CARDIOVASCULAR JOURNAL OF AFRICA • Volume 25, No 2, March/April 2014
AFRICA
79
Methods
One hundred and one consecutive, apparently healthy black
Nigerian students, staff and retirees of the Lagos University
Teaching Hospital and the College of Medicine, University
of Lagos, aged between 26 and 86 years were recruited. They
fulfilled the following criteria: age
≥
18 years, no history
of heart disease, including hypertension or other conditions
known to affect QT interval and QTd (e.g. diabetes mellitus,
dysautonomia), normal cardiac physical examination and fasting
blood sugar level
<
7 mmol/l. None of the subjects was on
treatment with drugs known to affect QT interval (e.g. statins,
macrolide antibiotics, halofantrine, amiodarone).
15
Exclusion criteria were the presence of sustained
non-sinus rhythm, intraventricular conduction defects and
electrocardiograms in which the end of the T waves could not be
reliably determined and/or QT interval from less than eight leads
could be analysed.
11
Subjects with suboptimal echo windows
were also excluded from echocardiographic examination.
Ethical clearance was obtained from the ethics and research
committee of the Lagos University Teaching Hospital. The study
was conducted to conform to the ethical tenets developed by the
World Medical Association, as espoused in the Declaration of
Helsinki. All subjects provided informed consent.
All subjects were classified by office BP as either
normotensive: normal BP (
<
120/80 mmHg) (
n
=
57) or
prehypertensive: prehypertensive BP (120–139/80–89 mmHg) (
n
=
44), according to the JNC-7 recommendations.
2
A detailed medical history was obtained, physical examination
was performed and anthropometric variables of height and
weight were obtained. Trained personnel obtained measures of
height and weight using a calibrated stadiometer and a weighing
scale. Each subject’s height was measured without shoes, in the
standing position, heels together, toes apart at a 45° angle and
the head in the Frankfort horizontal plane. Weight was measured
with the subject lightly clothed and without shoes. Body mass
index (BMI) was calculated according to the formula:
16
BMI
=
body mass (kg)/body height
2
(m
2
). BMI
<
25 kg/m
2
, 25 to
<
30
kg/m
2
, and
≥
30 kg/m
2
were classified as normal, overweight and
obese, respectively.
16
Resting blood pressure was measured three times for each
subject with a standard mercury sphygmomanometer on the right
arm in a sitting position following a minimum of five minutes’
rest by a physician. Phases I and V Korotkoff sounds were used
to determine systolic and diastolic BP measurements. The mean
of the last two measurements was used in the analysis.
Electrocardiography
All subjects had a resting simultaneous 12-lead electrocardiogram
(ECG) using an Esaote P80 Power electrocardiograph machine.
At a paper speed of 25 mm/s with the machine control set at
standard response, a standard lead II rhythm strip of 13–16
complexes and a minimum of three cardiac cycles per lead were
recorded. All electrocardiograms were analysed by a single
observer blinded to the clinical data.
QT and the preceding RR intervals were assessed manually
with callipers and mean values were determined in three
consecutive cycles. QT intervals were measured in all possible
leads from the beginning of the QRS complex to the point of
T wave offset, i.e. the point of the return of the T wave to the
isoelectric line.
11
In the presence of the U wave interrupting the
T wave, the nadir between the T and U waves was used to define
the point of T wave offset.
QT dispersion (QTd) in milliseconds was defined as the
difference between the shortest (QT
min
) and longest (QT
max
)
mean QT interval in each electrocardiogram.
11
The QT interval
was measured from the lead with the longest interval and was
corrected for subjects’ heart rate using Bazett’s formula:
17
QTc
=
QT
o
______
√
_
RR
where QTc is the corrected QT interval, QT
o
is the observed QT
interval in milliseconds, RR is the RR interval in milliseconds.
QTc
≤
440 ms and QTd
=
30–60 ms were considered normal.
18-20
ECG LVH was determined using the Araoye’s criteria
21,22
for LVH in blacks [i.e. (1) SV
2
+ RV
6
>
4.0 mV in males
≥
30
years, SV
2
+ RV
6
>
5.0 mV in males aged 15–29 years and SV
2
+ RV
6
>
3.5 mV in females; (2) flat or inverted T waves in V5 or
V6; (c) R1 amplitude
>
1.2 mV. ECG LVH is diagnosed when
any of the criteria is positive] and the Sokolow–Lyon voltage
criteria.
23
Araoye’s criteria has been shown to correlate well with
echocardiographic LVH in Nigerians.
24
Echocardiography
Transthoracic echocardiography was performed on the first
60 consecutive subjects using a Hewlett Packard Sonos 2000
machine. Using the American Society of Echocardiography
(ASE) recommendations,
25
the following measurements
were obtained: left ventricular internal diameter in diastole
(LVIDd), left ventricular internal diameter in systole (LVIDs),
interventricular septal thickness in diastole (IVSTd) and left
ventricular posterior wall thickness in diastole (PWTd).
Left ventricular mass (LVM) was derived using the ASE
formula:
25
Estimated LVM (g)
=
0.80 [1.04 (LVIDd + PWTd + IVSTd)
3
–
LVIDd)
3
] + 0.6 g
Left ventricular mass index was determined using two
different methods. Left ventricular mass index 1 (LVMI-1) was
calculated as the ratio of LVM to body surface area (g/m
2
).
25
Subjects were was considered to have LVH if LVMI-1 was more
than 134 g/m
2
for men and more than 110 g/m
2
for women.
26
The second LVMI, i.e. LVMI-2 was derived by indexing LVM
to height using the formula:
27
LVMI-2 (g/m
2.7
)
=
LVM/height
2.7.
However only LVMI-1 was used for the determination of the
presence or absence of LVH in the subjects.
Statistical analysis
The SPSS 17.0 statistical software was used for data analysis.
The data obtained were expressed as means and proportions.
Statistical significance of variables was tested using the
chi-square and Fisher’s exact test for categorical variables and
the Student’s
t
-test for continuous variables. Analysis of variance
was used to assess intra-observer variability of height and weight
measures of the first 35 subjects.
