Boston Scientific Product Advisory: Magnetic Reed Switch Performance in Certain Implantable Defibrillators
Boston Scientific Corporation has issued "Dear Doctor" letters (PDF, 160K) to convey important patient management information regarding CONTAK RENEWAL® 3 / 3 RF / 4 / 4 RF and VITALITY® HE implantable defibrillators manufactured between January 2006 and November 2007.
In rare instances, application of a magnet (typically in a clinic/hospital environment) may cause a magnetic reed switch located within the device to become permanently stuck in a closed position and prevent delivery of programmed tachy therapy. No patient deaths or injuries beyond device replacement have been reported as a result of this issue. CRT-Ds and ICDs currently being distributed are not subject to this advisory. Full details can be found in the following documents:
Description
Some Boston Scientific defibrillators include a component referred to as a “magnetic reed switch,” designed to sense the presence of a magnet. If Enable Magnet Use is programmed to On (nominally On) and a magnet is applied in emergent situations or during a medical/surgical procedure, the switch is designed to close and temporarily prevent delivery of undesired tachy therapy. When the magnet is removed, the magnetic switch is designed to open and thereby restore ability to deliver programmed tachy therapy.
Magnetic reed switch technology has historically demonstrated a very low but non-zero rate of failing to open upon magnet removal. However, certain Boston Scientific CRT-Ds and ICDs manufactured between January 2006 and November 2007 have exhibited a somewhat higher rate of magnetic reed switch failure. Approximately 34,000 of these devices remain actively implanted; no devices in this population are available for implant. Devices manufactured after November of 2007 have returned to historic performance rates and are not included in this advisory.
Clinical Implications
No patient deaths or injuries have been reported as a result of this issue, although some devices have been replaced. Most devices with a magnetic reed switch confirmed to be stuck in a closed position have remained implanted after Enable Magnet Use was programmed to Off .
Recommendations
Consistent with physician instructions for use and patient manual labeling, physicians should continue routine follow-up sessions and patients should be reminded to contact their clinic or go to the hospital emergency room immediately if they hear tones/beeps from their device. In addition, Boston Scientific recommends:In a hospital/clinic/surgery setting, if tones are heard upon magnet application but do not cease upon magnet removal, the device should be interrogated with a programmer and checked per normal standard of care.
- In the United States, use of the LATITUDE remote patient monitoring system may help identify loss of daily measurements and thereby facilitate timely detection of a stuck reed switch. [NOTE: A pop-up message and/or LATITUDE alert do not appear for missing Daily Measurements.]
- If a stuck magnetic switch is confirmed, program the Enable Magnet Use feature to Off, which ensures that programmed therapy will be provided to treat tachyarrhythmias. However, if Enable Magnet Use is programmed Off:
— A magnet will no longer inhibit tachy therapy.
— The Patient Triggered Monitor feature will no longer be available.
Boston Scientific Technical Services (phone information below) can help physicians re-activate Daily Measurements for devices with a stuck magnetic switch.
- After consultation with our independent Patient Safety Advisory Board, Boston Scientific does not recommend prophylactic explant. We further advise that physicians do not routinely program Enable Magnet Use to Off in the absence of a confirmed stuck magnetic reed switch because the benefits of magnet use to disable tachy therapy in emergent situations outweigh the probability of patient harm associated with a stuck reed switch.
Further Information
Quarterly updates for all product advisories are provided in the company's CRM Product Performance Report, found at www.bostonscientific.com/ppr. A search tool is also available to determine if a specific device is affected by this issue. Questions should be directed to local Boston Scientific representative, United States Technical Services at +1 (800) 227-3422, or European Technical Services at +32 2 416 7222.
