A Direct Transform of Discrete Non-Uniform ECG to a Time-Scale Representation

Adaptive sampling is an interesting alternative for biosignal acquisition, transmission and storage, however further processing of non uniform representations is still waiting for development. In this paper a direct non-uniform to time-scale (NUTS) transform is presented and applied to the ECG signal. Well accepted limits of bandwidth in particular sections of the ECG and established standards for the assessment of diagnostic quality help in evaluation of the influence the transform has to the diagnostic result. The transform uses a regular-grid Coiflet 5-th order nearly symmetric wavelet, but the novelty is a pointwise calculating of its correlation accordingly to non-uniform distribution of the electrocardio-gram samples. In tests with CSE Database files the proposed transform method yields not bit-accurate ECG signals, but the diagnostic results are more influenced by the non-uniform representation (for QRS mean deviation: +0.7 ms vs. original files) than by the transform itself (for QRS additionally: +0.6 ms) and all the results remain within the accuracy tolerance of the CEN industrial standard.