Observations on the configuration of the fetal electrocardiogram before and during labour

Sodium dichloroacetate stimulates cardiac mitochondrial metabolism and improves cardiac conduction in the ovine fetus during labor

Previous studies in our laboratory have suggested that the increase in stillbirth in pregnancies complicated by chronic maternal stress or hypercortisolemia is associated with cardiac dysfunction in late stages of labor and delivery. Transcriptomics analysis of the overly represented differentially expressed genes in the fetal heart of hypercortisolemic ewes indicated involvement of mitochondrial function. Sodium dichloroacetate (DCA) has been used to improve mitochondrial function in several disease states. We hypothesized that administration of DCA to laboring ewes would improve both cardiac mitochondrial activity and cardiac function in their fetuses. Four groups of ewes and their fetuses were studied: control, cortisol-infused (1 g/kg/day from 115 to term; CORT), DCA-treated (over 24 h), and DCA + CORT-treated; oxytocin was delivered starting 48 h before the DCA treatment. DCA significantly decreased cardiac lactate, alanine, and glucose/glucose-6-phosphate and increased acetylcarnitine/isobutyryl-carnitine. DCA increased mitochondrial activity, increasing oxidative phosphorylation (P_CI, P_CI + II) per tissue weight or per unit of citrate synthase. DCA also decreased the duration of the QRS, attenuating the prolongation of the QRS observed in CORT fetuses. The effect to reduce QRS duration with DCA treatment correlated with increased glycerophosphocholine and serine and decreased phosphorylcholine after DCA treatment. There were negative correlations of acetylcarnitine/isobutyryl-carnitine to both heart rate (HR) and mean arterial pressure (MAP). These results suggest that improvements in mitochondrial respiration with DCA produced changes in the cardiac lipid metabolism that favor improved conduction in the heart. DCA may therefore be an effective treatment of fetal cardiac metabolic disturbances in labor that can contribute to impairments of fetal cardiac conduction.

Fetal electrocardiography ST-segment analysis for intrapartum monitoring: a critical appraisal of conflicting evidence and a way forward

BACKGROUND

In the past century, some areas of obstetric including intrapartum care have been slow to benefit from the dramatic advances in technology and medical care. Although fetal heart rate monitoring (cardiotocography) became available a half century ago, its interpretation often differs between institutions and countries, its diagnostic accuracy needs improvement, and a technology to help reduce the unnecessary obstetric interventions that have accompanied the cardiotocography is urgently needed.

STUDY DESIGN

During the second half of the 20th century, key findings in animal experiments captured the close relationship between myocardial glycogenolysis, myocardial workload, and ST changes, thus demonstrating that ST waveform analysis of the fetal electrocardiogram can provide information on oxygenation of the fetal myocardium and establishing the physiological basis for the use of electrocardiogram in intrapartum fetal surveillance.

RESULTS

Six randomized controlled trials, 10 meta-analyses, and more than 20 observational studies have evaluated the technology developed based on this principle. Nonetheless, despite this intensive assessment, differences in study protocols, inclusion criteria, enrollment rates, clinical guidelines, use of fetal blood sampling, and definitions of key outcome parameters, as well as inconsistencies in randomized controlled trial data handling and statistical methodology, have made this voluminous evidence difficult to interpret. Enormous resources spent on randomized controlled trials have failed to guarantee the generalizability of their results to other settings or their ability to reflect everyday clinical practice.

CONCLUSION

The latest meta-analysis used revised data from primary randomized controlled trials and data from the largest randomized controlled trials from the United States to demonstrate a significant reduction of metabolic acidosis rates by 36% (odds ratio, 0.64; 95% confidence interval, 0.46-0.88) and operative vaginal delivery rates by 8% (relative risk, 0.92; 95% confidence interval, 0.86-0.99), compared with cardiotocography alone.

Relative versus absolute rises in T/QRS ratio by ST analysis of fetal electrocardiograms in labour: A case-control pilot study

Introduction

The additional value of ST analysis during labour is uncertain. In ST analysis, a T/QRS baseline value is calculated from the fetal electrocardiogram and successive T/QRS ratios are compared to this baseline. However, variation in the orientation of the electrical heart axis between fetuses may yield different T/QRS baseline values. In case of a higher T/QRS baseline value more ST events are encountered, although not always related to perinatal outcome. We hypothesised that we can partly correct for this effect by analysing T/QRS rises as a percentage from baseline (relative ST analysis). This study aimed to explore whether relative ST analysis has better diagnostic value for cord acidaemia compared to conventional ST analysis, where predefined fixed T/QRS ratios are used.

