Preventing smartphone induction of magnet mode in cardiac implantable electronic devices

Authors: Felix K Wegner, Dennis Korthals, Fabienne Kreimer, Julian Wolfes, Christian Ellermann, Moritz Martinovic, Christoph Kittl, Gerrit Frommeyer, Lars Eckardt

Abstract

Aims

Wireless charging capable smartphones may interact with cardiac implantable electronic devices (CIED). We hypothesized that magnetic shielding with a steel plate placed at the back of a smartphone may prevent interaction.

Methods and results

Sixteen CIED (6 pacemakers and 10 implantable cardioverters/defibrillators) from all manufacturers were consecutively implanted in a subcutaneous and submuscular location in an isolated porcine thorax and connected to an interactive heart simulator. Two smartphones (Apple iPhone 14 and Google Pixel 8 Pro) were placed on top of the implantation site, and signs of magnet mode induction were recorded. The Apple iPhone induced magnet mode in seven of 16 (44%) subcutaneously placed CIED. Placed in a magnetic phone case, the Apple iPhone induced magnet mode in six of 16 (38%) devices. Magnet mode induction was successfully prevented in all cases by placing a 1 mm thin steel plate at the back of the smartphone. The Google Pixel did not induce magnet mode in any of the 16 devices, even with a magnetic case. Submuscular CIED placement resulted in no occurrence of magnet mode induction by any smartphone. All devices were still able to be interrogated and responded to a CIED magnet.

Conclusion

The Apple iPhone induces magnet mode in close to half of subcutaneously placed CIED due to its MagSafe magnet. Neither a smartphone utilizing the Qi wireless charging standard nor magnetic smartphone cases confer the same risk. Submuscular CIED placement or magnetic shielding with a steel plate prevents magnet mode induction. The future Qi2.0 standard may exacerbate interaction risks.

Introduction

Cardiac implantable electronic devices (CIED) are widely used in modern cardiology for a variety of indications from permanent pacing to primary prevention of sudden cardiac death.^1–3^ While electromagnetic interference by early mobile telephones was a relevant concern, newer generations of mobile telephones and CIED show a very low incidence of electromagnetic interference.^4,5^ Magnet-sensitive switches in CIED are utilized in clinical practice in specific, controlled scenarios under the supervision of trained personnel, such as during surgery with electrocautery, device programming, or emergency therapy suspension. However, inadvertent activation of magnet-sensitive switches outside of a controlled environment, for example by wireless charging modules of modern smartphones, may pose a risk to patients with CIED.

Today, most patients with CIED use a smartphone capable of wireless charging, which is in close contact with the owner throughout the day.^6^ While Android smartphones use the ‘Qi’ wireless charging standard which does not utilize a relevant magnetic field,^7^ Apple iPhones (since the iPhone 12) use a permanently installed magnet at the back of the smartphone to aid in the alignment of the wireless charging module called ‘MagSafe’.^8^ There are some reports of magnet mode induction by iPhones with ‘MagSafe’ magnets in CIED.^9–12^ However, it is unclear whether this is a relevant problem across all CIED manufacturers in clinically relevant implantation sites and how interaction can best be prevented. The future ‘Qi2.0’ wireless charging standard developed by Apple in conjunction with the Wireless Power Consortium will incorporate permanently installed magnets like ‘MagSafe’. The ‘Qi2.0’ standard is expected to replace both the ‘Qi’ and the ‘MagSafe’ standard in the near future, likely exacerbating potential risks of CIED interference.^13^

The purpose of the present study was therefore to systematically investigate the interaction risk between modern smartphones, ‘MagSafe’-compatible accessories, and CIED across all relevant CIED manufacturers and evaluate strategies for prevention of interaction in an experimental porcine model. We hypothesized that magnetic shielding with a steel plate placed at the back of a smartphone may prevent interaction with CIED.

