The Medtronic EnRhythm MRI SureScan pacing system, approved mid November in Europe, is safe for use in the magnetic resonance (MR) environment, according to study data presented on Wednesday at the 2008 meeting of the Radiological Society of North America (RSNA). "This result corroborates results we saw in bench, animals, and human testing so far, and this device is already approved as a commercially available device in Europe and is now being implanted in humans," reported Emanuel Kanal, MD, Director of Magnetic Resonance Services at the University of Pittsburgh Medical Center, who reported on the first results of this study. (Read the abstract here.) "You can imagine this is a very exciting time as it is the first time in 20 years that we have had a pacemaker implanted in people anywhere in the world that is approved as MR-safe when used as it is labeled."

Estimates are that more than 30 million Magnetic Resonance (MR) studies are conducted per year globally. The elderly are the primary users of MR services, with likelihood for greater than 65 are twice that of those less than 65 years old. It is also estimated that an MR examination would be indicated for 50% to 75% of US IPG/Implantable cardioverter defibrillator (ICD) patients over the lifetime of their device, but unfortunately for those who perhaps most need an MR scan, the current devices restrict access to MRI.

In the study, the device was implanted in 245 patients at multi-centers, in Europe (17 centers) and Canada (5 centers), with a final intent to implant in 470 patients at 53 worldwide centers total. After the device was implanted, the study waited 6 weeks for stabilization to make sure the scanning thresh holds were less than or equal to 2 volts at 2 second durations. A trained cardiologist was present at MR scans to monitor pulsometry. The study was a prospectively designed, controlled, 1:1 randomized to receive MRI scans (MRI group) or no MRI scans (control group). Over fourteen clinically relevant MR studies were performed of the head and of the lumbar spine in clinical GE, Philips, and Siemens 1.5T MR scanners. Total scan time was typically 45 to 60 minutes. Studies included FSE/TSE sequences, FLAIR, DWI, 3D TOF MRA, and rapid contrast bolus MRA (w/o the contrast bolus), among others. "We exposed the device to very clinically significant MR sequences designed to maximize SSR, the power deposition, or the gradient DVT representing the change per unit time, over the pacing device as well as the leads coming from the pacing device itself."

After about six months of follow-up, 90 patients then underwent an elective MR scan, while 101 patients served as a control group. The patients were monitored at 3 months post implant (1 week post MRI) and then followed up at 4 months (1 month post MRI). About 84% (135/161) of the subjects were free of implant, pacing system related, and MRI related complications through 1 month post-MRI. The atrial leads thresholds there was no statistically significant or clinical significant different between the MRO group and the control group. The same was true for the ventricular leads thresholds. In fact, no MR-related complications were reported (0/88), and there were no significant threshold changes or differences in sensing between the two groups. "When we used the EnRhythm in the MR environment as the EnRhythm was designed to be used, we saw no adverse events that were the slightest bit clinically significant when compared to the control group who had the same device in them but were not exposed to the MR study," Dr. Kanal said in an interview with MedicExchange. Specifically, there were no MRI related complications, interference with pacemaker device functionality or unexpected lead performance issues were observed. "The results of this ongoing clinical trial (recall that the final intent is to implant in 470 patients at 53 worldwide centers total) indicate that this pacing system meets its performance requirements when used in accordance with the system’s labeling. These results corroborate those observed in preclinical bench, phantom, and animal testing."

The risks of MR to patients with conventional pacemakers have been known for two decades, and technologists routinely refuse to perform MRI on pacemaker patients. If the new device holds up well under European use and further study, it has the potential to greatly expand treatment and imaging options for these patients. "The irony is it’s the older patients who tend to get pacemakers and then are told they can not have MRI and the older patients also tend to be the patients who happen to need MRI more," Dr. Kanal said. He fielded a question from the audience regarding old intractable leads. "The problem might continue for those patients with chronic leads that are not extractable so that when the pacemaker is removed the old leads may need to remain and those patients would still not be allowed access to MR scans." This explains why it is critical that the leads also be MR compatible as is true for the EnRhythm system. "Considering the powerful history of over two decades of denying MR access to essentially all pacemaker patients, significant radiologist educational effort will be required in order to successfully change the industry's entrenched approach regarding permitting MR scans on patients in whom this specific device is implanted." Already planned for 2009 is an update for the MRI Safety Practice Guidelines for the College of Radiology.

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