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Randomized Controlled Trial
. 2017 Apr 14;12(4):e0175823.
doi: 10.1371/journal.pone.0175823. eCollection 2017.

The Electrical Heart Axis and ST Events in Fetal Monitoring: A Post-Hoc Analysis Following a Multicentre Randomised Controlled Trial

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Free PMC article
Randomized Controlled Trial

The Electrical Heart Axis and ST Events in Fetal Monitoring: A Post-Hoc Analysis Following a Multicentre Randomised Controlled Trial

Rik Vullings et al. PLoS One. .
Free PMC article

Abstract

Objective: Reducing perinatal morbidity and mortality is one of the major challenges in modern health care. Analysing the ST segment of the fetal electrocardiogram was thought to be the breakthrough in fetal monitoring during labour. However, its implementation in clinical practice yields many false alarms and ST monitoring is highly dependent on cardiotocogram assessment, limiting its value for the prediction of fetal distress during labour. This study aims to evaluate the relation between physiological variations in the orientation of the fetal electrical heart axis and the occurrence of ST events.

Methods: A post-hoc analysis was performed following a multicentre randomised controlled trial, including 1097 patients from two participating centres. All women were monitored with ST analysis during labour. Cases of fetal metabolic acidosis, poor signal quality, missing blood gas analysis, and congenital heart disease were excluded. The orientation of the fetal electrical heart axis affects the height of the initial T/QRS baseline, and therefore the incidence of ST events. We grouped tracings with the same initial baseline T/QRS value. We depicted the number of ST events as a function of the initial baseline T/QRS value with a linear regression model.

Results: A significant increment of ST events was observed with increasing height of the initial T/QRS baseline, irrespective of the fetal condition; correlation coefficient 0.63, p<0.001. The most frequent T/QRS baseline is 0.12.

Conclusion: The orientation of the fetal electrical heart axis and accordingly the height of the initial T/QRS baseline should be taken into account in fetal monitoring with ST analysis.

Conflict of interest statement

Competing Interests: Guid Oei is head of the research group "fundamental perinatology", which is a collaboration of the Eindhoven University of Technology and the Máxima Medical Centre. He was involved in the founding of Nemo Healthcare BV, that arose from this collaboration. Guid Oei is not a shareholder in this company. Rik Vullings is shareholder in Nemo Healthcare BV, the Netherlands. This does not alter our adherence to PLOS ONE policies on sharing data and materials. None of the other authors have any conflicts of interest.

Figures

Fig 1
Fig 1. The fetal vectorcardiogram for different orientations of the electrical heart axis.
In the top panels, the electrical currents within the heart during a cardiac cycle are depicted in terms of their vectorcardiogram; ventricular contraction (QRS-complex = large loop), relaxation phase (T-waves = small loop). From left to right, the entire vectorcardiogram has been rotated over 10 degrees to simulate a different orientation of the electrical heart axis. Note that these vectorcardiograms are 3-dimensional images and the 10 degree rotation was performed in 3-dimensional space. In the bottom panels, the fetal scalp ECG has been calculated by projecting the vectorcardiograms onto the scalp lead. Before rotation, the baseline T/QRS is 0.05 and the T/QRS rise resulting from hypoxia is 0.04, yielding no ST event. After rotation, the baseline T/QRS is 0.09 and the T/QRS rise resulting from the same level of hypoxia is 0.06, yielding a ST event.
Fig 2
Fig 2. Distribution of patient across the baseline T/QRS values.
For each initial baseline T/QRS value encountered in our data set, we counted the number of patients with that particular baseline, showing a non-symmetric distribution with the most frequent encountered baseline T/QRS ratio at 0.12.
Fig 3
Fig 3. The number of ST events per 1000 T/QRS values as a function of the initial baseline T/QRS value.
Cases with the same initial baseline T/QRS were grouped. The intensity of the black colour of the data points relates to the total number of T/QRS ratios that occurred in the group (right column in the graph). The red line represents a linear fit through the data points. There is an average increment of 1.42 ST events per 1000 T/QRS values for a rise of 0.1 of the initial baseline T/QRS. The correlation coefficient between data points and fit was 0.63 (p <0.001), as calculated with the linear regression model.
Fig 4
Fig 4. The pH of arterial cord blood and base deficit of the extracellular fluid as a function of the initial baseline T/QRS value.
Cases with the same initial baseline T/QRS value were grouped. The intensity of the black colour of the data points relates to the total number of patients that were represented in the group (right column in the graph). The red line represents a linear fit through the data points. The fit suggests a reduction in the pH of 0.0009 and an increase in the base deficit of 0.03 for a rise in 0.1 of the initial baseline T/QRS. The respective correlation coefficients between data points and fit are -0.04 (p = 0.14) and 0.03 (p = 0.34), as calculated with the linear regression model. Abbreviations: BDecf = base deficit in the extracellular fluid, pHart = pH of the arterial cord blood.

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Grant support

This research was financially supported by Dutch Technology Foundation STW. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Funding was received by RV.
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