Determining the input impedance of ECG amplifiers using accurate electrode modelling.

Area of Science:

• Biomedical Engineering
• Medical Instrumentation
• Electrophysiology

Background:

• The skin-electrode-amplifier interface significantly impacts electrocardiogram (ECG) recording quality.
• Current IEC 60601 standards specify minimum performance requirements for electrocardiographs.

Purpose of the Study:

• To investigate the influence of electrode properties and amplifier input impedance on ECG transient response.
• To establish optimal input impedance requirements for ECG amplifiers based on electrode electrical characteristics.

Main Methods:

• Accurate modeling of surface contact electrodes, including a double time-constant model.
• Analysis and simulation of DC and AC coupling modes for electrodes to amplifier input.
• Bench testing to validate simulation results and design constraints.

Main Results:

• The recommended minimum 10 MΩ amplifier input impedance is insufficient for modern adhesive, un-gelled, and dry electrodes.
• Input impedance as high as 10 GΩ and a low AC cut-off frequency (≤0.05 Hz) are suggested for accurate recordings.
• Signal distortions, including false S-wave creation and S-T segment depression, occur with insufficient input impedance.

Conclusions:

• Existing input impedance recommendations in standards are inadequate for contemporary ECG electrodes.
• Adopting the derived design constraints can prevent signal distortions and potential clinical misdiagnosis.
• Optimizing amplifier input impedance is crucial for reliable ECG signal acquisition.