Assessing patent ductus arteriosus in preterm infants from standard neonatal intensive care monitoring

Abstract

Monitoring patent ductus arteriosus (PDA) in premature infants is currently performed intermittently using echocardiography which requires considerable expertise. The aim of this pilot study was to investigate whether PDA status could be assessed from standard neonatal intensive care monitoring. Electrocardiography (ECG) and blood pressure (BP) waveforms were acquired from extremely preterm infants using standard neonatal monitors. We developed software using MATLAB to analyse ECG and BP waveforms and their interrelationships in terms of pulse transit time (PTT) and pulse wave velocity (PWV). The times from peak systolic BP to diastolic trough (BPFt) and from the diastolic trough to peak systolic BP (BPRt) were also calculated. PTT, BPFt and BPRt were normalised for heart rate (HR) termed NPTT, NBPFt and NBPRt, respectively. ECG, invasive aortic BP monitoring and echocardiography were performed in 14 preterm infants < 29 weeks' gestation in the first 3 days after birth. The median (range) birth weight of the infants was 0.90 (0.48-1.31) kg, gestation 26.6 (24.0-28.7) weeks, PDA diameter 1.6 (0.8-3.6) mm and mean BP 32 (16-40) mmHg. We found a significant positive correlation between PDA diameter and NPTT (r = 0.69, P = 0.007) as well as NBPFt (r = 0.65, P = 0.012) and NBPRt (r = 0.71, P = 0.005). No relationship was found between PDA diameter and pulse pressure.Conclusions: Interrelationships between ECG and BP traces as well as BP waveform time analysis are straightforward to measure and associated with PDA diameter. The results of this pilot study suggest that this approach may help provide biomarkers for continuous monitoring PDA diameter and function. What is Known: • Patent ductus arteriosus (PDA) in premature infants is associated with increased risk of developing chronic lung disease, necrotising enterocolitis and cerebral injury. • Currently PDA is assessed intermittently using echocardiography which requires considerable expertise and sometimes is not well tolerated by critically ill preterm infants. What is New: • Blood pressure (BP) and ECG waveform interrelation and BP trace time analysis, taking account of heart rate, relate to PDA diameter. • ECG and BP waveform phase difference as well as BP waveform time analysis may be useful in the continuous assessment of PDA function.

Keywords: Biomarkers; Echocardiography; Haemodynamics; Patent ductus arteriosus; Preterm infants.

Fig. 1

A Cardiac cycle length (L) is readily measured from the ECG as well as the time difference PTT (A) between the ECG R wave (red triangle) and the following BP systolic peak (blue square). The ratio PTT:L gives a dimensionless index NPTT that is normalised to HR. The difference in time between peak systole and end diastole (BPFt) is shown as B. The difference in time between end diastole and the following peak in systole (BPRt) is shown as C. The surrogate for isovolumic contraction time (MIVCT) was calculated as PTT (A)–BP rise time (C) in a single cardiac cycle. B Two examples of ECG (lower) and BP (upper) waveforms of two seconds duration with different PDA diameters. Infants with larger PDA had the dicrotic notch displayed towards the end of the dicrotic limb which can be attributed to the lower overall arterial resistance due to higher run off from the large PDA

Fig. 2

shows the effect of normalising data for HR. Figure 2 A shows non-normalised PTT and BPFt plotted against PDA diameter. Figure 2 B shows the relationship of HR normalised data (NPTT and NBPFt) plotted against PDA diameter

Fig. 3

Comparison of PTT and PWV compared with heart rate showing significant relationships