2.3.1: Speckle tracking strain imaging:
Speckle tracking strain analysis was used to assess left ventricular longitudinal strain. We performed the offline analysis using 2-D images from apical four chamber, three chamber and two chamber views to quantify the global longitudinal strain (GLS) using the Xcelera Q-Lab software. Images were selected to find clear myocardial border with frame rate between 100-140 fps. The echo contrast for the selected images was adjusted and manual tracing of the endocardial border at end diastole was performed to set the region of interest (ROI). The operator identifies and selects the hinge points of the mitral valve annulus and LV apex. The software allows a semi-automated detection of the LV borders. The system allows manual adjustment of the endocardial and epicardial surfaces.
Initially a 3-chamber view is selected; the first step is to select a point just below the aortic valve, then lateral hinge point of the mitral valve annulus and lastly the LV apex. The ROI is then automatically analyzed by the software and divided into six segments as well as the Aortic valve closure time for further analysis. The process is followed for the apical 4-chamber view with 3 points selections at the hinge points of the MV annulus and LV apex. In the 4-ch view, the six segments represent the basal, mid and apical segments of the left ventricular lateral wall and inter ventricular septum. Similar steps were applied to obtain speckle tracking of apical two chamber views.
Data from speckle tracking were displayed in longitudinal time-strain curves for each of the six segments and segmental peak strain was obtained from each curve. The peak longitudinal strain was defined as the most negative strain value at any time point during cardiac cycle. The mean strain of the of six segments were calculated to yield the strain value of that specific view. Aortic valve closure time and GLS is obtained in the apical 3-chamber view while GLS and EF are displayed numbers from the 4-chamber and 3-chamber views. The software then calculates the cumulative GLS as the average longitudinal strain value for the readings obtained from all the three views; and is displayed as bull eye pattern with 16 segment distributions.(12,13) (Figure 2)