Hair dryers, electric drills and other household appliances can cause pacemakers to fail under certain circumstances.

A study published Monday exposed 119 people with pacemakers to a variety of electromagnetic fields. It simulated the effects of electric razors, table fans, washing machines, vacuums, mixers, lawn mowers and other household appliances, along with the effect of standing near a power line or electrical substation.

The study found that when a strong magnetic field with high power – such as a hairdryer – is close to the chest, then the interference can affect the pacemaker, said author Dr. Andreas Napp, cardiologist at RWTH Aachen University Hospital in Germany.

People could experience heart palpitations, dizziness or fainting during electromagnetic interference with their pacemakers, although the effects generally subsided once the source of interference was removed, Napp said.

Most interference can be avoided if people with pacemakers maintain “a forearm’s length” — more than 12 inches — from household appliances or tools, Napp said, adding that any appliance that plugs into an electrical outlet emits electromagnetic fields.

People who work near large electrical transformers or manufacturing equipment may need to have their pacemakers reprogrammed, he added.

Pacemakers are a small, battery-operated device with wires threaded into the heart and are used to regulate a person’s heartbeat. In the U.S., more than 225,000 are implanted annually.

During the study, researchers set the pacemaker sensitivity to minimum and vendor’s recommended levels for each level of exposure. They upped electromagnetic field strength to the maximum allowed by German law until the pacemakers showed signs of interference.

At electromagnetic fields of 50 Hz to 60 Hz, the amount emitted by most U.S. appliances, more than a third of people with pacemakers at maximum sensitivity and more than 4 percent at nominal sensitivity experienced interference.

The interference for 114 pacemakers with bipolar lead wires was: nearly 72 percent set to maximum sensitivity showed signs of interference, and more than a third at nominal sensitivity when tested at maximum levels. Bipolar lead wires have two electrode sensors.

Researchers used a “worst case scenario” approach that simulated electrical appliances or tools being held very close to the chest, even if the devices are unlikely to be used that way in real life.

“Very, very few household items pose a risk to patients with pacemakers or ICDs,” said Dr. Kenneth Ellenbogen, an electrophysiologist and chief of cardiology at Virginia Commonwealth University Medical Center, who was not involved in the study. “This is much more of a theoretical concern and other than carrying one’s cell phone in a shirt pocket on the opposite side of the implanted pacemaker or defibrillator nothing else need be recommended.”

Prior research showed mobile phones placed on the chest near an implanted pacemaker or defibrillator, or while pacemakers are being programmed, could interfere with the heart devices.

“Powerful magnetic fields like at power plants or industrial settings and the MRI scanners” are more likely to interfere with pacemakers, said Ellenbogen.

“These occurrences are so rare that they are interesting to study how they actually occurred.” Napp pointed out that not every electromagnetic interference with pacemakers poses a risk for patients, which does not mean that there is no interference as pacemakers do not continuously record its occurrence.

This study was different from prior studies of interference because it exposed participants to a variety of electromagnetic field strengths, thus allowing to provide an individual interference threshold. Other studies typically have measured interference from only one type of device.

Napp said that continuous testing is important for electric cars, or other tools that have not yet been tested.

“It remains an important topic and of interest as new devices are developed and newer technologies have the potential to interfere with implanted devices,” said Ellenbogen.