A patient walked into the office of Dr. Luis Scott at the Mayo Clinic with a concern about the safety of his hybrid car. The patient’s question: Is it possible that electromagnetic interference from the car’s powerful electric motors could set off the patient’s implantable cardiac defibrillator and affect his heart’s rhythm—or even stop his heart?

Dr. Scott and his colleagues from the Mayo Clinic set out to answer his patient’s question, and what they found was reassuring…but not 100%.


An implantable cardiac defibrillator (ICD) is just what it sounds like—a small electrical device, surgically implanted, that automatically discharges an electrical shock to a patient’s heart, when needed, to restore normal heart rhythm. It’s most often used in people at high risk for sudden cardiac arrest from chaotic, dangerous heart arrhythmia. (For more info on ICDs, click here.) But if an ICD is subjected to electromagnetic interference from another device, the ICD may confuse that interference with a distress signal coming from the patient’s heart, and it may discharge an unnecessary shock. These shocks are not only painful, they might cause damage to the heart or even trigger an irregular and dangerous heartbeat.

Devices that can conceivably interfere with an ICD include cell phones, MP3 players, high-tension wires, metal detectors, electrical generators and industrial welders—so the concerns about hybrid cars expressed by Dr. Scott’s patient were not far-fetched. As more people buy hybrid (and pure electric) vehicles that rely on powerful motors for locomotion, ICD interference from the cars could, in theory, be a real problem not just for people driving the cars, but also for passengers, mechanics and anyone nearby.


At the Mayo Clinic, Dr. Scott enrolled 30 patients with ICDs—including at least several devices from each of the three major ICD manufacturers—to take turns sitting in a 2012 Toyota Prius Hybrid. The Prius was selected because it is the hybrid car most driven in the world (and the type owned by the patient who inspired Dr. Scott’s study). The car was lifted off the ground so its drive wheels could spin freely, simulating real-life driving speeds.

Participants took turns sitting in the driver’s seat and in the front and back passenger seats, and they also stood outside the car in the front and back—all while they were hooked up to a device that could measure any interference caused by the car’s electric engine and detect any irregularities in ICD function. Each position was evaluated when the car was idling…”driving” at 30 mph and 60 mph…and accelerating and decelerating at various rates.

Finish line: The researchers found that the levels of electromagnetic interference from the car were safe—they were lower than the limits set by the device manufacturers and regulatory agencies, and there were no episodes of inadvertent changes to any ICD’s functioning.

Would the same hold true for other models of hybrids and all-electric cars (which tend to use more powerful motors), as well as for people with other types of implanted electrical devices, such as pacemakers? Dr. Scott said that it is possible that this would be the case, though of course additional testing is needed to determine this. For now, based on his study, Dr. Scott was at least able to reassure his patient that the danger of electrical interference while driving, riding in or being near a Prius seems to be minimal, if it exists at all.