ST Analysis overview courtesy of Neoventa Medical.
What is ST Analysis?
During hypoxia, the ST interval of the fetal ECG waveform is affected indicating the fetus is suffering from oxygen deficiency. ST Analysis consists of highlighting theses changes. In adults, the ECG is commonly used to diagnose cardio-vascular diseases using a treadmill to induce physical stress. For a fetus, the birth is the treadmill. Changes in ST interval of the fetal ECG shows how the fetus handles the stress of labour and helps clinicians detect signs of hypoxia.
What is ST Analysis?
During hypoxia, the ST interval of the fetal ECG waveform is affected indicating the fetus is suffering from oxygen deficiency. ST Analysis consists of highlighting theses changes. In adults, the ECG is commonly used to diagnose cardio-
ST Analysis is used in combination with CTG
The fetal ECG contains a lot of useful information, as is proven in basic research and a number of published articles. But it is only in recent years that we have been able to use this knowledge and information due to technical development, and the signal processing technology is now able to accurately record the fetal ECG waveform. The condition of the fetal heart indicates the condition of the brain and the ST waveform reflects the energy balance in the myocardium. A normal ST waveform shows that the fetus has a sufficient oxygen supply with aerobic myocardial metabolism and a positive energy balance.
During hypoxia with anaerobic metabolism in the myocardium, there is an increase in the T-wave amplitude of the ECG, and the STAN monitor displays an automatic ‘ST Event’ alert. The STAN method is a combination of standard CTG parameters and ST Analysis. The fetal ECG is acquired via a spiral scalp electrode applied to the presenting part of the fetus and a skin electrode applied to the mother’s thigh. The results of the automatic ST Analysis are displayed as data points in the recording. If there is a significant change in the ST interval and a ‘ST Event’ alert is displayed, actions are recommended according to clinical guidelines 1
The fetal ECG contains a lot of useful information, as is proven in basic research and a number of published articles. But it is only in recent years that we have been able to use this knowledge and information due to technical development, and the signal processing technology is now able to accurately record the fetal ECG waveform. The condition of the fetal heart indicates the condition of the brain and the ST waveform reflects the energy balance in the myocardium. A normal ST waveform shows that the fetus has a sufficient oxygen supply with aerobic myocardial metabolism and a positive energy balance.
During hypoxia with anaerobic metabolism in the myocardium, there is an increase in the T-
ST Analysis improves decision-making
Despite developments within labour management, the need remains to improve fetal injury and mortality. Standard CTG has high specificity for classification of normality and severe pathological traces. ST Analysis grades the deviation. The combination of ST Analysis and standard CTG parameters provides more accurate information about the fetus during labour than CTG alone. ST Analysis is automatic, continuous and has been proven to be effective in large randomized controlled trials2. By providing clinicians with more precise information about the fetal state during labour, fetuses at risk can be detected and unnecessary interventions avoided.
Despite developments within labour management, the need remains to improve fetal injury and mortality. Standard CTG has high specificity for classification of normality and severe pathological traces. ST Analysis grades the deviation. The combination of ST Analysis and standard CTG parameters provides more accurate information about the fetus during labour than CTG alone. ST Analysis is automatic, continuous and has been proven to be effective in large randomized controlled trials2. By providing clinicians with more precise information about the fetal state during labour, fetuses at risk can be detected and unnecessary interventions avoided.
ST Analysis is cost effective
The STAN method is a cost effective alternative to CTG alone. In a recent health economic study3, a decision-tree model was used to compare the two treatment strategies. Baseline estimates were derived from the literature, and costs and effects were extrapolated to a life-time perspective taking into account the probability of developing cerebral palsy and its effect on quality adjusted life years. The analysis showed that the STAN method was both more effective and less costly, thus dominating over CTG alone. Significant quality adjusted life years (QALY) were gained by using the STAN method.
The STAN method is a cost effective alternative to CTG alone. In a recent health economic study3, a decision-
ST Analysis is evidence based medicine
ST Analysis has been evaluated in a large number of studies. The basic research was initiallyperformed in preclinical animal studies in the early 1970s. The first clinical randomized controlled trial4was published in 1993.The Cochrane Review on fetal ECG during labour supports the use of ST Analysis.
ST Analysis has been evaluated in a large number of studies. The basic research was initiallyperformed in preclinical animal studies in the early 1970s. The first clinical randomized controlled trial4was published in 1993.The Cochrane Review on fetal ECG during labour supports the use of ST Analysis.
The Cochrane Review on fetal ECG2
The objective of this review was to compare the effects of analysis of fetal ECG waveforms during labour with alternative methods of fetal monitoring. Three trials based on ST Analysis were included in the metaanalysis and it showed that ST waveform analysis was associated with fewer babies with severe metabolic acidosis at birth. This was achieved along with fewer fetal scalp samples and fewer operative deliveries. The reviewer concludes that these findings provide support for the use of fetal ST waveform analysis when a decision has been made to undertake continuous electronic fetal heart rate monitoring during labour.