Methods

The present study included CIED from all major manufacturers (Abbott, Chicago, IL, USA; Biotronik, Berlin, Germany; Boston Scientific, Marlborough, MA, USA; Medtronic, Minneapolis, MN, USA; Microport, Shanghai, China), which were implanted subcutaneously in an isolated porcine chest sample and connected to an interactive heart simulator (InterSim III, IB Lang). The experimental set-up has been previously described by our group.^14^ In brief, porcine specimens were obtained shortly after slaughter from a local butcher and ethics committee approval was not required by the local ethics committee. Devices were programmed according to relevant guideline recommendations.^15^

Subsequently, an Apple iPhone 14 and a Google Pixel 8 Pro smartphone were placed on top of the implantation site. Signs of magnet mode induction were noted for each CIED including audible signals, asynchronous pacing, inability to terminate ventricular tachyarrhythmias, and episodes of magnetic interference stored in the device memory.^16^ In all tested pacemakers, magnet mode induction was confirmed by a switch to asynchronous pacing mode, which was observed on the ECG monitor of the interactive heart simulator. In all implantable cardioverters/defibrillators (ICD), magnet mode induction was confirmed by the absence of tachytherapies while ventricular fibrillation was simulated in the interactive heart simulator. In addition, magnet mode induction was confirmed by a solid audible tone in Medtronic and Boston Scientific ICD and by a stored episode of magnetic interference in Abbott CIED.

Thereafter, each smartphone was placed in a ‘MagSafe’-compatible magnetic phone case (JETech, Shenzhen, China) and signs of magnet mode induction were recorded. Figure 1 shows the utilized smartphones and respective magnetic cases on visual inspection and fluoroscopy. For all cases of magnet mode induction, magnetic shielding was attempted by placing a 1 mm thin steel plate at the back of the respective smartphone (see Figure 2). The material and thickness of the steel plate were chosen due to pilot experiments, indicating a sufficient magnetic shielding when placed directly on top of an explanted CIED.

Afterwards, CIED were placed in a submuscular location 2.5 cm below the skin level in the isolated porcine thorax (see Figure 3) and the listed experiments were repeated. To ensure proper device function, magnet mode induction was tested with a ‘positive control’ of a CIED manufacturer-specific device magnet and all CIED were interrogated while in the submuscular location.

Results

The present study included 16 CIED from all major six pacemakers (one VVI-PM, four DDD-PM, and one CRT-PM) and 10 ICD (five VVI-ICD, one DDD-ICD, and four CRT-ICD). Table 1 lists the utilized CIED. All CIED were interrogated before and after testing for magnetic interaction with no change in relevant measurements in any of the included devices.

Subcutaneous cardiac implantable electronic device placement

Overall, the Apple iPhone 14 induced magnet mode in seven of 16 tested CIED (44%). Table 1 indicates the CIED that showed signs of magnet mode induction. Interestingly, magnet mode was induced in all tested VVI and DDD pacemakers but not in the included Boston Scientific CRT pacemaker. Furthermore, both Medtronic ICD showed signs of magnet mode induction. In contrast, none of the eight other tested ICD from Abbott, Biotronik, Microport, and Boston Scientific showed signs of magnetic interaction with the smartphones. When testing the 1 mm thin steel plate placed at the back of the Apple iPhone (see Figure 2), magnetic shielding was successful in all seven CIED that previously showed signs of magnet mode induction. In contrast to the Apple iPhone, the Google Pixel 8 Pro did not induce magnet mode in any of the tested CIED.

When testing both smartphones placed in ‘MagSafe’-compatible magnetic phone cases, the Apple iPhone induced magnet mode in six of 16 tested CIED (38%), while the Google Pixel showed no signs of magnetic interaction in any CIED. The Microport Reply DR pacemaker did not interact with the Apple iPhone placed in the magnetic case, while it showed signs of magnetic interaction when the smartphone was placed directly on top of the implantation site without the magnetic case. Magnetic shielding with the steel plate was again successful in all cases, with none of the six CIED that previously exhibited signs of magnet mode induction interacting with the Apple iPhone (see Table 1).

