Event and time-scale characteristics of heart-rate dynamics.

The cardiac system shows various scale dynamic activities from secondly to yearly. Therefore multiple time-scale characteristics of heart dynamics have received much attention for understanding and distinguishing healthy and pathological cardiac systems. In this paper we expand the multiple time-scale analysis into event and time scales to investigate scale characteristics in healthy and pathologic cardiac systems. To do this, we define a measure based on symbolic dynamics, which calculates complexity at each time and event scale, called the unit time block entropy (UTBE). This measure allows a reliable comparison of experimental data through matching the number of words and the total measurement time at the same time for all RR interval sequences which are composed of the time durations between consecutive R waves of electrocardiograms. We apply the UTBE to the healthy heart-rate (HR) group and pathological HR groups and find that the RR interval acceleration is more effective than the RR interval in distinguishing each group. And we also find that the normal and pathological HR groups are clearly distinguished in some specific event and time-scale regions.