TABLE OF CONTENTS Given the finite number of pages allowed in this book, all the possible metrics that researchers have chosen to quantify the EGG (and derived beat-to-beat timing sequences) cannot be detailed, nor all the possible applications of each metric be covered. Moreover, such a summary would be a transient document of only partial relevance in a few years from publication.
Rather, this chapter is intended to introduce the reader to the many different linear stationary and nonstationary qualities of the ECG, together with a selection of relevant metrics for evaluating these properties. This chapter is also intended to give an insight into possible approaches which are relevant to the different recording situations one may encounter (that vary based on activity, demographics and medical condition). It is important, although difficult, to differentiate between the concept of the nonstationary and the nonlinear nature of the ECG, since the application of a particular methodology or model will depend on prior beliefs concerning the relevance of these paradigms. In general, it is sufficient to apply linear techniques to quasi-stationary segments of ECG. However, to improve on such measures, it is important to understand the nonlinear nature of the ECG. Techniques for nonlinear analysis are therefore presented in Chapter 6. However, before reading the chapter on nonlinear analysis, it is advisable to read the following chapter, in which a selection of practically useful nonlinear and nonstationary models for both the ECG and the RR tachogram are presented.
