Development of Australian Reference Ranges for the Left Fetal Modified Myocardial Performance Index and the Influence of Caliper Location on Time Interval Measurement

Abstract

Objectives: To construct gestational age-adjusted reference ranges of the left fetal modified myocardial performance index (Mod-MPI) in the Australian population and assess the influence of valve click caliper position on constituent time intervals and the Mod-MPI. Methods: This is a prospective longitudinal study of 117 normal singleton fetuses undergoing 318 ultrasound scans at 4–6 weekly intervals between 18 and 38 weeks of gestation. The isovolumetric contraction time (ICT), isovolumetric relaxation time (IRT), and ejection time (ET) were measured at 3 different caliper positions in each fetus: beginning of the original valve clicks (‘original’), beginning of the reflected valve clicks (‘reflected’), and peak of valve clicks (‘peak’). The Mod-MPI was calculated as (ICT + IRT)/ET. Results: The Mod-MPI increased throughout gestation with means ± SD of 0.42 ± 0.05 ‘reflected’ and ‘peak’ versus 0.49 ± 0.03 ‘original’ at 19 weeks, and means of 0.46 ± 0.05 ‘reflected and peak’ versus 0.51 ± 0.08 ‘original’ at 36 weeks. Throughout gestation, ICT remained fairly constant and IRT increased, while ET decreased with ‘original’ click and remained constant for ‘reflected’ and ‘peak’ clicks. A modest increase in Mod-MPI was seen with increasing fetal heart rate. Analysis of repeatability for the 3 methods showed the following ICCs: ‘original’, 0.797 (95% CI 0.762–0.829); ‘reflected’, 0.809 (95% CI 0.775–0.839), and ‘peak’, 0.799 (95% CI 0.764–0.831). Conclusions: Detailed exploration of the morphology of mitral and aortic valve closure and opening clicks shows how selection of different phases of these clicks may significantly influence the Mod-MPI. We recommend that the peak of the valve clicks be standardized between research groups.

The (Pulsed-Wave) Doppler Fetal Myocardial Performance Index: Technical Challenges, Clinical Applications and Future Research

“…It is thought that a thinner click (e.g. reflected click) allows more precise measurement of time intervals [62]. …”

“…Regarding the first point, normal gestational age-adjusted reference values of second- and third-trimester singleton fetuses for the left Mod-MPI [59,62,67,68], right Mod-MPI [69,70], and uncomplicated monochorionic twin pregnancies have been published [7]. MPI has also been evaluated in first-trimester normal and complicated pregnancies [16,69,71,72,73,74,75,76,77,78,79], and compared with normal infants and children [11,54].…”

“…MPI has also been evaluated in first-trimester normal and complicated pregnancies [16,69,71,72,73,74,75,76,77,78,79], and compared with normal infants and children [11,54]. Reported Mod-MPI values for normal singleton fetuses range from 0.35 to 0.60 [9,11,54,55,62,67,68,79,80,81]. Some studies describe almost constant measurements throughout pregnancy [9,54,68,79,80], while others report gradual reductions [11,81] or increases [39,58,67] with gestational age (fig.…”

The short term fetal cardiovascular effects of corticosteroids used in obstetrics

“…As the normal distribution of Doppler measurements changes with gestational age, individual fetal measurements will be normalised prior to analysis to give a Z‐score (by expressing the deviation of the individual measurements from the gestational age mean in standard deviations). Mod‐MPI values will be compared against our previously published normal range 33 . Analysis techniques for repeated measures will be used to examine changes of Doppler flows, MPI, biophysical profile, and CTG from baseline to the follow‐up ultrasounds.…”

“…In adults, the MPI distinguishes between normal and abnormal ventricular function, and has been extrapolated to evaluation of the fetal heart in both normal and complicated pregnancies 31 . Our group has recently published a number of refinements to improve the repeatability of the mod‐MPI, 31 , 32 as well as producing Australian normal ranges for both left and right‐sided mod‐MPI 33 34 …”