Development of Normal Gestational Ranges for the Right Myocardial Performance Index in the Australian Population with Three Alternative Caliper Placements

Abstract

Objectives: To construct gestational age-adjusted reference ranges for the right fetal modified myocardial performance index (RMPI) in an Australian population and to assess the influence of valve click caliper position on constituent time intervals and the RMPI. Methods: A prospective cross-sectional study of RMPI from 235 normal fetuses at 17-38 weeks of gestation was performed. Two Doppler waveforms were obtained: tricuspid and pulmonary valves for ‘a' and ‘b' readings, respectively. The ultrasound machine settings were: Doppler sweep velocity 15 cm/s, angle of insonation <15°, minimal gain, and wall motion filter 300 Hz. The ‘a' and ‘b' intervals were measured at three different caliper positions in each fetus: at the beginning of the original valve clicks (‘original'), at the beginning of the reflected tricuspid and pulmonary closure clicks (‘reflected') and at the peak of valve clicks (‘peak'). RMPI was calculated as (a - b)/b. The three readings were obtained and averaged per examination, with intraobserver repeatability assessed by intraclass correlation coefficient (ICC) and 95% CI. Results: For ‘original', ‘reflected' and ‘peak' RMPI, mean ± SD, ICC (95% CI) were: 0.53 ± 0.10, 0.86 (0.83-0.89); 0.48 ± 0.10, 0.84 (0.81-0.87) and 0.48 ± 0.10, 0.89 (0.87-0.91), respectively. The RMPI increased by approximately 15% as gestation increased and decreased slightly with increasing heart rate. Conclusion: This is the first publication of reference ranges for RMPI based on caliper position. All methods showed good ICC, including the ‘peak' method which we have previously proposed for routine use based on its repeatability and ease of identification when measuring the myocardial performance index.

Is There a Measurable Difference between the Left and Right Modified Myocardial Performance Indices, and Does This Change to Reflect Unilateral Myocardial Dysfunction in Pathology?

“…Our findings showed that preceding 18 weeks gestation, mean LMPI and RMPI were identical within the same fetus (∼0.40), after which the difference between them increased, consistent with our previous normal range studies showing the RMPI increasing at a steeper rate with gestation [3,11]. The relative increase in RMPI (and hence DMPI) may reflect the physiological decrease in right ventricular compliance in comparison to the left with advancing gestation [21].…”

“…We calculated the DMPI normal range by measuring the peak of valve clicks, as our previous results demonstrated this to be most objective and repeatable [3,11,29,30]. In the current study, the DMPI had an ICC of 0.79 (95% CI 0.75-0.83), and repeatabilities for LMPI and RMPI were relatively unchanged.…”

“…a , b Spectral Doppler waveforms. c , d Schematic representations of valve clicks and time intervals (‘a' and ‘b') [11]. …”

“…We have previously published separate gestational age-adjusted reference ranges for both LMPI and right Mod-MPI (RMPI) for uncomplicated singleton pregnancies [3,11]. In a number of previously published studies, the mean RMPI of a population of healthy fetuses exceeded the mean LMPI by up to 30% [12,13,14,15,16,17,18,19,20,21,22], although the left and right measurements were either from different fetal cohorts or were only indirectly compared.…”

Assessment of modified myocardial performance index in foetuses with growth restriction

“…50 th percentile ranged from 0.45 at 12 to 0.57 at 40 weeks of gestation, respectively. Meriki et al [28] determined a reference range for Mod-MPI in 235 Australian singleton pregnant women between 18 and 37 weeks of gestation. 50 th percentile ranged from 0.48 at 18 to 0.57 at 37 weeks of gestation, respectively.…”