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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 25, No 5, September/October 2014
234
AFRICA
Methods
This prospective cohort study was approved by the University
of Abuja Teaching Hospital’s ethical clearance committee and
is in compliance with the Helsinki declaration. The minimum
age for participation in the study was 18 years but there was no
upper age limit. Recruitment for the present study was initiated
in December 2011 and data were obtained until August 2012.
Of the 220 patients with hypertension with or without
heart failure enrolled for the study, 10, representing 4.5% of
the total enrolment, were excluded because they were diabetic,
had regional wall motion abnormality on transthoracic
echocardiography, had serum creatinine greater than 170 µmol/l
or acute myocardial infarction. Therefore, 210 subjects were
studied, of whom 133 were subjects with a new referral for
hypertension to the Cardiology Unit, Department of Medicine,
University of Abuja Teaching Hospital, and 77 were subjects
with hypertensive heart failure, presenting consecutively to the
same unit.
Hypertension was defined according the JNC VII guidelines,
15
while heart failure was diagnosed according to the guidelines of
the European Society of Cardiology.
16
The functional status of
the HF subjects was according to the guidelines of New York
Heart Association functional classification.
17
All subjects gave
written informed consent to participate in the study.
Each subject had fasting blood sugar level, fasting lipid
profile, electrolyte, urea and creatinine levels, and full blood
count assessed. Each subject also had blood collected, processed
and plasma stored at –80°C until assayed for NT-proBNP.
Subjects also had a transthoracic echocardiography performed
on the same day that the sample was collected for NT-proBNP
assay, the samples being analysed at the Hatter Institute,
University of Cape Town.
All the subjects completed a standard questionnaire. Due to
the multiplicity of languages in Nigeria, the questionnaire was
not translated into any of the local languages. The majority of
the subjects were reasonably proficient in the English language.
Where there was a need for interpretation, both medical and
paramedical staff of the Cardiology Unit of the Department
of Medicine of University of Abuja Teaching Hospital assisted.
The questionnaire requested specific answers to date of birth,
gender, occupation, background diagnosis of hypertension,
background diagnosis of diabetes mellitus, history of angina
pains, history of alcohol consumption and history of smoking
habits. Details of anthropometric measurements, conventional
blood measurements and assays for NT-proBNP have been
reported in our previous publication.
18
Echocardiography was performed using a commercially
available ultrasound system (Vivid E). Subjects were examined in
theleftlateraldecubituspositionusingstandardparasternal,short-
axis and apical views. Studies were performed by an experienced
echocardiographer according to the recommendations of the
American Society of Echocardiography
19
.
In our echocardiography laboratory, the intra-observer
concordance correlation coefficient among the three
cardiologists involved in the study ranged from 0.76–0.93, while
that of the inter-observer concordance ranged from 0.82–0.95.
Measurements were averaged over three cardiac cycles. The left
and right atrial areas were measured at end-ventricular systole
when the atrial chambers were at their greatest dimension,
and with the bases of both atria at their greatest dimensions.
Other details of our echocardiography measurements have been
reported in our previous publication.
18
Statistical analysis
SPSS software version 16.0 (SPSS Inc, Chicago, IL) was used
for statistical analysis. Continuous variables were expressed as
mean
±
SD. Comparison of demographic, clinical, laboratory
and echocardiographic parameters among the three groups
was performed by ANOVA test of variance. Correlation
coefficients were calculated by linear regression analysis with
serum NT-proBNP log-transformed to establish normality,
and correlations between serum NT-proBNP and continuous
demographic, clinical, laboratory and echocardiographic data
were evaluated with Spearman’s regression.
Multivariate linear regression analyses were performed with
log-transformed NT-proBNP concentrations as dependent
variable, with the inclusion of demographic, clinical, laboratory
and echocardiographic parameters. A two-tailed
p
-value
<
0.05
was considered significant
Results
Table 1 shows the demographic, clinical and laboratory
characteristics of the subjects studied. Subjects with hypertensive
HF had the lowest weight of the three study groups, with a
body mass index of 25.4
±
4.5 kg/m
2
as against 27.6
±
6.6 kg/
m
2
for subjects with hypertension with or without LVH (
p
=
0.03). Hypertensive subjects with LVH had the highest levels of
mean arterial pressure and pulse pressure, while subjects with
hypertensive HF had the lowest levels.
There was no significant difference among the study
populations in the levels of fasting blood sugar, fasting lipid
profile, urea, creatinine, haemoglobin concentration and white
blood cell count. There was also no significant difference in the
NT-proBNP levels between the hypertensive subjects without
and those with LVH.
Fig. 1 shows the different concentrations of plasma
NT-proBNP in the hypertensive cohort. Subjects with
hypertensive HF had significantly higher NT-proBNP levels
when compared with other hypertensive subjects, whether with
or without LVH (
p
<
0.001).
Table 2 shows the echocardiographic characteristics of all
the subjects studied. Hypertensive subjects with LVH had
significantly higher interventricular and left ventricular posterior
wall hypertrophy when compared with hypertensive subjects
without LVH (
p
<
0.001 and 0.001, respectively), and when
compared with subjects with hypertensive HF (
p
<
0.001).
Hypertensive subjects with LVH also had higher LV mass and
LV mass index when compared with hypertensive subjects
without LVH and HF (
p
<
0.001). They had a smaller LV mass,
whether indexed or not, when compared with hypertensive HF
subjects (
p
<
0.001).
Hypertensive subjects without LVH and left ventricular HF
had the highest LV ejection fraction (
p
<
0.02) when compared
with hypertensive subjects with LVH, and when compared with
subjects with HF (
p
<
0.001). Apart from the right atrial area,
hypertensive HF subjects had significantly higher chamber
diameters. They also had the highest mitral E/A ratio and the
lowest tricuspid annular plane systolic excursion value.