MRI issues for hemodynamic monitoring and temporary pacing devices*

Determining the safety of MRI for patients who are implanted with hemodynamic monitoring or temporary pacing devices, including epicardial pacing wires and intracardiac pacing leads, requires careful consideration.

Cardiovascular catheters such as pulmonary artery hemodynamic monitoring/thermodilution catheters, including the Swan-Ganz catheter (Edwards Lifesciences), and temporary transvenous cardiac pacing devices generally contain no ferromagnetic components. But they may incorporate nonferromagnetic, electrically conductive materials. The MRI examination may induce voltages and currents in electrically conductive material sufficient to result in thermal injuries and burns to adjacent tissue (including myocardial tissue).

MRI examinations performed in patients with retained temporary epicardial leads, which consist of electrically conductive material, could theoretically lead to cardiac excitation or thermal injury. Such retained leads, however, are typically short in length, usually do not form large loops, and are generally not believed to pose a significant risk during MRI examinations.

Hartnell et al reported on 51 patients with retained temporary epicardial pacing wires who underwent clinical MR examination. Of those patients examined with electrocardiographic monitoring, no arrhythmias were noted. For all patients, no symptoms suggestive of arrhythmia or other cardiac dysfunction were noted (although the anatomic region examined and the energies used in the examinations were not specifically described). To date, there is no report of complications related to the MR scanning of a patient with retained epicardial leads.

One report in the literature describes a Swan-Ganz thermodilution catheter that "melted" at the skin entry site in a patient undergoing MRI examination. It was postulated that the radiofrequency fields transmitted by the MR system caused heating of the copper wires within the catheter. The ex vivo study of temporary transvenous pacing leads reported temperature increases of up to 63.1°C.

Preliminary results of a recent study confirmed that even unconnected temporary transvenous pacing (as well as permanent pacing) leads can undergo high temperature increases at 1.5T. In a chronic-pacemaker animal model undergoing MR examination at 1.5T, temperature increases of up to 20°C were measured, although pathological and histological examination did not demonstrate heat-induced damage of the myocardium. The MR imaging conditions that generated such elevated lead temperatures included use of the body RF coil to transmit RF energy over the area of the lead (e.g., an MRI examination of the chest/thorax).

Currently, no study has assessed the safety of temporary pacemakers (intracardiac lead and external pulse generator). Unlike permanent cardiac pacemaker devices, temporary pacemakers use unfixed intracardiac leads that are more prone to movement, longer leads that may be prone to induction of lead currents, and a less sophisticated pulse generator, which makes them likely more susceptible to electromagnetic interference.

RECOMMENDATIONS

Those few catheters that contain conducting wires and those few temporary transvenous pacing wires that have been tested have been labeled as "MR unsafe" (see www.MRIsafety.com). Patients with pulmonary artery hemodynamic monitoring/thermodilution catheters (such as the Swan-Ganz catheter) and similar catheters that have conductive wires or similar components should not undergo MRI examination because of the possible associated risks, unless in vivo testing provides labeling information or instructions for use that permit examinations to be performed safely.

Patients with nonferromagnetic pulmonary artery catheters that contain no electrically conductive pathways in the catheter may undergo MRI examination. It must be emphasized, however, that such conditions must be verified before such patients undergo MRI procedures.

Patients with retained temporary epicardial pacing wires are believed to be able to safely undergo MR procedures, and patients do not need to be routinely screened for the presence of such wires before scanning. Because of the possible risks involved with temporary-pacemaker external pulse generators, such generators should not be introduced into the MRI environment.

Although temporary transvenous lead heating can be minimized or avoided by scanning anatomic regions above (e.g., head/brain) or below (e.g., lower extremities) the cardiac pacing leads, scanning of patients with temporary transvenous pacing leads (without the pulse generator) is not recommended. Furthermore, because the harsh electromagnetic environment associated with the MR system can alter the operation of an external pulse generator or damage it, it may not be possible to reliably pace the heart of the patient during the MRI examination, which makes the issue of scanning a patient with a temporary transvenous/intracardiac lead irrelevant in most cases.

*Excerpted with permission from Levine GN, Gomes AS, Arai AE, et al; American Heart Association Committee on Diagnostic and Interventional Cardiac Catheterization; American Heart Association Council on Clinical Cardiology; American Heart Association Council on Cardiovascular Radiology and Intervention. Safety of magnetic resonance imaging in patients with cardiovascular devices: an American Heart Association scientific statement from the Committee on Diagnostic and Interventional Cardiac Catheterization, Council on Clinical Cardiology, and the Council on Cardiovascular Radiology and Intervention: endorsed by the American College of Cardiology Foundation, the North American Society for Cardiac Imaging, and the Society for Cardiovascular Magnetic Resonance. Circulation 2007;11;116:2878-2891. Frank G. Shellock was the senior author of this paper.

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