Cosmic Rays Affect Older ICDs

The background levels of atmospheric ionizing radiation, commonly known as cosmic rays, can affect the memory chip in a small number of its older-generation implantable cardioverter defibrillator (ICD) products, according to St. Jude Medical, Inc. (St. Paul, MN, US).

After extensive investigation, including testing at an independent nuclear laboratory, St. Jude has found that a particular static random access memory (SRAM) chip can be affected, at a low frequency rate, by background levels of atmospheric ionizing cosmic radiation. To date, the incidence of devices found to have been affected is only 60 out of 36,000. An estimated 26,000 devices remain in service.

This particular memory chip component was used in the following older generation devices: Photon DR (model V-230HV; certain serial numbers), Photon Micro VR/DR (models V-194/V-232), and Atlas VR/DR (models V-199/V-240). Although the incidence is low and there have been no serious patient injuries or deaths reported, St. Jude is taking a conservative approach in advising the medical community and regulatory agencies. In 2002, St. Jude began using a different design of the SRAM memory chip component, which does not share the same susceptibility to cosmic radiation.

"Because the incidence associated with this anomaly is low, St. Jude Medical's recommendation for monitoring at three-month intervals will be appropriate for the vast majority of patients,” said Dr. Bruce Wilkoff, director of cardiac pacing and tachyarrhythmia devices at The Cleveland Clinic and Heart Center and a member of the St. Jude medical advisory board.

A full copy of the company's advice to doctors can be found on St. Jude's website. This includes a description of the anomaly and its related risks as well as recommendations to doctors for patient monitoring.




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