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)