Optimized Positioning of ECG Electrodes for WSN Applications - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 179

We put more emphasis on the various existing approaches to the reduction of lead
set. In Section 9.4 , further details are presented on determining the minimal number
of electrodes and their optimization regarding positions and distances. Multivariate
statistical methods, i.e., PCA and regression analysis, are applied to the 31-channel
MECG measurement for selecting optimal electrodes and calculating a personalized
transformation matrix for the reconstruction of 12-lead ECG with minimum loss of
diagnostic information. In Section 9.5 , the proposed methodology is validated for a
real test case. The chapter concludes with a critical overview of the presented results
and required work for future wireless ECG systems.

9.2 Electrodes and Lead Types

The surface electrodes are electrical contacts positioned selectively on predefined
places on the body surface. The electrical potential difference between two body
surface electrodes is a consequence of the electrical currents through the heart
muscle and surrounding conductive tissues. The measured electric potentials
from different positions are strongly related to the diagnostic state of the heart, to
be evaluated in different parts of the heart muscle. The meaning of “lead” is his-
torically a combination of electrode potentials. Each lead represents an electrical
axis onto which the electrical activity of the heart is projected. One may consider
each lead to represent a different spatial perspective of the heart's electrical activ-
ity. There are two types of leads: unipolar and bipolar. A unipolar lead is, for
example, the potential difference between an electrode usually placed on the
chest and a reference potential, while a bipolar lead is a potential difference
between two electrodes. We will provide a concrete example from the standard
12-lead ECG system.

9.2.1 Standard 12-Lead ECG

The standard 12-lead ECG uses ten electrodes, six of them, V1-V6, are precordial
electrodes placed on the chest, the next three are limb electrodes placed on the right
(RA) and left arms (LA) and left leg (LL), and the last is ground electrode, placed
on the right leg (RL) [ 8 ]. Precordial chest electrodes are used to form six unipolar
leads while the electrodes at the extremities form three bipolar limb leads, I, II, and
III. Augmented limb leads aVR, aVL, aVF, derived from I, II, and III, are consid-
ered to be unipolar. V1-V6, I, II, III, and aVR, aVL, aVF, constitute the 12 leads
of the standard ECG. Figures 9.1 and 9.2 indicate the standard electrode positioning
in the 12-lead ECG.
Precordial leads are generated as electrical potential differences between pre-
cordial electrodes and Wilson's central terminal potential, which is the negative
“electrode” of all precordial leads, and these leads are therefore considered to be