With summer approaching, researchers caution that swimming pools may pose a
risk to patients with irregular heartbeats who've received implantable
The issue: a danger that electrical currents linked to standard pool
utilities such as lighting may "leak," causing a defibrillator to misread the
status of a patient's heart.
Implanted cardioverter defibrillators continuously monitor and control a
patient's heart rhythm.
"How common this is, we don't know," said Dr John Day, second vice president
of the Heart Rhythm Society, a group representing arrhythmia specialists. "It's
quite possible that there's underreporting going on, because when we see
patients and we see noise recorded on their device we can't account for where
it's coming from."
The concern stems from a few recent incidents that have been documented. In
two cases, people with defibrillators experienced device misreadings while in a
private family or hotel pool, and in another two cases, people experienced
unwarranted shocks from their defibrillators while in public pools.
The cases all involved younger arrhythmia patients between the ages of 8 and
23. However, the investigators said there's no reason to believe that patients
of all ages would not face a similar risk if they had such devices.
"I don't want to be an alarmist, because I do think we would have heard about
this sort of thing happening much more often than we have if it were a really
widespread problem," said study lead author Dr Daniel Shmorhun, a pediatric
cardiologist-electrophysiologist with Children's Cardiology Associates, an
affiliate of the Dell Children's Medical Center of Central Texas in Austin.
"The nice thing about defibrillators is that they put a time-stamp on all
activity," he noted. "So we were able to ask questions and delve into this after
two patients came in with interference noise on their devices. And we found that
both had been in pools at the time their defibrillators read the
Shmorhun and co-author Dr Arnold Fenrich are slated to present their findings
at the Heart Rhythm Society meeting taking place this week in Denver. Findings
presented at medical meetings are typically considered preliminary until
published in a peer-reviewed journal.
Arrhythmia is a chronic condition in which the heart's electrical system has
the potential to go awry - on occasion beating too fast, too slow, or
irregularly. While many instances of arrhythmia pose little harm, severe cases
can be life-threatening.
For such patients, implanted defibrillators can be life-savers, continuously
surveying a patient's heartbeat for signs of trouble and instantaneously
correcting for problems as they arise by sending out a corrective electrical
In the new study, Shmorhun and Fenrich reviewed the cases of two female
patients (one aged 8 years and one aged 23 years), in which their defibrillators
registered so-called "noise reversions" directly linked to time spent in
In each case their devices picked up the reversion, classified it as an
outside interference, reverted to a mode that actively ignored noise, and
thereby prevented any accidental shock.
After the lighting system was repaired in the family pool in which the
8-year-old had swum, the girl did not experience any further defibrillator
trouble, the researchers said. The older patient, however, simply decided to no
longer use public pools, and has experienced no further problems.
Others were not so lucky. For example, in the past year a 21-year-old male -
a competitive college swimmer and lifeguard - experienced not one but two shocks
while swimming in a public pool. "He remembers that he had his back against the
pool wall, quite close to lights in water," said Shmorhun. "And as he was moving
away from the light he got shocked."
Shmorhun and Fenrich believe that low-level electrical current leaking from
swimming pool wiring might be an "under appreciated cause" of unwarranted
"Water is an attractive source for electrical activity," Shmorhun explained.
"We don't think there would be an issue at all in, say, the ocean or bay. But in
a pool, where you have wires coming into the water from the outside, from the
house, from an ageing utility system, or an improperly grounded system, there is
a potential for this kind of problem. Or if a pool is not properly bonded -
meaning the pool circumference is not intact - there could be a problem," he
"I'm not sure anybody can really predict up front what pools are an issue,
and there's no practical means by which to easily test pools for this," Shmorhun
added. "At the same time, we don't know the overall incidence, although three
cases in the Austin area in one year seems like a lot to me. But at minimum,
[defibrillator] patients need to be counselled about the risk."
For his part, Heart Rhythm Society vice president Day said the finding should
not deter patients from swimming.
"We want our cardiac patients to be physically active. We don't want to
restrain them and we don't want to create alarm," Day said.
"But in each of these cases we had these underwater pool lights that had an
alternating current pool leak that could trigger a shock," noted Day, who is
also director of Heart Rhythm Services at Intermountain Medical Center in
Murray, Utah. "So, I think we certainly need pool safety. And clinically this is
just one more thing that should be considered as a potential source of a problem
for any patient with an implantable defibrillator."
Find out more about heart arrhythmias at the US
National Heart, Lung, and Blood Institute.