Of Special Interest to Electrophysiology and Cath Lab Staff/HeartNet
MedSun: Newsletter #24, May 2008

Low Frequency Magnetic Emissions and Resulting Induced Voltages in a Pacemaker by iPod Portable Music Players

By Howard Bassen (FDA)
BioMedical Engineering OnLine. February 2008, Volume 7.

Abstract

Background
Recently, malfunctioning of a cardiac pacemaker electromagnetic, caused by electromagnetic interference (EMI) by fields emitted by personal portable music players was highly publicized around the world. A clinical study of one patient was performed and two types of interference were observed when the clinicians placed a pacemaker programming head and an iPod were placed adjacent to the patient's implanted pacemaker. The authors concluded that "Warning labels may be needed to avoid close contact between pacemakers and iPods". We performed an in-vitro study to evaluate these claims of EMI and present our findings of no-effects" in this paper.

Methods
We performed in-vitro evaluations of the low frequency magnetic field emissions from various models of the Apple Inc. iPod music player. We measured magnetic field emissions with a 3-coil sensor (diameter of 3.5 cm) placed within 1 cm of the surface of the player. Highly localized fields were observed (only existing in a one square cm area). We also measured the voltages induced inside an 'instrumented-can' pacemaker with two standard unipolar leads. Each iPod was placed in the air, 2.7 cm above the pacemaker case. The pacemaker case and leads were placed in a saline filled torso simulator per pacemaker electromagnetic compatibility standard ANSI/AAMI PC69:2000. Voltages inside the can were measured.

Results
Emissions were strongest (˜ 0.2 µT pp) near a few localized points on the cases of the two iPods with hard drives. Emissions consisted of 100 kHz sinusoidal signal with lower frequency (20 msec wide) pulsed amplitude modulation. Voltages induced in the iPods were below the noise level of our instruments (0.5 mV pp in the 0 – 1 kHz band or 2 mV pp in the 0 – 5 MHz bandwidth.

Conclusion
Our measurements of the magnitude and the spatial distribution of low frequency magnetic flux density emissions by 4 different models of iPod portable music players. Levels of less than 0.2 µT exist very close (1 cm) from the case. The measured voltages induced inside an 'instrumented-can' pacemaker were below the noise level of our instruments. Based on the observations of our in-vitro study we conclude that no interference effects can occur in pacemakers exposed to the iPod devices we tested.

Additional Information:

Low Frequency Magnetic Emissions and Resulting Induced Voltages in a Pacemaker by iPod Portable Music Players. Bassen, Howard. BioMedical Engineering OnLine. February 2008, Volume 7.

http://www.biomedical-engineering-online.com/content/7/1/7


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