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electrodes, and improvement of wearing comfort of the investigated person are also
important issues. They are, however, in partial contradiction with the standard
12-lead ECG, which exploits distant electrodes positioned on arms and legs. The
number of electrodes can be reduced and their optimal positioning found that
differs from the standard 12-lead placing. The measurements from reduced
electrode sets can serve for the reconstruction of the standard 12-lead ECG, which
is directly applicable to the current medical knowledge. Because the 12-lead ECG
contains redundant information, a technically more legitimate approach would be
to develop adapted diagnostic rules based on the measurements obtained by the
reduced number of ECG electrodes that still carry the same information about the
heart activities, but such an approach would require too much time for new experi-
ments, validations, and education.
Wireless technology can be introduced into ECG measurements on different
levels and with different approaches. For example, a standard wired ECG device
can have wireless access to the medical center, which enables remote monitoring.
Measurements from the wired electrodes can be assembled in an on-body subsystem
equipped with a wireless transmitter that enables wireless data transfer from the
monitored subject to the diagnostic ECG device, enabling much more freedom of
movement for the monitored subject. Finally, a wireless electrode (WE) can be
implemented that enables the minimal use of wires on the body and, consequently,
the maximal wearing comfort. Such a solution could also minimize the disturbing
signals generated in the musculature that are considered as noise in the case of ECG
measurements.
All these options for introducing wireless technology for ECG measurements
can be combined to provide a fully wireless system. However, for the purpose of
this chapter, we will focus just on wireless electrodes, emphasizing two important
issues. First, the wireless electrode enables the measurement and transmission of
only local potential differences; therefore, we are limited to differential (bipolar)
measurements. Second, limitations of transmission bandwidth and power supply
require a significant reduction of the number of wireless electrodes, raising the
question about their minimal number required for an accurate reconstruction of the
standard 12-lead ECG with the adequate diagnostic information.
We have investigated in more detail the approach based on a reduced number of
electrodes and reconstruction of the standard 12-lead ECG. The minimal number of
electrodes has been determined, and their positions and distances optimized for
each investigated person. Personalized transformation matrices have been obtained
using multichannel ECG (MECG) measurements performed initially on each user
of the wireless ECG. Multivariate statistical methods, such as principal component
analysis (PCA) and regression analysis, have been applied on 31-channel measure-
ments for selecting the optimal positions of ECG wireless electrodes. Personalized
transformation matrices have been calculated for the reconstruction of 12-lead ECG
with minimum loss of diagnostic information. It has been shown that a linear
combination of only three independent potentials from wireless electrodes suffices
for an accurate reconstruction - significantly less than the ten independent poten-
tials needed by standard 12-lead ECG.
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