Study challenges FDA’s stance on CT risks to implanted devices

An FDA advisory warning that CT imaging may interfere with cardiac rhythm management devices may have overstated the risk, based on a retrospective study of 516 scans. The analysis, published online Feb. 26 in the Journal of the American College of Cardiology, found radiation to the devices did not result in any clinically significant events.

In 2008, the FDA issued a notification that exposure to radiation from CT imaging may interfere with the functioning of pacemakers and implantable cardioverter-defibrillators (ICDs), leading to inappropriate shocks, transient changes in pacemaker output pulse rates and other potential problems. The agency recommended keeping a physician on hand in case of an emergency and checking the device after CT imaging.

The imaging community responded that the FDA based its warning on limited peer-reviewed evidence and that the recommendations might undermine the quality of patient care, increase costs and divert resources. In 2013, the FDA updated its advisory and eased up on device checks and limited the need for a staff physician’s availability to continuous scans over devices of several seconds.

Ayman Hussein, MD, of the Cleveland Clinic, and colleagues designed their study to provide evidence about CT imaging interference in real-world practice. They identified 516 CT scans performed at two large centers between 2000 and 2010 on 386 patients where cardiac rhythm management devices were directly exposed to radiation. The study included 132 ICDs and 184 permanent pacemakers and represented a variety of manufacturers, protocols and radiation doses.

The composite endpoint was death, bradycardia or tachycardia requiring termination of the scan or an immediate intervention, unplanned hospital admissions, reprogramming of the device, inappropriate defibrillator shocks, or device replacement/revision thought to be due to CT imaging. The secondary outcome was changes in devices’ parameters, which was assessed using a control group as well as an imaged group.

Hussein et al did not find evidence of the primary outcome in any patients who underwent CT scans. They found no significant differences in changes in battery voltage or lead parameters from baseline to follow-up interrogations between the scan group and the control group. They noted potentially significant changes in device parameters in a small number of devices in both groups but found no definitive link to CT scans and none of the changes resulted in clinical events.

“Extrapolation from the previous FDA concerns would suggest that patients undergoing cardiac studies would be at increased risk,” they wrote. “However, no primary clinical outcomes were noted in our study, regardless of the type of CT, supporting that these studies are not associated with higher clinical risk. Advances in CT scanner technology have also further mitigated the radiation effects of CT studies.”

Their findings suggest that device reprogramming and inappropriate shocks with CT imaging are not common in routine practice, contrary to the FDA’s revised warning, and that checks after scans may not be necessary as long as there is no suspicion of dysfunction. They recommended physicians take a “prudent approach” for longer, continuous scans of pacemakers.

The study is limited by being retrospective and observational, they acknowledged, but the results provide real-world evidence for regulators in a re-evaluation of interference from CT radiation in patients with cardiac rhythm management devices.