ABSTRACT
Electronic equipment that displays electrocardiograms (ECGs), delivers pacing pulses, or defibrillates carries current in the form of electrons. The body, on the other hand, carries current in the form of ions. Electrodesphysically in contact with both the body and the instrument-translate, or transduce, between the body’s ionic current and the instrument’s electronic current. Transduction is best described as a chemical reaction between the material carrying the electronic current, usually a metal, and the material carrying the ionic current, a bodily fluid. For this reason, most of our understanding of how electrodes work has been borrowed from the field of chemistry. About one-half of this chapter is devoted to understanding the chemistry, hydrodynamics, and thermodynamics of the electrode-body interface. However, a second area of concern is that the body reacts to the presence of the electrode, a foreign substance. Depending on the electrode’s composition, shape, placement, and other factors, the body’s reaction to the
electrode could overwhelm the signal, impede the stimulating current, or mechanically destroy the electrode. Finally, the last section of this chapter describes several of the most common electrodes for stimulation and recording in electrocardiology.
