Medtronic tests MRI-friendly pacemaker

One of the most vexing dilemmas for patients with pacemakers is that an MRI scan may prevent the device from pacing the heart.

But on Monday, Fridley-based Medtronic Inc. announced that it has launched a 470-patient study using a new pacemaker system that may prove compatible with magnetic resonance imaging (MRI) scans, one of the most commonly used diagnostic tools in medicine.

"At some point, everyone gets an MRI," said Dr. J. Rod Gimbel, of East Tennessee Heart Consultants in Knoxville, who has written extensively about the interaction between MRI and implanted cardiac devices. But for 3 million pacemaker patients worldwide, MRI is not an option, even though it may be the only noninvasive diagnostic tool available.

If the Medtronic study is successful, the technology eventually may broaden to include implantable cardioverter defibrillators (ICDs), which shock an errantly beating heart back into rhythm, and perhaps to neurostimulators -- pacemaker-like devices that use electricity to treat a variety of diseases and conditions ranging from depression to movement disorders.

By creating a magnetic field, an MRI sends radio waves through the body, creating an image. MRI scans are used by doctors to visualize internal organs, blood vessels, muscles, joints, tumors and areas of infection.

But the process can be potentially deadly for pacemaker patients on rare occasions.

The interaction between pacemakers and the scan could cause the device to stop working, or deliver unusually rapid pacing that may prove lethal. On other occasions, the insulated wire, or lead, that connects the pacemaker to the heart may heat up during a scan and damage the heart muscle, Gimbel said.

But before Medtronic receives regulatory approval from the Food and Drug Administration (FDA) to sell the system in the United States, the company must prove the system is safe and effective. The clinical trial announced Monday will involve implanting all the patients enrolled with the new pacemaker system, although only two-thirds will undergo periodic MRI scans.

Although up to 75 hospitals will participate in the study nationwide, Abbott Northwestern Hospital is the only center involved so far in Minnesota. The study will compare the pacemaker's electrical system performance in patients getting the scans against those who were not scanned over a 30-month period.

Dr. John Lesser, director of the cardiac MRI/CT program at the Minneapolis Heart Institute who is involved with the study at Abbott Northwestern, doesn't anticipate any difficulty enrolling patients in the study. "I feel very comfortable with the design of the trial, and patients will have access to the very latest technology," he said.

The first implant in the U.S. clinical trial was performed last week by Dr. Brian Ramza at St. Luke's Hospital in Kansas City, Mo.