The effects of asymmetric volume conductor modeling on non-invasive fetal ECG extraction

TL;DR

This study demonstrates that asymmetric modeling of maternal-fetal tissues significantly impacts non-invasive fetal ECG signals, emphasizing the need to consider volume conductor effects for accurate clinical assessment.

Contribution

The paper introduces a simulation framework for modeling asymmetric maternal-fetal tissue effects on NI-FECG signals, highlighting their impact on signal morphology and diagnostic ratios.

Findings

Asymmetric volume conductor modeling causes over 70% error in T/QRS ratio

Significant changes in NI-FECG morphology due to tissue asymmetry

Homogeneous models underestimate the influence of vernix caseosa

Abstract

Objective: Non-invasive fetal electrocardiography (NI-FECG) shows promise for capturing novel physiological information that may indicate signs of fetal distress. However, significant deterioration in NI-FECG signal quality occurs during the presence of a highly non-conductive layer known as vernix caseosa which forms on the fetal body surface beginning in approximately the 28th week of gestation. This work investigates asymmetric modeling of vernix caseosa and other maternal-fetal tissues in accordance with clinical observations and assesses their impacts for NI-FECG signal processing. Methods: We develop a process for simulating dynamic maternal-fetal abdominal ECG mixtures using a synthetic cardiac source model embedded in a finite element volume conductor. Using this process, changes in NI-FECG signal morphology are assessed in an extensive set of finite element models including spatially variable distributions of vernix caseosa. Results: Our simulations show that volume conductor asymmetry can result in over 70% error in the observed T/QRS ratio and significant changes to signal morphology compared to a homogeneous volume conductor model. Conclusion: Volume conductor effects must be considered when analyzing T/QRS ratios obtained via NI-FECG and should be considered in future algorithm benchmarks using simulated data. Significance: This work shows that without knowledge of the influence of volume conductor effects, clinical evaluation of the T/QRS ratio derived via NI-FECG should be avoided.