Impact of magnetic resonance imaging on ventricular tachyarrhythmia sensing: Results of the Evera MRI Study

Studies have shown that magnetic resonance imaging (MRI) conditional pacemakers experience no significant effect from MRI on device function, sensing, or pacing. More recently, similar safety outcomes were demonstrated with MRI conditional defibrillators (implantable cardioverter-defibrillator [ICD]), but the impact on ventricular arrhythmias has not been assessed. The purpose of this study was to assess the effect of MRI on ICD sensing and treatment of ventricular tachyarrhythmias. The Evera MRI Study was a worldwide trial of 156 patients implanted with an ICD designed to be MRI conditional. Device-detected spontaneous and induced ventricular tachycardia/ventricular fibrillation (VT/VF) episodes occurring before and after whole body MRI were evaluated by a blinded episode review committee. Detection delay was computed as the sum of RR intervals of undersensed beats. A ≥5-second delay in detection due to undersensing was prospectively defined as clinically significant. Post-MRI, there were 22 polymorphic VT/VF episodes in 21 patients, with 16 of these patients having 17 VT/VF episodes pre-MRI. Therapy was successful for all episodes, with no failures to treat or terminate arrhythmias. The mean detection delay due to undersensing pre- and post-MRI was 0.60 ± 0.59 and 0.33 ± 0.63 seconds, respectively (P = .17). The maximum detection delay was 2.19 seconds pre-MRI and 2.87 seconds post-MRI. Of the 17 pre-MRI episodes, 14 (82%) had some detection delay as compared with 11 of 22 (50%) post-MRI episodes (P = .03); no detection delay was clinically significant. Detection and treatment of VT/VF was excellent, with no detection delays or significant impact of MRI observed.