Pacemakers, Defibrillators, and Hybrid Cars

With the interest and popularity of going "green" with hybrid cars (even with a select few of my fellow physician-bloggers) I thought it would be worthwhile to share a few tidbits about the potential for electromagenetic interference between hybrids and pacemakers or defibrillators. (Heck, maybe they'll need this info when they get older and have their pacer installed...)

There's been some recent reports of people returning their Toyota Prius or Camry Hybrid, Lexus GS450h, or other newer hybrid cars due to fears over interference with these cars' "smart keys" (which detect when the key is within three feet of the car) and pacemakers or automatic defibrillators. It seems these cars' smart key antennas transmit at frequencies of between 119 and 135 kHz with a relatively low power. Still, because of the wonders of physics, if a pacemaker or defibrillator were sufficiently close to one of these antennas, then there could be the potential for interference. But is there enough of a risk to trade back in a car?

Once again, it seems more devices are being developed out there than the pacemaker and defibrillator device manufacturers can test sufficiently to assure that nary an issue exists with outside electromagnetic interference. One only needs to look at the recently popularized iPod interference issues or the disclaimers on the Nintendo's Wii gaming system to see how far the hysteria can go.

So before more scary press releases occur, I called some pretty smart "engi-nerd" types from the manufacturers (Note: I use the term "nerd" here with respect, since I are one) to find out a bit more about the potential for excitement in people driving hybrids with pacemakers or defibrillators. Here's the basic gist:

Medtronic: Hybrid Cars: Cars that are powered, at any one time, with either batteries, gasoline or both.

"Gasoline engine: Maintain a 12" (30 cm) distance from the components of the ignition system of the gasoline engine and the Pacemaker or ICD. If closer than 10" (30 cm), there is the potential for Pacemaker reversion or inhibition and for ICD shock.

Electric power components: The DC/AC current used to power the electric motors and the permanent magnets associated with the motor operation can affect the Pacemaker or ICD. Maintain a 24" (60cm) distance between the electric motor and the implanted device. If the device is closer than 24" (60cm), there is the potential for Pacemaker reversion or magnet rate operation or disabling of ICD detection circuit or ICD shock."

St. Jude Medical:

"Cardiac pacemakers are electronic devices with sensing circuits designed to detect small electrical signals from the heart. Pacemakers may detect extraneous electrical signals from sources other than the heart and incorrectly interpret these signals as heart activity. Inhibition of the pacemaker, resulting in no output pulse to the patient's heart or reversion to asynchronous pacing may result. At this time we have no reports of large-scale electrical motors or generators affecting our pacemakers. However, this does not mean there is a total absence of affects related to electric motors of several hundred horsepower. Extraneous radiated noise from large-scale electrical motors will not cause damage to your pacemaker. If large-scale electrical motors do affect the pacemaker, inhibition or reversion to asynchronous pacing may potentially occur. Some patients can tolerate reversion to asynchronous pacing or some inhibition of their pacemaker. Any problems caused by radiated interference will end when the electrical interference ends or the patient leaves the immediate area. The risk of working with large-scale electrical motors may be reduced to an
acceptable level by observing proper techniques. Working on the motors with the power “OFF” will avoid electrical interference. In the power generating plants I have visited, the large motors and generators have been grounded and shielded which minimized the radiation of electrical noise."

Boston Scientific:

They recommend a 9 inch (22 cm) clearance from a smart key to any of the antennaes on hybrid cars. This more conservative distance was recommended by the Japan Association of Medical Equipment Industries' (JAMEI)(a la, Toyota) rather than Boston Scientific. It seems they are still in the process of their own testing. Boston Scientific's recommendations regarding smart keys and their devices, with diagrams of where the transmitting and receiving antennaes are housed, can be found on Boston Scientific's website (pdf file).

In summary with smart keys, there seems to be a consensus that the risk of interference with pacemakers or defibrillators is low, especially if the smart key is not left near the device (i.e., in a shirt pocket). Most felt the power of these "keyless" devices was sufficiently low (like the iPod, Wii, or cell phones) to limit concerns over their interference with pacemakers or defibrillators provided some common-sense distance precautions were maintained.

Regarding interference with the electric motor components of hybrid cars, two manufacturers have recommendations regarding being too near the engine and that operating a hybrid car should be quite safe, as long as the operator with a pacemaker or defibrillator does not try to become the mechanic for their own car.

-Wes