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BOSTON -- Performing non-thoracic MRI scans at 1.5 Tesla appears to be safe for patients with implantable cardioverter-defibrillators (ICDs) and pacemakers, a multicenter registry study showed.

Among 500 patients undergoing scans, there were no deaths, device failures, generator-lead replacements, losses of capture, or ventricular arrhythmias, according to Debra Doud, MD, of the Scripps Clinic in La Jolla, Calif.

In addition, the rate of clinically relevant changes in various device parameters was low, she reported at the Heart Rhythm Society meeting here.

Considering the large number of patients with cardiac devices, the aging of the population, the increasing indications for cardiac devices, and the strengths of MRI in examining soft tissue, "the availability of being able to perform these exams in this patient population is extremely important," Doud said in an interview.

Current guidelines state that MRI is contraindicated in patients with cardiac devices, and Medicare has not reimbursed for MRI scans performed in patients who have a device in place. Doud noted that Medicare has since begun reimbursing for such scans as long as the patient is enrolled in the registry.

The MagnaSafe Registry is expected to enroll 1,500 adult patients with pacemakers and ICDs who have a clinical indication for non-thoracic imaging. Patients are included if imaging modalities other than MRI are not acceptable for resolving clinical questions. The study is being conducted at 12 sites under an investigational device exemption from the FDA.

The researchers examined the devices before and after MRI. Pacemaker-dependent patients had their device programmed to an asynchronous pacing mode, and those who were not dependent had pacing functions deactivated. Tachyarrhythmia therapies were disabled in patients with ICDs who were not pacemaker dependent. Patients with ICDs who were pacemaker dependent were excluded.

The current analysis included the first 500 patients included in the registry -- 378 with pacemakers and 122 with ICDs. The devices used a total of 964 leads.

About one in every five patients (21%) was pacemaker-dependent.

MRIs were performed an average of 2.9 years after device implant. The average length of the scan was 42 minutes.

There were no major complications from the MRI scans.

Four patients developed self-terminating, hemodynamically stable atrial fibrillation during the scan; of those, three had a prior history of paroxysmal atrial fibrillation. There were also two cases of partial electrical reset, both in patients with pacemakers.

Using conservative cut-offs, there was a low rate of clinically relevant device parameter changes, and only two patients required device reprogramming, Doud said.

The actual impact of these device changes is unclear, and there have been no long-term consequences observed so far, she said.

An issue not addressed in the current analysis is whether the images obtained in these patients are usable. Doud said that she and her colleagues are in the process of preparing those data for presentation, but that out of more than 500 images she has seen, only one was uninterpretable because of an imaging artifact.

That came in a left shoulder scan of a patient with a left-sided ICD, although Doud noted that other such scans have been clear. Further research will be needed to identify factors that can affect image quality, she said.