CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 4, May 2012
200
AFRICA
The time-course changes of NT-proBNP and tissue
Doppler indices in patients undergoing mitral valve
replacement
DR PRAKASCHANDRA, T ESTERHUIZEN, DP NAIDOO
Abstract
Background:
In severe mitral regurgitation, a subset of
patients who are asymptomatic may develop left ventricu-
lar decompensation before changes in echocardiographic
parameters become evident. Since N-terminal brain natriu-
retic peptide (NT-proBNP) is used to detect early heart fail-
ure, we hypothesised that NT-proBNP would be activated in
patients with mitral regurgitation.
Methods:
Patients submitted to surgery were prospectively
evaluated over eight months in the Department of Cardiology
at Inkosi Albert Luthuli Central Hospital. Control patients
with severe mitral regurgitation were obtained from the
outpatient clinic. In order to define their value in identi-
fying left ventricular decompensation, NT-proBNP levels
and tissue Doppler imaging (TDI) indices were simultane-
ously measured and compared with conventional echocardio-
graphic indices at baseline and this was repeated at one week
and at six weeks after valve replacement.
Results:
Mean NT-proBNP levels were markedly elevated
pre-operatively in all surgical cases compared to controls
(
p
=
0.0001). The diastolic E-mitral/E-annulus ratio, meas-
ured using TDI, was higher in the study group, indicating
higher left ventricular filling pressure present in the study
group. NT-proBNP levels increased further at one week
after surgery and subsided at the six-week follow-up visit to
levels similar to the control group. The TDI diastolic ratio
also decreased at one week, and increased slightly again at
the six-week follow up. These changes were accompanied
by significant reduction in left atrium and left ventricular
chamber dimensions with an increase in the ejection fraction
from one to six weeks.
Conclusion:
Marked differences in mean NT-proBNP levels
and TDI ratios between the study and control groups suggest
that using TDI and NT-proBNP assays may detect covert left
ventricular decompensation.
Keywords:
mitral regurgitation, tissue Doppler imaging,
NT-proBNP, mitral valve replacement
Submitted 20/9/10, accepted 15/9/11
Cardiovasc J Afr
2012;
23
: 200–205
DOI: 10.5830/CVJA-2011-057
Chronic organic mitral regurgitation (MR) has a variable course
and requires careful monitoring by the clinician. Symptoms often
occur late due to the compliance properties of the left atrium
that allow it to accommodate large volumes of blood without
a significant rise in pressure. As the regurgitation becomes
more severe, contractile dysfunction may precede the onset of
symptoms associated with disease progression as the ejection
fraction (EF) declines but it may still remain in the normal
range. An EF less than 60% has been shown to be associated
with poorer survival rates after corrective surgery and is likely to
indicate covert contractile dysfunction in MR patients.
1
Although numerous qualitative and quantitative echo-
cardiographic modes have been developed, previous studies have
demonstrated that existing measures of severity of MR correlate
poorly with clinical signs and symptoms.
2
There are few data on
the newer echocardiographic modalities, notably tissue Doppler
imaging (TDI), the predictive values of which have not been
determined. While the mitral inflow measurements are preload-
dependent, diastolic tissue velocities measured using TDI are far
less influenced by these parameters and may be more reliable in
assessing contractile changes.
The development of contractile dysfunction and its relation to
the severity of volume overload in MR is not clearly understood.
Prolonged contractile dysfunction eventually becomes
irreversible even after the MR is corrected and is predictive
of both congestive heart failure and death.
1
In chronic organic
MR, there are as yet no clear definitions of BNP physiological
determinants and outcome implications. We hypothesised that
N-terminal brain natriuretic peptide (NT-proBNP) would be
activated in MR and, because this is a validated diagnostic test
in heart failure, it could prove to be an early marker for the
development of left ventricular (LV) dysfunction.
In this study we evaluated tissue Doppler imaging and
NT-proBNP levels in patients with severe chronic MR and
determined their time-course patterns following mitral valve
replacement.
Methods
The study population was selected from Inkosi Albert Luthuli
Central Hospital, Durban. Informed consent was obtained from
each patient, and in the case of minors, from the parent or legal
guardian. The study protocol conforms to the ethical guidelines
of the 1975 Declaration of Helsinki. Ethics approval was given
by the Biomedical Research Ethics Committee at the University
of KwaZulu-Natal, Nelson R Mandela School of Medicine (Ref
No. H112/06).
Department of Biomedical and Clinical Technology, Durban
University of Technology; and Department of Cardiology,
University of KwaZulu-Natal, Durban, South Africa
DR PRAKASCHANDRA, MMed Sci (Cardiology),
Department of Cardiology, University of KwaZulu-Natal,
Durban, South Africa
DP NAIDOO, MD, FRCP, FESC,
Department of Biostatistics, University of KwaZulu-Natal,
Durban, South Africa
T ESTERHUIZEN, MSc (Biostatistics)
