FROM THE NEW ENGLAND JOURNAL OF MEDICINE
Nonthoracic MRI was safe in patients who had implanted non–MRI-conditional pacemakers or implantable cardioverter defibrillators, as long as they followed a specific safety protocol before and after the imaging procedure, according to a report published online Feb. 23 in the New England Journal of Medicine.
Patients with implanted cardiac devices have long been advised to avoid MRI because of the potential for the magnetic field to induce heating of the cardiac leads, which could in turn produce thermal injury to the myocardium and adversely affect the device’s function. Certain cardiac devices that have been proved to pose no such hazards have been designated by the Food and Drug Administration as “MRI conditional.” However, an estimated 2 million patients in the United States and another 6 million worldwide have devices that are not MRI conditional, and at least half of these patients are predicted to require an MRI during their lifetimes, said Robert J. Russo, MD, PhD , of Scripps Research Institute and the La Jolla (Calif.) Cardiovascular Research Institute, and his associates.
The MagnaSafe Registry was established to monitor device-related clinical events and device alterations among adults undergoing nonthoracic MRIs at 1.5 T. Dr. Russo and his associates analyzed data in this registry from 19 medical centers during a 5-year period. They assessed 1,000 MRIs in 818 patients with pacemakers and 500 MRIs in 428 patients with implantable cardioverter defibrillators who were followed for 6 months after the imaging procedures. Most of these scans involved the brain or spine, and the median duration of exposure to the magnetic field was 44 minutes.
According to the safety protocol, all devices were interrogated immediately before the MRI and, depending on those results, were programmed to no pacing or asynchronous pacing during the scan with all tachycardia and bradycardia therapies inactivated. Immediately after the scan, all devices were reprogrammed to baseline settings, a full device interrogation was repeated, and, if necessary, further reprogramming was performed to maintain adequate pacing and sensing. A physician, nurse practitioner, or physician’s assistant with cardiac expertise attended each scan.
There were no deaths, lead failures requiring immediate replacement, losses of capture, or full electrical resets associated with any of the 1,500 MRI scans.
Four patients developed atrial fibrillation, and two developed atrial flutter, during or after the MRI; three returned to sinus rhythm while still in the scanning room, and the other three did so within 49 hours. There were six cases requiring partial generator electrical resets. “Changes in device settings were common, but relatively few exceeded our prespecified threshold criteria for a clinically important change,” Dr. Russo and his associates wrote ( N Engl J Med. 2017;376[8]:755-64 ).
Four patients reported feeling discomfort at the implant site during MRI, including one who felt a heating sensation and was removed from the scanner before completing the procedure. None of them had any further problems.
Some experts have suggested that to allow patients with cardiac devices to undergo MRI, the generators and leads could be removed before the procedure and replaced afterward. The findings of this study show that undergoing a nonthoracic MRI using this protocol would likely be a safer alternative, the investigators added.
This work was supported by St. Jude Medical, Biotronik, Boston Scientific, the Hewitt Foundation for Medical Research, and several philanthropic gifts. Dr. Russo reported ties to St. Jude Medical, Biotronik, Boston Scientific, and the Hewitt Foundation, and his associates reported ties to numerous industry sources.
