Music may speak to the heart, but it should do so via the ears:
that's the message from a new analysis showing that while iPod MP3
players do not interfere with pacemakers or implantable cardioverter-
defibrillators (ICDs), their headphones can. Physicians who tested
eight popular brands of headphones used with iPod devices say that
while the potential for interference differed among the headphones,
the message is the same.

"Because exposure of a pacemaker or defibrillator to portable
headphones can result in interaction between the two, we recommend
that pacemaker or defibrillator patients not allow portable
headphones to be near their device," senior author Dr William Maisel
(Beth Israel Deaconess Medical Center, Boston, MA), told
heartwire. "Enough headphones have enough magnetic field strength
that we believe that our recommendations apply to all portable
headphones; they do not apply to one particular brand or one
particular model."

But authors of the study, who spoke with heartwire during the
American Heart Association 2008 Scientific Sessions, say that the
problems arise only if people place the headphones directly over
their devices, less than 3 cm away.

"So patients shouldn't place them in a front shirt pocket or in a
front jacket pocket, and they shouldn't allow someone wearing
headphones to rest their head on their chest," Maisel
commented. "But if the headphones are kept a reasonable distance
away, we found no interaction. . . . It's fine for patients; in fact
we encourage patients to enjoy their music and listen to it in their
ears, but they shouldn't take off their headphones and drape them
around their necks so that the earbuds dangle over the chest."

Maisel, with first investigator Dr Sinjin Lee (Beth Israel Deaconess
Medical Center) said they were motivated to look at iPod headphones
in the wake of stories in 2007 addressing the potential interference
caused by iPods and other MP3 players. "We were skeptical that there
would be an interaction between MP3 players and defibrillators, but
we also know that portable headphones contain magnets--magnets are
used in speakers to vibrate and make noise that we listen to," and
magnets are a known cause of device interference," Maisel said.

When Music Speaks to the Heart

What they found is that while two iPod brands (the Shuffle and the
Nano) caused no interference with either pacemakers or ICDs, 14 out
of 60 patients (23%) experienced device interference from close
contact with headphones. Types of interference ranged from
inappropriate (asynchronous) pacing in four out of 27 pacemaker
patients to inhibition of ICD detection in 10 out of 33 ICD
patients. Close contact with headphones actually caused device
reprogramming in one patient.

Of note, measured magnetic field strength varied considerably
between headphone brands and was highest with clip-on type
headphones such as the Sony MDR Q22 LP and Phillips SBC HS430. For
the Sony clip-on headphones, the magnetic field strength at 2 cm was
20 G and over 300 G at 0 cm; a magnetic field strength of just 10 G
can interact with a pacemaker or defibrillator, Maisel noted.

The key, said Maisel, is that magnetic field strength falls off very
rapidly with distances, although physicians and patients should be
aware that headphone magnetic field strength is "on" whether the MP3
player is on or off and whether the headphones are attached to the
MP3 player or not.

But he also emphasized that as long as patients are aware that
headphones contain magnets, the risk is minimal. "Pacemaker and
defibrillator patients are told when they get their device and they
are repeatedly reminded not to expose their device to magnets. So
they're used to that message. The real message here is that portable
headphones have magnets in them, and if that message got out,
patients and doctors would know what to do from there. So I don't
think patients are particularly alarmed, nor do I think they should
be," Maisel said. "The other thing to remember is that as soon as
the headphones are removed from the device, the device function
returns to normal."

First author Lee also added that just because patients with these
types of devices tend to be older, physicians shouldn't assume
they're not hip enough to have an iPod or other MP3 player. "We
became interested in this because a lot of patients do ask us about
these things. A lot of our patients are older, but a lot of people
do have [digital music players] or they have family members and
grandchildren who use them a lot."

Commenting on the study for heartwire, Dr Kenneth A Ellenbogen
(Medical College of Virginia, Richmond) also urged an appropriate
reaction from patients with cardiac devices. "It's not a real issue,
clinically speaking. Yes, the magnetic field that headphones make--
some brands from some manufacturers--can be significant, but you
have to take your headphones off your ears and put them right over
your device. If somebody falls asleep and happens to have one of
these earphones and puts them over their device and then sleeps for
a couple of hours, this could potentially be a problem. But the take-
home message is, wear your headphones on your head, and don't put
them in your breast pocket."