Presented at the Neonatal Society 2007 Autumn Meeting.

Negrine RJS¹, Chikermane A², Wright JGC², Ewer AK¹

¹ Neonatal Intensive Care Unit, Birmingham Women’s Hospital and University of Birmingham, UK
² Department of Paediatric Cardiology, Birmingham Children’s Hospital, UK

Background: The myocardial performance index (MPI) is widely used for the assessment of cardiac function in adults and children (1). The MPI can be calculated for either ventricle using standard Pulse-Wave Doppler (PWD) or Tissue Doppler imaging (TDI). A higher MPI indicates relative myocardial dysfunction. This is the first study to investigate MPI in preterm neonates using both methods.

Objective: To assess the left and right MPI in preterm neonates using PWD and TDI.

Methods: Preterm neonates were scanned by a single investigator (RN) at less than 24hrs of age (D1) and/or at one week (W1). PWD tricuspid and mitral inflow were obtained from an apical 4-chamber view which was then altered to include LV outflow. The RV outflow was assessed from a parasternal view. TDI waveforms were acquired from an apical 4-chamber view using a Doppler pulse-wave sample gate at the lateral tricuspid and mitral annuli. Average readings were taken from 3-5 cardiac cycles. Ethical approval was gained from the South Birmingham REC.

Results: Forty one subjects were recruited with median gestational age 30weeks (range 25-34) and birthweight 1350g (range 724-2230g). 22 D1 and 32 W1 scans were performed with 19 subjects undergoing both. The mean (SD) MPI are shown:

The MPI values obtained are higher than those published from term infants (2-4). D1 and W1 LV MPI were significantly higher than the RV MPI using both methods (p<0.001). This may reflect relative LV dysfunction or an increased LV preload in the transitional circulation. The trend was for MPI to reduce from D1 to W1 with the reduction being more significant in the RV (p<0.0001). There was a significant difference between the RV MPI from W1 when comparing PWD and TDI (p<0.0001). There was no significant difference in ventricular ejection times using PWD or TDI so that differences in MPI arise from assessment of the isovolumetric times – these intervals are longer with TDI. The MPI of the smaller, sicker babies tended to be relatively higher.

Conclusion: The MPI enables quantification of neonatal myocardial function and may be useful in assessing sick preterm neonates. The TDI method of calculation may have advantages over the PWD calculation.

References
1. Tei C et al. Journal of Cardiology 1995;26:357 – 366.
2. Roberson DA & Cui W. J Am Soc Echocardiography 2006;19:1438-1445.
3. Roberson DA & Cui W. J Am Soc Echocardiography 2007;20:764-770.
4. Tsutsumi et al. Pediatrics International 1999;41(6):722-727.