Cardiovascular Journal of Africa: Vol 29 No 5 (September/October 2018)

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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 29, No 5, September/October 2018 310 AFRICA
The clinical prognostic significance of myocardial
performance index (MPI) in stable placental-mediated
disease
I Bhorat, M Pillay, T Reddy
Abstract
Aim: To determine whether a single elevated myocardial
performance index (MPI) value in the third trimester of
pregnancy is a marker for later adverse obstetric outcomes in
stable placental-mediated disease, defined as well-controlled
pre-eclampsia (PE) on a single agent and/or uncompensated
intra-uterine growth restriction (IUGR).
Methods: Fifty-five foetuses whose mothers had stable placen-
tal-mediated disease, either mild pre-eclampsia controlled
on a single agent, and/or uncompensated IUGR in the third
trimester, attending the Foetal Unit at Inkosi Albert Luthuli
Hospital, Durban, South Africa were prospectively recruited
with 55 matched controls. Recorded data for the subjects
included demographic data of maternal age and parity, sono-
graphic data of estimated foetal weight (EFW) and amniotic
fluid index (AFI), myocardial performance index (MPI), and
foetal Doppler data of the umbilical artery (UA), middle
cerebral artery (MCA) and ductus venosus (DV).
Results: The mean gestational age in the controls, the IUGR
and any PE cases was 31.4, 31.8 and 31.0 weeks, respectively.
The distribution of MPI values was significantly lower in the
controls compared to all other groups. The highest standard-
ised MPI values were observed in the PE–IUGR group, where
a median of 5.62 was observed. The only significant differ-
ences observed between the PE and IUGR groups was the UA
resistance index (p = 0.01), where the IUGR cases tended to
have higher UA values compared to the combined PE group.
Borderline statistical significance was observed for the MCA
resistance index values (p = 0.05) between these groups. The
overall adverse event rate in the cases was 49%. The highest
rate was observed in the PE + IUGR group, where eight out
of 12 (67%) experienced adverse events. MPI z-scores served
as a good marker of adverse events, as evidenced by the total
area under the curve (AUC) of 0.90 on the ROC curve. A cut-
off value of 4.5 on the MPI z-score conferred a sensitivity of
89% and specificity of 68% for an adverse event later in preg-
nancy. In univariate logistic regression, MPI z-score, AFI,
EFW, UA Doppler, CPR category, DV Doppler and MCA
Doppler were assessed separately as potential predictors of
adverse outcome. The only significant predictor of adverse
outcome was MPI z-score.
Conclusion: A single elevated value of the MPI (z-score >
4.5) in the third trimester in stable placental-mediated disease
was a strong indicator of adverse obstetric outcomes later
in pregnancy. This has the potential to be incorporated in
conjunction with standard monitoring models in stable
placental-mediated disease to predict an adverse event later
in pregnancy and thus to reduce perinatal morbidity and
mortality.
Keywords: myocardial performance index, intra-uterine growth
restriction, pre-eclampsia, foetal cardiac Doppler, Doppler ultra-
sonography
Submitted 31/10/16, accepted 21/6/18
Published online 15/8/18
Cardiovasc J Afr 2018; 29: 310–316
DOI: 10.5830/CVJA-2018-036
The myocardial performance index (MPI) is a potentially useful
predictor of global cardiac function.1-3 Our previous study
established normal reference ranges of modified MPI in the
second half of pregnancy and interpreted the findings in the
context of cardiac physiological principles.4 Our previous studies
have also suggested cut-off MPI values for adverse neonatal
outcome in both growth restriction and pre-eclampsia,5,6 and
shown it to be a useful predictor of adverse foetal outcomes in
other high-risk obstetric conditions.7 MPI is defined as the sum
of the isovolumetric contraction time (ICT) and isovolumetric
relaxation time (IRT) divided by the ejection time (ET). The
equation is MPI = ICT + IRT/ET.
Placental-mediated disease, which is an umbrella term for
describing different clinical phenotypes, including intra-uterine
growth restriction (IUGR), pre-eclampsia (PE) and abruptio
placentae, arises from a single pathophysiological event in the
first trimester relating to placental maladaptation and lack of
vascular remodelling of the spiral arterioles.8,9 In early-onset
pre-eclampsia (EO-PE), interstitial trophoblastic invasion is
downregulated while endovascular trophoblastic invasion is
limited to the decidua.
The clinical phenotype of PE represents a worse placental
pathological state than IUGR, with combined phenotypes
representing, in addition, obstructive vascular lesions in the
placental vasculature. The sentinel event for EO-PE, EO-IUGR
and combined phenotypes relates to placental maladaptation
in the first trimester.8 Therefore EO-PE, IUGR and combined
phenotypes can be considered as the same pathophysiological
process with differing degrees of pathological severity.
The heart plays a central role in the foetal adaptivemechanisms
to placental insufficiency and hypoxia. Significant alterations
Department of Obstetrics and Gynaecology,
Sub-Department of Foetal Medicine, University of Kwa-Zulu
Natal, Durban, South Africa
I Bhorat, MB ChB, FCOG, PhD,
M Pillay, MB ChB, FCOG
Biostatistics Unit, South African Medical Research Council
of South Africa, Durban, South Africa
T Reddy, MSc