Patients with a non-MRI conditional pacemaker or implantable cardioverter defibrillator (ICD) who received a nonthoracic MRI had no occurrences of death, lead failures, losses of capture or ventricular arrhythmias, according to a prospective registry analysis.

Lead researcher Robert J. Russo, MD, PhD, of the Scripps Research Institute in La Jolla, California, and colleagues published their results online in the New England Journal of Medicine on Feb. 22.

St. Jude Medical, Biotronik, Boston Scientific and the Hewitt Foundation for Medical Research funded the study.

The researchers noted that there are potential safety concerns with using MRIs in patients with pacemakers or ICDs, including the potential for magnetic field-induced cardiac lead heating. Thus, doctors and medical societies often recommend that patients with pacemakers or ICDs not undergo MRI scanning.

The FDA has recently began labeling cardiac devices as MRI conditional if they reduce the risks associated with MRIs. However, the researchers mentioned that two million people in the U.S. and an additional six million people worldwide use non-MRI conditional cardiac devices.

In this study, the researchers examined patients who were implanted with a non-MRI conditional pacemaker or ICD, were part of the MagnaSafe registry and were referred for clinically indicated nonthoracic MRIs at a field strength of 1.5 tesla.

They evaluated nonthoracic MRIs that were performed at 19 U.S. centers from April 2009 through April 2014, including 1,000 pacemaker cases (818 patients) and 500 ICD cases (428 patients). Three-quarters of the MRIs were performed on the brain or spine, and patients spent an average of 44 minutes in the magnetic field. The researchers tested the devices at a strength of 1.5 tesla but reprogrammed some of the devices based on a prespecified protocol.

“If the patient was not dependent upon their pacemaker, the device was turned off,” Russo said in a news release. “If they could not tolerate having the device turned off, it was set to a pacing mode that did not sense cardiac activity. The reason was that the pacemaker could sense the electrical activity (radiofrequency energy) from the MRI scanner and the function of the device could be inhibited, which could be catastrophic if you depend upon your pacemaker for your heartbeat.”

During the MRIs, there were no deaths, lead failures requiring immediate replacement or losses of capture in patients who were appropriately screened and had their device reprogrammed for imaging.

In addition, four patients had atrial fibrillation and two patients had atrial flutter during or immediately after the MRI. Further, five patients with pacemakers and none with ICDs had partial generator electrical reset.

The researchers acknowledged the study had a few limitations, including that the registry included generators and leads from multiple manufacturers. The study also excluded patients who were younger than 18 years old, those who had MRIs of the thorax and pacing-depending patients with an ICD.

The researchers plan on conducting a follow-up study and examining the risk for patients who need a chest scan at 1.5 tesla or an MRI of any anatomic area at 3.0 tesla.

“Patients with a standard or non-MRI-conditional pacemaker can undergo clinically indicated MRI without harm if a protocol such as the ‘MagnaSafe’ protocol used in this study is followed and patients are screened and monitored as described,” Russo said in a news release.