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

Abstract

BackgroundNon-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.MethodsA 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).Results8 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.ConclusionNIFECG 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.

A systematic review on the utility of non-invasive electrophysiological assessment in evaluating for intra uterine growth restriction

“…Broadly speaking, these encompass signal detection, enhancement, waveform detection and techniques for signal enhancement. These techniques however are beyond the scope of the review but can be accessed from previous work by our group [31].…”

“…The temporal intervals of significance include the P wave duration, PR interval, QRS duration, QT interval and T/QRS ratio. Information regarding these parameters can be sourced from previous work by our group [31] .

Fig. 3Cardiac time intervals illustrated on a fetal ECG beat.

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“…CTG produces an approximation of the fetal heart rate using autocorrelation techniques which compare and average it against the previous doppler waveforms [31, 57] . Due to this autocorrelation process however, the FHR obtained via CTG does not contain true beat to beat variability [31, 58, 59]. Furthermore, the signal obtained is of a lower resolution and is subject to various factors such as maternal expulsion efforts, uterine contractions and ventricular ectopics too [25].…”

“…CTG is unable to capture any CTI data which precludes any temporal or morphological analysis of the FECG complex [31].…”

A non-invasive multimodal foetal ECG–Doppler dataset for antenatal cardiology research

“…From a bio-electromagnetism perspective, the simple volume conductor approximation assumed the maternal body organs, layers of tissue and fat and amniotic fluid only attenuating the propagation of the fECG signal towards the maternal abdominal electrodes, which holds for early pregnancy but not throughout the whole gestation 36 , 37 . The layer with the lowest conductivity is the vernix caseosa , a protective waxy substance that covers the foetus that can greatly attenuate or even suppress the fECG 38 . Pioneering studies revealed how this substance presents an electrical impedance that is two orders of magnitude higher than that of amniotic fluid and foetal/maternal tissue 39 .…”