Investigations about the Distributions of Important Information in ECG Signals

Investigations about the Distributions of Important Information in ECG Signals

Piotr Augustyniak (AGH University of Science and Technology, Poland) and Ryszard Tadeusiewicz (AGH University of Science and Technology, Poland)
Copyright: © 2009 |Pages: 47
DOI: 10.4018/978-1-60566-080-6.ch006
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Abstract

This chapter presents an investigation of the distribution of medically relevant information in ECG signal timelines. ECG records clearly represent a cycle of heart evolution; its components, although partly superimposed, follow the time-related dependencies of heart function. During the initial inspection of the ECG, the cardiologist focuses his or her attention on several points of the trace, seeking signs of disease. It seems obvious, but is not often considered, that some segments of the signal are more important for a doctor than the remaining parts. Depending on a doctor’s habits and experience, the interpretation starts from the most severe or most suspected abnormality or from the most unusual signal component. The order of the ECG inspection is based on the investigation strategy and is determined by irregular distribution of medical information in the ECG. These assumptions have already been explored with regard to speech or audio signals, resulting in numerous successful applications, such as the MP3 compression algorithm.
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Investigation Of The Local Spectrum

Introductory Remarks

In the storage and transmission of an electrocardiographic signal (and for other sequences of samples), a full informative capacity (bandwidth) transmitting channel is usually used (Bailey et al., 1990). However, in the case of the ECG, the occurrence of particular signal components is limited by the physiology of intra-cardiac stimulus propagation. Additionally, the phases of a cardiac cycle are defined by cellular actions in tissues of different conduction speed, limiting their own variability and consequently the local bandwidth of the representing signal (Macfarlane & Lawrie, 1989). Moreover, the automatic recognition of the heart cycle phases, developed 40 years ago for medical purposes, is commonly used as a P, QRS, and T wave delimitation algorithm and nowadays yields results of acceptable reliability (Willems et al., 1985a, 1985b, 1987). These facts suggest that the electrocardiogram is a far more predictable signal than speech or audio signals, even in the case of pathologies. Therefore, the use of typical ECG pre-processing strategies (i.e., automatic wave recognition procedures) seems to be appropriate as background for the correct adaptation of the transmission channel instantaneous bandwidth to the local density of information. The first issue is to determine statistically the typical bandwidth or density of information and its variance for all ECG components. Different wave morphologies, for the QRS-complex in particular, should be considered. The work presented in this section is aimed at determining the indispensable minimum of parameters that the pre-processor should deliver for optimum bandwidth adjustment for the transmission or storage of records. The adjustment method is not taken under consideration here because it is constrained by technical aspects of implementation.

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