MRI Considerations for Patients with Temporary Epicardial Pacing Leads, Temporary Intracardiac Pacing Leads, Permanent Intracardiac Pacing Leads, and Permanent Epicardial Pacing Leads
MRI Considerations for Patients with Temporary Epicardial Pacing Leads, Temporary Intracardiac Pacing Leads, Permanent Intracardiac Pacing Leads, and Permanent Epicardial Pacing Leads Temporary Epicardial Pacing Leads and Temporary Intracardiac Pacing Leads
Although there is a theoretical risk that MRI examinations in patients with retained temporary epicardial leads (which consist of electrically conductive materials) could lead to cardiac excitation or thermalINJURY, such retained leads which are relatively short in length and do not form large conducting loops have not been found to pose a substantial hazard to patients during MRI procedures.
In 1997, Hartnell, et al. reported findings in 51 patients with retained temporary epicardial pacing wires who underwent clinical MRI procedures. Of those patients examined with electrocardiographic monitoring, no arrhythmias were noted, and for all patients, no symptoms suggestive of arrhythmia or other cardiac dysfunction were identified (although the anatomic region examined and the levels of RF power deposition used in the examinations were not specifically described). While the data in the Hartnell, et al. article may be somewhat flawed and, thus, should be considered mostly anecdotal, to date, there is no report of a complication associated with performing MRI in a patient with retained temporary epicardial leads.
By comparison, an ex vivo study of temporary intracardiac (i.e., endocardial), pacing leads reported temperature increases of up to 63.1 degrees C. Preliminary results of an investigation confirmed that even unconnected temporary transvenous pacing (as well as permanent pacing leads) leads can undergo high temperature increases at 1.5-Tesla/64-MHz. In a chronic-pacemaker animal model undergoing an MRI examination at 1.5-Tesla, temperature increases of up to 20 degrees C were recorded, although pathological and histological examination did not demonstrate heat-induced damage of the myocardium. The MRI conditions that generated such elevated lead temperatures included the use of the transmit body RF coil to deliver RF energy over the area of the intracardiac pacing lead (e.g., as would be used during an MRI examination of the chest/thorax).
To the best of knowledge of the members of a multi-disciplinary group of experts (i.e. the Consensus Group: Levine GN, Gomes AS, Arai AE, Bluemke DA, Flamm SD, Kanal E, Manning WJ, Martin ET, Smith JM, Wilke N, Shellock FG; 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) there is only limited information pertaining to the MRI safety aspects of temporary cardiac pacemakers (i.e., leads and external pulse generators). For example, a report by Pfeil, et al. (2011) suggested that temporary pacemaker myocardial pacing leads may be “compatible with MR scanning” at 1.5-Tesla, but further in vivo studies and carefully monitored patient investigations are needed before final safety recommendations can be made. Of note is that extra caution must be applied when using the transmit RF body coil over the area where the permanent pacing lead is located. Additionally, the possibility of induced currents must be considered.
Thus, because of the relatively low risk, patients with retained temporary epicardial pacing leads may undergo MRI procedures and, importantly, patients do not need to be routinely screened for the presence of such leads before scanning. Because of the possible increased risks involved with the external pulse generators used with temporary epicardial pacing leads, these devices should not be connected when a patient is undergoing MRI.
By comparison, scanning patients with temporary intracardiac pacing leads (without the pulse generator) is not recommended due to the possibility of excessive heating and/or induced currents associated with MRI. Abandoned Permanent Intracardiac Pacing Leads
Over the lifetime of using a permanent cardiac pacemaker, an intracardiac pacing lead may be “abandoned” and replaced due to lead fracture, insulation breaks, dislodgement, or other failures and abnormalities in pacing or sensing. For an abandoned lead that is not connected to a pulse generator, substantial heating may occur in relation to MRI examinations, as reported by Langman, et al. (2011, 2012).
