ST-waveform analysis of the fetal electrocardiogram could reduce fetal blood sampling

Reconstruction of Fetal Cardiac Vectors From Multichannel fMCG Data Using Recursively Applied and Projected Multiple Signal Classification

Previous attempts at unequivocal specification of signal strength in fetal magnetocardiographic (fMCG) recordings have used an equivalent current dipole (ECD) to estimate the cardiac vector at the peak of the averaged QRS complex. However, even though the magnitude of fetal cardiac currents are anticipated to be relatively stable, ECD-based estimates of signal strength show substantial and unrealistic variation when comparing results from different time windows of the same recording session. The present study highlights the limitations of the ECD model, and proposes a new methodology for fetal cardiac source reconstruction. The proposed strategy relies on recursive subspace projections to estimate multiple dipoles that account for the distributed myocardial currents. The dipoles are reconstructed from spatio-temporal fMCG data, and are subsequently used to derive estimators of the cardiac vector over the entire QRS. The new method is evaluated with respect to simulated data derived from a model of ventricular depolarization, which was designed to account for the complexity of the fetal cardiac source configuration on the QRS interval. The results show that the present methodology overcomes the drawbacks of conventional ECD fitting, by providing robust estimators of the cardiac vector. Additional evaluation with real fMCG data show fetal cardiac vectors whose morphology closely resembles that obtained in adult MCG.

Fetal magnetocardiography: development of the fetal cardiac time intervals

OBJECTIVES

To analyse the physiologic development of fetal cardiac time intervals throughout gestation using fetal magnetocardiography (FMCG).

METHODS

FMCG data of 163 uncomplicated pregnancies (19th and 42nd gestational week) were analysed. Mean value, standard deviation, minimum and maximum of the duration of the P-wave, the QRS-complex, the PR and the QT-interval were plotted against gestational age.

RESULTS

QRS-complex, P wave and QT-interval showed a significant lengthening between the 20th and 42nd gestational week. The mean of the QRS complex raised from 36+/-4.7 ms (week 21-24) up to 48+/-5.2 ms (> or =37th week), (p=0.0001). The mean of the P-wave was between 47+/-5.9 ms (week 21-24) and 53+/-9.5 ms (> or =37th week), (p=0.05) and the mean of the QT-interval was 198+/-18 ms (week 21-24) and increased up to 244+/-23.9 ms (> or =37th week), (p=0.009). The PR-interval did not show a correlation with gestational age.

CONCLUSION

FMCG provides sufficient information about all parts of the fetal cardiac conduction system from the 19th gestational week on. It offers the possibility to analyse the shape and the duration of the PQRST-complex.

European Community multi-Center Trial "Fetal ECG Analysis During Labor": ST plus CTG analysis

This report form part of the European Community Multi-Center Trial "Fetal ECG Analysis during Labor". Aim of this prospective trial was to identify changes in the fetal ECG waveform with cases of verified fetal hypoxia. In this paper we also report on the use of a newly developed automatic system for identification of ST waveform changes (ST Log). All ECG were recorded with the STAN recorder (Neoventa Medical AB, Gothenburg, Sweden). The ECG information was not displayed during labor in order not to influence the clinical management. This report includes data from 320 cases and include six cases of fetal intrapartum hypoxia. Twenty seven cases showed changes in ST waveform. All five cases with the most marked ST change (a rise in T/QRS of > 0.10 units and lasting more then 10 minutes) had signs of ongoing intrapartum hypoxia. Six out of six cases with evidence of intrapartum asphyxia, showed ST changes. On the basis of our multi-center trial it appears that the combined analysis of CTG and ST waveform changes provides an accurate way to identify adverse events during labor. The work is continuing with a new STAN recorder developed by Neoventa Medical in Göteborg and currently being tested in a Swedish randomized, controlled multi-center trial.

How useful is intrapartum electronic fetal heart rate monitoring?

