Fetal QRS detection and RR interval measurement in noninvasively registered abdominal ECGs

In the context of the CinC-challenge 2013 we present a method for fetal QRS detection in abdominal ECG recordings. Maternal ECG attenuation is based on PQSRT template subtraction and subsequent elimination of the first three principal components. Fetal QRS detection follows a matched filtering approach with an impulse-train filter and a second filter with complementary impulse response. The interspacing of the impulses corresponds to putative fetal RR intervals and is systematically varied, where the relation of both filter outputs permits assessment of the signal-to-noise ratio. In epochs of 1s duration, we use this information to dynamically combine information from an arbitrary number of abdominal channels into a virtual channel, and estimate the local RR interval and initial fetal QRS positions. In a final step these candidate positions are refined using a dynamic programming approach with constraints on SNR, signal amplitude and continuity of RR intervals. In the test set of 100 4-channel recordings (60s, 1 kHz), we observed good detection accuracy up to moderate SNRs, with an overall RMS-error of 9.35 ms versus reference RR-intervals from scalp recordings.