Pacemakers, ICDs, Pacing Wires and Loop Recorders

Cardiac pacemakers and implantable cardioverter-defibrillator (ICDs) were once considered absolute contraindications for MRI due to the following potential issues:

1. Movement and/or vibration of the pulse generator or leads
2. Temporary or permanent modification of the function (i.e., damage) of the device
3. Inappropriate sensing, triggering, or activation of the device
4. Excessive heating or induced current in leads
5. Electromagnetic interference

These problems were linked to pacemaker models produced before 1996. Several pilot studies, however, have shown that limited MRI of patients with nondependent pacemakers in a controlled and monitored environment can be performed safely if strict guidelines are followed. Because of these studies and the approval of several MRI conditional systems, pacemakers are now considered a relative contraindication. Note that guidelines from the American Heart Association (AHA) and the Food and Drug Administration (FDA) do not support MRI in pacemaker patients who do not have MRI conditional/approved systems.

• The pacemaker/ICD must be in place for more than 6 weeks. The patient must be not at or near Elective Replacement Indicator (ERI).
• The patient should be alert and responsive. If MRI is requested in an unresponsive patient, 1) attending to attending confirmation of the need for MRI, and not alternative imaging modalities, must be confirmed; and 2) informed consent is required.
• Patients should be scanned during normal workday hours (8am to 5pm) on 1.5T scanners in the hospital setting. 3T will only be considered for appropriate MRI conditional devices at Parnassus.
• Expedited approval is sometimes possible if 1) an MRI conditional device is documented in the EMR; and 2) an established, modified MRI scan protocol appropriate for pacers/ICDs will be used. To facilitate this, the specific device in question and MRI scan protocol should be clearly stated in the MRI requisition. Note that established scan protocols are in place for:
  • Brain
  • Cardiac
  • Abdomen
  • Knee
  • Spine following the manufacturer's guidelines regarding MRI protocol restrictions.
• The workflow for MRI conditional pacers/ICDs is as follows:

1. Prior to scheduling, the MRI conditional device should be confirmed.
2. An electrophysiology (EP) physician, nurse or a manufacturer representative will reprogram the pacer/ICD to the appropriate setting before and after the MRI. This will be done at the MRI scanner. Device interrogators for the four major manufacturers will be stored in the MRI suite.
3. Monitoring during the MRI scan will be performed by a Radiology nurse. Monitoring will entail pulse oximetry and heart rate, as well as continuous visual and voice contact with the patient.
4. If any issue arises (i.e., pain, discomfort, significant change in heart rate), the patient will be removed from the MRI scanner and the EP consult fellow will be called at 443-UCEP. If the patient is unresponsive or unstable, a code will be called. An external defibrillator should be easily accessible.

• If there is not an MRI conditional device, the workflow will be modified as follows:

1. Risk-benefit analysis should clearly show the benefits of MRI. The study should not be performed if similar clinical information could be obtained with another image modality. Indications for which MRI will be considered without an MRI conditional device include: Brain, Cardiac, or Other indications where the risk-benefit analysis is compelling.
2. An appointment with the EP clinic should be schedule prior to the MRI date to review the details of the pacer/ICD and leads, and confirm that MRI is appropriate. EP should document in their notes regarding the encounter that a full discussion of risks and benefits of MRI was performed with the patient.
3. On the day of the exam, an EP physician or nurse will reprogram the pacer/ICD to the appropriate setting before and after the MRI.
4. Monitoring during the MRI scan will be performed by a Radiology nurse for patients who are non-pacer dependent; EP staff will monitor patients who are pacer-dependent. Monitoring will entail pulse oximetry and heart rate, as well as continuous visual and voice contact with the patient.
5. If any issue arises (i.e., pain, discomfort, significant change in heart rate), the patient will be removed from the MRI scanner and the EP consult fellow will be called at 443-UCEP. If the patient is unresponsive or unstable, a code will be called. An external defibrillator should be easily accessible.

• Note that the presence of a coronary sinus lead is no longer a contraindication in patients with approved CRT-D devices (listed above).
• Thoracic MRI presents additional risk that should be considered. Multiple MRI exams should also be avoided, when possible.
• Appropriate personnel, a crash cart, and defibrillator must be available throughout the procedure to address an adverse event. Visual and voice contact with the patient should be maintained throughout the study. The patient should report any unusual sensations or problems so that, if necessary, the study can be terminated.
• Appointments will be coordinated to ensure that an MRI physicist and an attending radiologist are involved to tailor the study for minimum SAR while obtaining the essential clinical information.

Cardiac Loop Recorders typically contain no lead wires or large loops of electrically conductive material. Product details regarding the specific loop recorder in question should be reviewed prior to MRI.

The main issue to consider with MRI is that data stored on the device may be altered or erased. Data should be downloaded before the time of study, and this issue should be discussed with the cardiologist who manages the loop recorder.

Because loop recorders contain ferromagnetic components, patients may feel slight movement during scanning. While not a safety hazard, patients should be made aware of this before scanning.