMM echocardiographic studies. The end-diastolic and end-systolic dimension of the left ventricle and the diameter of the left atrium (LAD) and aortic root were evaluated from the right parasternal short- and long-axis views. Results of the AMM and CMM study were compared with the 2D study via linear regression and calculation of a coefficient of correlation. AMM increased the level of correlation with both the left ventricular dimensions and LAD. Bland-Altman analysis revealed that AMM increased the level of agreement with 2D measurements and CMM greatly underestimated LAD vs. AMM. In healthy dogs, cardiac AMM measurements are associated with greater accuracy and less variability than CMM. AMM has the potential to improve quantification of cardiac dimensions.