Recommendations for magnetic resonance imaging in patients with cardiac implantable electronic devices

Necessity, therefore, drove researchers to study the safety of MR in CIED recipients in vitro and in vivo, and later in patients. This work, in turn, led device manufacturers to make changes to the design of CIEDs and develop MR conditional systems. These changes include reducing ferromagnetic components, changing three-dimensional coil configurations, and adding heat-dissipating filters to the generator and leads. In light of accumulating evidence demonstrating its safety, numerous professional societies now support MR in patients with CIEDs, when using safety protocols.

In this edition of Heart, 11 British medical societies (ie, the Joint British Society (JBS)) from the fields of cardiology, cardiac electrophysiology, radiology and medical products regulation, provide recommendations and guidance for MR in patients with CIEDs. The fundamental principle underlying these recommendations is that when benefits of MR outweigh its risks, the scan should be performed after taking all appropriate safety measures. This principal follows the low rates of adverse events reported in large clinical studies that follow a safety protocol and numerous technological advances rendering CIEDs less susceptible to electromagnetic interference, coupled with the potential risks associated with invasive tests and missed or delayed diagnoses when using alternative imaging modalities. Moreover, MR conditional labelling infers that generator and leads were tested in specific combinations and scanning parameters. Any modification to the device system, or the scan acquisition protocol would render an otherwise conditional CIED as MR unlabeled despite lack of evidence demonstrating increased risk.

Prior to MR, CIED interrogation should be performed to identify issues that may render the system non-MR conditional. The underlying rhythm and pacing dependence of the patient should be determined. Identification of abandoned, fractured or epicardial leads may require review of prior chest X-rays and procedure records. Device arrhythmia logs should be reviewed for recent ventricular arrhythmias to gain a better understanding of the safety of turning off therapies during scan acquisition. If an MR scan is requested emergently, all safety protocols should be followed. Performing a scan without proper supervision and adequate programming of CIEDs is contraindicated. If this is not possible, alternative diagnostic modalities, empiric therapy, or referral to another facility with safe MR acquisition should be considered.

Recommendations for management of MR conditional devices

Written consent is not required with MR conditional CIEDs. Prior to scan acquisition, the device is programmed to MR Mode which uses OVO/ODO or VOO/DOO pacing depending on the presence or absence of a stable underlying rhythm, respectively. This reduces the risks associated with over-sensing electromagnetic interference leading to asystole or inappropriate tracking of electromagnetic interference leading to unwarranted pacing at the upper track rate and/or the risk of malignant arrhythmia due to ‘R-on-T’. Antitachycardia therapies are turned off in defibrillators to prevent inappropriate therapy attempts and voltage depletion.  In most cases, scanning in Normal Operating Mode is recommended with standard specific absorption rates (SARs). All MR conditional devices allow using 1.5 T scans and most allow 3 T, but checking MR conditional parameters set by the manufacturers is recommended. Metal artefact reduction techniques may be used for thoracic imaging. If malignant arrhythmias are detected, scanning should be halted promptly, advanced cardiac life support delivered and the device reprogrammed to deliver appropriate therapies. After the scan, full device interrogation should be performed and MR Mode disabled, reverting the CIED to its original settings. Any significant change in device parameters should be communicated to the patient and cardiologist.

Comparison to other guidelines

The 2017 Heart Rhythm Society (HRS) consensus statement encompassed 11 societies from several continents, as a collaborative effort to offer guidance on MR in CIED recipients. Overall, the HRS and JBS offer similar recommendations such as strict adherence to MR conditional parameters set forth by device manufacturers, rigorous institutional protocols that standardise workflows from referral to completion of the scan and minimise adverse events. Personalised, multidisciplinary discussions among all stakeholders are recommended to evaluate the risk–benefit ratio of performing the study based on clinical context. The guidelines differ, however, in their approach to defining the risks associated with MR image acquisition in unlabelled systems or MR conditional systems not fulfilling specified conditions. The JBS stratifies conditions that fail to meet MR conditional criteria from ‘lower’ with no increased risk, to ‘avoid’ where risk is unavoidably high/MR is not recommended. This risk-stratification tool is a useful resource to guide physicians and patients during shared decision-making. Another difference is the JBS’ recommendation that all new CIED implants should be MR conditional given strong odds of needing an MR during a person’s lifetime and the challenge of obtaining an off-label study with MR unlabelled CIEDs. The HRS consensus statement refrains from making a similar recommendation, listing instead relevant considerations when choosing a system including cost, alternative implant locations and need for multiple generator changes in one’s lifetime. The newest challenge at present is the desire to provide patients with physiological pacing systems, often using components that are not labelled as MR conditional. 

This summary accompanies the 2022 Joint British Society (JBS) recommendations for magnetic resonance (MR) imaging in patients with cardiac implantable electronic devices (CIED) and compares the document to the 2017 Heart Rhythm Society document. The two documents offer complementary guidance to any institution that wishes to implement an MR protocol for patients with CIEDs. In particular, the new JBS document offers a valuable risk-stratification tool to guide the risk–benefit analysis for an MR study and suggests phrases to be used during informed consent. In addition, the document acknowledges new data regarding the overall safety of MR in patients with abandoned leads when a safety protocol is followed. Furthermore, the JBS advocates for collaborative initiatives between cardiology and radiology departments in the UK to improve access of patients with CIEDs to MR.