CARDIOVASCULAR JOURNAL OF AFRICA • Volume 25, No 2, March/April 2014
80
AFRICA
The strengths of the relationship between QTd and
selected continuous variables were assessed with the Pearson’s
correlation coefficient. Variables that demonstrated significant
relationship to QT dispersion i.e. LVM, LVMI and LVMI-2
in the prehypertensive group were entered as independent
variables into a standard (simultaneous) multiple regression
model with QTd as the dependent variable. All tests were
two-sided and values were considered statistically significant
if
p
<
0.05.
Results
A total of 101 subjects aged between 26 and 86 years were
enrolled into the study. The age of the normotensive (
n
=
57) and
prehypertensive group (
n
=
44) of subjects ranged from 27–86
and 26–78 years, respectively. The ICC for the intra-observer
assessment of the measures of height and weight are 0.97 and
0.96, respectively.
Nineteen (43%) of the prehypertensive subjects had both
systolic (SBP) and diastolic blood pressure (DBP) within the
prehypertensive range.This subpopulation of the prehypertensives
with a mean age of 53.37
±
10.96 years consisted of four male
and 15 female subjects. Their mean QTd of 39.21
±
13.46 ms
was similar to QTd of the rest of the cohort (
p
>
0.05).
The clinical characteristics of the study group are presented
in Table 1. There were no differences in the age, gender and
anthropometric measurements of the two groups. The
prehypertensive group however had significantly higher BP indices.
The electrocardiographic measures of the two groups are
presented in Table 2. The heart rate, QTc, QTd and ECG LVH
status of the two groups were similar.
Table 3 shows the echocardiographic measurements of the
groups. The prehypertensive group had significantly higher
IVSTd, LVM, LVMI-1 and LVMI-2 values.
The relationships of QTd to LVH determined by ECG and
echocardiography are presented in Table 4. QTd was independent
of LVH status, not only in the whole cohort, but also in the two
groups.
QTd correlated significantly with LVM (
r
=
0.58,
p
=
0.003),
LVMI (
r
=
0.55,
p
=
0.006) and LVMI-2 (
r
=
0.49,
p
=
0.016)
in the prehypertensive subjects. Several other variables were
tested in both groups but did not correlate with QTd (
p
>
0.05):
age, weight, height, BMI, SBP, DBP, pulse pressure (PP), heart
rate, QTc, LVIDd, LVIDs, IVSTd, LVPWd, RWT and ejection
fraction (EF). None of the independent variables (LVM, LVMI
and LVMI-2 in the prehypertensive group) in the simultaneous
regression model with QTd as the dependent variable made
statistically significant contributions to the equation (computed
R
2
=
34%, adjusted
R
2
=
24%). The beta-values and the levels
of significance were 0.50 and 0.31 for LVM, 0.04 and 0.96 for
LVMI and 0.14 and 0.96 for LVMI-2.
Discussion
PHT is an intermediate stage between normal BP and
hypertension. The mechanisms of excess CV risk/end-organ
Table 1. Clinical characteristics of the study population
Characteristic
Total
population
n
=
101
Mean
±
2SD
n
(%)
Normotensive
group
n
=
57
Mean
±
2SD
n
(%)
Prehyperten-
sive group
n
=
44
Mean
±
2SD
n
(%)
p
-value
Age
59.96
±
13.54 50.74
±
13.89 55.84
±
12.65 0.06
Gender
0.94
Male
34 (33.7)
19 (33.3)
15 (34.1)
Female
67 (66.3)
38 (66.7)
29 (65.9)
Weight (kg)
69.10
±
13.10 68.02
±
12.32 70.50
±
14.05 0.20
Height (m)
1.63
±
0.08 1.63
±
0.07 1.62
±
0.10 0.44
BMI (kg/m
2
)
26.17
±
4.72 25.61
±
4.63 26.89
±
4.78 0.18
BMI class
0.35
Normal
45 (44.6)
29 (50.9)
16 (36.4)
Overweight
35 (35.6)
18 (31.6)
18 (40.9)
Obese
20 (19.8)
10 (17.5)
10 (22.7)
SBP (mmHg) 118.27
±
19.50 112.39
±
6.24 125.89
±
7.34
<
0.001
DBP (mmHg)
73.70
±
7.43 71.05
±
6.60 77.14
±
7.10
<
0.001
MAP (mmHg)
88.56
±
6.98 84.83
±
5.61 93.39
±
5.48
<
0.001
PP (mmHg)
44.56
±
9.04 41.33
±
6.86 48.75
±
9.83
<
0.001
BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood
pressure; MAP, mean arterial blood pressure; PP, pulse pressure.
Table 2. ECG measurements according to BP group.
Characteristic
Total
population
n
=
101
Mean
±
2SD
n
(%)
Normotensive
group
n
=
57
Mean
±
2SD
n
(%)
Prehyperten-
sive group
n
=
44
Mean
±
2SD
n
(%)
p
-value
Heart rate
(beats/min)
73.35
±
10.94 72.11
±
9.53 74.95
±
12.47 0.38
QRS (ms)
79.96
±
3.51 79.54
±
3.46 80.50
±
3.53 0.18
QTd (ms)
38.72
±
11.34 38.96
±
11.06 38.41
±
11.81 0.81
QTc (ms)
417.92
±
23.63 415.58
±
23.25 420.95
±
24.04 0.26
ECG LVH
Sokolow–Lyon 8 (7.9)
4 (7.0)
4 (9.1)
0.73
Araoye’s code
10 (9.9)
4 (7.0)
6 (13.6)
0.33
QTc, corrected QT interval; QTd, QT dispersion, QRS, QRS duration, LVH,
left ventricular hypertrophy.
Table 3. Echocardiographic measurements according to BP groups
Characteristic
Total
population
n
=
60
Mean
±
2SD
n
(%)
Normotensive
group
n
=
36
Mean
±
2SD
n
(%)
Prehyperten-
sive group
n
=
24
Mean
±
2SD
n
(%)
p
-value
LVIDd (cm)
4.52
±
0.44 4.50
±
0.41 4.55
±
0.49 0.64
LVIDs (cm)
2.90
±
0.43 2.93
±
0.41 2.84
±
0.46 0.43
IVSTd (cm)
1.05
±
0.21 1.00
±
0.20 1.15
±
0.21 0.01
LVPWd (cm)
0.88
±
0.14 0.88
±
0.15 0.91
±
0.13 0.29
RWT (cm)
0.40
±
0.09 0.39
±
0.09 0.41
±
0.09 0.57
LVM (g)
153.03
±
35.91 144.54
±
35.55 165.75
±
33.21 0.024
LVMI-1(g/m
2
)
84.93
±
18.64 80.45
±
18.65 91.65
±
16.84 0.021
LVMI-2 (g/m
2.7
) 50.49
±
12.02 47.51
±
12.00 54.96
±
10.84 0.017
EF (%)
72.72
±
8.73 71.44
±
8.57 74.65
±
8.80 0.17
Echo LVH
2(3.33)
1(1.67)
1(1.67)
1.00
LVM, left ventricular mass; LVMI, left ventricular mass index; LVH, left
ventricular hypertrophy; LVIDd, left ventricular internal diameter in diastole;
LVIDs, left ventricular internal diameter in systole; IVSTd, interventricular
septal thickness in diastole; PWTd, left ventricular posterior wall thickness
in diastole.
