More than a thousand patients with either a pacemaker or implantable cardioverter-defibrillator (ICD) underwent MRI without any long-term adverse effects, according to a recent study.
The prospective, nonrandomized study included 1,509 patients who had a “legacy” pacemaker (58%) or ICD (42%) that did not meet FDA criteria to be MRI-conditional. They underwent 2,103 thoracic and nonthoracic MRI examinations at magnetic field strength of 1.5 Tesla. The pacing mode was changed to asynchronous for pacing-dependent patients and to demand for other patients, and tachyarrhythmia functions were disabled. Results were published in the Dec. 28 New England Journal of Medicine.
In nine of the MRI exams, the device reset to a backup mode (0.4%; 95% CI, 0.2% to 0.7%). In eight of these, the reset was transient. One pacemaker, which had less than a month of battery life left, reset to ventricular inhibited pacing, could not be reprogrammed, and was subsequently replaced. The most common notable change in device parameters immediately after MRI was a decrease in P-wave amplitude; a decrease greater than 50% occurred in 1% of patients. No clinically significant adverse events were reported in long-term follow-up, during which the most common notable changes were decreases in P-wave amplitude (4%), increases in atrial capture threshold (4%), increases in right ventricular capture threshold (4%), and increases in left ventricular capture threshold (3%).
The results of this study, combined with a recent registry study, “provide complementary evidence that MRI scanning can be performed safely in patients with legacy devices, provided that an appropriate protocol is followed,” the authors said. They added numerous caveats, including “the need for appropriate device programming, monitoring by qualified personnel, and the availability of an external pacing backup” for pacing-dependent patients. Limitations of the study include that long-term follow-up information was not obtained from 20% of the patients and that all of the MRIs were performed at a field strength of 1.5 Tesla, so the results should not be extrapolated to higher or lower field strengths.