Greater use of noncardiac pacemakers raises MR safety concerns

The growing popularity of noncardiac pacemakers is putting additional pressures on radiologists to recognize them on MR imaging, check for their proper positioning and complications, and determine the MR compatibility of the various devices.

"Each patient with an implantable stimulator should be approached on a case-by-case basis to ensure maximum patient safety," said Dr. Galina Levin, a radiologist at Winthrop University Hospital in Mineola, NY, in an educational poster at RSNA 2004.

Gastric, bladder, vagal nerve, brain, and spinal stimulators are becoming more common due to their ability to assist in the management of otherwise surgically and medically refractory conditions. Unlike their cardiac counterparts, they are not considered to be absolute contraindications to MRI.

Spinal fusion stimulators have been cleared by the FDA for use in MR-related tests and procedures. Strict guidelines must be followed, however: continuous patient observation, proper cathode positioning in the spine, and verification of lead integrity with plain films. In vitro studies show significant heating effect in broken leads, according to Levin. No spinal cord stimulators are currently MR-compatible.

Manufacturers' manuals for vagal nerve stimulators suggest that a 1.5T magnet test demonstrates no adverse effects with the use of a transmit and receive type coil. Receive-only head coils and body coils, however, are strictly contraindicated with this device because of potential heat injury.

Deep brain stimulators are allowed in patients undergoing MRI but only under certain circumstances. Receive-only head transmit coils, full-body transmit coils, and head transmit coils that extend over the thorax are contraindicated in deep brain stimulation. Spontaneous voltage induction can result in uncomfortable shocks to the patient, Levin said.

In vitro studies show that MRI causes no significant lead movement or change in clinical responses to deep brain stimulation, but in vitro studies that look at lead heating have been less conclusive since a wide range of temperature changes were observed.

"There have been two recent case reports in the literature describing serious injuries with deep brain stimulators following MRI. In both patients, the implantation technique differed from the manufacturer's recommendations. A body coil was used in one of these reports," Levin said.