SNOWMASS, COLO. — Magnetic resonance imaging is by far the most problematic medical source of electromagnetic interference with implanted cardiac device function, according to Dr. William H. Spencer III.
Other potential sources of electromagnetic interference include radiotherapy, neurostimulators, electrosurgery, and radiofrequency catheter ablation of arrhythmias, as well as lithotripsy.
Device wearers don't need to worry about diagnostic x-rays, CT scanning, mammograms, ultrasound, and most forms of laser surgery, he said at a conference sponsored by the Society for Cardiovascular Angiography and Interventions.
Dr. Spencer shed light on the sources of interference that may affect implanted cardiac devices:
▸ MRI. The Food and Drug Administration and cardiac device manufacturers list MRI as absolutely contraindicated. Deaths have occurred. It has been estimated that if not for the contraindication, an MRI would be recommended for various indications in up to 75% of U.S. pacemaker and implantable cardioverter-defibrillators users during the course of the device's service life.
Device manufacturers have made development of MRI-safe pacemakers and ICDs a priority, but none exist yet.
▸ Radiotherapy. The damage to pacemakers and implantable cardioverter-defibrillators by radiotherapy is dose dependent, cumulative, and permanent, said Dr. Spencer, professor of medicine at the Medical University of South Carolina, Charleston.
Protocols should be in place for avoiding direct irradiation of the device, creating the greatest possible distance between device and radiation beam, and maximum shielding.
▸ Neurostimulators. Transcutaneous electric nerve stimulation, and the peripheral and spinal nerve stimulators used to treat neuropathic and orthopedic pain, can be used safely in patients with modern bipolar pacemakers. But the patient should first undergo testing at the stimulator's maximum output to ensure it doesn't trigger or deactivate the pacemaker.
▸ Electrosurgery. This creates one of the most powerful and dangerous electromagnetic fields found in the medical environment. The best option is to find an alternative form of surgery.
▸ Radiofrequency ablation. This procedure interacts unpredictably with cardiac devices. Turn off rate-responsive and antitachycardia features and program the device to asynchronous mode for the procedure duration. If the goal is to create complete heart block, a temporary pacemaker must be inserted to ensure ventricular capture.
▸ Shock wave lithotripsy. This method of breaking up kidney and other stones is not nearly the problem it once was. Indeed, only patients with an abdominally implanted device generator are at high risk, and those are now uncommon.