Magnetic resonance imaging, pacemakers and implantable cardioverter-defibrillators: current situation and clinical perspective

Abstract

New developments and expanding indications have resulted in a significant increase in the number of patients with pacemakers and internal cardioverterdefibrillators (ICDs). Because of its unique capabilities, magnetic resonance imaging (MRI) has become one of the most important imaging modalities for evaluation of the central nervous system, tumours, musculoskeletal disorders and some cardiovascular diseases. As a consequence of these developments, an increasing number of patients with implanted devices meet the standard indications for MRI examination. Due to the presence of potential life-threatening risks and interactions, however, pacemakers and ICDs are currently not approved by the Food and Drug Administration (FDA) for use in an MRI scanner. Despite these limitations and restrictions, a limited but still growing number of studies reporting on the effects and safety issues of MRI and implanted devices have been published. Because physicians will be increasingly confronted with the issue of MRI in patients with implanted devices, this overview is given. The effects of MRI on an implanted pacemaker and/or ICDs and vice versa are described and, based on the current literature, a strategy for safe performance of MRI in these patients is proposed. (Neth Heart J 2010;18:31-7.).

Keywords: implantable cardioverter-defibrillator; magnetic resonance imaging; pacemaker.

Figure 1

A) The strong static magnetic (B₀) field aligns the normally randomised oriented hydrogen nuclei (protons) in the human body, causing a net longitudinal magnetisation. In this situation, the protons rotate at a predefined frequency, the Larmor frequency. B) The radiofrequency (RF) pulse flips the net longitudinal magnetisation into the transverse plane (upper part). After the RF pulse is switched off, the original situation is restored. The transverse magnetisation will fade and a progressive increase in the longitudinal magnetisation will occur (lower part). C) Magnetic gradient fields alter the longitudinal magnetisation in a linear way along the axis causing small changes of the Larmor frequency of the protons. This enables the identification of proton position in 3D space.