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BOSTON -- A new implantable cardioverter-defibrillator (ICD) that is specifically designed to function safely in patients undergoing full-body magnetic resonance imaging (MRI) performed as planned, according to the results of the first randomized study of the device in humans.

"We were very pleased and reassured to show, in this first randomized study of a specific device developed and designed for MRI use, that it performed very well ... and met all safety and efficacy endpoints," reported , from the Medical University of South Carolina in Charleston, during a press conference.

He predicted that "about 10 years down the road all ICDs will be MRI compatible ... there's no downside to it per se ... so it's hard to imagine this won't become standard of care at some point."

His prospective study, reported in a late-breaking session at the and published simultaneously in the Journal of the American College of Cardiology (JACC), used a device with the same features as a commercially available ICD (Evera, Medtronic), "but with hardware and firmware modifications for MRI compatibility" and commercially available leads.

MRI is contraindicated in patients with conventional ICDs due to potential adverse effects of the magnetic field on the electrical functioning of the device, he explained.

The study included 263 patients (median age 60.4 years) from 42 centers and 13 countries who were implanted with the MRI-compatible ICD -- either single or dual chamber based on physician discretion.

Patients were then randomized 2:1 one month later to either undergo an elective MRI at 1.5 Tesla, or not (controls).

"There were 10 prespecified sequences on MRI," said Gold. "Everyone had the same sequences including head, neck, chest, abdomen, and spine."

"There were several observations as expected," he said. Two patients noted implant site warmth, one patient had back pain, one patient with a history of atrial tachycardia experienced this in the scanner, and one patient had a burning sensation in the forehead -- although an x-ray performed after the procedure could ascertain the cause, he noted.

One month after the MRI the study's three primary endpoints were assessed. These included a composite safety endpoint of freedom from sustained tachyarrhythmia during MRI, and at least 90% freedom from MRI-related complications within 30 days.

Two co-primary efficacy endpoints included changes from baseline in both ventricular pacing capture threshold (VPCT) and ventricular sensing.

"All three co-primary endpoints were met," reported Gold.

Specifically, "there were no complications associated with MRI in this cohort ... there was "no difference in pacing and sensing performance between the MRI and control group, and there was no impact on VF detection observed post MRI exposure."

In terms of change in VPCT from baseline, "only one patient met the endpoint of having greater than 0.5% increase in VPCT and, in fact, that was in the control group. No patient in the MRI had a significant increase," he said.

Measuring change from baseline in ventricular sensing amplitude, one patient in each group had a greater than 50% reduction -- which was the definition of failure.

"Most importantly we wanted to evaluate VT/VF detection post-MRI since ICDs are implanted primarily to detect and terminate ventricular tachyarrhythmias," he said.

There were 34 VT/VF episodes in 24 patients, from which a computer algorithm determined only one episode to be "undersensed" with a delay in detection of 0.19 seconds. "All episodes were appropriately detected and treated by this device," he concluded.

Together, the results are highly significant for noninferiority of the scanned device compared with the unscanned devices in the control group, said Gold. "These data support the system's safety and efficacy."

Gold's study "has significantly advanced safe MRI studies using 1.5 Tesla output in patients with the new, conditional ICD," wrote , in a commentary published alongside the study in the JACC.

But he added, "this approach is the beneficial tip of a troublesome iceberg. Millions of patients worldwide have nonconditional devices implanted, and MRI scanning techniques at 1.5 Tesla units and above are currently in use, with full effects on existing cardiac electrical devices yet to be determined. There are many issues still to be resolved, but such is the future of medicine."

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