CHICAGO — Patients with pacemakers and implantable cardioverter defibrillators that were not MRI-conditional were able to receive MRIs with almost no clinically relevant problems, according to findings from the MagnaSafe Registry.
While the results differ from the FDA guidance on MRIs for pacemakers and ICDs, the study was not designed to change product labeling, Robert J. Russo, MD, PhD, from Scripps Clinic, La Jolla, Calif., said during a presentation.
Russo and colleagues analyzed 1,000 patients with pacemakers and 500 patients with ICDs who had non–MRI-conditional devices. All underwent clinically directed non-thoracic MRIs at 1.5T.
Robert J. Russo
According to Russo, between 50% and 70% of patients will require MRI after placement of a pacemaker or ICD. Traditionally, there have been concerns that the leads of the devices might result in transmission of current with local thermal injury, and that there may be a decline in pacing electrical properties due to edema and fibrosis, he said.
The researchers hypothesized that the heart has the capacity to dissipate heat energy due to large circulating blood volume and that risk from a generator or lead removal would outweigh the risks from an MRI.
All patients had their devices interrogated and reprogrammed appropriately before the scan; all devices had magnet response disabled, pacemaker-dependent patients had their device programmed to an asynchronous setting, and non–pacemaker-dependent patients had their device programmed off. After the scan, the devices were reinterrogated and their baseline settings were restored, he said. Patients with ICDs who were pacemaker-dependent were excluded from the study, Russo said.
The primary clinical outcomes included death during scan, generator failure requiring immediate replacement, lead failure requiring immediate replacement, new onset of an atrial or ventricular arrhythmia during the scan, loss of pacemaker capture during the scan and electrical reset. Secondary outcomes included clinically relevant parameter changes in battery voltage, lead impedance, lead threshold, and P- and R-wave amplitude.
Russo reported no deaths, lead failures or loss of pacemaker capture during the study. One patient with an ICD experienced generator failure; six patients with pacemakers experienced partial electrical reset; and six patients (five in pacemaker group) experienced atrial fibrillation during the scan. Russo noted that of the patients who experienced AF, only one had new-onset AF; it was resolved within 48 hours.
“The one device failure was an ICD in which tachycardia therapy was inappropriately left in the active mode during the scan, with bradycardia therapy disabled,” Russo said. “Post-scan, the ICD could not be reinterrogated or reprogrammed, and immediate replacement was required. With tachycardia therapy active during the exam, the device interpreted the rapid on-off pulse of MR as ventricular fibrillation. It then attempted repetitively and unsuccessfully to form a charge in the capacitor. With its inability to deliver a shock, the device defaulted to faulty. No shocks were delivered in the examination.”
There were no clinically significant changes in battery voltage, lead threshold, P-wave amplitude, R-wave amplitude or high-voltage impedance, and the change in pacing lead impedance was negative, he said. The parameters did not change in the 321 patients who underwent multiple MRI scans, he added.
“The MagnaSafe Registry demonstrates that clinically indicated non-thoracic MRI at 1.5T can be performed with non-conditional standard devices at no significant clinical risk when patients are appropriately screened and the devices are appropriately programmed,” Russo said. “We hope that the results of the MagnaSafe registry may change the American Heart Association and the American College of Cardiology recommendations and Medicare coverage, but more importantly will improve access to clinically indicated MRI for patients with standard pacemakers and defibrillators.”
Future research will evaluate MRI at 3T in patients with pacemakers and ICDs, as well as thoracic MRIs in those patients, he said. – by Erik Swain
For more information:
Russo RJ. CS.04: Trials and Cardiovascular Registries. Presented at: American Heart Association Scientific Sessions; Nov. 15-19, 2014; Chicago.
Disclosure: The Registry is supported by grants from Biotronik, Boston Scientific/Guidant, the Hewitt Medical Research Foundation, St. Jude Medical and other philanthropic sources. Russo reports receiving research grants from Biotronik, Boston Scientific and St. Jude Medical.