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The iPhone 12, Pacemakers and Defibrillators

Concerns have been raised that magnets in the new iPhone could affect cardiac devices. They could, though the risk to patients is small.

This article was first published in The Montreal Gazette.

Reports have been circulating recently suggesting that the new iPhone can interfere with pacemakers and other cardiac devices. In general, phones pose no danger to medical equipment, as evidenced by the fact that nowadays everyone carries a cellphone in the hospital with no consequences. But a new research letter has suggested that the iPhone 12 may turn off a key feature of cardiac defibrillators and prevent them from delivering a life-saving electrical shock if a patient develops a fatal arrhythmia.

The problem stems from the addition of MagSafe technology to the newest iPhone. MagSafe allows you to charge your phone, not by plugging it in, but with a charger that magnetically clips to your phone like a magnet on a refrigerator. Unfortunately, that’s the problem. Magnets can disrupt how pacemakers and defibrillators operate.

We should first point out that pacemakers and defibrillators are different things. Pacemakers provide a small electrical stimulus to the heart to make it beat. If you have a slow heart rate, the pacemaker provides the electrical jolt to make sure your heart doesn’t go too slowly. Defibrillators are designed to give a high-energy shock to your heart if you have a life-threatening arrhythmia. And while defibrillators can also do double duty and function as pacemakers, pacemakers cannot function as defibrillators.

Importantly, if you have a normal heart rate, the pacemaker sits there and does nothing. Also, unless you are having an arrhythmia, the defibrillator will sit in your chest and do nothing. So in the days before complex computer software, the only way to test a pacemaker and make sure it was working normally was to use a magnet. Pacemakers and defibrillators have a small metallic switch inside them that is flicked on when you put a magnet directly over the device. That switch falls back to its normal position when the magnet is removed. When on, the switch puts the pacemaker into a special magnet mode, where it ignores any electrical activity in the heart and functions at a constant rate. If the pacemaker is functioning normally, it will pace the heart at 85 beats per minute. A paced rhythm at 65 beats per minute signifies a problem.

Putting a magnet on a defibrillator, though, has a different effect. It essentially renders the defibrillator blind. It will no longer detect any arrhythmias in the heart and will therefore not deliver a potentially life saving shock.

Patients with pacemakers or defibrillators are often counselled to avoid putting their phones too close to their device even though there was little evidence that cell phones can actually interfere with the devices’ function. A 2017 report in JACC and a more recent 2020 report in JACC Electrophysiology both concluded that cell phones and smart watches had little impact on a pacemaker’s or defibrillator’s function.

But the new iPhone 12 has something previous phones did not. The magnets in the iPhone 12 that allow for MagSafe charging can also turn off a defibrillator and switch a pacemaker to an asynchronous pacing mode. So if your phone happened to be in your breast pocket, mere inches from your defibrillator, it might be close enough for its magnetic field to affect your device.

To be fair, the phone would have to be very close to the pacemaker or defibrillator to have an effect and the device would return to normal if the phone was moved away. And this would only be problem if you happened to have a fatal arrhythmia while the iPhone was close enough to your defibrillator to stop it from delivering an electrical shock.

The likelihood of this happening is admittedly small. But given that you can put your phone in your pants pocket, it seems like an unnecessary risk to take for the rather paltry benefit of wireless phone charging.


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