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Abstract
Objective To measure the left and right ventricular myocardial velocities using tissue Doppler imaging (TDI) in the first 24 h of life in neonates.
Design Left and right ventricular peak systolic (S′), early diastolic (E′) and late diastolic (A′) myocardial velocities were measured using TDI alongside standard echocardiography (including peak diastolic atrioventricular flow, E). E/E′ ratio was calculated for both ventricles.
Setting UK neonatal intensive care unit.
Patients 43 neonates were prospectively recruited into three groups: term (n=16), preterm (30–36 weeks, n=12) and very preterm (<30 weeks, n=15).
Results Myocardial velocities increased with increasing gestation. Right ventricular velocities were significantly greater than left. E/E′ ratio decreased with increasing gestation. Left E/E′ ratio was higher than right in each group.
Conclusions TDI is feasible in preterm neonates and enables the acquisition of myocardial velocities. With increasing gestation, higher myocardial velocities and lower E/E′ ratios were found. The addition of TDI to standard neonatal echocardiography may provide additional information about cardiac function.
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Background
Many sick newborns experience cardiac dysfunction.1 Blood pressure monitoring and conventional echocardiography are currently used to assess cardiac function but have limitations in quantifying function in preterm neonates.1 ,2
Tissue Doppler imaging (TDI) via echocardiography filters low amplitude and high frequency Doppler signals from blood and displays high amplitude, low frequency signals from the myocardium, producing myocardial velocity waveforms.3 Peak systolic and diastolic velocities can then be obtained (figure 1). TDI is less preload and afterload dependent than pulse-wave Doppler (PWD) with theoretical advantages.4 The E/E′ ratio of early diastolic PWD atrioventricular blood flow (E) to the early diastolic peak myocardial velocity (E′) correlates with diastolic dysfunction in older subjects.5
Myocardial velocity waveform obtained using tissue Doppler imaging. A′, late diastolic peak velocity; E′, early diastolic peak velocity; S′, systolic peak velocity.
No previous study has investigated left and right ventricular myocardial velocities and E/E′ ratios in term and preterm neonates.
Our aims were to assess the feasibility of TDI in preterm and term neonates on day 1 of life, to analyse biventricular myocardial velocities and E/E′ ratios, and to compare the data to previous fetal and neonatal studies.
Methods
Ethics approval and written informed consent were obtained. Babies with congenital anomalies were excluded. Three groups were defined: term, preterm (30–36 weeks) and very preterm (<30 weeks).
What is already known on this topic
▶ The preterm myocardium is immature with many neonates experiencing cardiac dysfunction.
▶ Myocardial velocities are well validated in adult studies, with lower values reflecting myocardial dysfunction.
What this study adds
▶ Tissue Doppler imaging is feasible in preterm neonates.
▶ In both systole and diastole, myocardial velocities increase with increasing gestation.
▶ Right ventricular velocities are significantly greater than left.
Echocardiography
Standard echocardiograms were performed by one observer (RJSN) on day 1 of life using a Philips HD11xe system (S12-4Hz transducer) (Philips Healthcare, Best, The Netherlands). M-Mode echocardiography was undertaken to derive left ventricular fractional shortening (LVFS). ECG was recorded concurrently to time cardiac events. The size of the patent ductus arteriosus was determined using a published classification system.6
From an apical four chamber view, mitral and tricuspid inflow velocities were obtained by a PWD sample gate at the valve leaflet tip. Offline analysis, using average readings from three to five cardiac cycles, was used to calculate early diastolic flow velocity (E), late diastolic flow velocity (A) and their ratio (E/A).
TDI analysis
Myocardial velocities were obtained using an apical four chamber view. A PWD sample gate of 0.12 cm was positioned at the lateral tricuspid and mitral annuli (LTA and LMA) to acquire right and left ventricular velocities, respectively. Peak systolic (S′), early diastolic (E′) and late diastolic (A′) myocardial velocities were measured. An angle of <20° was maintained using 2D hold and the Doppler signal was not corrected. Offline analysis using average readings from three to five cardiac cycles was performed. E/E′ ratio was calculated for each ventricle.
Statistical analysis
Analysis was by GraphPad Instat v 3.05. One-way analysis of variance and t test were used for data comparison. To test intraobserver bias, 60 velocities were measured at the start and end of an examination. A further sample of 45 peak velocities was measured from the same waveform on two different occasions by two observers (RJSN and AC). All reproducibility data were assessed using Bland–Altman analysis.