Methods and materials

A case-control study was performed in 20 term human fetuses during labour; 10 cases (umbilical cord artery pH <7.05 at birth, defining acidaemia) and 10 controls (pH >7.20) were included. The fetal electrocardiogram was recorded using a STAN monitor. We electronically extracted all T/QRS values, baseline and episodic ST events from the STAN monitor and calculated the relative T/QRS changes. The cut-off for relative ST events was determined in a receiver operator characteristic (ROC) curve at optimal specificity for cord acidaemia. Parameters of interest were area under the curve (AUC) of the ROC curve for relative ST events and test performance of both conventional and relative ST analysis.

Results

Relative ST analysis showed an AUC of 0.99. The optimal cut-off value for relative T/QRS rise was determined at 0.70. Relative vs conventional (absolute) ST analysis showed a specificity of 100% vs 40% (p = 0.031); sensitivity 90% vs 90%; positive likelihood ratio infinity vs 1.5; negative likelihood ratio 0.10 vs 0.25, respectively.

Conclusion

Relative ST analysis seems to be a promising method to detect impending fetal acidaemia during labour. Further studies are required to determine the diagnostic accuracy.

A systematic review of cardiac time intervals utilising non-invasive fetal electrocardiogram in normal fetuses

BACKGROUND

Non-invasive fetal electrocardiogram (NIFECG) is an evolving technology in fetal surveillance which is attracting increasing research interest. There is however, only limited data outlining the reference ranges for normal cardiac time intervals (CTIs). The objective of our group was to carry out a systematic review to outline normal fetal CTIs using NIFECG.

METHODS

A systematic review of peer reviewed literature was performed, searching PUBMED,Ovid MEDLINE and EMBASE. The outcomes of interest included fetal CTIs (P wave duration, PR interval, QRS duration and QT interval) and a descriptive summary of relevant studies as well. The outcomes were grouped as early pre-term (≤ 32 weeks), moderate to late pre-term (32-37 weeks) and term (37-41 weeks).

RESULTS

8 studies were identified as suitable for inclusion. Reference ranges of CTIs were generated. Both PR interval and QRS duration demonstrated a linear correlation with advancing gestation. Several studies also demonstrated a reduction in signal acquisition between 27 and 32 weeks due to the attenuation by vernix caseosa. In this group, both the P wave and T waves were difficult to detect due to signal strength and interference.

CONCLUSION

NIFECG demonstrates utility to quantify CTIs in the fetus, particularly at advanced gestations. Larger prospective studies should be directed towards establishing reliable CTIs across various gestations.

Successful detection of the fetal electrocardiogram waveform changes during various states of singletons

Accurate assessment of fetal well-being is one of the most important tasks for obstetricians. It is still difficult to measure fetal electrocardiogram (ECG) during fetal movements. Recently, a new method, blind source separation with reference signals, was proposed for stable measurements. This method distinguishes weak signals from noisy mixed signals with little information about the sources. The aim of this study is to estimate the ability of this method for fetal ECG monitoring and to establish standard fetal ECG electrocardiogram values of normal singletons including during fetal movement. The subjects enrolled were 167 pregnant women with normal single pregnancy from 18- to 41-week gestation, who regularly visited Tohoku University Hospital, and 12 pregnant women with fetal abnormality. Fetal signals were successfully separated in 163 of 179 subjects at 91.1% success rate regardless of fetal movements. Time intervals of ECG (P, PR and QRS intervals and QTc) were measured. The standard curves of each interval through the gestational period were obtained. The data in active phase were compared to that in rest phase and the data obtained from normal and abnormal fetuses were investigated. PR intervals in the rest phase were prolonged compared to those in the active phase. Fetal ECG showed anomalous values such as PR interval or QTc prolongation in the abnormal fetuses. The fetal ECG was measured by the new method with or without fetal movements, and the standard fetal ECG values have been established. This study provides a foundation for further detailed clinical studies.

Changes in the PR interval--fetal heart rate relationship of the electrocardiogram during fetal compromise in chronically instrumented sheep

OBJECTIVES

The evaluation of the changes in the relationship of the PR interval and fetal heart rate during prolonged fetal compromise in sheep at levels of acidosis comparable to those seen during human fetal compromise and to see whether these changes are potentially of use in the detection of fetal distress.

STUDY DESIGN

A retrospective analysis of continuous fetal electrocardiogram recordings during graded fetal hypoxemia in 20 chronically cannulated fetal sheep was performed. Baseline recordings during normoxemia were compared with recordings during hypoxemia by use of Fisher's exact test and the Student t test.

RESULTS

Sixteen of the 20 cases could be used for final analysis. Twelve showed a statistically significant change from a predominantly negative relationship between the PR interval and the fetal heart rate during normoxemia to a predominantly positive relationship during hypoxemia. Two cases showed an obvious trend in the same direction, which was statistically not significant. In two other cases no change in the relationship was observed.

