A prospective study to assess the safety of MRI at a magnetic field strength of 1.5 Tesla in patients with a pacemaker (58%) or an implantable cardioverter–defibrillator (42%) that was not considered to be MRI-conditional (termed a “legacy” device) showed no long-term clinically significant adverse events. The study included 1509 patients with 2103 thoracic and nonthoracic MRI examinations. The pacing mode was changed to asynchronous mode for pacing-dependent patients and to demand mode for other patients. Tachyarrhythmia functions were disabled. No long-term clinically significant adverse events were reported. In nine MRI examinations (0.4%), the patient’s device reset to a backup mode. The reset was transient in eight of the nine examinations. The most common notable change in device parameters (>50% change from baseline) immediately after MRI was a decrease in P-wave amplitude, which occurred in 1% of the patients. At long-term follow-up (results of which were available for 63% of the patients), the most common notable changes from baseline were decreases in P-wave amplitude (in 4% of the patients); increases of capture threshold in atria (4%), in right ventricle (4%), and in left ventricle (3%), respectively. The observed changes in lead parameters were not clinically significant and did not require device revision or reprogramming. Source: http://www.nejm.org/
