Evaluation of an automated fetal myocardial performance index

Does matrix transducer technology improve quality and repeatability of four-dimensional tricuspid annular plane systolic excursion and mitral annular plane systolic excursion measurements?

Background

Novel ultrasound technology and software processing allow offline evaluation of tricuspid annular plane systolic excursion and mitral annular plane systolic excursion measurements. We wished to compare both novel 4D matrix (eM6C) and conventional (RAB6-D) transducers with variable settings (electronic spatiotemporal image correlation, spatiotemporal image correlation and four-dimensional real time) to determine if there was a significant difference in absolute value, quality and repeatability of the resultant reconstructed image and M-mode trace.

Methods

A blinded prospective cross-sectional study of normal fetuses from 23 to 38 weeks' gestation were recruited. After routine sonography, four-dimensional volumes were stored and analysed using GE 4DView™ software. Statistical analysis explored variability, correlations and repeatability of the measurements with chi-square analysis, intraclass correlations and the Bland-Altman comparison plots. A scoring system was devised for image quality.

Results

Eighteen participants generated 282 data volumes. Absolute values demonstrated some inconsistencies for both tricuspid annular plane systolic excursion and mitral annular plane systolic excursion measurements with variations between transducers: the highest for the RAB6-D/spatiotemporal image correlation setting and the lowest for the four-dimensional real-time settings. The RAB6-D/spatiotemporal image correlation setting was the most repeatable combination (intraclass correlation coefficient = 0.85). Poorest image quality (M-mode trace, four-chamber view, annuli) came from the RAB6-D/four-dimensional real-time combination with the eM6C/electronic spatiotemporal image correlation and RAB6-D/spatiotemporal image correlation settings being nearly identical.

Conclusion

We show that transducer and setting combinations influence absolute tricuspid annular plane systolic excursion/mitral annular plane systolic excursion measurements, so need to be articulated in future research. The transducer setting (electronic spatiotemporal image correlation/spatiotemporal image correlation/four-dimensional real time) was a more significant factor than the type of transducer (conventional vs matrix). Subjective image evaluation does not correlate well with repeatability of image acquisition. Further studies are needed to compare measurements using four-dimensional post-processing tools against conventional real-time measurements.

Poor Correlation between Fetal Tissue Doppler Imaging and Pulsed Wave Myocardial Performance Indices

INTRODUCTION

Both tissue Doppler imaging (TDI) and pulsed wave Doppler (PWD) Myocardial Performance Indices (MPIs) have been proposed as tools for functional fetal cardiology. We wished to determine if there was any correlation between TDI-MPI and PWD-MPI.

METHODS

A cohort of uncomplicated women with morphologically normal singleton fetuses between 22 and 39 weeks of gestation was recruited. A single sonologist acquired Doppler waveforms for evaluation of both left and right TDI-MPI and PWD-MPI. The PWD-MPI values were calculated using a previously published algorithm and the TDI-MPI time intervals were measured manually by a single operator.

RESULTS

Achievability and repeatability were high for both modalities. TDI produced significantly lower right MPI values yet significantly higher left MPI values, potentially reflecting their evaluation of physiologically different events, blood flow versus myocardial contraction.

CONCLUSION

This study demonstrates that MPIs measured from PWD and TDI have a weak correlation and cannot be used interchangeably, even with the exclusion of suboptimal TDI-MPI scans from the analysis. Given the lack of correlation between the two methods, the high variation in TDI waveform, and the lack of unified approach to TDI analysis, we feel further research is needed before adoption of this technique.

Fetal Cardiac Function: Myocardial Performance Index

The Myocardial Performance Index (MPI) or Tei index, presented by Tei in 1995, is the ratio of the sum of the duration of the isovolumetric contraction time (ICT) and isovolumetric relaxation time (IRT) to the duration of the ejection time (ET). The Modified Myocardial Performance Index (Mod-MPI), proposed in 2005, is considered a reliable and useful tool in the study of fetal heart function in several conditions, such as growth restriction, twin-twin transfusion syndrome, maternal diabetes, preeclampsia, intrahepatic cholestasis of pregnancy, and adverse perinatal outcomes. Nevertheless, clinical translation is currently limited by poorly standardised methodology as variations in the technique, machine settings, caliper placement, and specific training required can result in significantly different MPI values. This review aims to provide a survey of the relevant literature on MPI, present a strict methodology and technical considerations, and propose future research.

