With no published data examining the significance of computed tomography (CT) interference with cardiovascular implantable electronic devices (CIEDs) in real-world practice, a study published Feb. 26 in the Journal of the American College of Cardiology led by Ayman Hussein, MD, and a team of researchers at the Maryland Arrhythmia and Cardiology Imaging Group, University of Maryland, sought to assess the occurrence of these CT-related interactions mentioned in an U.S. Food and Drug Administration (FDA) advisory, and found that “the presence of cardiac devices should not delay or result in cancellation of clinically indicated CT imaging procedures.”

With their established ability to increase life expectancy, the use of CIEDs such as permanent pacemakers (PPMs) and implantable cardioverter-defibrillators (ICDs) have become increasingly commonplace on the worldwide stage. Because magnetic resonance imaging (MRI) can significantly interfere with the sensitive mechanisms of these instruments, CT scans had become the preferred method of investigating a patient’s inner anatomy.

In 2008 however, the FDA issued a public health notification warning that exposure to x-ray radiation during CT scanning could do just as much damage to patients with CIEDs as an MRI, bringing about unintended shocks, transient changes in a pacemaker’s output pulse rate, misinterpretation of signals produced by the x-rays as actual biological signals, and other malfunctions. For many in the medical community the FDA’s report and recommendations raised a number concerns, not from its findings, but from its lack of significant peer-reviewed evidence.

According to an editorial by Elena Arbelo, MD, PhD, and Josep Brugada, MD, PhD, Department of Cardiology, Thorax Institute, the FDA recommendations are based on "only two peer-reviewed publications with limited evidence of direct causality. In the study by Yamaji et al, six patients with an implanted pacemaker out of 11 showed transient lead over-sensing during a chest CT scan. Of note, none of these were associated to any clinically significant event. Both this report and one by McCollough et al, used in vitro phantom models to demonstrate the interaction of ionized radiation with CIEDs, but human studies of confirmed events were lacking. Notably, as shown by McCollough et al, only some CIEDs were sensitive to radiation exceeding certain dose rates and the interaction terminated immediately after the radiation beam moved of the region of the device. These authors could not provoke any permanent changes in the device programming."

Arbelo and Brugada add that "From a practical perspective, the observational design of the study by Hussein et al, may actually make this study results more, rather than less, important. The authors have validated in an everyday setting that pacemaker and ICD responses to radiation are transient and benign and that routine CT scanning on patients with CIEDs should not be restricted. The authors have to be commended for having undertaken such a study to clarify a clinical situation of major importance. To date, hundreds of thousands of patients have some sort of CIEDs during a CT scan, considering the widespread use of both, particularly in older patients. The risks associated with imaging procedures are small as compared with other risks. For instance, patients with a pacemaker or ICD, many require CT imaging for the evaluation of a lung tumor, during the evaluation of possible internal bleeding after car accident, etc. The relative risk from the natural course of any of these diseases as compared with the risk of imaging is remarkable."

Keywords: Accidents, Defibrillators, Implantable, Heart Rate, Life Expectancy, Magnetic Resonance Imaging, Maryland, Neoplasms, Pacemaker, Artificial, Phantoms, Imaging, Public Health, Tomography, Emission-Computed, Tomography, X-Ray Computed, United States Food and Drug Administration

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