It is essential for an obstetric anesthesiologist to be aware of the fetal status before undertaking care of the laboring mother. In the last 20 years electronic fetal monitoring has been the most widely used technique of evaluating the fetus in labor. Recently however, the ability to predict or improve fetal outcome using traditional interpretation has been questioned. This review presents a summary of the current technology and interpretation of intrapartum electronic fetal monitoring, as well as a discussion of its limitations and some of the developments in this field which may help improve the accuracy of fetal assessment. The new developments in fetal monitoring discussed in this article are computerized assessment of fetal heart tracings, heart rate variability analysis, fetal electrocardiogram waveform analysis, abdominal detection of fetal ECG, fetal scalp oxygen saturation, fetal pH sampling and transcutaneous oxygen and carbon dioxide measurement.

Antenatal fetal magnetocardiography: a new method for fetal surveillance?

OBJECTIVE

To establish the reliability of fetal magnetocardiography as a method of measuring the time intervals of the fetal heart during the antenatal period.

DESIGN

A prospective study.

SETTING

Wellcome Biomagnetism Unit, Southern General Hospital.

SUBJECTS

One hundred and six low risk pregnant women at 20 to 42 weeks gestation.

MAIN OUTCOME MEASURES

Success in obtaining QRS complexes, P waves and T waves. Correlation of time intervals with fetal outcome.

RESULTS

The technique was acceptable to pregnant women. A QRS complex was successfully demonstrated in 68 (67%) of the unaveraged traces. Using off-line averaging techniques on these 68 cases, P waves were obtained in 75% and T waves in 72%. Although good quality traces were obtained throughout the range of gestational ages, in general it was more difficult below 28 weeks. QRS duration (R2 = 7%, P = 0.02) demonstrated a positive linear correlation with increasing gestation. Of the 35 (51%) cases with umbilical vein pH analysis available, only one result was less than 7.2. No significant relation was found between measurements of the fetal waveforms and the pH results.

CONCLUSION

The technique of fetal magnetocardiography provides a significant advance in the technological field for the demonstration of QRS complexes and the full PQRST waveforms in gestations from 20 weeks onwards. With further technical improvements the clinical impact of this technique can be assessed more fully.

A comparative study of the fetal electrocardiogram recorded by the STAN an Nottingham systems

OBJECTIVE

To compare the T:QRS ratio recorded by the STAN and Nottingham fetal electrocardiogram (FECG) monitors.

DESIGN

Prospective observational study.

SETTING

London teaching hospital delivery suite and research unit.

METHODS AND SUBJECTS

The T:QRS ratios generated by the STAN and Nottingham FECG monitors were simultaneously recorded and compared using signals generated from a computer-produced ECG signal and signals from 11 term fetuses recorded during labour.

RESULTS

There was an acceptable level of agreement between the two systems with the computer-generated signals, but it was not clinically acceptable with the signals from the fetuses recorded during labour. Disagreements in the T:QRS values were probably due to differences in the reference points for the measurement of the S-T segment and T-wave height.

CONCLUSION

The different points of reference for measurement of S-T segment and T-wave height can explain poor agreement between the two methods of FECG waveform analysis. The suggested adopted points of reference are those corresponding to adult electrocardiographic methodology.

The use of the fetal electrocardiogram in labour

It is clear that considerably more work needs to be done before fetal ECG waveform analysis can be adopted for the purposes of routine fetal monitoring. It must be decided exactly what we want fetal ECG waveform analysis to achieve. If it is to reduce the number of operative deliveries performed in the presence of normal or intermediate CTG patterns then the fetal ECG shows promise, but its physiological significance in this context remains uncertain. If fetal ECG analysis is to be related to outcome, as opposed to events in labour, then several very large well conducted randomised prospective controlled trials will be needed. At present a large multicentre study (European Community Concerted Action Project 1989) is taking place in which a large number of intrapartum ECG records are being collected, blinded to the clinician and stored onto optical disc via a personal computer. A multicentre study in the United Kingdom using the Nottingham system is also being planned. We need await the outcome of these to verify if any of a variety of fetal ECG variables can be related to outcome. It behoves us to validate fetal ECG analysis against outcome measures that truly indicate whether the labour process has compromised or damaged the fetus. We must not fall into the trap of yet again wholeheartedly embracing a test that has not been properly validated.

