SNOWMASS, COLO. — The everyday, 21st century electronic communications environment poses unprecedented electromagnetic interference hazards for patients with pacemakers or implantable cardioverter defibrillators, Dr. William H. Spencer III cautioned at a conference sponsored by the Society for Cardiovascular Angiography and Interventions.
“What are you going to tell your patients in 2006 regarding smart phones and other wireless communication devices such as PDAs, wireless computers, and iPods?” asked Dr. Spencer, professor of medicine at the Medical University of South Carolina, Charleston.
And those are just the out-of-hospital exposure issues. Many other electromagnetic interference (EMI) hazards confront implanted cardiac device wearers in the medical environment. (See story above.)
Pacemakers can respond to EMI in unwelcome ways: complete inhibition of pacing, asynchronous pacing, rapid pacing, mode reset to a very safe pacing mode, or physical damage to the generator and/or pacing leads.
Implantable cardioverter defibrillators may deliver an inappropriate shock or antitachycardia therapy or—even worse—be inhibited from delivering therapy when needed. Device memory can be corrupted, making it impossible for physicians to reconstruct what happened when the device encountered EMI.
The important thing to know about EMI due to wireless communication devices is the 10-cm rule. All implanted cardiac devices now incorporate internal filters that are highly effective in rejecting all but the strongest electromagnetic signals—those originating within about 10 cm of the device or leads. For this reason patients shouldn't carry their cell phone in a shirt or breast pocket. The power level, which fluctuates during a call, is highest immediately before and during ringing.
Patients also should hold the phone to the ear farthest from the device, which is typically the right ear. However, studies show most patients don't consistently do this, probably because they're right-handed and want to use that hand for writing or driving while talking on the phone.
The exception to the 10-cm rule involves later-generation wireless computers. They tend to have higher power at the antenna, according to Dr. Spencer.
Walk-through metal detectors used in airport screening are safe provided the patient moves briskly through. Heart devices contain very little ferromagnetic material and shouldn't trip the alarm. But if the alarm does go off, under no circumstances should the patient submit to a search using a hand-held wand over the chest; far better to be thoroughly searched by hand.
Electronic article surveillance systems used in stores to prevent shoplifting can also cause problems. “The patient should be instructed to walk rapidly through the gate and not to tarry. Vendors should not put any distractions in the area of the gate. If you tarry around one of these things, you may have an adverse event,” the cardiologist continued.
EMI is really not an issue in the home provided electrical devices are properly grounded. Microwave ovens are safe.
However, arc welding—not just found in the workplace but, surprisingly, among do-it-yourselfers—creates tremendous EMI and should be avoided. Other industrial equipment needs to be approached on a case-by-case basis.
It's sometimes necessary to ask the medical device manufacturer to provide a technical consultant to conduct a comprehensive workplace EMI evaluation, said Dr. Spencer, who holds stock in Medtronic and Boston Scientific.