CONCLUSION

A changing relation between the PR interval and the fetal heart rate is of potential use in the detection of fetal compromise.

The fetal electrocardiogram

Advances in microprocessing technology have made fetal ECG analysis a feasible adjunct to fetal surveillance. Time interval and morphology changes of the FECG occur during fetal hypoxia. The use of these changes to detect a fetus at risk of intrapartum asphyxia awaits validation in terms of both future and ongoing clinical trials. Recognition of FECG changes during decelerations may improve the sensitivity of EFM. Antepartum FECG analysis has potential for the detection of a number of pathological fetal conditions, including intrauterine growth retardation, but remains hampered by low signal-to-noise ratios, rendering successful signal acquisition unreliable.

Improved intrapartum surveillance with PR interval analysis of the fetal electrocardiogram: a randomized trial showing a reduction in fetal blood sampling

OBJECTIVE

Our goal was to test the hypothesis that the addition of fetal electrocardiogram time-interval analysis to conventional electronic fetal monitoring would significantly reduce the number of cases requiring fetal scalp blood sampling without an increase in adverse outcome.

STUDY DESIGN

A randomized prospective trial was performed in 214 women with high-risk labor.

RESULTS

There was a significant reduction in the number of cases that had fetal blood sampling performed in the fetal electrocardiogram plus electronic fetal monitoring group (risk ratio for electronic fetal monitoring alone 3.53; p < 0.01, 95% confidence interval 1.39 to 8.95). The fetal blood samplings performed in the electronic fetal monitoring alone group were less likely to be abnormal (pH < 7.25, base excess < -8.0) than those performed in the fetal electrocardiogram plus electronic fetal monitoring group (risk ratio for electronic fetal monitoring alone 0.62, p = 0.05, 95% confidence interval 0.35 to 1.10). There was a trend of more infants with an arterial umbilical pH < 7.15 and a base excess less than -8.0 mmol/L at birth being unsuspected and more instrumental deliveries for presumed fetal distress being performed in the electronic fetal monitoring alone than in the fetal electrocardiogram plus electronic fetal monitoring group.

CONCLUSION

The addition of fetal electrocardiogram analysis to conventional electronic fetal monitoring during labor can reduce significantly the number of parturients undergoing fetal scalp blood sampling and can simultaneously increase its efficiency without an increase in adverse outcome.

Cumulative changes in the fetal electrocardiogram and biochemical indices of fetal hypoxia

Previous studies have shown that the relationship between P-R interval of the fetal electrocardiogram (FECG) and the fetal heart rate (FHR) varies according to the acid-base status of the fetus. In the normal fetus there is a negative correlation between these two parameters. However, as acidosis develops, the relationship becomes positive. In order to express this relationship in a quantitative form, an index known as the ratio index (RI) has been derived. This index provides a cumulative time based description of the relationship between the P-R interval and FHR for the whole labour. The aim of this study was to evaluate this derived index and compare it with fetal hypoxia. The FECG was recorded from 132 fetuses during labour using a fetal scalp electrode, and analysed using the Nottingham FECG system. Changes in the nature of this relationship between the P-R interval and heart rate were compared against biochemical markers of asphyxia, namely umbilical artery pH, lactate and umbilical venous norepinephrine and hypoxanthine. Significant correlations were demonstrated between the RI and umbilical arterial pH (r = -0.38, P < 0.01), lactate (r = 0.36, P < 0.01), log10norepinephrine (r = 0.37, P < 0.01), and hypoxanthine (r = 0.28, P < 0.01). The measurement of the ratio index during labour may be a useful method of determining fetal hypoxia during labour.

Fetal ECG waveform analysis should improve fetal surveillance in labour

Fetal heart rate (FHR) and fetal electrocardiogram (ECG) recordings were obtained from a scalp electrode with maternal thigh as reference and used for ST waveform analysis in 201 patients in labour. Nearly 45% had suspicious or abnormal FHR traces whilst only 27% had T/QRS ratio greater than 0.25 (mean +/- 2 SD). A normal T/QRS ratio identified 99.3% of fetuses with normal buffering capacity in cord artery blood. Of 13 infants with a cord artery blood pH less than 7.15, standard bicarbonate was less than 15.0 mmol/l in five who had an average T/QRS ratio less than 0.25 throughout labour. Of the eight with respiratory acidosis, five had an increase in T/QRS ratio greater than 0.25 for longer than 20 minutes prior to delivery, in two the ratio increased during the last few minutes and one had no change (pH 7.14). Persistent elevation of T/QRS in the first stage of labour identified those with decrease in buffer capacity in cord arterial blood (sensitivity of 94.1%). Acute hypoxia was recognized by the rapid rise in T/QRS. The specificity of T/QRS to identify fetuses at risk increased by combining the ST waveform analysis with FHR changes.

