Aug. 3, 2004 -- People with heart devices such as pacemakers and defibrillators have long been told to avoid magnetic resonance imaging (MRI) for safety reasons. But a new study shows that MRI may be safe for certain newer devices.
Scientists at Johns Hopkins University in Baltimore spent six months testing devices including nine pacemakers, 18 defibrillators, and 40 electrical systems connecting the device to the heart muscle with the most widely available scanner in the U.S.
The study's focus was to see if MRI interfered with the electrical impulses of the devices. The MRI scanner contains a strong magnet that is believed to cause pacemaker and defibrillator malfunction.
An artificial pacemaker is a small battery-operated device that can help control a regular rhythm to the heart's pumping. An electrical lead is placed on the heart and wires connect the battery-operated device to the heart lead.
A defibrillator is also an electrical device; it gives an electric shock to the heart when it pumps abnormally. By establishing a normal pumping rhythm, the heart can effectively deliver blood to the body organs. Abnormal electrical activity in the heart can lead to sudden death.
The results of the study show most modern devices are safe and perform well in both standard MRI scans and scans using electromagnetic fields at maximum strength.
"You can do a high-energy scan for a long period of time without doing any long-term damage to select devices," says the study's senior author, Henry Halperin, MD, MA, FAHA, professor of medicine, radiology, and biomedical engineering at Johns Hopkins University, in a news release. "These data suggest that certain modern pacemakers and ICDs [implantable cardioverterdefibrillators] may indeed be MRI-safe," write the authors.
Older ICDs, made before 2000, were damaged, but overall, "newer ICD systems and most pacemakers were unaffected," write the researchers. "This may have majorclinical implications for current imaging practices."
But before anyone with a heart device considers getting an MRI, caution should still be exercised. The study's authors write that MRI imaging should be a last resort for patients with heart devices. They suggest MRI scanning be used when all other noninvasive imaging tests don't work.
The researchers also write that patients would need to be fully advised about the potential risks associated with malfunctioning of these heart devices, which include death. A doctor knowledgeable about the device would need to be present during the MRI, blood pressure and other vital signs would need to be monitored during the scan, and the heart device would have to be programmed to "therapy off" during the scan and reprogrammed immediately after the MRI.
MRI is used for diagnosing cancer and cardiovascular conditions, as well as for guiding devices during some kinds of surgery. Heart device makers don't claim their products to be MRI-safe or compatible.
The study was done on dogs and in labs, not on humans. The study, which appears in the online edition of Circulation, was funded in part by heart device manufacturers Medtronic Corp. and St. Jude Medical Inc. Halperin is a paid consultant for Medtronic and co-investigator Ronald Berger, MD, PhD, is a paid consultant to Guidant Corp., which also had products in the study. Medtronic Corp. is a WebMD sponsor.