Results
All subjects had structurally normal hearts (table 1). In the preterm group, all subjects had normal blood pressure and none was receiving inotropes. In the very preterm group, no subject was hypotensive at the time of study but two were receiving dopamine.
Demographic data
Heart rate reduced significantly with increasing gestation (p<0.001) (table 2). There was a significant difference in the LVFS obtained from the three groups, with increased LVFS in the more mature infants (p<0.001) (table 2).
Blood pool analysis and E/E′ ratio
Differences in transtricuspid early diastolic flow velocity (E) and late diastolic flow velocity (A) were not significant between the groups. There were significant differences in transmitral E and transmitral A flow (p<0.01, p=0.02). The transtricuspid and transmitral E/A ratios both increased with increasing gestational age but only reached statistical significance for transmitral E/A (p<0.0001) (table 2).
TDI examinations were successful in all subjects. In all groups velocities were higher in the right ventricle than in the left ventricle (table 3). Myocardial velocities increased with increasing gestational age at both sites in all cardiac cycle phases. Peak systolic (S′) and early diastolic (E′) velocities increased significantly at both sites with increasing gestational age (p<0.0001). Peak late diastolic (A′) velocities demonstrated a clear increasing trend at both sites but the results were not significant. The peak late diastolic (A) velocity was higher than early diastolic (E) in all gestational groups. With increasing gestation, the E/E′ ratio decreased significantly for both ventricles (p<0.001). In the term and preterm groups, the left ventricle E/E′ was significantly higher than the right ventricle E/E′ (p<0.001 and p<0.02, respectively). The very preterm left ventricle E/E′ was higher than the right ventricle E/E′, but these differences were not significant.
Myocardial peak velocities obtained using tissue Doppler imaging
Reproducibility of TDI
The mean (SD) of the intraobserver difference of each TDI peak velocity was 0.097 (0.24) cm/s. When re-analysing data, the means (SD) of interobserver and intraobserver difference were 0.35 (0.055) and 0.085 (0.038) cm/s, respectively.
Discussion
This is the first study to compare the myocardial velocities and E/E′ ratios obtained from both ventricles in term and preterm neonates. The use of TDI in such patients is feasible and provides a quantifiable measure of myocardial function. TDI examinations are straightforward for a competent echocardiographer and can become part of the routine echocardiogram.
There was a clear trend for increasing velocities and decreasing E/E′ ratios with increasing gestation. In all groups, peak velocities in the right ventricle were higher than in the left ventricle.
An elevated E/E′ ratio correlates with diastolic dysfunction.5 Our data demonstrate that with increasing gestation the E/E′ ratio decreased significantly for both ventricles and that the left ventricle E/E′ was significantly higher than the right ventricle E/E′ for each gestational group. This could be interpreted as normal gestation related maturation of myocardial tissue or may represent a relative biventricular diastolic dysfunction in preterm neonates.
Within the very preterm group, more subjects received respiratory support and the effect of this on TDI myocardial velocities is difficult to assess. These infants were sicker and velocities may be lower as a result of their immaturity and/or concurrent pathologies. The lower myocardial velocities seen in more premature subjects were still apparent in those breathing spontaneously.
The peak velocities obtained from term infants in our study are comparable to previously published data,2 ,7 as are the reproducibility of our findings.7 The E/E′ ratios from our term subjects are also comparable although differing slightly.2 ,7
TDI has also been studied in fetuses.4 Gestational trends and maturational changes in the ventricular function of the fetal heart have been demonstrated. Increasing velocities with increasing gestation and right sided dominance of the fetal heart with increasing gestation have also been shown. Our data demonstrate similar velocities to comparably aged fetuses; however, our more preterm population had lower myocardial velocities, especially diastolic velocities.
Conclusion
Although our pilot study is small, we have shown that TDI is feasible in neonates and provides information directly from the myocardium. Both systolic and diastolic function can be analysed in one waveform. Myocardial velocities may prove to be clinically useful in the cardiac assessment of newborns. We have compared data from both ventricles in different gestational groups, adding to the published data. The application of TDI may complement our ability to assess neonatal cardiac function when examining sick neonates. However, further studies are required in order to define the precise role of TDI in these patients.
Acknowledgments
The authors thank the cardiac applications team at Philips Medical for their technical advice regarding the HD11xe scanner. The authors also thank the Medical Physics team and Judi Humphreys at Birmingham Women's Hospital for technical support during the study.
Footnotes
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Competing interests None.
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Ethics approval This study was conducted with the approval of South Birmingham Research Ethics Committee.
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Provenance and peer review Not commissioned; externally peer reviewed.