M. Zhou et al.: Radioprotection 2025, 60( 4), 373 – 381 375 Fig. 1. Voltage injection system configuration.
simultaneously measuring the voltage applied to the phantom. Its high-impedance input ensures measurement fidelity and minimizes loading effect. The device’ s supporting software LabOne ®, enables direct adjustment of field levels and real time monitoring on a PC.
This setup was simulated in the CST Studio ®, showing that same EF induction distribution may be obtained as in laboratory EF exposure( Zhou et al., 2024). Under exposure of 1 kV / m at 50 Hz, the induction gradually decreases upwards in the upper part of the phantom( funnel shape), with an average induced EF of 0.8 mV / m, same to that in the thorax where impulse generators are installed; the induction remains constant in the lower part of the phantom( cylindrical shape), with an induced EF of 4 mV / m as in the heart, where the sensing lead tip is located( Fig. 1C). In vitro testing may be carried out using it, as long as the same configuration of the device is applied as in laboratory exposure. To simulate the real-case implantation environment and to observe the dysfunctions caused by EF exposures, heart signals of 1 Hz( 60 bpm) were continuously sent to cardiac implants via optic fiber during the assessment using a cardiac signal generation unit( ECG Unit) applied in the laboratory exposure system( Zhou, 2023). Typically, physicians set the sensitivity of cardiac implants to be 3 – 4 times lower than the cardiac signal amplitude. In this study, the amplitude of cardiac signals was configured to be 4 times the sensitivity setting. Therefore, VIS assessment is validated for reproducing the same exposure conditions to the cardiac implant and allowing observation of real-case interference without an exceptional experimental environment.
At low frequencies, the dominant effect is the induction of electric current density in the body, which is considered an assessable quantity due to its direct association with biological effects. Therefore the interference investigation may be conducted also based on the study of the induced voltages on the leads. A measuring system dedicated to evaluating the induced voltages on cardiac implants under EF at ELFs was designed and applied for the study of laboratory EF exposure( Zhou et al., 2024). The findings enabled the determination of equivalence factors between real case exposure and laboratory EF exposure. In this work, the measuring system was designed to conduct measurements of induced voltages on cardiac implants for VIS, while maintaining the same device implantation configuration. Consequently, the equivalence for VIS to the real case may be determined accordingly, along with the association of exposures.
3 Results
3.1 Establishment of VIS assessment
The measuring system and the same device implantation configuration in the study of laboratory EF exposure( Zhou et al., 2024), were used in the VIS to evaluate the induced voltages at the input of cardiac implants under EF exposure at power frequency( 50 Hz). The induced voltages were measured with increasing voltage injection levels. The results were postprocessed to obtain the component at 50 Hz in order to eliminate the potential external inference from other frequencies. Figure 2 shows the measurement results in VIS for bipolar and unipolar sensing. The blue dots represent the induced voltages obtained with the measuring system, while the black lines show the simulation results. Linearity between the injected voltage and the induced voltage can be observed in both bipolar and unipolar sensing mode. The gradients of the trend lines from the results indicate the induced voltage for normalized injection( 1 mV). We measured an induced voltage of 772 mV and obtained 668 mV by simulation for unipolar sensing, with an injection of 1 mV. For bipolar sensing, we measured 121 mV and obtained 117 mV by simulation for bipolar sensing, with an injection of 1 mV as well.
Previous study has performed such measurements for laboratory EF exposure( Zhou et al., 2024). The induced voltages for a normalized electric field exposure of 1 kV / m were 438 mV / 80 mV( unipolar / bipolar), corresponding to induced voltages of 183 mV / 22 mV( unipolar / bipolar) in real case. Integrating with the findings in VIS, the association of two exposure systems and real case may be established based on the induced voltage quantities. Figure 3 demonstrates this association for both unipolar sensing and bipolar sensing. For a given exposure in real case( horizontal axis), the EF levels required to conduct an assessment in the laboratory EF exposure system can be found on the left axis; the injected voltages that are required in the VIS assessment can be found on the right axis. The exposure levels are limited to real-case exposure of up to 35 kV / m, complying with the exposure limit value( ELV) of EN 50647. The exposure references given by the ICNIRP guidelines and the IEEE standard C95.1-2019 were labeled in the figures, along with the Action Levels( ALs) indicated in the Directive 2013 / 35 / EU. These figures may work as lookup tables for non-clinical investigation of an employee bearing a CIED in the specific assessment process. By checking the voltage injection dose required to reproduce