Computational Intelligence in Cardiology and Heart Disease Diagnosis - Computational Intelligence in Biomedical Engineering - page 160

(a) (b)

FIGURE 4.12
Surface ECG electrodes distributed by Nikomed U.S.A. Inc. (http://www.
nikomedusa.com). The electrode (a) is made of foam and wet gel, whereas
electrode (b) is made of solid gel and is porous allowing the skin to “breathe.”

pose less risk of infection. Stainless-steel electrodes employ potassium citrate
or potassium sulfate as the interface electrode paste, but their polarization
considerably exceeds Ag/AgCl electrodes. Dry contactless or capacitative elec-
trodes may be used in the case where amplifiers have high input impedance;
these can be applied directly to the skin without gel paste.
Specialized electrodes have also been used according to the environment of
operation. Utsuyama et al. (1988) used two electrodes (VL-00-S, Medicotest)
for recording bipolar ECG in aquatic environments. These electrodes were
sheathed in transparent plastic cases (6.5 cm diameter and 5 mm depth) and
attached with adhesive tape to prevent electrode movement when the subjects
dived into the water. Thin rubber skirts about 2 cm wide were also used to
hold the electrodes in place.
The voltages obtained during a normal ECG depend upon the placement of
the recording electrodes (leads) on the body's surface. There are several ECG-
recording methods ranging from ambulatory recording, Holter tape, 12-lead
recording, sleep ECG recording, and body surface potential mapping. The
most widely used method is based on recording of ECG using 12-lead elec-
trodes. Figure 4.13 shows a layout of the surface electrodes for the recording
of 12-lead ECG. The term “lead” is used to distinguish recording a potential
difference between a pair of electrodes as opposed to the voltage obtained by
a single electrode. Table 4.1 summarizes the various leads that are described
in the following.
Bipolar or standard leads are electrodes attached to the limbs and are usu-
ally termed leads I, II, and III. In lead I, the positive electrode is attached
to the left arm, whereas the negative electrode is attached to the right arm.
The potential difference is then obtained by subtracting the right-arm voltage