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Combined cardiotocographic and ST event analysis: A review

https://doi.org/10.1016/j.bpobgyn.2015.05.007Get rights and content

Highlights

  • Five RCTs compared CTG + ST-analysis to CTG only.

  • Fetal blood sampling and standardized “STAN clinical guidelines” were used.

  • Fetal blood sampling and vaginal operative delivery was significantly reduced.

  • The effect on metabolic acidosis differs in the published studies.

  • The learning curve was not taken into account in any RCT.

ST-analysis of the fetal electrocardiogram (ECG) (STAN®) combined with cardiotocography (CTG) for intrapartum fetal monitoring has been developed following many years of animal research. Changes in the ST-segment of the fetal ECG correlated with fetal hypoxia occurring during labor. In 1993 the first randomized controlled trial (RCT), comparing CTG with CTG + ST-analysis was published. STAN® was introduced for daily practice in 2000.

To date, six RCTs have been performed, out of which five have been published. Furthermore, there are six published meta-analyses. The meta-analyses showed that CTG + ST-analysis reduced the risks of vaginal operative delivery by about 10% and fetal blood sampling by 40%. There are conflicting results regarding the effect on metabolic acidosis, much because of controveries about which RCTs should be included in a meta-analysis, and because of differences in methodology, execution and quality of the meta-analyses. Several cohort studies have been published, some showing significant decrease of metabolic acidosis after the introduction of ST-analysis.

In this review, we discuss not only the scientific evidence from the RCTs and meta-analyses, but also the limitations of these studies.

In conclusion, ST-analysis is effective in reducing operative vaginal deliveries and fetal blood sampling but the effect on neonatal metabolic acidosis is still under debate. Further research is needed to determine the place of ST-analysis in the labor ward for daily practice.

Introduction

Electronic fetal heart rate (FHR) monitoring is a widely used method for assessing fetal status during labor. It aims to enable clinicians to identify hypoxic fetuses at risk for deterioration and provide prerequisites for a decision to intervene, and to deliver either vaginally or by cesarean section, thereby avoiding neonatal and long-term injury due to intrapartum asphyxia. Although little evidence exists regarding its efficacy, monitoring through cardiotocography (CTG) continues to be the method of choice in modern labor and delivery units in developed countries [1]. Despite this, there has been no significant reduction in the incidence of long-term neurologic morbidity (including cerebral palsy) and research has been stimulated by the low true positive predictive value of CTG for metabolic acidosis, which often results in unnecessary interventions and a significant increase in the cesarean section rate during the last 40 years due to concerns during labor. The addition of fetal blood sampling (FBS) is believed to hamper this effect; however, systematic reviews report no evidence of benefit in reducing the operative interventions [2]. Furthermore, FBS has also been shown to have a poor positive predictive value for intrapartum hypoxia [3]. This is probably due to the fact that performance of FBS requires expertise, is invasive, and must be repeated with persisting CTG abnormalities, and thus is often not performed when indicated [4].

Other tools for fetal surveillance, for example, fetal pulse oximetry, have not been successful maybe due to the well-known challenge lying in developing new and emerging technologies, related not only to the need to provide basic physiology data but also to meet requirements of data acquisition, signal processing, and data presentation [5]. Furthermore, any method in the fetal monitoring area requires understanding and compliance to clinical guidelines as well as a positive attitude toward changes of practice, a truly challenging perspective in such a medico-legally loaded field. Other important aspects related to evaluating the effect of medical technology are the choice of outcome parameters, the study design, the clinical setting of a trial, the ownership of the technique, as well as financial support available for its development. Moreover necessary clinical trials are expected to meet evidentiary standards that were never applied to existing technologies.

ST-analysis of the fetal electrocardiogram (ECG; STAN®) was introduced in the labor wards in 2000, after many years of research, starting with experimental animal research. Early animal studies observed that changes in the ST-segment of the fetal ECG correlated with fetal hypoxia occurring during labor [6], [7]. The ST analyzer (STAN® monitor; Neoventa Medical, Goteborg, Sweden) was developed to combine traditional CTG with automatic analysis of the ST-segment of the fetal ECG. Changes in the shape of the ST-segment are noted automatically and an ST event is generated for a significant ST-change (Fig. 1). Guidelines have been developed defining whether intervention is required according to changes occurring in the CTG in combination with ST-changes of the fetal ECG (Table 1) [8].