The ECG waveform

Different portions of the ECG waveform are influenced differently. The QRS waveform is influenced principally by ventricular muscle mass but may be influenced by differences in ventricular filling which occur with cardiac failure or transiently with cord compression. The PR interval normally has a positive correlation with the R-R interval but this correlation becomes negative, probably as a result of catecholamines, when the fetus is stressed. This difference between PR/RR correlation may help distinguish vagally mediated decelerations from those associated with hypoxia. The ST waveform becomes elevated when myocardial oxygen delivery is insufficient to maintain aerobic metabolism to meet the energy demands of the myocardium, and anaerobic metabolism occurs with the production of lactate; this is a dynamic situation and may occur at different levels of oxygenation in different fetuses, depending on their ability to compensate and the workload on the myocardium. It is very likely that changes in PR/RR relationships and the ST waveform will be useful in intrapartum monitoring in the future, and this contention is supported by recent analysis of PR/RR and ST segment shifts (Figure 16). It seems clear that the detailed study of the ECG waveform provides more, and perhaps clinically more useful, information from the same signal and electrode as heart rate, and it is no longer reasonable to ignore it. However, as clinicians we have an extraordinary ability to move with disenchantment from one method of fetal monitoring to another of no proven value, with a firm but unreasoned conviction that it is better. ECG analysis is by no means ready for clinical use if we are to avoid the same pitfalls as continuous FHR monitoring. Further clinical assessment will not be easy. In modern obstetric practice asphyxiated infants are fortunately not common, so there are practical difficulties in monitoring sufficient numbers of patients to evaluate new indices of asphyxia, as well as the difficulties of defining an objective endpoint. Thorough clinical (probably multicentre) studies are needed with well defined endpoints and this is beginning. Further fetal lamb studies are also needed, particularly to examine the interrelationships between changes in heart rate, PR interval and ST waveform; it is hoped that this chapter has emphasized the importance of such animal studies in understanding the physiological and therefore clinical background to any change.(ABSTRACT TRUNCATED AT 400 WORDS)

The intraventricular conduction time of fetal heart in pregnancies complicated by rhesus haemolytic disease

The duration and shape of the fetal QRS complex were studied in 88 pregnancies complicated by rhesus isoimmunization. A clear correlation between ventricular depolarization time and haemoglobin levels at birth was observed. A single QRS value greater than 4 SD above the normal mean value, or a tendency to rapid increase was very suggestive of a bad prognosis, while a QRS duration below +4 SD or declining in sequential determinations reflects a temporary compensation of fetal conditions. From the QRS complex analysis a clear indication appeared of the constant and early involvement of the heart in terms of myocardial hypertrophy and/or cardiac enlargement. The sensitivity of QRS to anaemia and the feasibility of continuous non-invasive monitoring might allow, with the determination of bilirubin concentration in amniotic fluid, improvement in the management of rhesus haemolytic disease.

The normal condition of the fetal electrocardiogram during labour

A real-time computer system was employed to monitor continuously the fetal electrocardiogram (ECG) during labour. Signals from a scalp electrode were amplified, filtered and passed through an interface system to a digital computer. From 110 patients studied, 37 were selected by rigid criteria which fulfilled a strict definition of normal fetal condition in labour and delivery. The mean values and the range of the various parameters of the fetal ECG complex were defined. As a large amount of data was generated by the system, a method was developed to display the short and long-term dynamic behaviour of the fetal ECG during labour in the form of labour profiles. By further averaging of these labour profiles, the pattern of normal behaviour was established. Certain changes in the fetal ECG, previously thought to be characteristic of fetal distress, occurred in normal patients. The P-R interval was up to 10 per cent shorter during contractions towards the end of labour and there was a long-term trend towards the end of labour for the P-R interval to fall by 7 per cent. The P wave amplitude fell by 30 per cent over the last hour. These trends were statistically significant. The QRS complex was found to lengthen slightly towards the end of labour, but the R-T interval and ST segment displacement displayed no significant changes.

Neonatal electrocardiographic changes in relation to cardiotocographic changes

Electrocardiograms (ECG) were made immediately after delivery in 28 infants with normal cardiotocographic patterns in labour and in 29 with abnormal patterns. Changes in the S-T segment and T-wave were quantified in a scoring system. High and peaked T-waves (high T/QRS-ratios) were significantly more common in the group with abnormal cardiotocographic patterns. The infants with ECG-changes also had significantly lower Apgar scores and more neonatal complications. The immediate postpartum ECG seems to be a useful indication of the accumulated hypoxic stress to which the child has been subjected in labour.