Monday, December 04, 2006

Pacemaker, Defibrillators, and "Killer Magnets"

Bloggers learn to love and hate the media. On one hand they help disseminate information, but when it is done poorly, misinformation can be worse than the news they intend to spread. Such is the case when headlines read like 'Fridge Magents "Can be a killer."'

So what are they talking about? First of all, Johnny Everyman is not likely to be struck down by refrigerator magnets. What clever Swiss researchers (published in the December issue of Heart Rhythm) did is note that when the more powerful, readily-available magnets made from neodynium-iron-boron (NdFeB) magnets of sufficient size (0.8-1.0 cm) are placed within three centimeters of a pacemaker or defibrillator, it can effect a special magnetic switch inherent to all of these devices. Since some jewelry is being manufactured with these strong magnets (and I am aware of newer magnetic name tags that might be placed near the device), then the pacemaker or defibrillator might be affected.

So what happens?

Pacemakers and defibrillators contain a small "reed switch" that is sensitive to magnetic fields that allows patients and their doctors an opportunity to affect their device to perform specific functions outlined below.

In the case of pacemakers, the activated reed switch tells the pacemaker to pace, irrespective of the person's underlying rhythm, at a specific rate (determined by the manufacturer of the pacemaker). When the rate changes, this tells doctors how much voltage is left in the person's pacemaker, and uses the paced rate to act like a battery meter, telling doctors when the pacemaker battery voltage is getting low. It does NOT inhibit pacemaker output. (Oh, there will be some wise guy that says that pacing that does not synchronize with one's heart rhythm could land in the "vulnerable period" of the cardiac cycle and induce an abnormal rhythm (and yes, that can occur), but magnet checks are done tens of thousands of times a day in the US and I have never heard of someone dying from this with conventional pacemakers).

In the case of a defibrillator (that treats abnormally fast and slow heart rhythms), the reed switch acts slightly differently. Again, a magnet over the person's defibrillator does NOT inhibit pacing at all. In the case of a defibrillator, a magnet over the device that is powerful enough to trip its reed switch will suspend detection of rapid heart rhythms while the magnet is over the device. In the case of this article, this will only happen if a magnet is held within three centimeters of the device. That's only 1.5 inches, folks. In other words, one of these fridge magnets or pieces of jewelry would have to be held virtually right over the device to have any effect. Certainly, if the person had the unfortunate luck that a rapid heart rhythm occurs when a magnet of sufficient strength is over the device, then the device would not detect this rapid heart rhythm and it could be fatal. But the odds of that happening are very, very low. Remember, most of us don't attach refrigerator magnets to our chest. And the titanium can that makes up a pacemaker or defibrillator is not magnetic, so even if a person with a defibrillator tried to place a refrigerator magnet on their, it wouldn't stick. Carrying a refrigerator magnet in your hand is much farther than three centimeters from the device. So before you rush to replace all of your refrigerator magnets, take heart, you can still use them and will live to tell about it.

I think this study is interesting and warrants consideration for pacemaker and defibrillator patients, but a healthy dose of reality and awareness needs to temper the lethal hysteria generated by the investigator’s comments and the press’s eagerness to promulgate hysteria in the interest of improving readership.


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