Optimized Positioning of ECG Electrodes for WSN Applications - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 178

A wireless electrode is composed of two skin electrodes connected by a conducting
wire, with appropriate electronics for digitalization and transmission of the
measurements. A small set of electric potentials from wireless electrodes can be
used in the reconstruction of the standard 12-lead ECG. Wireless electrodes can
constitute a BWSN that eliminates the need for additional wires and therefore
improves the applicability of ECG device technology. Wireless technology is appli-
cable in clinical ECG devices but is maybe even more promising for personal and
mobile ECG devices, because of increased mobility and comfort.
Several research and experimental projects have shown the feasibility of such an
approach [ 1 ]. We have shown that the accuracy of the reconstructed ECG can even
be improved with a personalized approach. Our results show that the number of
wireless electrodes can be reduced to three, if positioned optimally for each inves-
tigated subject. Such a positioning contributes to the diagnostic information and
therefore increases the reliability of the reconstructed standard 12-lead ECG.
Advances in the area of computerized electrocardiology should lead to consid-
erably improved ECG systems in the near future [ 1 ]. A particular area of recent
interest is the use of limited lead systems that obtain ECG information from just a
few recording sites. Such approaches involve the application of a transformation to
yield the more familiar 12-lead ECG. Several approaches have been proposed for
reducing the number of electrodes. The most popular is the EASI lead system [ 2 ],
which is commercially available from Philips Medical Systems. This system consists
of three bipolar leads while others, like Wei's [ 3 ], Drew's [ 4 ], and Nelwan's [ 5 ], use
a subset of the conventional 12-lead ECG set. Some of the leads used in these
systems are bipolar and some unipolar. Detailed descriptions of the leads obtained
from wireless electrodes, their positioning, and the principles for reconstructing
12-lead ECG, are given in the following sections.
The methodology for the reconstruction of standard 12-lead ECG, which is
proposed in this chapter, was supported by multichannel ECG (MECG) measure-
ments that were obtained by 31 or 35 ECG electrodes placed on the front and
back part of the human torso in positions that were determined by an orthogonal
mesh [ 6 ]. The distances between the neighboring electrodes in the mesh were
5-7 cm. The MECG provides 31 or 35 independent ECG potentials referenced
to a common potential, while potential differences between any two electrodes
can be regarded as bipolar leads. There are a lot of possible bipolar leads, but
we addressed only the pairs that are composed of neighboring electrodes that
are close enough. Their potential is electrically equivalent to the potential
obtained from a wireless electrode of the same dimension as the distance
between neighboring MECG electrodes. In this way we can emulate different
numbers and positions of the wireless electrodes in the research and develop-
ment of the reconstructed 12-lead ECG. Such a selection enables a straightfor-
ward design of strip-like wireless electrodes connected in a BWSN, which is our
final goal [ 7 ].
The rest of this chapter is organized as follows. The 12-lead ECG is introduced
in the next section with some basic terminology used in electrocardiography. An
overview of different lead sets used for ECG recording is presented in Section 9.3 .