Precautions when performing high dose x-ray examinations of patients with implanted electronic devices
(Computed Tomography; lateral exams of the hip, lower spine, or abdomen)
On July 14th, 2008, the FDA issued a Public Health Notification regarding possible malfunction of electronic medical devices caused by CT.
While CT scanning can affect the function (behavior) of such devices, most often very transiently, in general, it is safe for patients with these devices to undergo CT examinations in which the device moves briefly (less than 3 seconds) through the x-ray beam as occurs in most clinical CT examinations. About 60,000,000 CT scans are performed in the USA every year and many of these implantable cardiac rhythm management devices have been in use for several years and yet there have been no reported deaths or life-threatening clinical adverse consequences from this effect. The effects of CT on devices have been carefully studied in a phantom model for only one manufacturer and the occasional effects encountered were transient and unlikely to be symptomatic. Reference citations are found in the FDA notification.
Medical professionals should become aware of this effect and how to recognize it and report these incidents to the FDA.
These devices include cardiac pacemakers, cardioverter-defibrillators, neurostimulators, and insulin pumps. The problems only occur when the device is within the direct x-ray beam. They are due to the radiation interacting with the electronics in the devices and producing electric currents that can cause a temporary malfunction while the device is in the x-ray beam. Problems are more likely when using single-location dynamic scanning, perfusion scanning, or CT fluoroscopy directly over the device because this prolongs the time that the device is exposed to the radiation. Extra caution should be exercised when performing these procedures. Only the electronics in the device are radiation sensitive, the leads or wires are not. The device itself cannot be damaged by the radiation. Problems that occur with these devices appear to be rare and do not seem to be a threat to the health or life of the patient. At this time, the following procedures should be used for each of these devices when performing the listed exams:
For All Devices
Ask the patient if they have any implanted electronic devices and then check the CT scout view for the presence of any devices. Observe the patient for any adverse effects and report these effects. The only exams for which there is any concern are those in which the device is within the direct x-ray beam. For example pacemakers will not be affected by any head scans.
Cardiac pacemakers, cardioverter-defibrillators (Computed Tomography)
These devices must not be turned off during the exam. Inform the patient before the scan that rarely a CT scan may cause a subtle reprogramming of the device and if they have any physical symptoms indicating that this may have happened they should have the device’s operation and settings checked by a cardiologist. Observe the patient for any adverse effects after the scan and take and record the patient’s heart rate after the scan, if the patient is symptomatic. In CT cardiac imaging, try to avoid including the device within the radiation field.
Neurostimulators (Computed Tomography)
There have been reports of patients receiving shocks from these devices during a CT scan when the device was not turned off. None of the patients sustained injuries from the incidents. Our policy is that the devices do not need to be turned off for a conventional CT scan, since the risk to the patient is extremely small. The patient should be observed for any adverse effects, during and immediately after the CT scan. However the risk to the patient may be greater if multiple sequential scans are performed at the same location over the device. Thus consultation with the physician responsible for the neurostimulator should be done before any CT perfusion studies are performed if the device will be in the x-ray beam, otherwise arrange to perform the exam so that the device is not within the x-ray beam. There is no problem if only the leads are in the x-ray beam.
Insulin pumps (Computed Tomography; lateral exams of the hip, lower spine, or abdomen)
Many insulin pump manufacturers recommend that patients not expose the pump to X-rays. We need to avoid any inadvertent administration of insulin due to an x-ray exposure. Please remove or turn off the patient’s insulin pump off during the X-ray examination, or shield or position the pump outside the primary beam.
Conclusion
Any event that is recognized should be reported to the FDA. Employing methods to decrease the probability of a symptomatic event may be prudent, but those who perform CT examinations should be aware that based on our current knowledge, the risk of an adverse clinical event is remote.