Methods:

A total of 629 patients who had an ICD and clinical indication for MRI were enrolled consecutively after physician referral between February 2003–January 2015. Exclusion criteria included patients with new or newly adjusted leads (i.e., within 4 weeks), patients with permanent surgical epicardial leads and nonfunctional leads, patients with subcutaneous ICD systems, or patients who were pacing-dependent with an ICD without asynchronous pacing capability. Device reprogramming to asynchronous pacing method was performed for patients with an intrinsic heart rate of <40 bpm, and an inhibited pacing method was used for all other patients. Pacing features and therapies deactivated during MRI included those to treat tachyarrhythmias, premature ventricular complex detection, noise discrimination, rate response, and ventricular sense response. After MRI was complete, all devices were reprogrammed to their original settings. MRIs were performed with a standard magnetic field strength of 1.5 Tesla. ICD device interrogations were performed at baseline and immediately after MRI completion. Thereafter, devices were interrogated at least every 6 months and more often for symptom-driven reasons. Follow-up interrogation was stopped at the last available consecutive interrogation after MRI or when all MRI-exposed device components (i.e., generator and leads) were replaced or removed. Death data were obtained from clinical records, obituaries, and death certificates. Deaths were classified as either cardiac or noncardiac, and cardiovascular deaths were classified as arrhythmia-related or non–arrhythmia-related.