Reference ranges of fetal heart function using a Modified Myocardial Performance Index: a prospective multicentre, cross-sectional study

OBJECTIVES

The primary aim of this study was to establish the normal reference ranges of the fetal left ventricular (LV) Modified Myocardial Performance Index (Mod-MPI). A secondary aim was to evaluate the agreement between manual and automatic measurements for fetal Mod-MPI.

DESIGN

A prospective, multicentre, cross-sectional study.

PARTICIPANTS

Normal singleton pregnancies.

METHODS

The LV functions of normal singleton pregnancies were assessed in nine centres covering eight provinces in China using unified ultrasound protocols and settings and standardised measurements by pulsed Doppler at 20-24, 28-32 and 34-38 weeks of gestation. The isovolumetric relaxation time (IRT), isovolumetric contraction time, ejection time (ET) and Mod-MPI were measured both automatically and manually.

RESULTS

This cross-sectional study included 2081 fetuses, and there was a linear correlation between gestational age (GA) and Mod-MPI (0.416+0.001×GA (weeks), p<0.001, r²=0.013), IRT (36.201+0.162× GA (weeks), p<0.001, r²=0.021) and ET (171.418-0.078*GA (weeks), p<0.001, r²=0.002). This finding was verified using longitudinal data in a subgroup of 610 women. The agreement between the manual and automated measurements for Mod-MPI was good.

CONCLUSIONS

We constructed normal reference values of fetal LV Mod-MPI. Automatic measurement can be considered for ease of measurement in view of the good agreement between the automatic and manual values.

Fetal Myocardial Performance Index in the Third Trimester of Pregnancy: Feasibility and Reproducibility of Conventional Spectral Doppler versus Spectral Tissue Doppler Technique

OBJECTIVE

This study aims to compare completion rates and reproducibility of myocardial performance index (MPI) using conventional spectral Doppler versus tissue Doppler in an unselected high-risk third trimester population.

STUDY DESIGN

This was a prospective cross-sectional study of high-risk pregnancies at ≥28 + 0 weeks' gestation. Conventional spectral and tissue Doppler MPI of the left ventricle (LV) and right ventricle (RV) was attempted on all patients.

RESULTS

Seventy-nine pregnancies were evaluated. LV tissue Doppler MPI was completed more frequently than LV conventional spectral Doppler MPI (63/79, 79.7% vs. 45/79, 55.7%), p-value <0.01. RV tissue Doppler MPI was completed more frequently than RV conventional spectral Doppler MPI (68/79, 86% vs. 42/79, 53.2%), p-value <0.01. In obese subjects (n = 50) LV tissue Doppler MPI was completed more frequently than LV conventional spectral Doppler MPI (37/50, 74% vs. 26/50, 52%), p-value <0.01. RV tissue Doppler MPI was completed more frequently than RV conventional spectral Doppler MPI (40/50, 80% vs. 25/50, 50%), p-value <0.01. intraclass correlation coefficient for all modalities ranged between 0.73 and 0.93, except for LV conventional spectral Doppler intraobserver variability which was 0.22.

CONCLUSION

Tissue Doppler had statistically higher completion rates than conventional spectral Doppler, including the obese subgroup, with evidence of strong reproducibility in the third trimester.

Measurement of cardiac function by cardiac time intervals, applicability in normal pregnancy and twin-to-twin transfusion syndrome

BACKGROUND

To detect early cardiac deterioration, a simple and stable tool is needed. Measurement of time intervals in a simple 4-chamber view using color-coded tissue Doppler imaging is a relatively new approach to assess fetal cardiac function. The aim of this study was to evaluate the applicability of this modality and to construct reference ranges for cardiac time intervals.

METHODS

We performed a prospective longitudinal cohort study in healthy fetuses. We used linear mixed models to construct age-adjusted reference ranges for shortening time (St) and lengthening time (Lt) in three cardiac regions: global heart and right and left ventricular wall. St and Lt were expressed as percentage of the cardiac cycle. Feasibility and intra- and interobserver variabilities were evaluated. We applied the technique to twin-twin transfusion syndrome (TTTS) recipients before laser therapy to test the diagnostic performance.

RESULTS

A total of 251 recordings were obtained from 54 healthy singletons. St decreased and Lt increased with gestational age in all regions. We found a high feasibility (99.6%) and excellent intra-/interobserver variability for St (0.96/0.94) and Lt (0.99/0.96) of the global heart. Left and right ventricle performance parameters were good. In TTTS recipients, St was prolonged (p < 0.01) and Lt was shortened (p < 0.01) in all regions and the feasibility was excellent (96.6%).

