Two-electrode impedance-sensing cardiac rhythm monitor for charge-aware shock delivery in cardiac arrest

This paper presents a two-electrode cardiac rhythm-monitoring amplifier that also senses the impedance between the same electrodes. Online monitoring of the body and electrodes impedances during high-voltage (HV) energy delivery or defibrillating, is needed to precisely estimate the amount of charge being delivered to the cardiac muscle. By adjusting the HV stimulus waveform, the amount of charge and thus energy delivered to the cardiac muscle can be precisely controlled for each patient. Additionally, online monitoring of the cardiac impedance ensures proper electrodes connectivity during both electrocardiogram (ECG) signal monitoring and HV energy delivery. The proposed amplifier employs two current sources of the same value and opposite direction (one at each electrode) to adaptively source through the chest an out-of-band (1 kHz) sinusoidal current and measure the resulting voltage to infer the cardiac impedance. This is done in superposition with ECG monitoring due to the same modality of the signal (i.e. voltage). A functional prototype with low-cost off-the-shelf components was implemented and tested demonstrating the feasibility of the proposed technique.