MRI scanning

A study published in the New England Journal of Medicine assessed the risks associated with MRI in patients with a pacemaker or defibrillator. Study outcomes suggest that the risks associated with temporary removal of the device are greater than proceeding with MRI scanning while the device is in place.

 

Cardiovascular devices, such as pacemakers and implantable-cardioverter-defibrillators (ICD), are used in patients with heart disease to monitor and control abnormal rhythms. Pacemakers are used to treat arrhythmias and with a low level of electricity can keep the heart beating at a normal rate. The ICD is placed under the skin and keeps track of heart rate. If an abnormal rate is detected, the device can deliver a shock to restore a normal heart rate. Magnetic Resonance Imaging (MRI) is a commonly used imaging technique that uses magnetic fields and radio waves to produce detailed images of organs, bones, and tissues inside the body.

Initially, it was advised that patients with pacemakers and ICD not undergo MRI because of the possibility that the magnetic field might heat cardiac leads (thin wires embedded in the heart) which could result in a thermal injury or interfere with the device’s ability to pace the heartbeat. Over the past twenty years, advancements in device design have decreased the risk associated with MRI. Devices are now labeled as “MRI-conditional” if there are no known hazards associated with MRI. However, approximately 6 million people worldwide have devices that do not meet the criteria to be MRI-conditional and it is predicted that half of them will at some point need an MRI. A registry called MagnaSafe was created to keep track of study participants and monitor their health and device after undergoing a nonthoracic (thoracic scans excluded due to increased perceived risk) MRI with a strength of 1.5 tesla (unit for magnetic fields). All of the 1500 participants (1000 pacemaker, 500 ICD) were over 18 and had a non-conditional-MRI device implanted after 2001.

The study followed a specific protocol for device interrogation, programming, patient monitoring, and follow-up to maximize safety. Devices were checked before and after the MRI, and each participant was monitored for several endpoints, including death during MRI, device failures requiring immediate replacement, and induced arrhythmia. No patient that went through the study protocol experienced death or had a device or lead failure. Six patients experienced arrhythmias that lasted less than 49 hours. Limitations of the study include a heterogeneous population with variability in devices from different manufacturers, and multiple MRI exposures in some patients. Overall, the authors conclude that the risk associated with removing the device is likely greater than proceeding with the MRI scan while the device in place. In addition, they describe a protocol for the procedure and monitoring of patients with cardiac devices that require MRI scanning.

 

Written By: Katherine M. Evely, MS



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