0630pacemakerDr. Karthik Ramaswamy explains why a standard pacemaker is so dangerous inside an MRI machine.
And it's not for the reason you might think.
"Metal itself is not the problem," said Dr. Karthik Ramaswamy, a cardiac electrophysiologist with Northeast Georgia Heart Center.
People with certain types of metal objects inside their bodies, such as steel rods, plates or staples, cannot have an MRI because the machine contains gigantic magnets that could actually pull these objects out.
In recent years, most medical devices have been made with types of metal that don't contain iron, so they aren't affected by magnets. But with pacemakers, there's another issue: MRI machines also generate radio-wave pulses that disrupt the rhythm of the pacemaker.
This could cause an abnormal heartbeat or even cardiac arrest. The energy also can cause heat to build up in the leads (the wires that run from the pacemaker to the heart), essentially burning the patient from the inside.
"MRI has always been absolutely (inadvisable) if you have a pacemaker," Ramaswamy said. "What they usually have to do instead is a CT scan."
But for imaging certain parts of the body, no other test is as accurate as an MRI. For diagnosing serious neurological conditions such as multiple sclerosis and brain tumors, for example, an MRI is almost always needed.
"It is the test of choice in many cases," said Dr. Lee Martin, a radiologist at Northeast Georgia Medical Center. "CT scans may not show the abnormalities as well."
Martin said more than 3 million people have implanted pacemakers, and their doctors are deprived of a tool that could help them diagnose and treat these patients.
But now, there's a technological breakthrough that could change the situation. Northeast Georgia Medical Center is the first hospital in the state to participate in a clinical trial for a new kind of pacemaker that is MRI-safe.
The device is called EnRhythm MRI SureScan, manufactured by Medtronic.
"The purpose of this trial is to demonstrate the safety and efficacy of this device in humans," said Ramaswamy. "They've tested it in animals and had satisfactory results."
Ultimately, 470 patients from a number of cities will be enrolled in the 30-month study. All will get the same pacemaker, but only two-thirds will be given MRI scans. The health of the patients who receive the scans will then be compared to those who don't.
Ramaswamy said so far, two patients have received the pacemakers at the Gainesville hospital. Both were men in their 70s.
"The trial is totally voluntary," he said. "Any patient who needs a pacemaker and meets the criteria, we ask them if they're interested in participating. Usually in trials like this, people do want to be involved. They say they like the idea that they may be helping future patients."
Ramaswamy said insertion of the device is the same as for any cardiac pacemaker.
"Implantation takes about an hour and is done under local anesthesia," he said. "We insert it under the skin below the clavicle (collarbone), and under X-ray, we thread the leads to the heart."
Patients are usually kept overnight for observation and go home the next day.
Ramaswamy said the SureScan will work as well as any other pacemaker in terms of preventing the heart from beating too slowly. The differences will become apparent only if the patient has an MRI scan.
He said the SureScan can be programmed so that its rhythm does not conflict with the pulses of an MRI machine. And its leads are made with a material that does not absorb heat.
If the clinical trial shows that the SureScan is safe and effective, the device can be approved by the FDA and will be available for any doctor to use.
Martin said it's likely that once the SureScan is approved, all pacemakers will be made with this new technology.
"If you have a device that precludes people from getting the test of choice (an MRI) and one that doesn't, which one would you want?" he said.
Ramaswamy said the new pacemaker "could revolutionize how we practice." And he enjoys being on the cutting edge of research.
"It's exciting that we're doing this in Georgia," he said.