Right now, people who have a heart pacemaker implanted in their chest cannot undergo a magnetic resonance imaging (MRI) scan. Although pacemakers are miracle machines that do a good job of maintaining an acceptable heart rate, the devices are believed to be too delicate to withstand the MRI's high-strength electromagnetic field. It's feared that the electromagnetic force might overheat or displace an implanted pacemaker's wires, or damage its electronics, or even injure the heart muscle itself.
This is unfortunate because some have estimated that at least half of the people with implanted pacemakers could benefit from an MRI scan at some future time. MRI scans have become an invaluable, commonly used diagnostic test for abnormalities of the brain, spine, joints, liver, and other organs.
Heart pacemakers are most often implanted in people whose heart rate is so slow that they are in danger of losing consciousness. More recently, pacemakers have been used to manage heart failure. As a result, millions of Americans have implanted pacemakers, and the numbers of new implants have averaged about 225,000 per year over a recent 5-year period.
Although it will not help those with a pacemaker presently in place, future patients may be able to get MRI scans if a newly developed and improved device (called the EnRhythm system) gets FDA approval. Recently, Dr. Bruce L. Wilkoff from the Cleveland Clinic Foundation gave MRI scans to 211 patients with the EnRhythm pacemaker and found no adverse effects to the patients or the machines. The MRI machines used in Wilkoff's randomized clinical trial, however, were operating at reduced scanner strength.
More hopeful news: Other studies have recently shown that MRIs can be safely done in individuals fitted with certain new pacemaker models that can be temporarily reprogrammed, using a scanner with a much weaker electromagnetic field. At this time, however, the Food and Drug Administration (FDA) has not rated any pacemakers, even these reprogrammable ones, as MRI-safe.
And, should these devices be approved after careful testing, patients will still require close monitoring throughout the MRI procedure.
Fortunately, people with implanted pacemakers or defibrillators are able to safely undergo diagnostic tests using computed tomography (CT), another powerful scanning technique.
