ST waveform analysis for monitoring hypoxic distress in fetal sheep after prolonged umbilical cord occlusion

Abstract

IntroductionThe inconclusive clinical results for ST-waveform analysis (STAN) in detecting fetal hypoxemia may be caused by the signal processing of the STAN-device itself. We assessed the performance of a clinical STAN device in signal processing and in detecting hypoxemia in a fetal sheep model exposed to prolonged umbilical cord occlusion (UCO).MethodsEight fetal lambs were exposed to 25 minutes of UCO. ECG recordings were analyzed during a baseline period and during UCO. STAN-event rates and timing of episodic T/QRS rise, baseline T/QRS rise and the occurrence of biphasic ST-waveforms, as well as signal loss, were assessed.ResultsDuring baseline conditions of normoxemia, a median of 40 (IQR, 25–70) STAN-events per minute were detected, compared to 10 (IQR, 2–22) during UCO. During UCO STAN-events were detected in five subjects within 10 minutes and in six subjects after 18 minutes, respectively. Two subjects did not generate any STAN-event during UCO. Biphasic ST event rate was reduced during UCO (median 0, IQR 0–5), compared to baseline (median 32, IQR, 6–55). ST-waveforms could not be assessed in 62% of the recording time during UCO, despite a good quality of the ECG signal.ConclusionsThe STAN device showed limitations in detecting hypoxemia in fetal sheep after prolonged UCO. The STAN device produced high false positive event rates during baseline and did not detect T/QRS changes adequately after prolonged fetal hypoxemia. During 14% of baseline and 62% of the UCO period, the STAN-device could not process the ECG signal, despite its good quality. Resolving these issues may improve the clinical performance of the STAN device.

The Noninvasive Fetal Electrocardiogram During Labor: A Review of the Literature

“…[13][14][15][16] Because the NI-fECG uses multiple leads, one of the limitations of STAN, which only uses a single lead scalp electrode, is avoided. [17][18][19] To conclude, NI-fECG for FHR monitoring is a promising technique that is noninvasive, is patientfriendly, and provides accurate information. Future studies should focus on evaluating and improving signal quality of the NI-fECG, especially during the second stage of labor.…”

“…In contrast to STAN, the NI-fECG provides a multilead fetal ECG and therefore may overcome the current shortcomings in ST waveform analysis. [17][18][19] NI-fECG is not a new technique, as first recordings were made in the early 1900s. 20 However, difficulties in acquiring and processing the electrophysiologic signals limited the development of this technique.…”

Why -aVF can be used in STAN as a proxy for scalp electrode-derived signal; reply to comments by Kjellmer et al.

“…In our recent paper " ST waveform analysis for monitoring hypoxic distress in fetal sheep after prolonged umbilical cord occlusion " [1], we concluded that the performance of the STAN device in clinical practice is potentially limited by high false-negative and high false-positive STAN-event rates and loss of ST waveform assessment capacity during severe hypoxemia. This conclusion evoked comments by Kjellmer, Lindecrantz and Rosén that can be summarized as follows: 1) STAN analysis is based on a unipolar lead but the authors used a negative aVF lead, and they did not validate this methodology; 2) The fetuses used in the study were too young to display the signals that the authors were trying to detect.…”

ST analysis of the fetal electrocardiogram – Comments on recent experimental data

“…In their paper, Andriessen at al present a validation of fetal ECG analysis and the clinical STAN device in midgestation fetal lambs exposed to 25 minutes of umbilical cord occlusion [1]. The study presents results that contrast remarkably from previously published experimental data which raises a number of questions and comments.…”