The Skeptical Cardiologist

Beware The Magnets in Your Wearable Wristbands and in Apple iPhone 12: They Can Suspend Life-Saving Defibrillator (ICD) Therapy and Alter Pacemaker Function

In October of 2020 Apple announced its iPhone 12, “the best iPhone ever” with “a powerful 5G experience and advanced technologies that push the boundaries of innovation for users who want the most out of iPhone.”

One innovation that  users may not have anticipated was the ability of  this iPhone iteration to deactivate their implantable cardiac defibrillators (ICD).

ICDs which are designed to deliver life-saving electrical shocks to correct abnormal heart rhythms like ventricular tachycardia or fibrillation and  cardiac pacemakers are designed to respond to nearby magnets by changing their function. In essence, these sophisticated devices are rendered dumb.

Amongst the advanced technologies Apple put in the iPhone 12 was “an array of magnets around the wireless charging coil” for pairing with various MagSafe fitted chargers and accessories:

MagSafe improves wireless charging for a better, more efficient experience and introduces an ecosystem of easy-to-attach accessories that beautifully complement iPhone 12 Pro models. MagSafe delivers a unique experience to iPhone, featuring an array of magnets around the wireless charging coil, optimized for alignment and efficiency, that perfectly connects to iPhone every time. MagSafe chargers efficiently provide up to 15W of power while still accommodating existing Qi-enabled devices. Charging solutions include the MagSafe Charger and MagSafe Duo Charger for use with iPhone and Apple Watch, as well as new silicone, leather, and clear cases that easily snap onto the back of iPhone, and a leather wallet. Customers can also expect innovative MagSafe accessories from third-party manufacturers.
Apple GIF showing how the MagSafe “clicks” into position

An electrophysiologist at Henry Ford, Joshua Greenberg, became concerned about possible adverse interactions between iPhone’s magnets and implantable cardiac devices and performed a test on a patient with an ICD manufactured by Medtronic Inc. (Minneapolis, MN)

In a letter to the Editor of Heart Rhythm Journal in early January of this year he and his co-authors describe what happened:

Once the iPhone was brought close to the ICD over the left chest area, immediate suspension of ICD therapies was noted and persisted for the duration of the test

This is a big deal because “suspension of life-saving therapies” means that should the patient go into ventricular tachycardia or fibrillation during this time they would just drop dead without receiving a life-saving shock from the ICD.

Previous Advice and Evidence on Cell Phone/ICD Interaction

Patients with ICDs and pacemakers have long been given recommendations to keep cell phones more than 6 inches from their pacemakers due to concern about cell phone-emitted electromagnetic fields being misinterpreted by the devices as intrinsic cardiac electrical activity with subsequent inhibition of pacing activity or inappropriate activity. Patients are routinely instructed to use the ear opposite the pacemaker site and not to put the phone in a shirt or jacket pocket adjacent to the site.

However, these recommendations are based on studies performed decades ago and since then both cardiac device technology and cell phone technology has evolved and advanced and heretofore there has been no evidence for adverse interactions.

In fact reports of adverse interactions were so rare a 2017 paper in the Journal of the American College of Cardiology, tested the hypothesis that “technological advances may have rendered current recommendations obsolete.”

They tested (cell phone held directly above the implanted devices” in3 smartphones (Samsung Galaxy S3, Nokia Lumia, and HTC One XL) on 307 patients with implantable cardiac devices (52% ICD, 48% pacemaker from 8 manufacturers) and found only one device was affected by electromagnetic interference.

The authors concluded

We therefore suggest the current recommendation to maintain a 15-cm gap between phone and generator may be too stringent and thereby cause unnecessary apprehension.

A more recent study showed minimal risk of electromagnetic interference from ICDs and smartphones without a magnetic array. This study evaluated the interaction of iPhone 6 or Apple Watch (first generation) with “51 pacemakers, 5 cardiac resynchronization therapy pacemakers, 46 implantable cardioverter-defibrillators, 43 cardiac resynchronization therapy defibrillators, and 3 implantable loop recorders.”

With unusual prescience, the authors of the 2017 JACC study noted that “the rapid evolution of implantable cardiac device and mobile phone technology obliges us to be aware that such safety recommendations require continual re-evaluation.”

Magnetic Wrist Bands and ICDs

A case report in Heart Rhythm describes the wristband magnets in Fitbit and Apple Watch deactivating a Medtronic ICD up to distances of 2.4 and 2.0 centimeters, respectively.

A 55-year-old woman with history of sustained ventricular tachycardia secondary to arrhythmogenic right ventricular dysplasia was treated with a dual-chamber ICD for secondary prevention. She was recommended to avoid strenuous exercise to reduce arrhythmic risk. She subsequently purchased an Apple Watch with fitness tracking capabilities to monitor her heart rate, which she wore sometimes overnight. While asleep one night, she was awoken by several beeps emanating from her implanted cardiac device. Subsequent interrogation of the device showed no alerts or abnormal parameters. Upon further investigation, it was found that the device had reverted to magnet mode, owing to magnetic interference from the fitness watch’s wristband. No other possible sources of interference were identified. This was replicated in the office, where interrogation of the ICD confirmed magnetic reversion when placed in proximity to the wristband. The watch itself did not have magnetic interference.

Apple’s Response

On January 23/2021, three weeks after the Greenberg letter, Apple issued a confusing press release regarding the iPhone 12 and magnetic interference with medical devices:

Though all iPhone 12 models contain more magnets than prior iPhone models, they’re not expected to pose a greater risk of magnetic interference to medical devices than prior iPhone models.

Apple went on to give this advice:

Medical devices such as implanted pacemakers and defibrillators might contain sensors that respond to magnets and radios when in close contact. To avoid any potential interactions with these devices, keep your iPhone and MagSafe accessories a safe distance away from your device (more than 6 inches / 15 cm apart or more than 12 inches / 30 cm apart if wirelessly charging). But consult with your physician and your device manufacturer for specific guidelines.

Apple is implying that the iPhone 12 is no more likely to shutdown ICDs than other cell phones or that earlier iPhone versions have this capability but we didn’t know it. It is possible that any cell phone with wireless charging capabilities could interact with ICDs and pacemakers in the same manner.

Beware The Cell Phone Magnets If You Have an ICD or Pacemaker

If you are, like me, perpetually unaware of the location of my iPhone or my Apple Watch (whether on or off my body), it is highly likely they will not infrequently come within 6 inches of your left (or for some individuals right) upper chest region. Depending on your device this could render you unprotected from ventricular rhythm abnormalities (ICD) or put your pacemaker into an asynchronous pacing mode.

Phil Mar, an electrophysiologist at Saint Louis University School of Medicine, agrees that this is a significant new and heretofore unrecognized issue.

Our advice to patients with pacemakers or ICDs (or the future possibility of one) would be to not buy an iPhone 12 or a wearable wristband with magnets. In fact, Phil, would extend this to spouses of ICD patients since most couples sleep in the same bed.

This was not a problem with earlier iPhones without the array of magnetics and not seen with Apple Watch without the magnetic wrist bands but it is possible it extends to any cell phone with wireless charging.

It occurs to me that, the safest approach for patients would be to have their personal cell phone tested for interaction with their cardiac device by their cardiologist or electrophysiologist early after implantation. Such a check will become the norm for my patients.

-Peizomagnetically yours,


Special thanks to Phil Mar for his input.

After writing this post I encountered evidence on Twitter that the iPhone 12 can convert standard pacemakers to asynchronous mode.

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