CARDIOVASCULAR JOURNAL OF AFRICA • Vol 21, No 2, March/April 2010
80
AFRICA
ysis of prospectively collected data. Eligible patients were men
and women aged 18 years and older with established hyperten-
sion, who were attending the hypertension clinic at the hospital.
Diagnosis of hypertension was based on systolic blood pressure
of
≥
140 mmHg and diastolic blood pressure of
≥
90 mmHg or
those on antihypertensive therapy.
13
Subjects with a previous history or symptoms of ischaemic
heart disease, echocardiographic evidence of regional wall
motion abnormalities, or established congestive heart failure
were excluded from the study. Other exclusion criteria included
patients with hypertrophic cardiomyopathy, left bundle branch
block and those with incomplete echocardiography reports.
Ethical approval was obtained from the institution’s ethical
review board.
The estimated minimum sample size was 255 hypertensive
subjects. The calculation of the minimum sample size was based
on the prevalence of echocardiographic LVH in hypertensive
subjects at the UCH, Ibadan, which was between 16.5 and 25.8%
depending on the cut-off value used in defining LVH.
14
The study
power was 80% (20% beta error) and the alpha error was set at
5% (0.05).
Clinical evaluation
Baseline clinical and demographic characteristics were obtained
from the subjects’ case notes. These included date of birth (age),
gender, history of diabetes, history of smoking, duration of their
hypertension, and family history of hypertension. Also obtained
were the blood pressure, pulse rate, body weight and height at the
time of echocardiography. Body mass index (BMI) was calcu-
lated using the formula:
BMI (kg/m
2
)
=
weight
_____
height
2
Body surface area (BSA) was calculated using the formula of
Dubois:
15
BSA (m
2
) = 0.0001
×
71.84
×
[weight (kg)]
0.425
×
[height (cm)]
0.725
Echocardiography
All the echocardiograms were performed with the use of a
commercially available echo-machine (ALOKA SSD-1, 700)
and a 3.5-MHz linear array transducer. This was performed
on each subject in the left lateral decubitus position. All meas-
urements were made according to the American Society of
Echocardiography leading edge-to-leading edge criteria.
16
LV measurement was obtained at end-diastole and end-systo-
le. The LV measurements recorded included interventricular
septal thickness at end-diastole (IVSTd), posterior wall thick-
ness at end-diastole (PWTd), and the LV internal dimensions at
end-systole (LVIDs) and end-diastole (LVIDd). Other parameters
obtained were left atrial diameter, aortic root diameter, indices
of LV diastolic function [early-filling velocity (E-velocity), late-
filling velocity (A-velocity) and deceleration time (DT)].
Two experienced cardiologists performed the echocardiogra-
phy. In our laboratory, the intra-observer concordance correla-
tion coefficient ranged from 0.76 to 0.98 while that of the inter-
observer concordance ranged from 0.82 to 0.96.
17
Calculation of echocardiographically derived
variables
Left ventricular mass was calculated using the formula that has
been shown to yield values closely related (
r
=
0.90) to necropsy
LV weight and which has good inter-study reproducibility.
18
LVM (ASE)
=
0.8 [1.04 (IVSTd
+
LVIDd
+
PWTd) 3
+
0.6 g
Relative wall thickness was calculated as twice the posterior wall
thickness/LV internal dimension in diastole. Relative wall thick-
ness of 0.43 or greater was considered abnormal.
19
LV hypertro-
phy was considered present when LV mass exceeded 51 g/m
2.7
in
both men and women.
Haemodynamics
Left ventricular volumes were estimated using the formula
of Teichholz
et al
.
20
These include: LV end-diastolic volume,
LV-end systolic volume, stroke volume and cardiac output. These
measurements have been validated with the invasive Doppler
echocardiographic method.
21
LV end-diastolic volume (EDV) (ml)
=
7[LV internal in diastole
(LVIDd)
+
2.4]
×
LVIDd
LV end-systolic volume (ESV) (ml)
=
7[LV internal in systole
(LVIDs)
+
2.4]
×
LVIDs
Stroke volume (SV) (ml)
=
EDV – ESV
Cardiac output (CO) (ml)
=
SV
×
heart rate (HR)
Mean arterial blood pressure (MAP) (mmHg) was calculated as:
diastolic BP
+
1/3 pulse pressure
Total peripheral resistance was assessed as:
MAP
×
80
________
CO
Pulse pressure (mmHg) was estimated as: SBP – DBP
Fractional shortening (%)
=
100
×
(LVIDd – LVIDs)
_________________ LVIDd
Ejection fraction (%)
=
100
×
(EDV – ESV)
______________ EDV
The ratio of pulse pressure to stroke volume was used as an indi-
rect estimate of global arterial stiffness.
22,23
LV peak wall stress (dynes/cm
2
) was calculated as:
0.86
×
(0.334
×
SBP
×
LVIDd)
_______________________
(PWTd
×
1
+
PWTd) – 2 LVIDd
LV systolic wall tension (dynes)
=
1.333
×
SBP
×
LVIDs
________________
2
Statistical analysis
SPSS version 11.0 (SPSS, Inc, Chicago Illinois) was used for
statistical analysis. Continuous variables were expressed as mean
±
SD and categorical variables as percentages. We assessed
differences in categorical variables by Chi-square analysis while
the unpaired
t
-test was used for comparison of continuous vari-
ables between men and women.
