MRI in patients with cardiac implantable electronic devices (CIED) has increasingly become a requirement in radiological departments 1-8. Especially in the setting of patients with MR conditional pacemaker systems, where all the manufacturer's instructions are followed and a standardized institutional workflow is in place, it is considered relatively safe based on ample clinical evidence and is supported by clinical guidelines and consensus papers of different societies 1-6.
The article below aims to summarize important steps in the setting of an MRI for patients with a cardiac conduction device and provide useful links.
This article does not replace national guidelines, consensus statements, manufacturer’s instructions and institutional workflow protocols on the topic. In particular exact recommendations for when to avoid scanning and specific requirements in high-risk situations and the setting of MR non-conditional systems vary among the different consensus recommendations 1-6 and local institutional protocols and those statements should be respected and followed.
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Requirements
The following technical and personnel requirements should be fulfilled 1-5:
standardized institutional workflow process or operating procedure and documentation 7,8
up-to-date MR system (usually with a cylindrical bore and better 1.5 tesla)
personnel trained in interrogation and programming cardiac conduction devices
close cooperation between radiology and cardiology/cardiac electrophysiology
monitoring equipment: pulse oximetry (preferred) and/or ECG
resuscitation equipment: including an external defibrillator
available personnel trained in basic and advanced cardiovascular life support
Workflow process
Before booking the scan the following conditions should be looked at under all circumstances 3-5:
clinical appropriateness of the scan
MR safety screening: determination of the MR conditional status and risk assessment
specification and ensuring of a suitable scan protocol and scan parameters
patient consent and appointment allocation
The following additional steps should be undertaken in the setting of MR non-conditional CIEDs 3,5:
appropriate risk assessment
consideration of alternative imaging modalities
discussion of risk-benefit and patient consent
On the day of the examination, the following steps should be undertaken before the scan 3,5:
availability of personnel trained in basic and advanced cardiovascular life support
availability of external defibrillator (ideally with transcutaneous pacing)
confirmation of standardized MRI safety screening and documentation
device interrogation and programming
monitoring during the scan: pulse oximetry ± ECG
MRI scan acquisition as per MRI conditions (specified by the manufacturer in MR conditional systems and by the institutional protocol in MR non-conditional devices)
image review
device interrogation and reprogramming to normal settings
appointment for routine cardiac conduction device follow-up
improved safety precautions when scanning patients with MR non-conditional or MR unlabelled pacing devices
MR safety screening
MR safety screening forms an important step within the standardized workflow for MRI in patients with cardiac conduction devices and should take place, checked and documented before each MRI examination. It includes the identification and verification of the MR conditional status, a risk assessment 2-5 as well as determining whether changes have been made to the system.
MR conditional status
Identification and verification of MR-conditional status is usually the first important step in the MR safety screening process, as the clinical risk of MRI for patients with MR-conditional cardiac conduction devices is considered to be very low as long as the device is MR-conditional as a whole (generator and leads in combination) and the manufacturer's conditions and instructions are followed 2-5.
The process includes the identification of the respective device, usually with the patient's pacemaker ID card, and the verification of the MR conditional status either with the device’s respective MR instruction manual or directly on the manufacturer’s website (external links at the end of this article).
During the verification of the MR conditional status, it is usually advisable that both the radiologist and the cardiologist or cardiac physiologist work through the corresponding radiological and cardiological checklists to ensure that all the requirements can be met during the scan.
Is only a part of the components (i.e. the generator) MR conditional and one part is not, or is the combination of the components not approved by the manufacturer the device is not considered MR conditional 2-4. The required MR conditions usually include partial or whole body approval requirements about other implants, patient position, MR field strength, design and coils that are approved as well as the following scanning parameters 4:
maximal slew rate (dB/dt)
maximal spatial field gradient
maximal specific absorption rate (SAR)
operating mode
B1+rms adjustments (on 3 Tesla)
Risk assessment
The risk assessment is the second important step in the MR safety screening process and should be performed to identify and stratify additional risk factors, especially in a setting of MR non-conditional or MR unlabelled pacemaker systems 1-5.
The risk assessment should be performed according to the institutional protocol, usually by the cardiac electrophysiologist/cardiologist and radiologist in cooperation 2-5 and in the setting of MR non-conditional or unlabelled systems it should contain a risk/benefit assessment 1-5.