The objective of this review was to compare the effects of analysis of fetal ECG waveforms during labour with alternative methods of fetal monitoring. Three trials based on ST Analysis were included in the metaanalysis and it showed that ST waveform analysis was associated with fewer babies with severe metabolic acidosis at birth. This was achieved along with fewer fetal scalp samples and fewer operative deliveries. The reviewer concludes that these findings provide support for the use of fetal ST waveform analysis when a decision has been made to undertake continuous electronic fetal heart rate monitoring during labour.
The Swedish Randomized Controlled trial5
This was the second, large-scale Randomized Controlled trial to compare outcome after using CTG alone and CTG+ST waveform analysis. The study included 4966 term fetuses in three large labour wards in Sweden. After exclusion of inadequate recordings and fetuses with malformations (574 fetuses in all) the findings showed a 61 % decrease in the number of fetuses born with cord artery metabolic acidosis in the CTG+ST group, at the same time as a 28 % decrease in operative interventions due to fetal distress. These findings were in line with the results from the Plymouth trial: it was concluded that intrapartum monitoring with CTG combined with automatic ST waveform analysis increases the ability of the obstetrician to identify fetal hypoxia and to intervene more appropriately, resulting in an improved perinatal outcome.
This was the second, large-
Follow-up of the children from the Swedish trial 6
The aim of the study was to evaluate the neonatal outcome of the Swedish Randomized Controlled trial, with a focus on the complicated or adverse neonatal cases. The results show a reduction in the incidence of newborn infants with marked neurological symptoms in the CTG+ST group. Of the 29 fetuses from both arms with complicated or adverse outcome, 22 fetuses had presented a fetal heart rate and ST pattern that indicated a need for intervention according to the STAN clinical guidelines. There was a significant decrease in the number of live-born with moderate or severe neonatal encephalopathy in the CTG+ST group, as compared to the group of CTG alone. The authors concluded that the most important finding of the study was the prevalence of ST changes that are detected at an appropriate point in time to allow for earlier and more consistent intervention.
The aim of the study was to evaluate the neonatal outcome of the Swedish Randomized Controlled trial, with a focus on the complicated or adverse neonatal cases. The results show a reduction in the incidence of newborn infants with marked neurological symptoms in the CTG+ST group. Of the 29 fetuses from both arms with complicated or adverse outcome, 22 fetuses had presented a fetal heart rate and ST pattern that indicated a need for intervention according to the STAN clinical guidelines. There was a significant decrease in the number of live-
STAN US clinical usage study7
This is a prospective, Non-randomized study enrolling 530 patients from diverse populations and providers in six university and community medical centres. It is the first clinical usage study of ST Analysis in the US. The objective of the study was to show that US obstetrical staff,´once trained, can appropriately interpret and apply the STANsystem. The study included a structured training program and a pilot and credentialing phase before the actual clinical use. The results of the study demonstrated that ST Analysis´can be applied to support obstetric decision making and that unneeded interventions for non reassuring fetal heart rate can be safely avoided. The authors conclude that US clinicians can use the ST Analysis effectively and in a manner similar to that of experienced STAN users.
This is a prospective, Non-
Virtual study reviewing STAN tracings8
The aim of this study was to evaluate if the addition of ST waveform analysis to standard CTG would improve the consistency and accuracy of clinical decision-making for intervention during labour. Seven experienced European STAN users performed a blinded CTG interpretation on the same 51 completed intrapartum cases containing examples of both healthy and compromised term fetuses. When ST Analysis was added to the CTG, the rate of intervention was significantly decreased for cases with pH >7.14. More importantly, the observer agreement demonstrated a marked improvement in the timing of appropriate intervention, from 68% to 92% with the addition of ST Analysis.
The aim of this study was to evaluate if the addition of ST waveform analysis to standard CTG would improve the consistency and accuracy of clinical decision-
STAN in clinical practice9
This is a prospective observational study of the introduction of ST Analysis in two maternity wards during two years in the city of Goteborg, Sweden. Out of the total population of 14,687 term deliveries, 4,830 were monitored using ST Analysis. The units were equipped with eight STAN units and an additional three units the last six months of the study. The usage of ST´Analysis increased from 28.1% the first year to 37.7% th second year and was associated with a significant reduction in metabolic acidosis in the total population from 0.76% to 0.44% respectively. The rate of operative deliveries in the total population did not change during the study period.
This is a prospective observational study of the introduction of ST Analysis in two maternity wards during two years in the city of Goteborg, Sweden. Out of the total population of 14,687 term deliveries, 4,830 were monitored using ST Analysis. The units were equipped with eight STAN units and an additional three units the last six months of the study. The usage of ST´Analysis increased from 28.1% the first year to 37.7% th second year and was associated with a significant reduction in metabolic acidosis in the total population from 0.76% to 0.44% respectively. The rate of operative deliveries in the total population did not change during the study period.
