MRIs, Heart Implants Can Coexist Safely

Study still urges caution for those with pacemakers, defibrillators

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HealthDay Reporter

MONDAY, Aug. 2, 2004 (HealthDayNews) -- Experimental research is challenging the longstanding rule that forbids magnetic resonance imaging (MRI) for people with implanted pacemakers and defibrillators.

But the finding won't lead to an immediate change in medical practice, said Dr. Henry R. Halperin, leader of the group reporting the research in the Aug. 3 issue of the journal Circulation.

"What our studies show is that modern pacemakers and defibrillators can be MR safe if precautions are taken in order to ensure that patients are adequately monitored and tested," said Halperin, a professor of medicine, radiology, and biomedical engineering at Johns Hopkins University School of Medicine. "It can be done, but it's not ready for prime time."

The use of MRI, a sophisticated imaging technique, has been ruled out for the 2 million to 3 million Americans with implanted pacemakers and defibrillators. The reason: The intense magnetic field generated by MRI machines interferes with the delicate circuitry and lead wires that pacemakers and defibrillators use to emit electric pulses to keep the heart beating properly.

But a series of studies with models and animals shows that magnetic resonance imaging can potentially be used with properly designed pacemakers and defibrillators, Halperin said.

"We used some models filled with fluid to simulate the properties of the body," he said. "We also did animal studies in which we implanted the devices, did a high-powered MR scan after one month, then waited a month and looked at the heart tissue under a microscope. We saw no damage."

About half the people with implanted pacemakers or defibrillators are potential candidates for MRI scans, which are used to help diagnose many heart conditions, cancer, and other diseases, Halperin said. The same technology used to make the implanted devices safe from the emissions of cell phones and microwave ovens can be applied to make them safe for MRIs, he said.

That advice is already being heeded, said Dr. Emanuel Kanal, professor of radiology and neuroradiology at the University of Pittsburgh Medical Center and chairman of the American College of Radiology's MR safety committee.

"It is definitely a focus of the industry to develop pacemakers and defibrillators that are safer," Kanal said. "There has been tremendous progress in the area toward the ability to design and build devices that eventually will be truly MR-safe."

But right now, radiologists are taking a wary approach to the issue, Kanal said. They are aware of Halperin's work, and a paper discussing its implications for medical practice has been submitted to the journal Radiology, he said.

What's more, the findings of the Hopkins researchers are reflected in the updated 2004 version of the American College of Radiology White Paper on MR Safety, he said.

That statement says MRI scans of people with implanted pacemakers or defibrillators "should be done on a case-by-case and site-by-site basis."

"The expertise necessary to safely do so is exceedingly rare throughout the MR industry today," the statement says.

So the current situation is that MRI "can be done in certain circumstances, but that cannot be applied across the board," Kanal said.

More information

The American College of Radiology has more on magnetic resonance imaging.

SOURCES: Henry R. Halperin, M.D., professor of medicine, radiology, and biomedical engineering, Johns Hopkins University School of Medicine, Baltimore; Emanuel Kalan, M.D., professor of radiology and neuroradiology, University of Pittsburgh Medical Center; Aug. 3, 2004, Circulation

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