New Data Begs FDA Rethink of CT Scan Warning on Cardiac Devices

Shelley Wood

February 26, 2014

BALTIMORE, MD — Back in 2008, the US FDA issued an advisory warning physicians that CT imaging tests might interfere with electronic devices, including pacemakers and implantable cardioverter defibrillators (ICDs). That warning, however, was based on scant published evidence from real-world practice.

Now, five and a half years later, researchers who reviewed 10 years' worth of CT scans at their hospitals have found no signs of potential interference from CT imaging on implanted electronic cardiac devices[1].

Their findings are published today in the Journal of the American College of Cardiology along with an editorial charging that the FDA may have been "reckless" in issuing the public-health advisory in the first place, potentially deterring patients from undergoing scans that could have picked up problems far more serious than the potential—and seemingly unproven—risks to their devices[2].

Speaking with heartwire , senior author on the study, Dr Timm Dickfeld (University of Maryland, Baltimore), suggested that the FDA likely had access to unpublished case reports or other information that "crossed their internal threshold" and triggered the action. But the wording of its advisory was "unfortunate," he said: too detailed and prescribing actions that didn't correlate well with what radiology practices were already doing.

Dickfeld, with Dr Ayman Hussein and colleagues (University of Maryland), note in their paper that the FDA's 2008 recommendations include having a physician ready to take emergency measures to manage adverse events, as well as checking the device before and after CT imaging to make sure it's functioning properly. Such measures "have the potential to affect quality of care by avoiding medically necessary CT scans as well as diverting healthcare costs by implementing safety policies and procedures that have not been demonstrated to be appropriate or necessary," they write.

A Decade's Worth of CT Scans

For their review, Hussein and colleagues looked at all patients with pacemakers and ICDs who underwent CT imaging between July 2000 and May 2010 at two high-volume hospitals—a total of 516 scans. They found no instances of death, bradycardia, or tachycardia requiring termination of scan or an immediate intervention and no unplanned hospital admissions, device reprogramming, inappropriate shocks, or device replacement or revision due to CT imaging.

Potentially significant changes in device parameters were observed in a small group of devices, but these were seen both in the CT group and in a control group that had not undergone CT imaging. "No definitive link to CT was confirmed, and there were no associated clinical consequences," the authors write.

Despite the FDA advisory, most patients undergo CT imaging without any special considerations for their cardiac rhythm devices and without routine device interrogations, suggesting that clinicians may not be heeding the FDA warnings. To do so, write Hussein et al, would be logistically challenging and costly, particularly given the exploding numbers of people with implanted devices, as well as the numbers sent for CT tests.

The accompanying editorial takes an even stronger stand. "We believe the FDA was overreacting when issuing the 2008 alert," Drs Elena Arbelo and Josep Brugada (University of Barcelona, Spain) write.

Physicians, they point out, are already accustomed to making risk/benefit decisions every day. In the case of a patient with an implanted cardiac rhythm device referred for a CT scan, the benefits may well exceed the risks. "For instance, patients with a pacemaker or ICD [may] require CT imaging for the evaluation of a lung tumor, during the evaluation of possible internal bleeding after a car accident, etc. The relative risk from the natural course of any of these diseases as compared with the risk of imaging is remarkable."

Unfortunately, regulatory agencies "when trying to guarantee the safety of a product . . . often neglect the potential of benefit," Arbelo and Brugada conclude. "We count on these regulatory agencies to provide us with a well-defined profile of both potential toxicity and efficacy, based on solid evidence."

A Softer Stance

In March 2013, the original FDA advisory was updated, no longer emphasizing routine device checks and now specifying "that a staff physician should be available when the CT involves scanning over the device continuously for more than a few seconds," Hussein and colleagues note.

But the possibility of device reprogramming and inappropriate shocks are still mentioned in the advisory, and those may not be warranted, given this new evidence, the authors observe.

To heartwire , Dickfeld characterized the FDA update as "softened" wording but added that he's unaware of what new evidence may have prompted the FDA's updated advice. As of yet, he says, the FDA has not directly contacted him and his colleagues about their study, although investigators have presented some of the data at medical meetings.

"The advisory itself is still out there," he said. "I hope our study can close the loop a bit and provide some assurance to physicians and also to patients. We don't know what the effect was of this advisory, but we do know from our own colleagues that there was a significant amount of uncertainty."

Dickfeld disclosed receiving consulting and grant support from Biosense Webster and grant support from General Electric. Study coauthors, as well as Arbelo and Brugada, disclosed having no conflicts of interest.

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