Magnetic resonance imaging of pacemakers and implantable cardioverter-defibrillators without specific absorption rate restrictions

AIMS: The purpose of the current study is to evaluate the safety profile of patients with pacemakers or implantable cardioverter-defibrillators (ICDs) undergoing a medically necessary magnetic resonance imaging (MRI) scan without limitation on peak specific absorption rate (SAR). Recent series suggest that MRI scanning can be performed safely in select patients with pacemakers or ICDs. These studies, though, limited peak SAR. METHODS AND RESULTS: One-hundred and three patients with a total of 240 leads underwent a total of 127 scans of any body landmark using usual protocols with standard peak SAR settings for the scan. No patient was pacemaker dependent. Thresholds were obtained immediately before and after the scan. For all scans, the median (25th and 75th percentiles) peak SAR was 2.5 (1.3, 3.2) W/kg whereas the median scan time was 1650 (1236, 2099) s. Pre- and post-scan pacing thresholds were unchanged 0.7 (0.5, 0.8) vs. 0.6 (0.5, 0.8) V at 0.5 ms, P=NS, though the sensed amplitudes 6.7 (2.9, 11.5) vs. 6.1 (2.9, 11.2) mV, P<0.0001 and pacing impedances 500 (440, 609) vs. 491 (437, 593) Omega, P<0.0001 both decreased significantly. CONCLUSION: The current series suggests that MRI scans may be performed safely in appropriately selected patients up to a peak SAR of 3.2 W/kg. Furthermore, peak SAR level poorly predicts the safety profile of patients with pacemakers or ICDS who are exposed to an MRI environment.