Frequency-Based Maternal Electrocardiogram Attenuation for Fetal Electrocardiogram Analysis

Abstract

Fetal electrocardiogram (ECG) waveform analysis along with cardiac time intervals (CTIs) measurements are critical for the management of high-risk pregnancies. Currently, there is no system that can consistently and accurately measure fetal ECG. In this work, we present a new automatic approach to attenuate the maternal ECG in the frequency domain and enhance it with measurable CTIs. First, the coherent components between the maternal ECG and abdominal ECG were identified and subtracted from the latter in the frequency domain. The residual was then converted into the time domain using the inverse Fourier transform to yield the fetal ECG. This process was improved by averaging multiple beats. Two fetal cardiologists, blinded to the method, assessed the quality of fetal ECG based on a grading system and measured the CTIs. We evaluated the fetal ECG quality of our method and time-based methods using one synthetic dataset, one human dataset available in the public domain, and 37 clinical datasets. Among the 37 datasets analyzed, the mean average (± standard deviation) grade was 3.49 ± 1.22 for our method vs. 2.64 ± 1.26 for adaptive interference cancellation (p-value < 0.001), thus showing the frequency-based fetal ECG extraction was the superior method, as assessed from our clinicians’ perspectives. This method has the potential for use in clinical settings.

Frequency Domain Template Subtraction Approach to Attenuate Maternal Electrocardiogram in Fetal Electrocardiogram

“…Some commonly used approaches, such as independent component analysis (ICA) or projection operators, require many channels to reliably identify the maternal source signals, which will then be attenuated in the subsequent steps [9,18]. The introduced frequency domain approach recently requires reference maternal cardiac signal measured from an independent source to attenuate the maternal cardiac cycles in the abdominal ECG [10].…”

“…Similarly, Weiner filter [10], Kalman filter [19], and its extension have been used to attenuate the maternal cardiac cycles in the abdominal ECG. Techniques such as the Kalman filter and its extension, Weiner filter, and template subtraction will work well for stationary data.…”

“…The numerator in the coherence spectrum indicates the estimate of the cross-spectrum spectrum between the template and the cardiac cycles in the record, and the denominator indicates the product of the auto-spectra of the template and the cardiac cycles in the record. Following [10], the spectral gain is defined as follows:…”

“…In all these technologies, the maternal ECG (MECG) is a major interference in FECG. Several signal processing techniques have been developed to attenuate the interfering MECG, and they include projection operators [8,9], principal component analysis [10], independent component analysis, and frequency domain or coherence subtraction approach [10,11]. Our recent work demonstrated that coherence subtraction approach outperformed other approaches [10].…”

“…Several signal processing techniques have been developed to attenuate the interfering MECG, and they include projection operators [8,9], principal component analysis [10], independent component analysis, and frequency domain or coherence subtraction approach [10,11]. Our recent work demonstrated that coherence subtraction approach outperformed other approaches [10]. The coherent subtraction approach requires an independently recorded MECG as a reference signal to attenuate the maternal cardiac cycles in the abdominal ECG.…”