CARDIOVASCULAR JOURNAL OF AFRICA • Vol 24, No 5, June 2013
AFRICA
155
views, using the modified Simpson’s rule. LA volumes were
measured using the area–length method from apical four- and
two-chamber views, according to the guidelines of the American
Society of Echocardiography.
6
Left atrial maximum volume (LAV
max
) was measured at the
end of LV systole, just before the opening of the mitral valve,
LA minimum volume (LAV
min
) was measured at the end of
LV diastole, right after the closure of the mitral valve, and
LA pre-atrial volume (LAV
p
) was obtained from the diastolic
frame before initial mitral valve re-opening elicited by atrial
contraction. LA reservoir function was assessed using LA
total EF
=
(LAV
max
– LAV
min
)/LAV
max
, LA conduit function was
assessed using LA passive emptying fraction (LAPEF)
=
(LAV
max
– LAV
p
)/LAV
max
, and LA booster pump function was assessed
using LA active emptying fraction (LAAEF)
=
(LAV
p
– LAV
min
)/
LAV
p
.
For 2D STE analysis, we obtained 2D gray-scale harmonic
images in three apical planes (long axis of LV, four- and
two-chamber). Three consecutive heart cycles were recorded and
averaged. The frame rate was set between 60 and 90 frames per
second.
7
Echocardiograms were digitally stored and later analysed
off-line using acoustic-tracking software (Echo-Pac version 7.0,
GE Vingmed).
8
A 16-segment LV model was obtained from the
four- and two-chamber, and long-axis recordings.
9
Two-dimensional strain software identified the endocardial
border, and after tracing myocardial motion, was automatically
tracked in each imaging view. Strain rate measurements from
16 segments were averaged to assess a LV global longitudinal
parameter based on peak systole (LV-GLSRs), early diastole
(LV-GLSRe), and late diastole (LV-GLSRa) (Fig. 1).
The LA myocardium was divided into six equidistant regions
from apical four- and two-chamber views, while only three were
analysed in the apical long-axis view because the remaining
three in this view are part of the aortic valve and ascending aorta
and not LA myocardium. The software generates strain rate
curves for each atrial segment. Global strain and strain rate were
also calculated by averaging values from 15 atrial segments.
Lastly, we can get global LA peak positive strain rate during
ventricular systole (LA-GLSRs), global LA peak negative strain
rate during early ventricular diastole (LA-GLSRe) and global
LA peak negative strain rate during late ventricular diastole
(LA-GLSRa) (Fig. 2).
To assess inter- and intra-observer variabilities, variabilities
in the measurements of LA-GLSRs, LA-GLSRe, LA-GLSRa,
LV-GLSRs, LV-GLSRe and LV-GLSRa were evaluated in
20 subjects selected randomly. To assess the inter-observer
variability, selected images were analysed by a second observer
blinded to the values obtained by the first observer. To assess
the intra-observer variability, selected images were analysed
at a different time by an observer blinded to the results of the
previous measurements.
10
Fig. 1. Measurement of global longitudinal left ventricular
strain rate from an apical four-chamber view. The dashed
curve represents the global longitudinal ventricular strain
along the cardiac cycle. LV-GLSRa
=
left ventricular glob-
al longitudinal peak late diastolic strain rate. LV-GLSRs
=
left ventricular global longitudinal peak systolic strain
rate. LV-GLSRe
=
left ventricular global longitudinal peak
early diastolic strain rate. AVC
=
aortic valve closure.
Fig. 2. Measurement of global longitudinal left atrial strain
rate from an apical four-chamber view. The dashed curve
represents the global longitudinal atrial strain along the
cardiac cycle. GLSRa
=
left atrial global longitudinal
peak negative strain rate during late ventricular dias-
tole. GLSRs
=
left atrial global longitudinal peak positive
strain rate during ventricular systole. GLSRe
=
left atrial
global longitudinal peak negative strain rate during early
ventricular diastole. AVC
=
aortic valve closure.
TABLE 1. CLINICAL FEATURES OF PATIENTSWITH
NSTEMI AND THE CONTROLS
Controls
(
n
=
40)
NSTEMI
(
n
=
51)
p
-value
Age (years) (mean
±
SD)
60.1
±
9.8
62.9
±
11.1 0.272
Male,
n
(%)
35 (87.5)
43 (84.3)
0.238
Female,
n
(%)
5 (12.5)
8 (15.7)
0.179
Height (cm)
167.06
±
6.97 166.67
±
7.30 0.546
Weight (kg)
61.56
±
10.16 62.31
±
9.70 0.626
Smoking
23
41
0.057
Body mass index (kg/m
2
)
57.5
80.4
0.087
Hypertension (%)
1.69
±
0.16 1.77
±
0.15 0.001
Diabetes mellitus,
n
(%)
0
28 (54.9)** 0.001
Hyperlipidaemia,
n
(%)
0
12 (23.5)** 0.001
Occluded coronary artery,
n
(%)
0
26 (51.0)**
–
RCA,
n
(%)
–
2 (3.9)
–
LAD,
n
(%)
–
11 (21.6)
–
LCX,
n
(%)
–
8 (15.7)
–
RCA
=
right coronary artery, LAD
=
left anterior descending artery,
LCX
=
left circumflex coronary artery. **
p
<
0.01.