CONCLUSIONS

The assessment of fetal cardiac function by measurement of cardiac time intervals is technically feasible with good reproducibility, even in difficult scanning circumstances such as TTTS. It is possible to discriminate between healthy and compromised fetuses with this technique.

Fetal myocardial performance index in assessment and management of small-for-gestational-age fetus: a cohort and nested case-control study

OBJECTIVE

To assess the clinical utility of the fetal myocardial performance index (MPI) in assessment and management of the small-for-gestational-age (SGA) fetus/growth-restricted fetus (FGR).

METHODS

This was a prospective cohort study in metropolitan Australia of patients referred in the period June 2012 to March 2015 to fetal medicine services at 24-38 weeks' gestation for suspected singleton SGA/FGR (estimated fetal weight (EFW) < 10^th centile with or without abnormal umbilical artery (UA) Doppler) pregnancy. Patients had MPI assessed in addition to routine measures, and were followed through to birth. We compared MPI values against those of a local reference population and gestational age-matched controls, and assessed the correlation with perinatal outcome and other Doppler measures.

RESULTS

Fifty-two cases were included, 38 diagnosed < 32 weeks and 14 diagnosed ≥ 32 weeks. None demonstrated significantly elevated left, right or delta MPI compared with the reference population or with gestational age-matched controls at the time of first MPI evaluation. There were no consistent longitudinal patterns in MPI that would suggest its clinical utility. The mean ± SD gestational age at delivery was 34.6 ± 3.8 weeks and birth weight was 1.7 ± 0.6 kg, and the median neonatal hospital admission time was 27 days, confirming a pathological cohort. There were no significant correlations between left, right or delta-MPI and perinatal outcome, although there were significant correlations between UA, middle cerebral artery (MCA) and ductus venosus (DV) Doppler and perinatal outcome (birth weight, gestational age at birth and length of neonatal hospital stay). Exploratory subgroup comparisons (EFW < 3^rd vs 3^rd -10^th centile; early- vs late-onset; abnormal vs normal UA Doppler) found only minor differences in MPI, reaching statistical, but not clinical, significance, only in the EFW < 3^rd vs 3^rd -10^th centile comparison.

CONCLUSIONS

MPI did not demonstrate clinical utility in either triage or longitudinal follow-up of an SGA/FGR cohort presenting to fetal medicine services. Given that prior research suggesting its utility originates from single-center cohorts, while multicenter, large cohorts have suggested little utility or no additional utility if routine UA/MCA/DV Doppler is performed, publication bias may have affected previous reports. It seems unlikely that MPI has clinical utility in assessment and management of SGA/FGR fetuses. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Beat-to-beat variability of fetal myocardial performance index

OBJECTIVES

To determine whether there is beat-to-beat (BTB) variability in the fetal left myocardial performance index (MPI), as evaluated by an automated system, and whether there is a correlation between MPI and fetal heart rate (FHR).

METHODS

This was a prospective cross-sectional study of uncomplicated, morphologically normal, singleton pregnancies at 20-38 weeks' gestation. Multiple cineloops for left MPI measurement were acquired during a single examination of each fetus. Raw cineloop data were analyzed by our automated MPI system (intraclass correlation coefficient of 1.0 for any given waveform) to produce a set of MPIs. The corresponding instantaneous FHR was measured for each individual cardiac cycle for which MPI was calculated.

RESULTS

Data from 29 fetuses were analyzed; mean MPI was 0.52, mean FHR was 150 beats per min and the median number of cardiac cycles examined per fetus was 70 (interquartile range, 31-115). Marked BTB variability was noted; median coefficient of variation was 10% (range, 5.5-13.9%). FHR was weakly correlated with absolute MPI (r = 0.22; P < 0.05). BTB variation in MPI as a percentage of the mean MPI was not significantly correlated with FHR (r = 0.031; P = 0.146). When standard error of the mean of all MPI values was divided by the mean for each case, it showed that at least four cardiac cycles should be averaged to reduce MPI variability to approximately ± 5%.

CONCLUSION

There is significant BTB variability in fetal left MPI, which has an overall weak correlation with FHR. This could be a factor affecting the consistency of MPI values reported by different research groups. Variability would be reduced by averaging 4-5 cardiac cycles per fetus. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.