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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 25, No 5, September/October 2014
236
AFRICA
Pearson correlation analysis of clinical and echocardiographic
variables with log-transformed NT-proBNP in the study
population is shown in Table 3. NT-proBNP was significantly
associated with left ventricular ejection fraction (
p
=
0.01)
but not with tricuspid annular pulmonary systolic excursion
(TAPSE). It was also significantly correlated with age (
p
<
0.04),
pulse pressure and mean arterial pressure (
p
=
0.002 and
p
=
0.002, respectively), systolic blood pressure (
p
=
0.007), serum
creatinine level (
p
=
0.038) and right atrial area (
p
<
0.0001).
There was no significant correlation between NT-proBNP and
body mass index, right ventricular diameter in diastole, inter-
ventricular septal wall thickness in diastole, posterior wall
diameter in diastole, left atrial area, LV mass index, transmitral
E/A ratio, deceleration time and TAPSE.
In multivariate linear regression analysis (Table 4), independ-
ent predictors of NT-proBNP in the study population included
LV ejection fraction (
t
=
2.11;
p
=
0.037), right atrial area (
t
=
1.99;
p
=
0.048) and LV internal diameter in systole (
t
=
2.21;
p
=
0.029).
Discussion
This study has shown that NT-proBNP differentiates hypertensive
LVH from hypertensive HF not only in Caucasians,
9
but also in
black African hypertensive subjects. We found no significant
difference in the concentrations of NT-proBNP between
hypertensive subjects with LVH and those without LVH, which is
in keepingwith previous findings.
5,24,25
NT-proBNP concentrations
were not correlated with LV mass index, interventricular septal
wall thickness or posterior wall thickness in diastole, which
is similar to other findings.
9
This lack of correlation between
NT-proBNP and LV mass index might explain why NT-proBNP
is not a good marker for differentiating hypertensive LVH from
hypertension without LVH and HF.
NT-proBNP correlated with both mean arterial pressure and
pulse pressure. Age and plasma creatinine levels were found
to correlate with NT-proBNP concentration in our study, in
keeping with previous reports that NT-proBNP rises with
increasing age,
26,27
and worsening renal status.
28
Similar to previous findings, we showed no correlation
with deceleration time and trans-mitral E/A ratio, which are
indices of left ventricular function. Richard
et al
.,
31
however,
found a relationship between LV diastolic function and plasma
BNP levels using newer diastolic indexes measured from tissue
Doppler imaging and colour M-mode that allow more accurate
characterisation of myocardial relaxation and left ventricular
filling.
Unlike some previous studies, our study did not only assess
remodelling of the left-sided chambers and LV systolic function,
but also remodelling of the right heart chambers, LV diastolic
function and right ventricular systolic function.
Even though there was no significant correlation between the
concentration of NT-proBNP and TAPSE, the right atrial area,
which is a measure of remodelling of the right cardiac chamber
and an indirect measure of right ventricular function, correlated
significantly with NT-proBNP. This suggests right cardiac
chamber remodelling had some effect on the concentration of
plasma NT-proBNP in our hypertensive cohort. Correlation
between BNP and right atrial size has been previously
described.
32,33
Hypertensive subjects with LVH had significantly worse LV
systolic function compared to subjects without LVH (
p
<
0.02),
which may support the fact that hypertensive subjects with LVH
have worse cardiovascular profile compared to those without
hypertrophy.
34
Our subjects with hypertensive HF were much younger, with a
mean age of 53.0
±
11.9 years compared to the developed countries
where HF is a disease of the elderly, with an average age of 76
years.
35,36
Hypertensive HF presenting in a relatively young cohort
in this Nigerian population is a reflection of the presentation of
the complications of hypertension at an early stage.
Long distance and often lack of funding to cover the travel
fare are important aspects of late presentation to healthcare.
37
This presentation of hypertensive HF at a relatively early age
has the potential to undermine national productivity as a
consequence of the number of active life years lost by the most
active workforce of the population.
Conclusion
This study has shown that NT-proBNP is a good marker in
differentiating hypertensive HF from hypertension with or
without LVH. Our finding supports the need to introduce
NT-proBNP point-of-care machines
39
in our cardiology practices
in sub-Saharan Africa. Currently, the use of point-of-care tests
in resource-limited settings such as ours has focused mainly on
infectious diseases that need prompt diagnosis and treatment,
such as HIV infection, tuberculosis and malaria,
40
and diabetes
care.
41
Therefore the need for the introduction of point-of-
care NT-proBNP assays for early diagnosis while awaiting
echocardiography in our cardiology practice cannot be over-
emphasised. For such a point-of-care test to be very effective in
the sub-continent, there is a need to further reduce the cost of
these devices compared with what is obtainable in Europe and
the United States.
Our sincere appreciation goes to Sir Maurice Hatter and all members of staff
of the Hatter Institute for Cardiovascular Research in Africa, Department
of Medicine, Faculty of Health Sciences, University of Cape Town, South
Africa, members of staff of the Cardiology Unit, Department of Medicine,
University of Abuja Teaching Hospital, Gwagwalada, Abuja, and Servier
Pharmaceuticals. This work was partly funded by a grant from the Pulmonary
Vascular Research Institute, Medical Research Council of South Africa and
the University of Cape Town.
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