Interference Reduction in Ecg Recordings by Using a Dual Ground Electrode

− Power distribution lines are a major source of interference in ECG recordings obtained with surface electrodes. Displacement currents coupled to electrodes, their leads and directly into the body, and stray capacitance in power supply transformers, result into differential-mode, common-mode and isolation-mode interference. Shielding electrode leads reduces displacement currents coupled to them. Amplifiers with high common-mode and isolationmode rejection ratio reduce common-mode and isolationmode interference, but interference coupled in differential mode cannot be reduced by shielding neither by amplifier design. We propose the use of a grounded electrode close to each recording electrode instead of the customary “rightleg” ground electrode, to reduce differential-mode interference. We provide a qualitative model to explain that interference reduction, and experimental evidence to show its effectiveness even for non-isolated recording systems in the presence of strong power-line interference.