A lower risk has been associated with the following conditions 5:
recent implantation (<6 weeks) 3
unmet condition due to additional implants
unmet patient position exclusion zone (e.g. thoracic scan)
scanning beyond SAR restrictions
temporary surgical epicardial pacing wires (without external components)
scanning pacemaker systems at 3T that are labeled MR conditional systems at 1.5T only
mismatched systems with MR conditional generators and unlabelled or not-matching leads
An intermediate risk has been associated with the following 5:
MRI non-conditional or MR unlabelled systems
generators in a non-pectoral location
inactive battery-depleted pacemaker systems
abandoned leads (capped or not capped)
A high risk has been associated with the following factors 3-5:
battery depleted or at replacement interval (unknown)
permanent epicardial leads
fractured or damaged leads
abnormal lead parameters (e.g. high capture thresholds)
component advisory warning
a temporary system with an external generator
very old pacemaker systems (e.g. pre-2000 market release)
Situations where MRI scanning should be avoided include the following 5:
ICD devices in pacing-dependent patients where it is not possible to maintain asynchronous pacing
scanning active cardiac conduction devices without interrogation and programming before the scan
Also, some authors and guidelines discourage MRI scanning in the setting where lead abnormalities are present 7,8, especially in the setting of fractured leads and epicardial leads 3.
Day of the MRI scan
Device interrogation and programming
Device interrogation and programming are done by specifically trained personnel such as a cardiac technologist, electrophysiologist or cardiologist before and after the MRI scan with a CIED programming unit (pacing system analyzer). This includes switching the system into 'MRI mode' and back to normal pacing mode 2-6. This is done to minimize the risk of inappropriate pacemaker/defibrillator activation or inhibition of pacing.
Specific instructions for MR conditional pacing systems are usually available within the device’s respective MR instruction manual from the manufacturer.
In patients with MR non-conditional devices, the cardiac electrophysiologist or cardiologist will need to determine the pacing mode, which will be probably a non-pacing mode (ODO/OVO/OAO) or inhibited pacing mode (DDI/VVI/AAI) in most not pacing-dependent patients and an asynchronous pacing mode (VOO/DOO/AOO) in pacing-dependent patients 1-3. In addition, different advanced features such as tachycardia detection, therapeutic strategies and 'magnet response' need to be deactivated before a scan 2-4. Programming and reprogramming should take place immediately before and after the MRI scan and the patient should be monitored until the settings are restored 2-4. Sensing amplitude drops, capture threshold changes and lead impedance changes should be documented and followed up after one week 1-3,7,8. Also, patients with MR non-conditional devices should be followed up in 3-6 months or one week with further follow-ups, if there were changes in the electrophysiological parameters after the MRI 3,7,8.
MRI scanning
The MR scan is conducted by the MR technologist under patient monitoring by additional staff.
It also differs from a normal MRI in that specific conditions have to be met. In the case of patients with MR conditional devices, these are the manufacturer's instructions, in the case of MR non-conditional or unlabelled pacing systems it would be scanning conditions defined by the local radiology team.
At the start of the scan it usually involves the review and adjustment of the allowed scan regions, patient position and the above specified MR-related parameters but also to make sure that the equipment prohibited by the manufacturer (e.g. special radio-frequency coils) is not used 2-4.
Monitoring and safety considerations
Adequate patient monitoring is an absolute requirement during the scan for both MR conditional and MR non-conditional CIEDs.
In MR conditional devices it should be performed according to manufacturer’s standards and usually pulse oximetry waveform monitoring is sufficient. Visual and voice contact with the patient should be established by the MR technologist and monitoring personnel.
For patients with higher risks and/or MR non-conditional pacing systems, additional ECG monitoring should be considered and has been recommended 3,4. However, it should be taken into account that ECG derivation with pacemaker systems is often impeded by artefacts 4. Safety requirements during the scan include the following 3,5:
presence of personnel trained in basic life support
available personnel trained in advanced cardiovascular life support (ACLS) on-site
an external defibrillator (ideally with transcutaneous pacing capability)
emergency resuscitation equipment
In the setting of MR non-conditional cardiac conduction devices, the presence and availability of proficient personnel trained in advanced cardiovascular life support and programming the device as well as a cardiologist is increasingly important and/or required 2-5.
In the setting of an emergency that requires resuscitative measures, the patient should be immediately moved outside the scanner room 2,3.
Practical points
it is advisable to define specific scanning hours, where sufficient trained personnel is available
it is beneficial to store scanning instructions (e.g. scan parameters, approved scanning regions and coils) in the radiology information system (RIS) during the MR safety screening
it is advisable to have all patients with cardiac conduction devices sign a patient consent form, even if that is not required by national guidelines so that this is not a problem on the day of the scan in the setting that some manufacturer requirements (e.g. unmet scan location, additional minor implants) cannot be met
institutions with no/lower experience of scanning patients with cardiac conduction devices should set up an institutional protocol first and start scanning MR-conditional systems only for a certain amount of time before advancing to patients with MR non-conditional or unlabelled pacing systems and patients with intermediate or higher risk
MRIs for the assessment of regions close to the cardiac conduction device (e.g. thoracic, cardiac or scans of the shoulder) are often impeded by artifacts from the generator or leads and might require an alternative scan protocol 2,3
scanning a cardiac conduction device that has not been appropriately interrogated and reprogrammed before the scan should be avoided by all means
External links
If any of these links are broken or for other problems and questions, please contact [email protected].
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