Noninvasive Fetal Electrocardiography Part II: Segmented-Beat Modulation Method for Signal Denoising

Abstract

Background:Fetal well-being evaluation may be accomplished by monitoring cardiac activity through fetal electrocardiography. Direct fetal electrocardiography (acquired through scalp electrodes) is the gold standard but its invasiveness limits its clinical applicability. Instead, clinical use of indirect fetal electrocardiography (acquired through abdominal electrodes) is limited by its poor signal quality.Objective:Aim of this study was to evaluate the suitability of the Segmented-Beat Modulation Method to denoise indirect fetal electrocardiograms in order to achieve a signal-quality at least comparable to the direct ones.Method:Direct and indirect recordings, simultaneously acquired from 5 pregnant women during labor, were filtered with the Segmented-Beat Modulation Method and correlated in order to assess their morphological correspondence. Signal-to-noise ratio was used to quantify their quality.Results:Amplitude was higher in direct than indirect fetal electrocardiograms (median:104 µV vs. 22 µV; P=7.66·10-4), whereas noise was comparable (median:70 µV vs. 49 µV, P=0.45). Moreover, fetal electrocardiogram amplitude was significantly higher than affecting noise in direct recording (P=3.17·10-2) and significantly in indirect recording (P=1.90·10-3). Consequently, signal-to-noise ratio was initially higher for direct than indirect recordings (median:3.3 dB vs. -2.3 dB; P=3.90·10-3), but became lower after denoising of indirect ones (median:9.6 dB; P=9.84·10-4). Eventually, direct and indirect recordings were highly correlated (median: ρ=0.78; P<10-208), indicating that the two electrocardiograms were morphologically equivalent.Conclusion:Segmented-Beat Modulation Method is particularly useful for denoising of indirect fetal electrocardiogram and may contribute to the spread of this noninvasive technique in the clinical practice.

T-Wave Alternans Identification in Direct Fetal Electrocardiography

“…HRAMF to identify TWA from indirect FECG, and will have to deal with high levels of noise, interferences and artifacts affecting it [11] and with the fact that TWAA is usually lead-dependent [12] (typically, indirect FECG recordings are multi-lead [13]). The main finding of this paper is that fetuses show TWA, even though in healthy conditions, when usually TWA in adults is considered an indicator of cardiac risk [5].…”

Noninvasive Fetal Electrocardiography Part I: Pan-Tompkins' Algorithm Adaptation to Fetal R-peak Identification

“…Analogously to what described above, the maternal component was subtracted using the Segmented-Beat Modulation Method [7, 14-16] in order to get 4 channels of IFECG.…”

Quantification of Fetal ST-Segment Deviations

“…Specifically, during labor, when the membranes were ruptured and the uterine cervix was dilated, a scalp electrode was applied to the fetal head and FECG was recorded [5]. All acquisitions (sampling frequency: 1000 Hz) were performed at the Department of Obstetrics at the Medical University of Silesia, and are part of "Abdominal and Direct Fetal Electrocardiogram Database" [10] of PhysioNet (www.physionet.org) [11], freely accessible on the web under the ODC Public Domain Dedication and License v1.0.…”

“…After application of our fetal R-peak detection algorithm [12], FECG is filtered for noise reduction by applying the Segmented-Beat Modulation Method (SBMM) [5,13,14], Successively, the median (for further noise reduction) beat is computed in representation of the FECG morphology.…”