Session PB4.1

Calculating Optimal Virtual Lead from Multichannel ECG by Minimizing Morphological Beat-to-Beat Variability

K Noponen*, T Seppänen

University of Oulu
Oulu, Finland

A novel measure of the morphological beat-to-beat variation of signals derived from ECG is presented. Using the new measure, we explore the task of finding an optimal mapping of the electric activity of the heart into a single virtual lead in the sense of least beat-to-beat variability. Small morphological variation is often a desired property, for example in the detection of the onsets, peaks and offsets of the individual ECG waves.
In ambulatory measurements, the processing of several channels with an embedded device is often infeasible due to resource limitations. Therefore, either the system must be restricted to operate on a single lead or the measured leads have to be mapped into a new single channel signal that is used in later processing stages. This task is formulated as an optimization problem in which we seek an optimal functional that maps the electric heart vector to a real value at each time instant. For brevity, we restrict to time-invariant linear functionals, but other classes of functionals are briefly discussed with some examples.
For our results, we have measured ECG in different body positions and respiration depths. In total, there were 25 healthy volunteers between 19 to 53 years old. Ten of them were females and the rest were males. A Medilog AR12 Digital ECG Recorder with RAFE lead system was used. For each person, the 18 minute recordings were made using 16 bit amplitude resolution and 512 Hz sampling rate.
The results show that it is possible to find a virtual lead with lesser beat-to-beat variability compared to the leads of the standard ECG. Furthermore, the new measure gives precise quantitative information about the beat-to-beat variability present in the standard lead set. Our general exposition of the subject matter opens up many ways in which the methods presented can be extended in future to non-linear and time-varying functionals.

(Abstract Control Number: 58)