AHA Scientific Statement

 Excerpts

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;116:2878-2891.)
© 2007 American Heart Association, Inc.

Glenn N. Levine, MD, FAHA; Antoinette S. Gomes, MD, FAHA; Andrew E. Arai, MD, FAHA; David A. Bluemke, MD, FAHA; Scott D. Flamm, MD; Emanuel Kanal, MD; Warren J. Manning, MD, FAHA; Edward T. Martin, MD, FAHA; J. Michael Smith, MD; Norbert Wilke, MD; Frank S. Shellock, PhD

Most important to the issue of patient safety during MR examination is the "do no harm" approach. If there is a question as to the safety of the MR study, unless circumstances dictate otherwise and the benefits of the examination are believed to outweigh the possible risks, the examination should be deferred until it can be verified that study of the patient is safe. If it cannot be discerned that the patient can safely undergo MR examination, alternative imaging modalities should be used whenever possible.

The very flow of electrically conductive blood in the presence of powerful static magnetic fields produces very small voltages that may produce electrocardiographic aberrations, including elevation of the ST segment, T-wave abnormalities, and even the appearance of arrhythmias. The stronger the static magnetic field, the greater the magnitude of these observed perturbations. This phenomenon may complicate monitoring of the heart rhythm during scanning, lead to inappropriate inhibition of pacemaker function, or create arrhythmia artifacts on event loop recorders

Coronary Artery and Peripheral Vascular Stents

Most coronary and peripheral vascular stents that have been tested have been labeled as "MR safe"; the remainder have been labeled as "MR conditional."1 Tested coronary artery stents (including tested drug-eluting coronary stents) that are nonferromagnetic (all currently used coronary stents) can be safely scanned at 3 T or less any time after implantation. MR examination at ≤3 T in patients with peripheral stents that are nonferromagnetic can be performed immediately after implantation. The timing of MR examination at ≤3 T in patients with peripheral stents that are weakly ferromagnetic should be determined on a case-by-case basis. For cases in which there is a clear potential clinical benefit of scanning in the days to weeks after implantation, the benefits of the MR examination will likely outweigh the risks of the examination, and MR examination should generally be performed. In patients with chronic conditions in which it makes little difference whether the scan is performed at a given time or weeks later, it may be prudent to defer MR examination until {approx}6 weeks after device implantation.


Aortic Stent Grafts

Background Data
The majority of endovascular aortic stent grafts, but not all, are made from nonferromagnetic or weakly ferromagnetic materials. Thus far, there have been several published studies of MR examinations in patients with aortic stent grafts that have not noted any adverse clinical events related to the MR examinations.44,45

 Zenith AAA endovascular graft (Cook) evaluated through bench testing in MR systems with static fields of ≤1.5 T, exhibited significant deflection and torque of the stainless steel metallic component and therefore did not meet standard "MR safe" bench test criteria.46

Most stent grafts create minimal artifacts, which allows for diagnostic visualization of the endostent lumen and for evidence of endostent leak. However, 3 stent grafts (Zenith AAA endovascular graft [Cook], Endologix AAA stent [Endologix], and Lifepath AAA stent [Edwards Lifesciences Corp]) show severe susceptibility artifact that makes evaluation of the endostent lumen or surrounding tissues problematic.47

Labeling/Recommendations
Most aortic stent grafts are  "MR safe"; the Zenith AAA endovascular graft stent has been labeled as "MR unsafe."1,3 Patients with stent grafts made from nonferromagnetic materials may be scanned immediately after implantation at 3 T or less. The timing of MR examination at 3 T or less in patients with aortic stent grafts that are weakly ferromagnetic should be weighed on a case-by-case basis.

The approved manufacturer’s labeling for the Zenith AAA endovascular graft states in part, "Adverse events have not been reported clinically in patients who have undergone MRI. However, sufficient data are not available to demonstrate MRI safety and there may be potential risks (eg, device migration, vessel damage) that could be associated with force applied to the metallic components of the Zenith AAA Endovascular Graft. Therefore, a careful assessment of these potential risks and the potential benefits to the patient should be completed before use of MR imaging."46 The writing group agrees with this approach.

Although patients with the Endologix AAA or Lifepath AAA stents may undergo MR imaging, because of the artifacts created by these stents, MR examination is not recommended as the modality of choice for examinations specifically targeted toward evaluation of the stent grafts.

Prosthetic Heart Valves, Annuloplasty Rings, and Sternal Suture Wires

The presence of a prosthetic heart valve or annuloplasty ring that has been formally evaluated for MR safety should not be considered a contraindication to an MR examination at 3 T or less (and possibly even 4.7 T in some cases) any time after implantation.

MR examination of patients with sternal wires is generally considered to be safe.

