Friday, July 30, 2010

When your ICD’s reed switch fails.

But first, what’s a reed switch?



Implantable defibrillators have a built-in tiny reed switch that is activated whenever a magnet is placed over the device. The presence of a magnetic field near the reed switch causes it to close and tells the device to temporarily suspend tachycardia detection and therapy.

For as long as the magnet is over the device, no shocks are delivered to the patient in case of ventricular tachycardia (VT) or fibrillation (VF). Once the magnet is removed, the switch opens again, restoring the device’s ability to deliver shocks.

This is a particularly useful feature during surgical procedures where electrocautery is used. Electrocautery and certain other types of surgical tools may cause the ICD to deliver unnecessary shocks due to oversensing.

Figure: magnetic reed switch.


The bad news:

Last week, Boston Scientific announced that the reed switch in some of their ICDs might get permanently stuck. It goes without saying that a jammed reed switch in your ICD would not be good, since it would preclude the delivery of potentially life-saving shocks.

Boston Scientific says that the affected ICDs were manufactured during 2006 and 2007 and include the CONTAK RENEWAL models 3 and 4, and the VITALITY DR HE. Affected devices are no longer available for implant, but there are still about 34,000 people out there with these devices.

To know if you have one of these devices, go to Boston Scientific’s online “Device Lookup Tool” and enter your device’s model and serial numbers. These numbers can be found in your medical device ID card.

Boston Scientific says that the risk of harm is remote and that no deaths or injuries have been reported. A PDF of this current advisory can be downloaded here.

Now, the good news:

Boston Scientific ICDs (and CRT-Ds) can be programmed to recognize a magnet or to ignore it altogether. So, in the unlikely event that your device’s reed switch gets stuck, your doctor can program the ICD to ignore the defective switch and the device will no longer inhibit tachycardia therapy.

Also, it’s good to know that the ICD will emit audible tones (synchronized to your heart beat) whenever the reed switch is closed or in the event it needs to tell you something is wrong. So, if the device is beeping, have it checked out right away.

More information, including copies of the letters to physicians and patients can be viewed and downloaded from the Heart Rhythm Society's web site.

Image from here.

3 comments:

RJD said...

Now the bad News:

"Now, the good news: Boston Scientific ICDs (and CRT-Ds) can be programmed to recognize a magnet or to ignore it altogether. So, in the unlikely event that your device’s reed switch gets stuck, your doctor can program the ICD to ignore the defective switch and the device will no longer inhibit tachycardia therapy."

I would not allow such a device in my body. I have had a lead go bad and the ICD uncontrollably tried to shock even every 30 seconds. This is not an entirely rare event, note the recent St. Jude recall for that very lead. The ER room people see these events and have for years. This was moderated to once every several minutes by a St Jude magnetic that failed to fully disarm the defective magnetic switch. Consequently over the course of half an hour I received two dozen wrong, dangerous, painful and psychologically terrifying shocks (let's call them what they are and dispense with the marketing fog of "therapies"). ICDs can be very harmful devices that need powerful controls to inhibit them as well as positive controls to fire them. That which does not save you, may instead kill you instead. Let's have truth in advertising.

aygun said...

I recomend everyone to se this :

Implantable defibrillator teardown

http://www.youtube.com/watch?v=Gzw6c3Bi4TU

You will see that the modern ICD's have tiny Hall effect sensors. This kind of switches turn the device in comunication mode .

Also see this :

Pacemaker Teardown
http://www.youtube.com/watch?v=o8RY0l1s6aA

Cheers !

aygun said...

Just see this :

Implantable defibrillator teardown
http://www.youtube.com/watch?v=Gzw6c3Bi4TU

Pacemaker Teardown
http://www.youtube.com/watch?v=o8RY0l1s6aA

The new ICD's have instead reed switches some HALL effect sensors .

HALL effect sensors are much safer because they are need for directional magnetic field .

http://www.electronics-tutorials.ws/electromagnetism/hall-effect.html