Effects of dc bias currents on ECG electrodes

The effects of small dc bias currents on the offset potentials of disposable ECG electrodes (four brands of Ag-AgCl and two brands of stainless steel) were examined. After periods ranging from a few minutes to several days, samples of all electrode types exhibited offset potentials exceeding 200 mV after subjection to dc bias currents over 200 nA. All Ag-AgCl electrodes were able to withstand bias currents of 200 nA with minimal changes in offset for periods up to 7 days. The stainless electrodes exhibited large offset potentials within minutes after subjection to bias currents of only 100 nA.