Measurement of skin-electrode impedance for a 12-lead electrocardiogram

In electrocardiographic recording one of the main sources of error is an imperfect mechanical contact in the skin-electrode interface because it causes high impedances that can contribute to distortion in the ECG. We measured contact impedance to determine the corresponding values to a reliable contact in this interface in 10 electrodes of the standard 12-lead ECG of 5 normal subjects from 1 Hz to 50 kHz. An impedance decrease for increasing frequency and a wider dispersion in low frequencies was observed. In the ECG frequency range, maximum contact impedances varied from 20 kΩ in 50 Hz and 100 Hz to 75 kΩ in 1 Hz. Because we are interested in analyzing ECG low frequency waves, we use the range of impedance values in 5 Hz for each electrode to detect a poor electrode placement in the 12-lead ECG recording.