Fetal ECG and STAN technology – a review10
This review of the STAN method includes physiological, signal processing and clinical aspects. The two randomized controlled trials comparing ST Analysis+CTG to CTG alone have shown a significant decrease in children born with metabolic acidosis along a decrease in operative deliveries due to fetal distress. In addition, inter-observer agreement for ST Analysis was higher than for CTG alone. The review highlights the importance of educational models, as described in several studies. The authors conclude that ST Analysis+CTG have the potential to significantly improve outcome when appropriate education, training and use of STAN according to guidelines are provided.
This review of the STAN method includes physiological, signal processing and clinical aspects. The two randomized controlled trials comparing ST Analysis+CTG to CTG alone have shown a significant decrease in children born with metabolic acidosis along a decrease in operative deliveries due to fetal distress. In addition, inter-
References
1. Fetal electrocardiogram: ST waveform analysis in intrapartum surveillance.
Amer-
European STAN expert group). BJOG 2007. Available free online at:
2. Cochrane Review: Fetal electrocardiogram (ECG) for fetal monitoring
during labour. Neilson JP. The Cochrane Library, Issue 3, 2006.
during labour. Neilson JP. The Cochrane Library, Issue 3, 2006.
3. The long-term cost-effectiveness of fetalmonitoring during labour: a comparison
of cardiotocography complemented with ST analysis versus cardiotocography alone.
E Heintz, aT-H Brodtkorb, aN Nelson,bL-A Levina a. BJOG 2007:8.
of cardiotocography complemented with ST analysis versus cardiotocography alone.
E Heintz,
4. Plymouth randomised trial of cardiotocogram only versus ST waveform
plus cardiotocogram for intrapartum monitoring in 2400 cases. Westgate J,
Harris M, Curnow JSH, Greene KR Am J Obstet Gynecol, 1993;169:1151-60.
plus cardiotocogram for intrapartum monitoring in 2400 cases. Westgate J,
Harris M, Curnow JSH, Greene KR Am J Obstet Gynecol, 1993;169:1151-
5. Cardiotocography only versus cardiotocography plus ST analysis of fetal
electrocardiogram for intrapartum fetal monitoring: a Swedish randomised
controlled trial. Amer-Wåhlin I, Hellsten C, Norén H, Hagberg H, Herbst
A, Kjellmer I, Lilja H, Lindoff C, Månsson M, Mårtensson L, Olofsson P,
Sundström AK, Maršál K. Lancet 2001;358:534-38.
electrocardiogram for intrapartum fetal monitoring: a Swedish randomised
controlled trial. Amer-
A, Kjellmer I, Lilja H, Lindoff C, Månsson M, Mårtensson L, Olofsson P,
Sundström AK, Maršál K. Lancet 2001;358:534-
6. Fetal electrocardiography in labor and neonatal outcome: Data from the
Swedish randomised controlled trial on intrapartum fetal monitoring.
Norén H, Amer-Wåhlin I, Hagberg H, Herbst A, Kjellmer I, Maršál K, Olofsson P,
Rosén KG. Am J Obstet Gynecol 2003;188:183-192.
Swedish randomised controlled trial on intrapartum fetal monitoring.
Norén H, Amer-
Rosén KG. Am J Obstet Gynecol 2003;188:183-
7. United States multicenter clinical usage study of the STAN 21 electronic
fetal monitoring system. Devoe LD, Ross M, Wilde C, Beal M, Lysikewicz
A, Maier J, Vines V, Amer-Wåhlin I, Lilja L, Norén H, Maulik D. Am J
Obstet Gynecol. 2006;195: 729–34.
fetal monitoring system. Devoe LD, Ross M, Wilde C, Beal M, Lysikewicz
A, Maier J, Vines V, Amer-
Obstet Gynecol. 2006;195: 729–34.
8. ST-segment analysis of the fetal ECG improves fetal heart rate (FHR) tracing
interpretation and clinical decision making. Ross GM, Devoe LD, Rosén KG.
J Matern Fetal Neonatal Med. 2004;15(3):181-5.
interpretation and clinical decision making. Ross GM, Devoe LD, Rosén KG.
J Matern Fetal Neonatal Med. 2004;15(3):181-
9. STAN in clinical practice – The outcome of 2 years of regular use in the city
of Gothenburg. Norén H, Blad S, Carlsson A, Flisberg A, Gustavsson A,
Lilja H, Wennergren M, Hagberg H. Editor’s choice: Am J Obstet Gynecol.
2006;195:7-15.
of Gothenburg. Norén H, Blad S, Carlsson A, Flisberg A, Gustavsson A,
Lilja H, Wennergren M, Hagberg H. Editor’s choice: Am J Obstet Gynecol.
2006;195:7-
10. Foetal ECG and STAN technology – a review. Amer-Wåhlin I et al. European
Clinics in Obstetrics and Gynaecology. 2005 June 17; Published online.
Clinics in Obstetrics and Gynaecology. 2005 June 17; Published online.
ST Analysis on STAN S31