MRI Safe for Those With Pacemakers, Defibrillators

The finding applies only to recent models of these implanted devices, however

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TUESDAY, March 8, 2005 (HealthDay News) -- Contrary to widespread belief, individuals with implanted pacemakers or defibrillators can, in many cases, safely undergo magnetic resonance imaging (MRI) scans, researchers conclude.

But they stress that this finding probably only applies to pacemakers or defibrillators made within the last seven years, and that the MRI machine should be set to a relatively low level of energy output.

Currently, more than two million Americans have implantable heart devices, and exerts have long thought it unsafe for these patients to have the scans, which rely on magnetic energy.

During their four-month study, the Johns Hopkins Medical Institutions researchers tested 18 different pacemakers and 15 implantable defibrillators in 33 patients undergoing 38 separate MRI scans. MRI energy levels were lowered and the devices' pacing programs were adjusted.

All the patients and devices were closely monitored during the MRI scans, some of which lasted up to 90 minutes, in order to assess any possible problems, such as heating of the electrical leads in the devices or in the tissue surrounding the devices.

Repeat measurements were made, on average, 24 days after the MRI scans in order to assess whether the patients experienced any long-term complications. The study found no such complications.

Based on the findings, the Hopkins team developed new guidelines for the use of MRI scans on people with implantable heart devices. Those guidelines warn that only modern devices, mostly those made within the last seven years, are safe in MRIs. The guidelines also call for low-energy-level MRI scans for patients with implantable devices. MRI scan settings higher than two watts per kilogram may result in overheating of the device, the experts conclude.

Close monitoring by a cardiologist and radiologist are advised and MRIs should only be used when clinically necessary and when alternative diagnostic tests are not recommended, the guidelines state.

The study was to be presented Tuesday at the American College of Cardiology scientific sessions in Orlando.

More information

The National Library of Medicine has more about pacemakers and defibrillators.

SOURCE: Johns Hopkins Medical Institutions, news release, March 8, 2005

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