Speckle tracking and global longitudinal strain(GLS) analysis
Strain imaging was performed semi-automatically. Three standard apical views were recorded (apical four-chamber, apical two-chamber, and apical three-chamber) at the end of expiration in three consecutive cardiac cycles, with a frame rate ranging between 40 and 60 frames per second. Offline analysis was conducted using approved software available on the Acuson ultrasound equipment. Endocardial borders were meticulously traced manually in each image. Aortic valve closure was automatically identified by the software and edited if necessary. Longitudinal strain values were calculated by the software and presented in the bull’s-eye tomogram, numeric values and as the average global longitudinal strain (GLS) among the 16 segments. GLS was measured in two cardiac cycles, and the average value was used for the final analysis. The normal value for GLS was considered as the absolute value greater than 18% [