SMRT Signals • February 2017 • Vol.6 Issue 1

INFORMATION FOR YOU:

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 thermal injury, 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 (Figure 1).

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.]

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.

Figure 1. Example of permanent epicardial pacing leads.