Boston Scientific Plagued by Another Defibrillator Advisory

Just what Boston Scientific (BSX) didn't need was another advisory about their defibrillators: this one regarding prolonged charge times on the Vitality and Assure defibrillator (ICD) lines and the Contak Renewal biventricular cardiac resynchronization defibrillators (CRT-D) during their middle of life indicators.

This advisory occurred in Europe. The text of the advisory reads as follows:

The MHRA has received 31 reports of early explants from four of the above device models (1870, 1871, 1872, A135) during the middle-of-life (MOL) phase. Replacement has been due to observation of premature elective replacement / end of life indicators (ERI/EOL), caused by long capacitor charge times. The MHRA has also become aware of confusion about ERI/EOL indicators throughout implant duration.

Incident reports have included devices displaying:

• extended charge times where no replacement / end of life indicators have been observed
• ERI where charge times have extended beyond 26 seconds giving rise to potentially inappropriate therapy delay for some patients
• EOL indicators with charge times in excess of 30 seconds without ERI being observed in the first instance.

Boston Scientific ICDs / CRTDs are designed to regularly monitor both battery voltage and capacitor charge time, and flag ERI when specified limits are exceeded. Charge time ERI is flagged whenever two charges (capacitor reform or therapeutic shock) occur within a 24hr period in which both exceed the specified limit. Increase in charge time (due to a rise in battery impedance) is an expected behaviour of ICDs that have lithium-silver-vanadium-oxide batteries. However, early batteries used in some of the above models have a tendency to exhibit a more exaggerated increase in battery impedance during the MOL phase, due to a battery manufacturing anomaly.
Boston Scientific has confirmed that the above models have been programmed with temporarily extended ERI charge time limits during the MOL (middle of life) phase (compared to unaffected models). This is to prevent premature tripping of ERI due to the battery impedance characteristic. In January 2007, Boston Scientific issued a product update about this issue via their website. The company issued a more detailed and informative product update about this problem in March 2007. The MHRA is issuing this Medical Device Alert to ensure that all UK clinicians who implant these devices, or manage patients already implanted with these devices, are aware of Boston Scientific’s communication and can therefore consider the clinical implications of long charge times that may be inappropriate for some patients.

Action:
• Be aware of:
- extended capacitor charge times during device MOL phase, as documented in the most recent Boston Scientific product update (see the MHRA’s website for March 2007 issue)
- the higher prevalence of long charge times in earlier manufactured devices (see Appendix 2 below)
- the potential for earlier manufactured devices to pass from ERI to EOL in less than three months.
• At the next scheduled follow-up, review capacitor charge time history and evaluate the appropriateness of charge time according to patient condition and device dependency, giving priority to those who have not been followed up within the last three months (see Appendix 1 below).
• Consider the risks (infection etc) and benefits of elective device replacement where capacitor charge time is judged to be inappropriate for an individual patient.
• Consider scheduling future patient follow-ups at three monthly intervals – where the device is around MOL, to increase the likelihood of detecting longer charge times, early ERI and/or EOL as appropriate.
• Consider programming the ‘Beep When ERI is Reached’ feature to ‘ON’ (default) for all affected patients.
• Remind patients to contact their follow-up centre immediately if they hear beeping from their device and/or experience arrhythmias/resumption of symptoms that remain uncorrected by the device.
• Consult the Boston Scientific website for future related product updates.
• Report all instances of device failure to the MHRA and Boston Scientific.
• Report explants to the National Pacing and ICD Database.

For non-medicos: check with your doctor if you have one of the above ICD models. Fortunately, no deaths or significant injury have occurred with this advisory.

-Wes