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. 2022 May 11:11:20480040221096209.
doi: 10.1177/20480040221096209. eCollection 2022 Jan-Dec.

Measurement of the cardiac time intervals of the fetal ECG utilising a computerised algorithm: A retrospective observational study

S C Chivers  1   2 , T Vasavan  1 , M Nandi  3 , B R Hayes-Gill  4 , I A Jayawardane  4 , J M Simpson  2 , C Williamson  1 , W P Fifer  5   6 , M Lucchini  5   6
Affiliations

Measurement of the cardiac time intervals of the fetal ECG utilising a computerised algorithm: A retrospective observational study

S C Chivers et al. JRSM Cardiovasc Dis. .

Abstract

Objective: Establish whether the reliable measurement of cardiac time intervals of the fetal ECG can be automated and to address whether this approach could be used to investigate large datasets.

Design: Retrospective observational study.

Setting: Teaching hospitals in London UK, Nottingham UK and New York USA.

Participants: Singleton pregnancies with no known fetal abnormality.

Methods: Archived fetal ECG's performed using the MonicaAN24 monitor. A single ECG (PQRST) complex was generated from 5000 signal-averaged beats and electrical cardiac time intervals measured in an automated way and manually.

Main outcome measure: Validation of a newly developed algorithm to measure the cardiac time intervals of the fetal ECG.

Results: 188/236 (79.7%) subjects with fECGs of suitable signal:noise ratio were included for analysis comparing manual with automated measurement. PR interval was measured in 173/188 (92%), QRS complex in 170/188 (90%) and QT interval in 123/188 (65.4%). PR interval was 107.6 (12.07) ms [mean(SD)] manual vs 109.11 (14.7) ms algorithm. QRS duration was 54.72(6.35) ms manual vs 58.34(5.73) ms algorithm. QT-interval was 268.93 (21.59) ms manual vs 261.63 (36.16) ms algorithm. QTc was 407.5(32.71) ms manual vs 396.4 (54.78) ms algorithm. The QRS-duration increased with gestational age in both manual and algorithm measurements.

Conclusion: Accurate measurement of fetal ECG cardiac time intervals can be automated with potential application to interpretation of larger datasets.

Keywords: ECG; Fetal; abdominal fetal ECG; algorithm; cardiac time intervals; pregnancy; signal to noise ratio.

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Conflict of interest statement

Declaration of conflicting interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.
Figure 1.
Flowchart delineating the process from data acquisition to result generation in preliminary study and main study.
Figure 2.
Figure 2.
Example of fECG complex plotted with markings after being processed by the algorithm. The markings of the algorithm can be compared with manual observations (as shown) or plotted alone. (PRStart_A and PRStart_B are algorithm derived measures delineating the start of the P wave).
Figure 3.
Figure 3.
Bland Altman plots demonstrating agreement between manual and algorithm measurements of (A) manual PR interval and algorithm derived PR1, (B) manual PR interval and algorithm derived PR, (C) manual QRS interval and algorithm derived QRS, and (D) manual QT interval and algorithm derived QT.
Figure 4.
Figure 4.
Linear regression demonstrating the correlation between gestation and measurements of the fetal cardiac time intervals: (A) PR Manual and GA, (B) PRAlg_B and GA, (C) PRAlg_A and GA, (D) QRSMan and GA, (E) QRSAlg and GA, (F) QTMan and GA, (G) QTAlg and GA, (H) T-Amplitude and GA, (I) P amplitude and GA.
Figure 5.
Figure 5.
Fetus with sudden onset tachycardia. (A) Signal average complex from period of normal heart rate showing normal PR interval and QRS duration, (B) Signal average complex from period of sudden onset tachycardia showing a change in the P wave and T wave morphology, (C) Raw maternal and fetal ECG signal with fetal QRS complexes shown with arrow and confirming that the fetal ventricular rate is over 200 beats per minute, (D) Heart rate files showing fetal heart rate greater than 200 beats per minute (arrow) and maternal heart rate 80–120 beats per minute.
Figure 6.
Figure 6.
Fetus with Bradycardia. (A) Raw maternal and fetal ECG signal with fetal QRS complexes shown with arrow confirming that the fetal heart rate is 110 beats per minute, (B) Signal averaged complex generated in Matlab at fetal heart rate of 110 beats per minute for measurement of the cardiac time intervals, (C) Heart rate file demonstrating fetal heart rate (arrow) over time. Maternal heart rate shown in this trace as 50–60 beats per minute.
See this image and copyright information in PMC

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