Tuesday, July 15, 2008

CT Scanners and Pacemakers

Well, the phone lines were jumping today. It seems the FDA has issued a "Preliminary Public Health Notification" that CT scanners might cause some medical devices, including pacemakers and defibrillators, to "malfunction:"
Most patients with electronic medical devices undergo CT scans without any adverse consequences. However, FDA has received a small number of reports of adverse events in which CT scans may have interfered with electronic medical devices, including pacemakers, defibrillators, neurostimulators, and implanted or externally worn drug infusion pumps. There have been similar reports in the literature.

It is possible that this interference is being reported more frequently now because of the increased utilization of CT, the higher dose-rate capability of newer CT machines, an increase in the number of patients with implanted and externally worn electronic medical devices, and better reporting systems.

We are continuing to investigate this issue while working with device manufacturers and raising awareness in the healthcare community. To date, no patient deaths have been reported from CT scanning of implanted or externally worn electronic medical devices.
Specifically, for pacemakers, the effect has been described only as "transient changes in pacemaker output pulse rate."

Recall that pacemakers must sense existing heartbeats and respond with pacing when no signals are detected. If the pacemaker or defibrillator senses outside signals, it might interpret that "noise" as a biologic signal and respond accordingly. So, if a pacemaker senses outside "noise" and interprets it as a biologic signal, it might briefly inhibit pacing. If a defibrillator senses such "noise" as a biologic signal, it might either inhibit pacing or, if the noise detected is of a sufficiently high frequency for long enough, it might respond with an attempt to correct the rhythm by rapid pacing or a shock (depending on how the defibrillator was programmed).

From the FDA's announcement, it appears the problem primarily occurs when a high radiation dose is emitted from the scanner directly over the device - and this is usually only a brief phenomenon. Whether is is a new finding, or just better reported, remains to be seen (I suspect the latter).

The biggest impact of this announcement will be for device companies and EP nurses, doctors, and technicians - since the implication from this disastrous "early notification" is that we might have to check every pacemaker or defibrillator after every CT scan performed (you've got to be kidding me!).

The lack of guidance for heart rhythm specialists by the FDA and the Heart Rhythm Society in this regard is stunning and warrants review. It seems the Heart Rhythm Society just parrots the FDA's announcement. Perhaps it was because maybe it's not such a big deal after all:
MedSun is the FDA's Medical Product Safety Network of 350 hospitals spread throughout the United States. Information from 132 of these facilities indicated that they have not experienced any CT medical device interference, while 3 have had from 1 to 3 events that may have been CT scan induced. Fifteen MedSun facilities indicated they take some precautionary steps when CT scanning patients who have electronic medical devices.
In short, this seems like a "cover your ass" move by the FDA that threatens to potentially scaremonger our patients.

I guess thanks to the Congressional oversight these days, when it comes to such notifications, the FDA is damned if they do and damned if they don't.



Anonymous said...

I got the Cardiosource notification the other day and was awaiting your review!
Thanks for cutting thru the BS and getting to the meat of the matter.

I agree re: (you've got to be kidding me!). If we had to interrogate every patient who got a CT scan we'd be in radiology a large part of the day.

BTW, what is your policy re: pts going to the OR for routine surgical procedures? Say they have a permanent pacer (not necessarily ICD) implanted and are going for hernia repair or chole. Do you interrogate everyone after electrocautery?


DrWes said...


BTW, what is your policy re: pts going to the OR for routine surgical procedures? Say they have a permanent pacer (not necessarily ICD) implanted and are going for hernia repair or chole. Do you interrogate everyone after electrocautery?

Briefly, our OR patients present unique challenges in the management of their pacers and defibs. Each is handled slightly differently: pacer-dependent patients are seen pre-op and reprogrammed DOO (or VOO) to force pacing and inhibit sensing from their device. Post-op, devices are interrogated and programmed back to their original settings. ICD therapies are usually NOT turned off, but rather a magnet is used to suspend detection in case it's needed in the OR (except in cases of head and neck surgery, where the ability to get to the device is compromised - then we program the device off and the patient is not removed from telemetry until the device is reprogrammed back on). GI endoscopies are NOT routinely interrogated post-procedure (data exist regarding this approach).

That's a brief summary (but in no way inclusive), but we do check most devices post-op after electrocautery to assure no power-on reset modes, etc.

Hope that helps.

Anonymous said...

Yes, it does. Thanks.
I went today to our tertiary referral center where our ICDs are implanted. The EP attending offered to contact his Medtronic people arrange a mini-ICD course for me. He also offered to allow me to participate in his ICD clinic for 1-2 weeks for hands on training. Quite tempting, but it is 2 hours away from home and I'd have to find a dog sitter for 2 weeks. I used to be an EP lab RN in the mid 90s when the Jewel was still investigational, so have some basic knowledge, but have likely forgotten more than I remember. Having me familiar with interrogation would help them a lot, so we'd bug them less :)

Rogue Medic said...

Now that they are publicizing this, will there be more reports that come in of device "irregularities" during CT?

I know that they are supposed to be reported, but how many have not been reported to the FDA.

Anonymous said...

As a CT Technologist and Vendor Applications Specialist I have seen this occur twice in eleven years of cardiac scanning, and once for a lumbard spine with a neuro stimulator. My first occured 4 years before the FDA alert and now just recently. I am quite amazed on how few people know of this potential malfunction of medical devices in CT.