An iPad 2 in close proximity of an implantable cardioverter-defibrillator (ICD) can trigger a magnet mode and potentially prevent therapeutic shocks, according to a study published online April 10 in the Journal of the American Heart Association.

Newer electronic devices such as Apple’s iPad 2 and other tablets coming on the market use magnets in the cover and frame. ICDs include a variety of magnetic sensors, observed Teri M. Kozik, PhD, RN, CNS, of St. Joseph’s Medical Center in Stockton, Calif., and colleagues, making the devices potentially vulnerable to electromagnetic interference when patients hold tablets close to their bodies.

“Unplanned static magnetic fields can potentially prevent therapeutic shocks, while induced current from RF [radiofrequency] signal sources may be incorrectly sensed as an arrhythmia and treated inappropriately,” they wrote.

This raises safety concerns, particularly as more tablets with magnets come on the market. To test the effect of the iPad 2 on ICDs, they enrolled 27 patients with various models of subcutaneous ICDs and monitored device function in various scenarios.

First they interrogated the ICD for baseline function and settings. Each participant held an open iPad 2 with its Smart Cover attached in a reading position, which varied from 12 to 18 inches from the ICD. The ICD was interrogated for one minute.

Each participant then reclined with the iPad 2 and placed it directly over his or her ICD. The researchers moved the tablet around the region of the implanted ICD to ensure all sites for a magnetic mode trigger would be tested. The ICD was interrogated again and researchers made sure it was functioning properly at the end of the visit.

Magnet mode was triggered on 33 percent of the participants. In two of those patients, the ICD was programmed off when the tablet was placed over it and it did not turn on again when the iPad 2 was removed. All magnet mode responses were reproducible. All of the patients with triggered ICDs remained in baseline rhythm and were not affected.

Kozik and colleagues detected no noise or oversensing from the iPad 2, and they found little difference in response based on the participant’s body mass index.

They proposed that the location of the magnetic sensor in the ICD may explain why some but not all of the ICDs were triggered by the iPad 2 magnets. The two patients whose ICD remained in the off mode had older Boston Scientific Vitality 1 ICDs.

“[A]s shown in this study, patients with older devices that develop a magnet mode trigger with an iPad 2 are at risk for untreated tachyarrhythmias, since their ICDs may remain off for an extended period of time,” they cautioned. Programming resumed in newer ICD models after the iPad 2 is removed.

Kozik et al recommended that patients refrain from placing iPad 2s directly on top of their ICDs. In certain older model ICDs, physicians should disable the “change tachy mode with magnet” feature for safety reasons. When implanting an ICD, physicians should turn on magnet mode monitoring. They also called for a larger study that includes more models and manufacturers of ICDs and other manufacturers of tablets.