By comparison, a study by Higgins, et al. (2014) that involved patients with abandoned pacemaker and implantable cardioverter defibrillator (ICD) leads reported that the use of MRI in patients with abandoned cardiac device leads may be feasible when performed under careful monitoring conditions and with other precautions in place. However, until further studies define safe-scanning conditions for abandoned intracardiac pacing leads, MRI healthcare professionals should be aware of the higher risk of RF-induced lead tip heating and other possible MRI-related issues. Abandoned Permanent Epicardial Pacing Leads
It should be noted that, retained temporary epicardial cardiac pacing leads (commonly found post cardiac surgery) are not the same as epicardially implanted permanent cardiac pacing leads. Permanent epicardial pacing leads are less commonly found in patients (less than 1% of all permanent pacing leads) than permanent intracardiac pacing leads.
Permanent epicardial pacing leads are implanted by surgeons, usually in the setting of recurring hardware infection to avoid endocardial indwelling (i.e., intracardiac pacing leads) or in congenital heart disease where access to cardiac chambers is a difficulty from an endocardial approach (Personal Communication, Saman Nazarian, M.D., Ph.D., Cardiac Electrophysiology, The University of Pennsylvania Perelman School of Medicine Philadelphia, PA). Because of the inherent qualities (i.e., materials, length of leads, etc.) of these pacing leads, it is advisable to exercise caution for patients with abandoned permanent epicardial cardiac pacing leads similar to how patients with abandoned intracardiac pacing leads are managed with respect to MRI issues.
[Portions of this document were excerpted with permission from Levine GN, Gomes AS, Arai AE, Bluemke DA, Flamm SD, Kanal E, Manning WJ, Martin ET, Smith JM, Wilke N, Shellock FG. 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. Circulation 2007;116:2878-2891. Reviewed and updated 2017.] REFERENCES
Achenbach S, et al. Effects of magnetic resonance imaging on cardiac pacemakers and electrodes. Am Heart J 1997;134:467-473.
Bottomley PA, Kumar A, et al. Designing passive MRI-safe implantable conducting leads with electrodes. Med Phys 2010;37:3828-43.
Dempsey MF, Condon B, Hadley DM. Investigation of the factors responsible for burns during MRI. J Magn Reson Imag 2001;13:627–631.
Hartnell GG, et al. Safety of MR imaging in patients who have retained metallic materials after cardiac surgery. Am J Roentgenol 1997;168:1157–1159.
Higgins JV, et al. Safety and outcomes of magnetic resonance imaging in patients with abandoned pacemaker and defibrillator leads. Pacing Clin Electrophysiol 2014;37:1284-90. Kanal E. Safety of MR imaging in patients with retained epicardial pacer wires. Am J Roentgenol 1998;170:213-4.
Langman DA, et al. Abandoned pacemaker leads are a potential risk for patients undergoing MRI. Pacing Clin Electrophysiol 2011;34:1051-3.
Langman DA, et al. Pacemaker lead tip heating in abandoned and pacemaker-attached leads at 1.5 Tesla MRI. J Magn Reson Imag 2011;33:426-31.
Langman DA, et al. The dependence of radiofrequency induced pacemaker lead tip heating on the electrical conductivity of the medium at the lead tip. Magn Reson Med 2012;68:606-13.
Levine GN, et al. 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. Circulation 2007;116:2878-2891.
Luechinger R, et al. In vivo heating of pacemaker leads during magnetic resonance imaging. Eur Heart J 2005;26:376-383.
Pfeil A, et al. Compatibility of temporary pacemaker myocardial pacing leads with magnetic resonance imaging: An ex vivo tissue study. Int J Cardiovasc Imaging 2011;28:317-26.
Shellock FG, Valencerina S, Fischer L. MRI-related heating of pacemaker at 1.5- and 3-Tesla: Evaluation with and without pulse generator attached to leads. Circulation 2005;112;Supplement II:561.
