For the EMF sources that are not listed in the “whitelist” of the EN50527-2-1, the evaluation of the possible risk for the PM employee generally starts by measuring the field strength around the EMF source and comparing the measured values to the immunity levels stated in EN45502-2-1 standard [8
]. For frequency, below 450 MHz, the radiated field emitted by the EMF source must be converted into the induced voltage at the PM input stage. This can be done using computational dosimetry or through the conversion formulas reported in the annex E of the EN50527-2-1 [4
]. At frequency above 450 MHz, the radiated field strength can be immediately compared to the immunity level of the EN45502-2-1 standard [8
]. If the immunity levels are exceeded, a specific risk assessment is required. If the measured field does not exceed the immunity levels, the PM can be expected to work uninfluenced. However, if there is not a history of uninfluenced behavior at the workplace, sufficient to exclude severe (clinically significant) interaction, a specific risk assessment is still required.
The results of the in vitro testing/measurements on the electrosurgical units, the transcranial stimulators, and the arc welders can be considered an example of how the specific risk assessment for worker with a PM can be performed, according to one of the methodologies proposed by the EN50527-2-1 [4
]. The in vitro testing/measurements approach has been widely used to assess the electromagnetic compatibility of implantable medical devices: Different types of phantoms have been proposed to host the AIMD and to simulate the interactions with the EMF source of interest. When the wavelength of the interference signal is several times shorter than the dimensions of the human body (e.g., GSM, UMTS, LTE phones, WiFi transmitters, UHF RFID signals), the phantom can be limited to the size needed to host the AIMD [15
]. At lower frequency (e.g., 1.5 T MRI scanner, LF—HF RFID, power supply lines), the dimensions of the phantom cannot be neglected and more realistic shapes are used [18
]. Given the aim of this paper, that is, to describe a general procedure that can be adopted for the risk assessment of workers with AIMD, a realistic, human-shaped phantom was used.
The main advantages of in vitro testing/measurements are that they are safe, since the direct involvement of the workers is not needed, and they allow provocative testing, i.e., allow testing the performance of the device not only in realistic exposure conditions, but also in worst-case scenarios, which may be far from actual practice, but that enhance the interaction between the EMF source and the implanted device. As an example, the PM lead path can be arranged in a path that is not feasible as a clinical implant, but that maximizes the coupling with the electric or the magnetic field. Consequently, safety margins (in terms of power, distance) can be defined even when the EMF source does not produce any effect in standard conditions. However, this approach requires multiple and high-level expertise regarding the implantable device and the EMF source technology, and experimental set-up that could be rather complex and expensive. It is important also to underline that in vitro tests can be adopted for risk assessment only if a series of requirements are met:
The workplace environment is such that a phantom, a monitoring device, and test personnel can be accommodated for the duration of anticipated testing;
A fully functional pacemaker and leads of the same manufacturer and model as that implanted in the PM employee can be obtained from the manufacturer or the physician;
A monitoring device to record and analyze the activity of the PM during the test is available.
In addition, the implant layout and the programmed parameters must be the same as in the PM employee.
The in vitro testing/measurement approach provides useful information not only on the occurrence of an unwanted effect on the AIMD behavior, but also on the clinical relevance of such an effect. Indeed, both these aspects must be considered in the general risk assessment procedure, and the consequent risk mitigation actions can point at reducing the occurrence of an unwanted event, its clinical relevance, or both, until the residual risk for the AIMD employee is considered acceptable.
The results presented in this paper are valid for the specific AIMD, EMF source, and environments that were investigated, and cannot be generalized to other scenarios, even if similar. A different programming of the AIMD or a different environment around the EMF source could modify the interactions and the consequent effects of the EMF on the AIMD. These results can be used to identify a general situation where the foreseeable risks for a worker with a PM exposed to a particular EMF source deserve a specific assessment.
To date, few studies have addressed the electromagnetic compatibility of PM with ESU or TMS [21
]. These studies focused on the effects on a patient with a PM, but did not consider the case of healthcare personnel that use such EMF sources in the work environment. The exposure scenario is definitely different for the two cases, and thus the results found for the patient are not valid for healthcare personnel. No specific studies are available on the possible effect of arc welders and AIMD.
The tests on the ESU did not show any changes in PM activity, even in the worst-case conditions (maximum electric and magnetic field coupling). Thus, it can be assumed that, for the PM and ESU models under test, no specific action must be taken to guarantee the PM employee safety.
The TMS systems caused the inhibition of the pacing activity (not for more than a single beat) and triggered the “noise reversion modality” in the PM. Such behavior was observed for the 2 Hz repeated stimulation and with the TMS coil placed parallel to the loop formed by the PM lead, close to the chest of the human torso-shaped phantom. Given the magnetic nature of the field generated by the coil, this configuration generated the maximum coupling between the coil and the implant. The noise reversion modality cannot be considered a malfunction of the PM, since it is a specific functionality that is activated when the PM recognizes at its input stage a high level of noise, which could interfere with its ability to sense the spontaneous activity of the heart. Thus, in this modality, the sensing activity is turned off and the PM starts stimulating at a fixed rate. Theoretically, an external stimulation concurrent with a physiological beat can induce a ventricular fibrillation. However, modern PM algorithms are able to prevent such risk, synchronizing the start of the asynchronous stimulation with the last sensed beat, and thus minimizing the actual risk for the PM-bearer. The initial pacing inhibition for no more than a single beat does not represent as well a clinical relevant effect for the employee safety. Thus, proper training of healthcare personnel on the particular configurations that should be avoided in the case of the PM employee and on the possible consequences on the PM behavior can be considered sufficient for the risk assessment.
The measurements on the arc welder when the typical good-practice procedures for welder workers were simulated (that is, with the cable raised from the floor to the worktable) did not reveal any effect on the PM behavior, both in the continuous and in the pulsed welding modality. The PM remained uninfluenced also when the cable was fixed to the phantom belt. Similarly to what observed for the TMS, the PM behavior was affected only in those configurations associated with the maximum magnetic field coupling. When the cable was placed over the phantom’s shoulders (one or both), it formed a loop almost parallel to the plane of the PM implant. In these configurations, the continuous welding caused partial inhibition of the pacing at the beginning of the arc activation, for no more than a single beat. For pulsed welding, a prolonged inhibition was observed: During the arc activation, a missing beat was recorded after almost each emitted pulse. In one test, the arc activation caused the complete inhibition of pacing activity, which was restored only when the arc was switched off. For a PM-dependent worker, such inhibition of the pacing activity can be dangerous and represents a serious hazard for his safety [23
]. Consequently, the risk assessment shall lead to the definition of mitigation actions to limit as much as possible the occurrence of such unwanted events (e.g., proper training and information, safety distances, or even worker relocation).
The in vitro testing/measurements approach adopted in this study is just one of the possible approaches for the risk assessment of workers with AIMD. Other approaches, such as in vivo measurements [25
] or numerical modeling [26
], can be used as alternative methodologies or sources for complementary data. In any case, the EN45502 [3
] standard family represents the main guidance that the employer shall follow to properly perform the risk assessment.