VAPORHCS/OHSU J: Safety of Clinically Indicated Magnetic Resonance Imaging in Patients With Permanent Pacemakers (PPM) and Implanted Cardioverter Defibrillators (ICDs)

1. Abstract

Ferromagnetic Implants such as PPM's and ICD's are traditionally accepted as contraindications to MRI due to safety concerns. The hypothesis is that these procedures can be safely performed when appropriate safety precautions and vetting practices are implemented.

This is a cohort study. 1000 patients with a clinical need for MRI will be included in the study at OHSU. The type of device and leads will be ascertained and a safety protocol will be strictly adhered to. 2. Background

It has been estimated that 50-75% of patients with implanted devices (pacemakers and ICDs) will develop an indication for magnetic resonance imaging (MRI) examination. Thus, there are approximately 200,000 patients annually denied MRI scans because of the presence of PPMs and ICDs in the United States. The current standard of care is not to perform these scans, and instead to utilize other (inferior) imaging, and make clinical decisions without the benefit of MRI imaging. This is the current standard of care of OHSU, where only pacemaker patients who are not pacemaker dependent can undergo MRI scans, per radiology policy. However, this leads to gaps in care for some patients who would clearly benefit from an MRI scan. In some centers, it has been shown that when proper precautions are taken, MRIs can be safely performed on patients with PPMs and ICDs. The published experience from Johns Hopkins reports over 500 scans performed without any adverse outcomes.(1) There are also several smaller studies documenting the safe experience with MRI scanning in device patients (reviewed in (1), table 4)

The main concerns which have led to restrictions on MRIs in patients with cardiac rhythm devices are the following:(2)

1. Force and torque-ferromagnetic devices in a magnetic field are subject to static and gradient magnetic field induced force and torque. However, the maximum force that a modern PPM or ICD generator would be subject to is 100g, far under what would be needed to dislodge a device.
2. Current induction-the gradient magnetic fields in the MRI scanner could induce current in conductors in the field. However, the maximum observed current in vitro has been less than 0.5mA, far less than what is required to capture myocardium.
3. Heating-Leads and other metallic devices can act as antennae, and may heat in the magnetic field, however, no heating greater than 0.5deg C were observed in vitro.
4. Inappropriate pacing/shock/inhibition of pacing-Pacemakers and ICDs have the possibility of receiving electromagnetic interference from the MRI and having this lead to inappropriate pacing, inhibition of pacing, ICD shocks, reprogramming, or loss of function.