Type of Exam
Approximate Length of Time On High-Field MRI (minutes)
Approximate Length of Time on Open MRI (minutes)
Brain without contrast
25
35
Brain with contrast
40
50
Lumbar Spine without contrast
20
45
Lumbar Spine with and without contrast
40
60
Conversion of 63.1 degrees C
=
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Guidelines to Prevent Excessive Heating and Burns Associated with MRI
Guidelines to Prevent Excessive Heating and Burns Associated with Magnetic Resonance Procedures*
Magnetic resonance (MR) imaging is a relatively safe diagnostic modality. However, damaged radiofrequency coils, physiologic monitors, electronically-activated devices, and external accessories or objects made from conductive materials have caused excessive heating, resulting in burnINJURIES to patients undergoing MR procedures. Heating of implants and similar devices may also occur, but this tends to be problematic primarily for objects made from conductive materials that have elongated shapes or that form loops of a certain diameter. For example, excessive MRI-related heating has been reported for leads, guidewires, catheters (e.g., catheters with thermistors or other conducting components), and external fixation systems, and cervical fixation systems. In the United States, many incidents of excessive heating have been reported in patients undergoing MR procedures that were unrelated to equipmentPROBLEMS or the presence of conductive external or internal implants or materials [review of data files from U.S. Food and Drug Administration, Center for Devices and Radiological Health, Manufacturer and User Facility Device Experience Database, MAUDE]. In a review of the MAUDE database over a 10 year period, Hardy and Weil (2010) indicated that 419 thermal injuries were associated with MRI. These incidents included first, second, and third degree burns that were experienced by patients. In many of these cases, the reports indicated that the limbs or other body parts of the patients were in direct contact with transmit body radiofrequency (RF) coils or other transmit RF coils of the MR systems. In other cases, skin-to-skin contact points were suspected to be responsible for theseINJURIES, however, the exact mechanism responsible for these incidents is unknown. MR systems require the use of RF pulses to create the MR signal. This RF energy is transmitted through free space from the transmit RF coil to the patient. When conducting materials are placed within the RF field, a concentration of electrical currents sufficient to cause excessive heating and tissue damage may occur. Therefore, only devices with carefully designed current paths can be made safe for use during MR procedures. Simply insulating conductive material (e.g., wire or lead) or separating it from the patient may not be sufficient to prevent excessive heating or burns from occurring for some devices. Furthermore, certain elongated shapes (i.e. depending on the length and the transmit RF frequency) exhibit the phenomenon of “resonance” that increases their propensity to concentrate RF currents. At the operating frequencies of present day MR systems, conducting loops of tens of centimeters in size can createPROBLEMS and must be avoided, unless high impedance techniques are used to limit the RF current. Importantly, even loops that include small gaps separated by insulation may still conduct currents. Pietryga et al. (2013) reported a case of a thermal burn that occurred during MRI that was likely caused by invisible silver embedded microfibers in the fabric of an undershirt. As the prevalence of fabrics containing nondetectable metallic microfibers increases for use in athletic clothing or other garments, the importance of having patients change into gowns or other appropriate attire that do not contain metallic materials is advised as another means of preventing MRI-related burns.
To prevent excessive heating and possible burns in association with MR procedures, the following guidelines are recommended:
The patient should change into a gown or other appropriate attire that does not contain metallic material.
Prepare the patient for the MR procedure by ensuring that there are no unnecessary metallic objects contacting the patient’s skin (e.g., drug delivery patches with metallic components, jewelry, necklaces, bracelets, key chains, etc.).
Prepare the patient for the MR procedure by using insulation material (i.e. appropriate padding) to prevent skin-to-skin contact points and the formation of “closed-loops” from touching body parts.
Insulating material (minimum recommended thickness, 1-cm) should be placed between the patient’s skin and transmit RF coil that is used for the MR procedure (alternatively, the transmit RF coil itself should be padded). There should be no direct contact between the patient’s skin and the transmit RF body coil of the MR system. This may be accomplished by having the patient place his/her arms over his/her head or by using elbow pads or foam padding between the patient’s tissue and the transmit RF body coil of the MR system. This is especially important for MR examinations that use the transmit RF body coil or other large RF coils for transmission of RF energy.