Protocols to guide the use of a medical device have to be assessed and approved by the company responsible for the technology as part of the CE-marking process and by the FDA before any use in the United States. This implies that a change of guideline is limited by regulations similarly to change of an indication in relation to drugs. The premarketing approval (PMA) process, required for any new methodology, is the most stringent process that requires full documentation, including basic pathophysiology, signal processing, data presentation, control of device design, production, and software and adequate clinical data to support its safe and efficient use. On the basis of all these data and years of efforts, marketing approval is granted based on specific indications and method of use, and is enforced by law. Thus, it is not just the availability of a specific technology that allows a clinician to apply it, but the limit up to which it is approved for use.

Section snippets

The technique

The STAN® concept is based on the association between changes of the ST-interval of the fetal ECG and the function of the fetal myocardium during hypoxia. The changes in fetal ECG associated with fetal distress are either an increase in T-wave amplitude, quantified by the ratio of T-wave amplitude to QRS-amplitude (T/QRS ratio), or a biphasic ST-segment. An increase in T-wave amplitude and subsequently in T/QRS ratio has been associated with a catecholamine surge, activation of β

Randomized clinical trials

Five RCTs, which included 15,365 patients, have been performed since 1993, all comparing continuous CTG-only monitoring with continuous CTG monitoring with ST-analysis *[10], *[11], *[12], *[13], *[14]. Details of the studies are shown in Table 2. All trials used FBS in both arms.

Westgate et al. published the first randomized controlled trial (RCT) on the effect of intrapartum fetal ECG [10]. In this trial of 2434 women monitored with CTG or CTG + ST-analysis during labor, absolute values of

Meta-analysis of the RCTs

Six meta-analyses [15], [16], [17], [18], [19], *[20], including these five RCTs, have been performed, of which one is an individual patient data meta-analysis (IPDMA) [19] and one is a “correction” of errors performed in the first five meta-analyses [20]. Details are shown in Table 3. The IPDMA offers numerous statistical and clinical advantages over an aggregate data meta-analysis as it increases the power to detect differential treatment effects across individuals in RCTs. The IPDMA showed

Cohort studies

Since the introduction of STAN, several cohort studies are published [4], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], as summarized in Table 4. Recent observational studies investigating the effects of long-term use of ST-analysis have shown a reduction in the incidence of metabolic acidosis (base deficit in extracellular fluid (BDecf)) over time.

Nevertheless, it should be kept in mind that, as with all new medical technologies requiring

Immature or anatomically abnormal hearts

ST-analysis in labor is based on the presumption that the fetal ECG waveform in the examined fetus is normal and that the fetal myocardium will react to hypoxia by switching from an aerobic to anaerobic metabolism with glycogenolysis. As such, this precludes analysis in fetuses with a high likelihood of abnormal ECG shapes, such as fetuses with cardiomyopathies and cardiac defects. Less evidently, the preterm myocardial metabolism is also different from the term metabolism because of a

Cost-effectiveness

Reports of two slightly different cost-effectiveness analyses have been published, based on the results of two of the larger randomized trials [47], [48]. In essence, both studies balanced the cost of STAN equipment and operator training in ST-analysis against the costs of FBS, vacuum extraction, and metabolic acidosis. Neither of the studies considered any cost for operator training in CTG interpretation. The first study, based on the Swedish trial, found ST-analysis to be the most

Studying medical technology

Any systematic review of evidence needs to take into account the quality of the evidence. Any study, whether randomized or observational, may have flaws such as problems in methods of recruiting patients, in the clinical setting, or in the delivery of the treatment that can cast doubt on the generalizability of the results. Heterogeneity and publication bias are relevant to all comparisons of evidence from both randomized, controlled studies and observational studies. A current consensus exists

Conclusion

ST-analysis has been extensively studied in both RCTs and observational studies. The results are conflicting. Most meta-analyses show that additional use of ST-analysis for intrapartum monitoring does not reduce the incidence of metabolic acidosis, but does reduce the incidence of operative vaginal deliveries and the need for FBS. However, criticism related to the published evidence in terms of interpretation of studies introduces a doubt if evidence in the case of fetal monitoring will ever be

Conflicts of interest

There are no conflicts of interest.

Practice points

  • Changes in the ST-segment of the fetal ECG are associated with fetal hypoxia.

  • The STAN concept is based on a combined interpretation of CTG and ST-changes.

  • Use of CTG + ST-analysis reduces the risk of vaginal operative delivery and the number of fetal blood samples.

  • There are particular situations, such as anatomically abnormal heart, maternal diabetes, maternal fever, or growth-restricted fetuses, in which the development of ST-changes can be

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