To elucidate the effectiveness of magnetic shielding, the magnetic field strengths of the smartphones and cases with and without the steel plate were subsequently tested with a Gaussmeter (ZMST-5, Metrolab Instruments, Geneva, Switzerland). Figure 4 illustrates the results of the magnetic field measurement. Specifically, the magnetic field strength was 4.2 mT at the back of the iPhone and 2.7 mT when the iPhone was placed in the magnetic case. This was reduced in both instances to 0.3 mT by application of the steel plate (see arrows in Figure 4).

Submuscular cardiac implantable electronic device placement

Subsequently, all CIED were placed in a submuscular location in the porcine thorax at a distance from the skin level of 2.5 cm (see Figure 3). All CIED still responded to a manufacturer-specific device magnet and were able to be interrogated by the respective manufacturer’s programmer. Neither the Apple iPhone nor the Google Pixel induced magnet mode in any of the tested CIED. Additionally, placing the smartphones in magnetic smartphone cases did not induce magnet mode in any CIED placed in a submuscular location (see Table 1).

Discussion

This is the first study evaluating the effectiveness of different strategies for prevention of smartphone induction of CIED magnet mode in clinically relevant implantation sites in a porcine model. Our main findings are as

• The Apple iPhone induces magnet mode in about half of tested CIED, with a focus on pacemakers and Medtronic ICD.
• The Google Pixel does not pose a relevant risk of interaction, as it does not include an active magnetic ring for alignment of the wireless charging module.
• Both magnetic shielding with a steel plate and submuscular CIED placement reliably prevent magnet mode induction.

More than two-thirds of patients with CIED routinely use a smartphone in daily life.^6^ While studies in smartphones incapable of wireless charging reported a very low interaction risk,^5^ we were able to show that ‘MagSafe’-compatible smartphones (since the Apple iPhone 12) have a relevant interaction potential with subcutaneously implanted pacemakers and ICD. Our findings are in line with case reports and studies describing the magnetic fields measurable at the back of ‘MagSafe’-compatible iPhones.^9–12^

Greenberg et al.^9^ first reported a case of magnet mode induction in a Medtronic ICD by an Apple iPhone 12 in 2021. We were able to show that despite minor changes to the ‘MagSafe’ magnet including a rotation of 90 degrees and a change in battery position, the possibility of magnet mode induction persists in more recent iPhone models. Furthermore, we were able to demonstrate that this is a phenomenon specific to the ‘MagSafe’ wireless charging standard, as an Android smartphone utilizing the ‘Qi’ wireless charging standard without a continuously operating magnetic ring such as the Google Pixel 8 Pro does not pose a risk of magnet mode induction.

Previously, very high rates of magnet mode induction were reported when iPhones were placed directly on top of CIED ex vivo.^10^ In line with a study by Lacour et al.^11^, our results indicate that the risk in clinical practice is probably lower and considerably influenced by the distance between a ‘MagSafe’-enabled iPhone and respective CIED. In this regard, the rate of magnet mode induction in a subcutaneous CIED placement in the present study was slightly higher than in the in vivo experiments by Lacour et al.,^11^ which were conducted in patients with an estimated CIED implantation depth of 1.5 ± 0.9 cm. In the present study, no signs of magnet mode induction were seen at a submuscular implantation depth of 2.5 cm.

Our results, together with a possible lack of awareness in both patients and cardiologists, may explain the scarcity of clinical reports describing events of magnet mode induction by smartphones. However, we were able to show a tendency of Medtronic CIED to interact with ‘MagSafe’-compatible smartphones, which were reported to respond to a doughnut magnet at a much greater distance than CIED of other manufacturers.^11^

When placing both smartphones in ‘MagSafe’-compatible magnetic phone cases, the underlying risk of magnet mode induction posed by the respective smartphones outweighed the interactive potential of the magnetic cases. On fluoroscopy, we were able to show that the utilized magnetic cases are built of a collection of small square magnets in contrast to the continuous ring included in the iPhone 14. The iPhone 14 considerably exceeded a magnetic field strength of 1 mT below which CIED should not interact with magnetic fields according to the ISO 14117 norm,^17^ both on its own and when placed in the magnetic case. However, we were able to document that shielding with a steel plate reduces the magnetic field strength markedly below 1 mT, which explains its effectiveness. The tested magnetic smartphone case attached to the Google Pixel 8 Pro did not exceed 1 mT and therefore did not confer a risk of magnet mode induction in our experimental model.

