Assessing Fetal Wellbeing: The Potential of Modified Myocardial Performance Index (Mod-MPI) alongside Doppler Indices
A recent study investigated fetal hemodynamics in pregnancies complicated by absent or reversed end-diastolic flow (AEDF) in the umbilical artery, comparing outcomes in AEDF positive, AEDF negative, and control groups.The research highlighted significant differences in pulsatility index (PI) values across the three groups for the umbilical artery, middle cerebral artery, and both uterine arteries (p < 0.001). Specifically, the AEDF (+) group exhibited a markedly elevated umbilical artery PI (UA-PI) of 2.03 ± 0.23 compared to 1.01 ± 0.19 and 1.01 ± 0.14 in the AEDF (-) and control groups, respectively, indicating increased placental vascular resistance and fetal circulatory loading. A "brain-sparing response" was observed in the AEDF (+) group, characterized by lower middle cerebral artery PI (MCA-PI) values (1.54 ± 0.45), suggesting preferential blood flow directed towards the fetal brain as a compensatory mechanism for hypoxia. Moreover, significantly higher PI values were found in the right (1.74 ± 0.57) and left (1.95 ± 0.71) uterine arteries within the AEDF (+) group, pointing to maternal-origin uterine perfusion insufficiency.
The study also explored the role of Modified Myocardial Performance Index (Mod-MPI) as an indicator of fetal cardiac function. While the composite mod-MPI did not show significant differences between groups, analysis of its individual components – isovolumetric relaxation time (IRT), isovolumetric contraction time (ICT), and ejection time (ET) – alongside conventional Doppler indices (UA PI, MCA PI, and the cardio-thoracic ratio or CPR) showed potential for incremental value in identifying fetuses at risk. The E/A ratio, a measure of left ventricular diastolic function, remained similar across groups despite reductions in both E and A velocities in the AEDF (+) subgroup, suggesting proportional declines in early and late diastolic filling accompanied by a shortened systolic ejection time.
Although receiver operating characteristic (ROC) analyses of the individual MPI components yielded area under the curve (AUC) values below 0.50 in this dataset, the researchers propose that a combined predictive model incorporating UA Doppler abnormalities, CPR < 1.0, and alterations in MPI components (ET shortening, prolonged IRT, reduced E/A ratio) could be clinically beneficial. They suggest future, larger, prospective, multicenter studies are needed to establish clinically applicable cut-offs and refine antenatal surveillance strategies for fetal growth restriction (FGR).
The study acknowledges limitations, including its single-centre design which may limit generalizability. Measurements obtained via pulsed-wave Doppler are susceptible to variations due to fetal position, breathing, heart rate variability, and operator technique. The absence of long-term neurodevelopmental and cardiac follow-up data also restricts the ability to correlate prenatal Doppler findings with later functional outcomes. Despite these limitations, the study underscores the potential of integrating Mod-MPI components with established Doppler indices to enhance the assessment of fetal wellbeing in high-risk pregnancies.
