The Food and Drug Administration Tuesday approved the first pacemaker that is specifically designed for use in a magnetic resonance imaging environment. The powerful magnetic field that MRIs create can interfere with a normal pacemaker's operation, damage its components, cause the pacemaker or its leads to become dislodged, or interfere with its ability to capture a signal from the heart. As a result, an estimated 200,000 Americans, most of them elderly, have to forgo an MRI scan each year because of their pacemaker. The Revo MRI SureScan pacing system, developed by Medtronic Inc. has hardware and leads that are designed to minimize these problems, the company said. Additionally, the device can be put into a "safe" mode before an MRI scan begins to protect it from malfunctioning and ensure that it doesn't deliver unneeded pacing therapy or withhold needed therapy. The FDA is requiring training for cardiologists and radiologists who use the system.