Evidence is mounting that MRI scans may be safe for people with pacemakers or implanted defibrillators, according to the latest study on the issue that appeared in the American Journal of Cardiology.
Manufacturers currently warn against putting the devices into MRI scanners, whose strong magnetic field might in principle cause the metal wires from the devices to heat up and burn heart tissue. This could also upset the electrical properties of the delicate devices.
For the study, Robert Russo and colleagues at Scripps Clinic in La Jolla, California, reviewed medical records for 109 patients with pacemakers or implantable cardioverter-defibrillators. Each had undergone one or more medically necessary MRIs such as scans to look for brain tumors.
The devices were turned off during the scans or, if the patients didn't have a viable heartbeat without them, set to a constant rhythm that wouldn't be upset by the scanner's magnetic field.
There were no deaths, no device failures and no heart rhythm disturbances in any of the patients. While there were slight changes in the electrical measurements before and after the scan, they weren't deemed big enough to have any impact on the patients.
"A small number of clinically relevant changes in device parameter measurements were noted," Russo and his colleagues wrote. "However, these changes were similar to those in a control group of patients who did not undergo MRI."
Russo said the findings are not definitive and need to be confirmed in a bigger study, but he and others noted that more and more centers have started doing MRIs on patients with heart devices if there are no other good alternatives.
"With this study, and the several studies prior, there are really no clinically relevant changes that occur in 99.9 percent of the devices that get scanned," said Christopher Kramer, a spokesperson for the American Heart Association (AHA), who was not involved in the study.
Although U.S. health regulators have already approved one MRI-compatible pacemaker, thousands of patients still live with older models. Between 50 and 70 percent of those might eventually need an MRI, Russo said.