Originally Published MDDI October 2004

R&D DIGEST

Heart Devices May Be Safe for MRI Scan

Maria Fontanazza

The benefits of magnetic resonance imaging (MRI) may soon be available to those with modern pacemakers and implantable cardioverter-defibrillators. A study conducted at The Johns Hopkins Medical Institute (Baltimore) found that some modern devices manufactured after 2000 are safe in standard- and maximum-strength MRI scans.

A major implication of the study is the development of pacemakers specifically designed for safe use in the imaging machines. “I think it's up to the device manufacturers to produce them,” says the study's senior author, Henry Halperin, MD. A professor of medicine, radiology, and biomedical engineering at The Johns Hopkins University, Halperin believes “it's certainly possible—they just have to do it.”

“I think there will be a strong movement to have all electrical devices around the heart made to be MRI compatible over the next several years,” said David Bluemke, MD, clinical director of MRI at The Johns Hopkins Hospital. “Already, it appears that some newer pacemakers have some resistance to adverse affects in strong magnetic fields.”

A noninvasive technique for imaging the body, MRI scanning has never been recommended for people with implanted heart-assist devices. The reaction of the scanner with lead components in the heart device generates intense heat, resulting in mechanical hazards, such as rapid pacing and device failure. The interactions are responsible for tearing soft tissue and even death, which led FDA to label the devices as a contraindication to MRI.
Used to treat arrhythmia, the smaller, modern pacemakers and defibrillators have less magnetic material and better protection against electromagnetic interference. The filters are on a feedthrough, a device that allows electric wires to pass through the titanium casing, and are a critical aspect of making the device MRI safe, explained Halperin. “Our understanding of the problem is that there are certain inductive circuits present on the older models and fewer present on the newer [models].”

According to the study, which was published in August 2004 in Circulation on-line, nine pacemaker models and 17 implantable cardioverter-defibrillators were tested in General Electric's 1.5-T MRI scanner. The approved in vivo and in vitro testing measured factors that included device function and damage, lead heating, and force and torque generated by the MRI machine.

“Basically, MRI scanners came into use in the early 1980s when pacemakers weren't nearly as sophisticated as they are today,” said Halperin. Since the current devices were not manufactured with the intent to be MRI compatible, Halperin still cautions their use in MRI scanning machines.

The study was funded by the Bogle Foundation, Medtronic Inc., St. Jude Medical Inc., and the National Institutes of Health. Halperin is also a consultant for Medtronic Inc.


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