Yu.A. Bulgakov1, T.A. Vityazeva2, A.A. Mikheev3

1–3 Ryazan State Radio Engineering University named after V.F. Utkina (Ryazan, Russia)

For an adequate assessment of the amplitude-time parameters of the electrocardiosignal, it is necessary to first get rid of the interference acting on it, in particular, the isoline drift. The operation of isoline drift removal by high-pass filters is provided in modern electrocardiographs. At the same time, the operating instructions indicate the possibility of distortion of the ST segment. This, in turn, may lead to an insufficiently adequate assessment of the diagnostically significant parameters of the ST segment.

The use of interpolation methods for isolating the isoline drift signal ensures the preservation of informative components of the electrocardiosignal spectrum (ECS). However, the frequency range of the isoline drift signal, which can be isolated from a mixture of ECS and isoline drift, is significantly limited. This is explained by the fact that with an increase in the frequency of change of the isoline drift signal, its sampling frequency, equal to the heart rate (HR), remains unchanged, therefore, the accuracy of its recovery gets worse. When half of the heart rate is reached, the restoration of the isoline drift signal becomes impossible.

Purpose – the purpose of the work is to consider methods for eliminating the isoline drift, which allow to expand the frequency range of the isolated isoline drift signal while maintaining the amplitude-time parameters of all elements of the electrocardiosignal.

The specified goal can be achieved by converting the samples of the isoline drift signal taken at the TP interval of the electrocardiosignal into complex discrete samples (CDS)with further filtering of the obtained sequences by a low-pass filter (LPF).

Given spectral zones, for example, the first and second, can be suppressed in the spectrum of the CDS sequence. At the same time, the maximum frequency of the signal in the zero spectral zone allocated by the LPF can theoretically be increased to the discretization frequency, that is, to the heart rate.

The features of CDS filtering in the task of isoline drift isolation have been considered. It has been noted that the LPF should be made as a FIR filter. Direct filtering by the FIR filter of the CDS sequence, due to the significant difference in the sampling frequency of the ECS (about 500 sps) and the cutoff frequency of the LPF (about 1 Hz), requires significant computing costs.

It has been shown that computational costs can be significantly reduce by using multi-speed signal processing (MSSP). Mathematical expressions linking the value of the maximum decimation coefficient with the initial sampling frequency and the duration of discrete samples have been obtained.

The process of isolating the isoline drift of the ECS on the basis of multi-speed low-frequency filtration of CDS formed on the TP interval of the ECS has been modeled.

The obtained mathematical expressions make it possible to form complex discrete samples of the isoline drift signal, which provide, by suppressing the first and the second spectral zones, expanding the frequency range of the isoline drift signal and further isolation of this signal based on multi-speed low-frequency filtering while preserving the informative components of the electrocardiosignal.

Bulgakov Yu.A., Vityazeva T.A., Mikheev A.A. Isolation of the isoline drift of the electrocardiosignal based on complex discrete samples and multi-speed low-frequency filtering. Biomedicine Radioengineering. 2022. V. 25. № 4. Р. 54-61. DOI: https://doi.org/10.18127/ j15604136-202204-07 (In Russian)

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