Making pacemakers MRI-friendly

Medtronic is seeking regulatory approval for a pacemaker that's compatible with MRIs.

By Janet Moore, Star Tribune

In all of medical technology, few products have been as enduring as the pacemaker.

The device, which paces a heart that beats too slowly, has saved countless lives and enjoyed an extraordinary run, as medical devices go, and has helped build Minnesota's formidable medical economy.

But in the past decade or so, an unsettling truth has emerged about pacemakers, something none of its inventors could have imagined: Patients implanted with the silver-dollar-sized device are warned against getting MRI scans. The interaction between the tiny battery-powered devices and the powerful magnetic imagers is seen as terribly risky, and potentially harmful.

Now, Medtronic Inc. has developed a pacemaker system that is MRI-compatible under most circumstances. Its competitors are working on their versions, as well.

Already approved in Europe, Fridley-based Medtronic's Revo MRI Pacemaker System will be evaluated by a Food and Drug Administration (FDA) panel of experts on March 19. If the device clears the panel, it's likely the agency will approve it for sale in the United States.

In the evolution of pacemaker technology, this advance looms large -- and potentially could spread to other devices implanted in the body that react with MRI scans.

"Fifty years ago, no one thought about the use of MRIs and now it's become commonplace," said Dr. David Steinhaus, medical director of Medtronic's cardiac rhythm disease management business. "More and more, these patients who get pacemakers are going to need MRIs, so the ability to do MRIs on these patients will be really important."

Each year, more than 60 million people worldwide undergo magnetic resonance imaging procedures to diagnose cancer, Alzheimer's disease, heart and artery diseases and muscle, bone and back pain, among other conditions. At the same time more than 3 million people worldwide have been treated with a pacemaker, and each year another 1 million patients are implanted with the device. An estimated 200,000 pacemaker patients are denied MRIs annually because of the risks involved.

The relatively high magnetic- and radio-frequency fields produced during the popular scan may interfere with a pacemaker's therapy. For example, the pacemaker may stop working, particularly worrisome if the patient is dependent on the device to keep their heart beating. The rate at which the device paces the heart may speed up, and cause erratic pacing. The metal tip of the lead, or wire that connects the device's circuitry to the heart, may heat up and burn heart tissue. Or, the scan could cause internal components of the device made out of ferrous metals to vibrate or shift.

As MRI scans grow more popular, the need for MRI-compatible devices has become pronounced. The National Council on Aging (NCOA) estimates that a patient with an implantable device has a 50 percent to 75 percent likelihood of needing an MRI over the lifetime of their device.

Dr. Jerry Froelich, a professor of radiology at the University of Minnesota who co-chairs the American College of Radiology's Magnetic Resonance Making Safety Committee, says he's not aware of pacemaker patients who have died after undergoing an MRI. "But why risk it? It's not something most people want to do," he said.

To avoid any consequences, doctors try using other imaging methods in a pinch as substitutes for an MRI, such as CT scans, but often the alternatives are not particularly good ones for doctors.

"It depends on the problem the patient has -- you do the best you can do," Froelich said.

Usually placards in MRI clinics warn about implantable devices, and pre-scan questionnaires often ask patients if they have an implantable device. Still, a recent NCOA study of 1,077 older adults, caregivers and physicians found that three in 10 patients with an electronic implantable device have an MRI despite the risks. Of that group, about 20 percent reported problems with their device afterward. The $40,000 study, funded by Medtronic, also found that nearly a third of patients, and more than half of their caregivers did not recall being advised about the risks of MRI.

First-to-market benefits

If Medtronic is successful in gaining FDA approval, the company will reap the benefit of being first-to-market with a new, and presumably coveted, device.

The company says it spent 12 years developing an MRI pacemaker. This was done, in part, by modifying the hardware to minimize the level of energy transmitted where the lead and the device connects. The device can also be programmed by a doctor before a scan to eliminate the impact the MRI may have on pacing therapy.

The company has not yet released the results of a 470- patient clinical trial testing the device -- that will occur as the panel date approaches.

Other med-tech companies are working on their versions of an MRI-friendly pacemaker, too.

Little Canada-based St. Jude Medical Inc. hopes to introduce its Accent MRI pacemaker internationally by the end of the year, and is in discussions with the FDA to begin clinical trials in the United States later this year. St. Jude says its device can withstand full-power scans of the thoracic cavity. Medtronic says its second-generation MRI pacemaker, called Advisa, will have the same feature, but the Revo device probably will not include that feature.

Boston Scientific Corp., whose cardiac rhythm business is based in Arden Hills, said its next-generation platform of pacemakers will be MRI-safe, but a spokeswoman declined to offer further details.

It's an interesting twist in a market segment that most analysts see as mature, one that is often benignly ignored by Wall Street in favor of the pacemaker's more-lucrative high-voltage cousin, the implantable cardioverter defibrillator (ICD). Pacemakers typically sell for $5,000 to $10,000, while ICDs, which shock an errantly beating heart back into rhythm, cost about $30,000. ICD wearers are also advised to avoid MRI scanners.

"I see it as a stable, if unexciting, market," said Venkat Rajan, a medical device industry analyst at Frost & Sullivan. An MRI-compatible device will "definitely provide a boost for the marketplace, it's a technology that had been needed for some time."

The Millennium Research Group estimates the worldwide pacemaker market to be about $3.3 billion. Last year, sales of the device from market leader Medtronic were flat at $1.9 billion.

Rajan and others say pacemakers are just the beginning -- other implantable MRI-compatible medical devices will likely follow. "We started with the pacemaker and we'll work going forward with ICDs as well," said Medtronic's Steinhaus. "One can imagine that sometime in the future all these devices will somehow be compatible with MRI machines."