A Prospective Pediatric Clinical Trial of Digital Music Players: Do They Interfere with Pacemakers?

Christine C. Chiu, M.Sc.; June Huh, M.D., Ph.D.; Laura De Souza, B.Sc.; Armando Alfaro-Ramirez, M.D.; Robin Clegg, M.D.; Laura Fenwick, B.Sc.; Robert M. Hamilton, M.D., M.H.Sc.; Joel A. Kirsh, M.D.; Gil J. Gross, M.D.; Dongsheng Gao, Ph.D.; Elizabeth A. Stephenson, M.D., M.Sc.


J Cardiovasc Electrophysiol. 2009;20(1):44-49. 

In This Article


Patient Recruitment

The Hospital for Sick Children research ethics board approved this study, which was not sponsored by industry. Patients who attended pacemaker or ICD clinic during the period of August 2007 to February 2008 were invited to participate in this study. We calculated that a sample size of 70 patients was required to detect pacemaker interference at a rate of 10% at the 0.05 level of significance, with a power of 80%.[4] Written informed consent was obtained, and the study was conducted after routine pacemaker follow up assessment and programing.


The study comprised testing at least two types of DMP in each patient. The iPod™ (Apple Computer Inc., Cupertino, CA, USA) DMP had a 30 GB hard drive, while the Sansa™ (SanDisk Corp., Milpitas, CA, USA) DMP was an MP3 player with a 4 GB flash memory. Patients were also encouraged to bring their own DMP or other portable electronics for testing.

Pacemaker and ICD Settings

In our practice, the usual programmed pacemaker sensing configuration was bipolar, atrial sensitivity setting ranged from 0.3 to 1.0 mV, and ventricular sensitivity setting ranged from 2.0 mV to 2.8 mV. For Medtronic pacemakers capable of high-rate data collection, the high-rate detection was temporarily set to 80 bpm and the counter was cleared prior to the study. For St. Jude Medical pacemakers, the high-rate data collection was not adjusted from nominal as they do not allow data collection less than 175 bpm. All ICDs studied had dedicated bipolar sensing usually programmed at 0.3 mV, and the maximal sensitivity tested during the study was 0.15 mV. We did not make any attempts to change the ICD tachycardia detection limits for the study but rather relied on the marker and electrogram (EGM) data to show interference information such as oversensing, artifacts, or tachycardia detection.

Test Protocol

At the end of routine pacemaker clinic assessment, DMP testing was performed. Patients were continuously monitored by a 6-lead ECG. The order of testing DMPs was randomized. Initial testing was conducted at the patient's usual programmed pacemaker settings. During continuous ECG recording and with the programmer wand away from the patient, the DMP was placed directly over the pacemaker pocket and turned on in "play" mode for 5 seconds then turned off. This sequence was repeated three times to test the reproducibility of response. Due to time constraints, testing without the programmer wand over the pacemaker was conducted only at the patient's usual pacemaker settings as this most simulates the clinical scenario. Subsequent testing was then repeated with the programmer wand positioned 1 cm adjacent to the DMP, this distance was maintained by a small 1 cm plexiglass block for consistency. The EGM and marker data were recorded continuously along with ECG. Care was taken to ensure that stable telemetry was obtained prior to start of testing as well as maintaining a constant position of the programmer wand. The next set of tests was conducted after adjusting the pacemaker to the maximal sensitivity setting in bipolar configuration, and then in unipolar configuration. For patients known to have sensing abnormalities in a particular sensing configuration, only the usual programmed setting was tested for the study. If interference of pacemaker function was seen, then testing was repeated by positioning the DMP 6 inches above the pacemaker pocket without any changes in the position of the programmer wand. The 6 inches distance was maintained throughout by a custom-made plexiglass block.

Additional testing was conducted for patients who brought in their own DMP, cellular telephones, or portable electronic games. These were tested at the patient's usual programmed pacemaker settings. Cellular telephones were placed directly on top of the pacemaker pocket, turned on, dialed out a call followed by receiving a call. Electronic game units were placed directly over the pacemaker area, turned on to the "play" mode. This portion of the study was performed for the patient's interest and was not analyzed due to variability of the portable electronics tested.

Outcome Measure

The primary outcome measure was pacemaker interference defined as any one of the following associated with the use of DMP: inhibition of pacing, inappropriate pacing, oversensing, or detection of high-rate episodes.[3] The secondary outcome measure was interference with programmer telemetry associated with the use of DMP as evidenced by loss of telemetry, presence of artifacts on the EGM, or corrupted marker data.

Statistical Analysis

Descriptive summary statistics are reported, continuous variables are presented as mean ± standard deviation (SD). The Chi-square or Fisher's exact test was used to compare proportion of differences in pacemaker interference by grouping DMP based on memory storage technology: hard drive versus flash memory. P value of <0.05 was considered statistically significant.


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