Well, to be fair, Chien probably just read the iPad user guide, where the warning is plainly written:
iPad has magnets along the left edge of the device and on the right side of the front glass, which may interfere with pacemakers, defibrillators, or other medical devices. The iPad Smart Cover and iPad Smart Case also contain magnets. Maintain at least 6 inches (approximately 15 cm) of separation between your pacemaker or defibrillator and iPad, the iPad Smart Cover, or the iPad Smart Case.
Strong magnets (and not just those on an iPad) can affect defibrillators in several ways -- first, they can put the devices into a test mode that increases the heart rate depending on how much battery life is left in the defibrillator. Second, the defibrillators are designed to be shut off by magnets as a safety precaution. The iPad that Chien used was an iPad 2, which triggered the test mode in 30 percent of patients who put the tablet onto their chest.
While the Bloomberg article and headline provided some titillating reading, Chien didn't "discover" anything. Instead, the 14-year-old and her cardiac electrophysiologist father Walter just used 26 volunteers to test how commonplace the iPad magnet effect is. If Chien should be lauded for anything, it's waking the public up to actually reading those user guides and safety warnings that we all ignore on a regular basis.
In the meantime, if you have a defibrillator or pacemaker implant, don't put the iPad on your chest. Ever.