Cardiac Closure and Occluder Devices

Patients with nonferromagnetic cardiac closure and occluder devices may undergo MR procedures at any time after implantation. The timing of MR examination at 3 T or less in patients with cardiac closure or occluder devices that are weakly ferromagnetic should be weighed on a case-by-case basis. For cases for which there is a clear potential clinical benefit of scanning in the days to weeks after implantation, the benefits of the MR examination will likely outweigh the risks of the examination, and MR examination should generally be performed.

Inferior Vena Cava Filters

Studies of MR examination of both animals and humans with implanted IVC filters have thus far not reported complications or symptomatic filter displacement..

Most IVC filters that have been tested have been labeled as "MR safe"; the remainder of IVC filters that have been tested are classified as "MR conditional."

Patients who have been treated with nonferromagnetic IVC filters can undergo MR examination any time after filter implantation.

In patients who have been treated with a weakly ferromagnetic IVC filter (Gianturco bird nest IVC filter [Cook], stainless steel Greenfield vena cava filter [Boston Scientific]), it is advised that the patient wait at least 6 weeks before undergoing an MR examination unless there is a strong clinical indication to perform the MR examination sooner after implantation, and as long as there is no reason to suspect that the device is not positioned properly or that it is not firmly in place.

Loop Recorder (Event Monitor)

Background Data
The 9526 Reveal Plus insertable loop recorder (ILR; Medtronic) is a single-use, subcutaneously implanted programmable device that contains 2 surface electrodes used to continuously record the patient’s electrocardiogram. The electromagnetic fields produced during MR imaging may adversely affect the data stored by the Reveal Plus ILR.

Ex vivo evaluation of the Reveal Plus ILR did not suggest significant risk of device movement or dislodgment.76 Clinical MR study of 10 patients with these loop recorders demonstrated no adverse clinical events, and no damage to the devices. Of note, interrogation of the devices after MR revealed tachyarrhythmias and bradyarrhythmias recorded during the examinations that were believed to be artifacts.77

Labeling/Recommendations
The Reveal Plus ILR has been labeled as "MR conditional."1 Patients with a Reveal Plus ILR can undergo MR examination any time after implantation, provided there is no reason to believe the device is not well implanted. Because of the theoretical risk of electromagnetic fields adversely affecting data stored by the device, all stored data should be downloaded before scanning. Because this device contains ferromagnetic components, the patient may feel slight movement of this device.76 Although this does not represent a safety hazard, the patient should be informed of this possibility to avoid undue concern.

Permanent Cardiac Pacemakers and Implantable Cardioverter Defibrillators

A pacemaker or ICD should be considered a strong relative contraindication to routine MR examination, which is therefore discouraged. Patients who have a pacemaker or ICD should not undergo an MR study if an alternative diagnostic test is available, and MR imaging should only be considered in cases in which the potential benefit to the patient clearly outweighs the risks to the patient. Risks to the patient are likely increased in centers without highly experienced personnel in both function and programming of the device and operations/pulse sequences of the MR scanner. Thus, scanning should only be performed at extremely experienced centers with expertise in MR imaging and electrophysiology. If such scanning is performed, the risks of MR scanning should be discussed specifically and clearly with the patient, and the written informed consent should specifically list risks, including (1) pacemaker/ICD dysfunction, (2) pacemaker/ICD damage, (3) arrhythmia, and (4) death.

Any institution at which MR scanning of pacemakers/ICDs is performed should have some formal program of quality control to track adverse events. The patient’s heart rhythm and vital signs should be monitored throughout the MR examination. A physician with pacemaker/ICD expertise should be in attendance during scanning, and a "crash cart," including a defibrillator, must be available throughout the procedure to address any adverse events. A person with expertise in MR physics and safety should be involved with the scan to optimally plan the scan to minimize risk. The pacemaker/ICD should be interrogated before and after the procedure.

Although 1 study found that ICDs manufactured after 2000 may be more resistant to changes in function during MR examination, this finding should not be taken as a "green light" to routinely scan patients with such ICDs.

Fractured leads may pose a particularly high risk of thermal injury, and MR examination should not be performed in patients with pacemakers or ICDs with known lead fractures.

Retained Transvenous Pacemaker and Defibrillator Leads

Retained transvenous pacemaker and defibrillator leads (leads left in the body after explantation of the permanent pacemaker or ICD generator) pose significant theoretical risks. Patients with retained transvenous pacemakers or ICD leads be approached similarly to those with pacemakers or ICDs

Hemodynamic Support Devices

Hemodynamic support devices, including intra-aortic balloon pumps, right ventricular assist devices, and left ventricular assist devices, are complex devices with variable degrees of ferromagnetic materials, moving parts, and electrical components. Although formal evaluation of these devices in regard to MR safety has not been conducted, it is believed that these devices should be considered absolute contraindications to MR