Low-field magnetic resonance imaging: increased safety for pacemaker patients?

AIMS: The number of low-field (<0.5 T) magnetic resonance (MR) scanners installed worldwide is increasing due to a favourable cost and safety profile and improved patient comfort using an open-scanner design. Therefore, the aim of our study was to evaluate a strategy for the safe performance of magnetic resonance imaging (MRI) at a field strength of 0.2 T, in pacemaker (PM) patients without limitations on scan region, PM dependency, or the presence of abandoned leads. METHODS AND RESULTS: One hundred and fourteen PM patients, including PM-dependent patients and patients with abandoned leads, examined at a 0.2 T MR scanner due to an urgent clinical need for an MRI examination, were evaluated. All PMs were reprogrammed before MRI: if heart rate was <60 bpm, the asynchronous mode (with a rate of 80 bpm) was programmed to avoid MR-induced inhibition; if heart rate was >60 bpm, sense-only mode (ODO/OVO/OAO) was used to avoid MR-induced competitive pacing and potential proarrhythmia. Patients were monitored with electrocardiogram (ECG) and pulse oximetry. All PMs were interrogated before and after MRI, including measurement of lead impedance, pacing capture threshold (PCT), and battery voltage. All MRI scans were completed safely. No induction of arrhythmias or inhibition of PM output occurred. There were no statistically significant changes in lead impedance, PCT, or battery voltage (P>0.05). CONCLUSION: Low-field MRI of PM patients, including high-risk PM patients and MRI scan regions, can be performed with an acceptable risk-benefit ratio under controlled conditions.

Magnetic resonance imaging at 1.5-T in patients with implantable cardioverter-defibrillators.

OBJECTIVES: Our aim was to establish and evaluate a strategy for safe performance of magnetic resonance imaging (MRI) at 1.5-T in patients with implantable cardioverter-defibrillators (ICDs). BACKGROUND: Expanding indications for ICD placement and MRI becoming the imaging modality of choice for many indications has created a growing demand for MRI in ICD patients, which is still considered an absolute contraindication. METHODS: Non-pacemaker-dependent ICD patients with a clinical need for MRI were included in the study. To minimize radiofrequency-related lead heating, the specific absorption rate was limited to 2 W/kg. ICDs were reprogrammed pre-MRI to avoid competitive pacing and potential pro-arrhythmia: 1) the lower rate limit was programmed as low as reasonably achievable; and 2) arrhythmia detection was programmed on, but therapy delivery was programmed off. Patients were monitored using electrocardiography and pulse oximetry. All ICDs were interrogated before and after the MRI examination and after 3 months, including measurement of pacing capture threshold, lead impedance, battery voltage, and serum troponin I. RESULTS: Eighteen ICD patients underwent a total of 18 MRI examinations at 1.5-T; all examinations were completed safely. All ICDs could be interrogated and reprogrammed normally post-MRI. No significant changes of pacing capture threshold, lead impedance, and serum troponin I were observed. Battery voltage decreased significantly from pre- to post-MRI. In 2 MRI examinations, oversensing of radiofrequency noise as ventricular fibrillation occurred. However, no attempt at therapy delivery was made. CONCLUSIONS: MRI of non-pacemaker-dependent ICD patients can be performed with an acceptable risk/benefit ratio under controlled conditions by taking both MRI- and pacemaker-related precautions. (Implantable Cardioverter Defibrillators and Magnetic Resonance Imaging of the Heart at 1.5-Tesla; NCT00356239).