No previous study systematically evaluated strategies for prevention of magnet mode induction. In the present study, we were able to show that both magnetic shielding with a thin steel plate and submuscular device implantation reliably protect against the risk of smartphone induction of magnet mode in at-risk devices.

Placing a steel plate at the back of an iPhone is an easy and low-cost option for magnetic shielding. Since the magnetic ring in ‘MagSafe’-compatible Apple iPhones is continuously in operation, the steel plate magnetically attaches to the back of the phone and does not need a mount to be held in place. It is slim enough to fit under most smartphone cases, and the cost for material and processing in our example was equal to 2 US dollars. The steel plate has no effect on the near field communication (NFC) functionalities of the smartphone. It deactivates wireless charging but can easily be removed and reattached to the smartphone. In the future, our results may encourage the development of smartphone cases with integrated mechanisms for magnetic shielding.

In contrast, submuscular device placement is only feasible during initial implantation and device generator changes. Current CIED implantation guidelines allow for both a subcutaneous and a submuscular device implantation,^18^ with a substantial proportion of CIED implanted subcutaneously because of the ease of subcutaneous placement and possible concerns about perioperative bleeding. Our results may encourage cardiologists and surgeons to evaluate a submuscular device placement in suitable patients to reduce the risk of magnetic interaction. However, this may not eliminate the interaction risks in patients with a low body mass index in whom the tested implantation depth cannot be reached. Conversely, a depth of CIED placement of 2.5 cm might be achievable subcutaneously in very adipose patients. Our results support Apple’s recommendation of keeping 15 cm distance between its current iPhones and CIED;^19^ however, this may not be feasible or desired by all patients in daily life.

Recently, the Wireless Power Consortium that supports the ‘Qi’ wireless charging standard utilized in Android smartphones reached a deal with Apple to incorporate ‘MagSafe’-type magnets in a new wireless charging standard termed ‘Qi2.0’.^13^ This new standard may soon replace the ‘Qi’ wireless charging standard in Android smartphones. While more than half of smartphone owners in the USA use an Apple iPhone, Android has a market share of about two-thirds in Europe and worldwide.^20^ Therefore, the possible integration of magnets in Android smartphones may increase the relevance of our finding for European and global cardiologists as interaction risks in clinical practice are expected to rise considerably. In this regard, our results can be used to advise patients both on surgical implantation techniques, precautions for daily life and possible strategies for magnetic shielding in high-risk situations.

Limitations

This is a preclinical, experimental study in a porcine model. Therefore, caution should be exercised when applying results to clinical practice. However, porcine models are well established for CIED interaction studies.^14,21–23^ We decided to conduct experiments with one ‘MagSafe’-compatible iPhone and one ‘Qi’-compatible Android smartphone as well as a representative selection of CIED from all major device manufacturers since we expect results to be transferrable to other similar smartphones and CIED. Nonetheless, we cannot exclude the possibility of individual CIED that were not tested to react differently to magnetic interaction.

Conclusions

A ‘MagSafe’-compatible Apple iPhone 14 induces magnet mode in close to half of subcutaneously placed ICD and pacemakers due to its installed magnet. Neither a smartphone utilizing the ‘Qi’ wireless charging standard nor ‘MagSafe’-compatible accessories confer the same risk. Magnetic shielding with a thin steel plate or submuscular CIED placement prevents interaction with the ICD or pacemaker. Our results can be used to specifically instruct patients in high-risk situations and may encourage the development of specific smartphone cases capable of magnetic shielding. The future ‘Qi2.0’ standard incorporating a magnet in most smartphones regardless of manufacturer may exacerbate the risk of magnet mode induction by smartphones.