Use only electrically conductive devices, equipment, accessories (e.g., ECG leads, electrodes, etc.), and materials that have been thoroughly tested and determined to be safe or otherwise acceptable for MR procedures.
Carefully follow the MR Safe or MR Conditional criteria and recommendations for implants and devices made from electrically-conductive materials (e.g., bone fusion stimulators, neurostimulation systems, cardiac devices, cochlear implants, etc.).
Before using electrical equipment, check the integrity of the insulation and/or housing of all components including surface RF coils, monitoring leads, cables, and wires. Preventive maintenance should be practiced routinely for such equipment.
REMOVEall non-essential electrically conductive materials from the MR system prior to the MR procedure (i.e. unused surface RF coils, ECG leads, EEG leads, cables, wires, etc.).
Keep electrically conductive materials that must remain in the MR system from directly contacting the patient by placing thermal and/or electrical insulation between the conductive material and the patient.
Keep electrically conductive materials that must remain within the transmit body RF coil or other transmit RF coil from forming conductive loops. Note: The patient’s tissue is conductive and, therefore, may be involved in the formation of a conductive loop, which can be circular, U-shaped, or S-shaped.
Position electrically conductive materials to prevent “cross points”. A cross point is the point where a cable crosses another cable, where a cable loops across itself, or where a cable touches either the patient or sides of the transmit RF coil more than once. Even the close proximity of conductive materials with each other should be avoided because cables and RF coils can capacitively-couple (without any contact or crossover) when placed close together.
Position electrically conductive materials (e.g., cables, wires, etc.) to exit down the center of the MR system, not along the side of the MR system or close to the transmit RF body coil or other transmit RF coil.
Do not position electrically conductive materials across an external metallic prosthesis (e.g., external fixation device, cervical fixation device, etc.) or similar device that is in direct contact with the patient.
Allow only properly trained individuals to operate devices (e.g., monitoring equipment) in the MR environment.
Follow all manufacturer instructions for the proper operation and maintenance of physiologic monitoring or other similar electronic equipment intended for use during MR procedures.
Electrical devices that do not appear to be operating properly during the MR procedure should beREMOVED from the patient immediately.
RF surface coil decoupling failures can cause localized RF power deposition levels to reach excessive levels. The MR system operator will recognize such a failure as a set of concentric semicircles in the tissue on the associated MR image or as an unusual amount of image non-uniformity related to the position of the transmit RF coil.
Do not permit patients to wear clothing items (e.g., sportswear, underwear, yoga pants, etc.) that have metal-based fibers.
Closely monitor the patient during the MR procedure. If the patient reports sensations of heating or other unusual sensation, discontinue the MR procedure immediately and perform a thorough assessment of the situation.
The adoption and regular practice of these guidelines will ensure that patient safety is maintained, especially as more conductive materials and electronically-activated devices are used in association with MR procedures. [*The document, Guidelines to Prevent Excessive Heating and Burns Associated with Magnetic Resonance Procedures, was developed by the Institute for Magnetic Resonance Safety, Education, and Research (IMRSER) and published with permission. Reviewed and updated 2017.] REFERENCES Abdel-Rehim S, et al. Burns from ECG leads in an MRI scanner: Case series and discussion of mechanisms. Ann Burns Fire Disasters 2014;27:215-8. Bashein G, Syrory G. Burns associated with pulse oximetry during magnetic resonance imaging. Anesthesiology 1991;75:382-3. Bennett MC, et al. Mechanisms and prevention of thermal injury from gamma radiosurgery headframes during 3T MR imaging. J Appl Clin Med Phys 2012;13:3613. Brown TR, Goldstein B, Little J. 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ADDRESSfor reprints: Deborah A. Langman, Ph.D., Peter V. Ueberroth Bldg., Suite 1417, 10945 Le Conte Avenue, Los Angeles, CA 90095. Fax: 310‐825‐0880; e‐mail: dlangman@mednet.ucla.edu
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