The fetal electrocardiogram: ST waveform analysis during labour

Intrapartum fetal surveillance is still under debate, despite 30 years of clinical experience and numerous clinical trials. Waveform analysis of the fetal electrocardiogram has emerged not as an alternative to cardiotochography but as a support tool to allow more accurate interpretation of intrapartum events. During hypoxia, the healthy fetus is utilizing a series of defense mechanisms. Among these, the increase in sympathetic activity, with an increase in circulating adrenaline, activates the myocardium with an increase in workload (the product of cardiac output, myocardium contractility and blood pressure). If there is an imbalance between myocardial oxygen supply and consumption, determined by the workload, then anaerobic metabolism, with a breakdown of myocardial glycogen stores starts and high T waves emerges. ST depression with negative T waves has recently been observed during hypoxia experiments in experimentally growth retarded guinea pigs whilst their normally grown littermates showed ST elevation. These findings have stimulated the development of a dedicated fetal ECG monitor - STAN - incorporating both standard CTG and ST waveform analysis. The STAN concept has now been taken through the process of recognized validation including several prospective studies and a large randomized trial in Plymouth of 2400 high risk, term deliveries. The T/QRS ratio is only one parameter to be used - equally important is to identify the occurrence of ST depression with biphasic negative T waves and to interrelate the CTG and the ST waveform as outlined in the clinical guidelines (table I). This table contains the clinical experience gained over many years and has formed the basis for the first randomized controlled trial comparing ST waveform + CTG with CTG only. Obviously, when the T/QRS ratio is used as the only component of such a scheme, confusion emerges. The analysis should also contain cases with significant intrapartum hypoxia. Recent findings indicate that only when cord artery pH falls below 7.0 and when there is substantial metabolic acidemia is there a significant risk of intrapartum asphyxia. Metabolic acidemia should be estimated from base deficit in the extracellular fluid and the combination of cord artery and vein data should allow for a more accurate assessment of intrapartum events, including the assessment of the duration of hypoxia. The Plymouth trial has tested the hypothesis that the combination of ST wave form and CTG analysis compared with CTG analysis only would reduce operative interventions for fetal distress without placing the fetus at a risk.(ABSTRACT TRUNCATED AT 400 WORDS)

Randomised trial of cardiotocography alone or with ST waveform analysis for intrapartum monitoring

It is possible to record the fetal electrocardiographic waveform (ECG) from the scalp electrode used in labour for detection of fetal heart rate. Animal and observational studies of changes in the ST waveform of the ECG during hypoxia suggest that a combination of heart rate and ST waveform analysis might improve the predictive value of intrapartum monitoring. In a randomised trial, we have studied intervention rates and neonatal outcome for high-risk labours monitored either by conventional cardiotocography (CTG) or by ST waveform analysis plus CTG. 1200 women with pregnancy of at least 34 weeks' gestation were assigned to the groups when the decision to apply a fetal scalp electrode was made. Neonatal outcome was assessed by umbilical-cord blood gas analysis, Apgar scores, resuscitation needed, and postnatal course. All recordings were retrospectively viewed by an observer unaware of clinical details to check adherence to the trial protocol. The addition of ST waveform monitoring to CTG substantially reduced the proportion of deliveries for fetal distress (ST + CTG 27/615 vs CTG 58/606; p less than 0.001). The groups did not differ in rate of operative delivery for other reasons, incidence of asphyxia at birth, or neonatal outcome. Metabolic acidosis and low 5 min Apgar scores were less common in the ST + CTG than the CTG group, but not significantly so. The only case of birth asphyxia in the ST + CTG group was identified by both heart rate and ST changes. The review of recordings showed that the reduction in intervention rate was among cases with CTG patterns classified as normal or intermediate, whereas there was no difference in intervention rates among cases with abnormal recordings. Our findings confirm that ST waveform analysis discriminates CTG changes in labour and that our protocol for interpretation is safe. Further randomised studies are warranted.