Status of MRI exams and implanted cardiac devices: A review
Clinical research studies are increasingly confirming that some patients with implantable cardiac electronic devices may be able to safely undergo magnetic resonance imaging (MRI) exams. Although many new devices that have become available are specifically approved by the U.S. Food and Drug Administration (FDA) for use in a MR scanner (MR-conditional), a growing body of peer-reviewed literature suggests that non-FDA-approved devices (MR-nonconditional) may also be safely scanned, and should no longer be considered an absolute contraindication to MRI. A concise review of this subject has been published in the Journal of Magnetic Resonance Imaging.
In their article, radiologists at the University of Arizona’s Department of Medical Imaging and Division of Cardiology in Tucson explain that patients who have nonconditional ICEDs should not automatically be excluded from having MRI scans. Rather, they should be pre-screened, assessed, and monitored throughout the procedure by skilled electrophysiology staff. Collaboration by clinical staff in the radiology and cardiology departments is an absolute necessity, both to develop and maintain specific protocols for patients with ICEDs and to work together with respect to these patients to ensure the clinical appropriateness, their eligibility, and their safety during and after the procedure. Most importantly, clinicians and staff must be thoroughly trained and knowledgeable of MRI safety.
Lead author Bobby Kalb, MD, associate professor of medical imaging and clinical director of MRI, and colleagues noted prior work that described people with ICEDs have at least a 50% chance of needing an MRI during their lifetime. ICEDs approved for use with MRI systems are growing. However, patients with implanted MR-conditional devices that are designed to improve compatibility with the MRI environment are still a minority of ICED users.
MR-conditional devices differ from nonconditional ones in that they have less ferromagnetic material, contain solid-state Hall sensors that are less likely to be inappropriately activated, and are less susceptible to the issues of lead-tip heating and storage-charging issues. To be deemed MR-conditional, the ICED should also meet the following requirements:
- The CIED generator and leads are manufactured by a single vendor.
- No nonconditional hardware is present, including abandoned, epicardial, or nonfunctioning leads.
- The device can be programmed for the MR scan.
- The duration of the time of the implant before a scheduled MRI procedure is greater than the vendor-specified minimum.
Adverse events and concerns
The most commonly reported adverse event occurring with a nonconditional ICED is altered function of the device. Asynchronous pacing or inhibition of pacing may also occur, as well as the inability of the ICED to detect tachyarrhythmias. The ICED may lose its ability of its storage capacitor to charge, causing the battery to deplete. Power-on resets and electrical reset to factory settings may occur.
Another concern is that ICED leads may act as an antenna for the RF pulse emitted by the scanner. This could induce RF current to flow from the lead into surrounding tissues. However, recent studies have not identified evidence of tissue injury, which the authors attribute to the cooling effects of flowing blood acting as a protective mechanism against large increases in the temperature of the lead tip.
Movement and torque of the ICED is another concern, the effect of the static magnetic field on ferromagnetic objects. This is of negligible concern for patients with current generation devices, the authors advise.
The authors also report that no comparative effectiveness studies have been performed to compare conditional and nonconditional ICEDs using the same scanning protocols. Just as with patients with nonconditional devices, they advise that patients with MR-conditional devices still require monitoring during the exam and that skilled personnel are needed to modify device settings.
Clinical workflow protocols
The article includes a synopsis of protocol recommendations.
Patients who may undergo a MRI exam need to have a preclinical assessment with electrophysiology experts of cardiology departments. First and foremost, an assessment of the type and conditionality of the ICED is need. This assessment encompasses the hardware design of the device and its programming as well as identification of abandoned or fractured leads and other implanted hardware. A clinical evaluation needs to be made to determine if the patient is pacing dependent. A collaborative decision needs to be made by the ordering physician with cardiology and radiology regarding the cost/benefit analysis of the exam.
If the exam is approved, exam scheduling needs to include scheduling of electrophysiology staff or the ICED device representative to be present.
Informed consent needs to be obtained when the patient arrives for the exam. At the MRI suite, the patient needs to be placed on MR-safe monitoring devices for ECG, heart rate, and pulse oximetry. After completing an ICED evaluation to confirm correct functioning of the device and adequate pacing capture thresholds, the device is programmed to settings that will allow safe MR scanning. Clinical staff trained in advanced cardiac life support is required to monitor the patient during the procedure. Resuscitation equipment is needed to be in the MRI suite and a physician available. Following the procedure, the ICED requires complete evaluation and reprogramming, with a routine follow-up appointment scheduled for the patient at his/her pacer clinic.
The article also briefly reviews specialized topics of retained leads, 3T MRI, performing thoracic MRI exams, and waiting periods for patients with recently implanted devices.
REFERENCE
- Kalb B, Indik JH, Ott P, et al. MRI of Patients With Implanted Cardiac Devices. J Magn Reson Imaging. Published online August 4, 2017. doi: 10.1002/jmri.25824