MRI With Pacers, ICDs: Safe, a Few Minor Issues, Says MagnaSafe Registry

May 10, 2012

May 10, 2012 (Boston, Massachusetts) — Interim findings from the MagnaSafe Registry show there were no important safety issues but some alterations in programming and transient impedance changes during nonthoracic magnetic resonance imaging (MRI) in patients with pacemakers and implantable cardioverter defibrillators (ICDs) [1].

No instances of imaging-associated death, device failure, generator or lead replacement, loss of capture, or electrical reset occurred with MRI, which was performed consistently at 1.5 T.

Of less apparent significance, according to Dr Debra Doud (Scripps Clinic, La Jolla, CA), who presented the analysis here at Heart Rhythm Society 2012 Scientific Sessions, were the battery-voltage changes seen in 12% of ICDs and device parameter changes seen in a tenth of pacemaker and a third of ICD patients.

Dr. Debra Doud

"We can't say whether any of those changes were clinically significant in any way," she told heartwire . Little is known about the normal variability of those parameters over 15 to 45 minutes, what it typically takes to complete an MRI scan. So what was observed could conceivably be within the normal range. What was important, she said, was that there were no clinical consequences or serious device effects.

The MagnaSafe results are based on the first third of a planned 1500-patient enrollment for the prospective observational study, which is aimed at clarifying cautions and hazards, if any, of clinically indicated MRI in the presence of implanted "non–MRI-conditional" rhythm-control devices: the vast majority that aren't designed specifically to be compatible with MRI.

The few important device issues seen with scans suggest there potentially may be limited need for ICDs specifically designed to be "MRI-safe."

But whether or not there are advantages to such devices, "there still will be a large number of patients with non–MRI-conditional devices who need to undergo an MR scan for one reason or another. And certainly [going ahead with the scan] is much safer than lead extraction and putting in an MR-conditional device for patients who already have a device."

The analysis included 500 adults at 12 centers who had received a pacemaker or ICD after 2001 who had a "strong clinical indication" for a nonthoracic MRI scan. Those who weren't pacemaker-dependent had their device's pacing functions deactivated and those who were dependent had the devices programmed to an asynchronous mode. Pacing therapy and shocks were disabled for ICD patients who weren't pacemaker-dependent.

"The one population of [device] patients we had to exclude was those with ICDs who were pacemaker-dependent," Doud said, because devices from some manufacturers don't allow ICD functions to be disabled without turning off the pacing functions.

The devices were interrogated before and after the scans, of which about 40% were of the spine, 30% of the brain, and 5% of the abdomen or pelvis.

Among the observations:

  • Four patients developed self-terminating bouts of atrial fibrillation (AF) during the scan, including patients with a documented paroxysmal AF history and one patient with no history of AF.

  • In two cases, several programming settings reverted to default settings during the scan; they were manually reprogrammed to prescan settings.

  • There were two cases of partial electrical reset.

  • A decrease in battery voltage by at least 0.04 V was seen in 1% of pacemaker patients and 12% of ICDs; impedance changes ≥50 ohms in a pacing lead in 3% of pacemakers and 5% of ICDs were observed, along with an impedance change of at least 3 ohms in a high-voltage lead in 18% of ICDs.

  • A drop of at least 25% in R-wave amplitude occurred in 3% of both pacemakers and ICDS; but there were no decreases in P- or R-wave amplitudes of at least 50%.

  • One or more device parameter changes occurred in 11% of pacemakers and 32% of ICDs.

Doud said that in practice at her center, thoracic and even cardiac MRI scans are performed routinely on patients with conventional pacemakers and ICDs. But device patients needing thoracic or cardiac MRI were excluded from MagnaSafe "at the request of the FDA."

Doud had no disclosures. Disclosures for the coauthors are listed in the abstract.

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