What are the contraindications for MRI (Magnetic Resonance Imaging) procedures in patients with implants, such as pacemakers (implantable cardioverter-defibrillators)?

MRI Contraindications in Patients with Implants

All implants must be categorized as MR Safe, MR Conditional, or MR Unsafe before any MRI procedure, with absolute contraindications now limited primarily to MR Unsafe devices, abandoned/epicardial leads, and devices implanted less than 6 weeks prior. 1

Classification System for All Implants

The modern approach eliminates the ambiguous term "MR compatible" in favor of three precise categories 1:

• MR Safe: Contains no material presenting hazards at any field strength—proceed without restrictions 1
• MR Conditional: Safe under manufacturer-specified conditions only—requires verification of exact make/model and adherence to scanning parameters 1
• MR Unsafe: Presents unacceptable risk—absolute contraindication to MRI 1

Cardiac Implantable Electronic Devices (CIEDs)

Absolute Contraindications for Cardiac Devices

Exclude patients with the following from MRI 1, 2:

• Leads implanted less than 6 weeks (risk of dislodgement during lead maturation period) 1, 2
• Abandoned leads (prone to dangerous heating) 1, 2
• Epicardial leads (prone to heating) 1, 2
• Non-MR-conditional devices without appropriate safety protocols and monitoring 1

Pacemakers: Relative Contraindication with Protocols

Pacemakers transitioned from absolute to relative contraindication in 2006 with introduction of MR-conditional devices 1. However, the approach differs dramatically based on device type:

MR-Conditional Pacemakers (Preferred)

• Verify MRI-conditional status directly with manufacturer specifications—never assume based on age or manufacturer alone 2
• Most approved for 1.5T scanning; some newer systems have 3T data 2
• Follow manufacturer's automatic mode-switching protocols via external physician-activated device 2

Conventional (Non-MR-Conditional) Pacemakers

The European Society of Cardiology provides Class IIb recommendation for MRI at 1.5T in conventional pacemakers, indicating less favorable benefit-risk ratio 2. This requires:

• Mandatory consultation with electrophysiology specialist before proceeding 2
• Record baseline device parameters: lead impedance, capture threshold, P/R wave amplitude, battery voltage 1, 2
• Pacemaker-dependent patients: Program to asynchronous mode (VOO/DOO) to prevent inappropriate inhibition from electromagnetic interference 1, 2
• Non-pacemaker-dependent patients: Program to inhibited mode (VVI/DDI) to avoid inappropriate pacing 1, 2
• Continuous ECG monitoring by qualified personnel throughout entire scan 1, 2
• Deactivate rate-responsive and other non-essential pacing functions 1
• Immediately re-check all device variables post-MRI and compare with baseline 1, 2
• Restore original programming after scan completion 1, 2

Critical pitfall: The closer the scanning area to the device system, the higher the risk of complications including radiofrequency-induced lead tip heating, pacing inhibition, and arrhythmia induction 1, 2.

Implantable Cardioverter-Defibrillators (ICDs)

ICDs remain a stronger contraindication than pacemakers 1. While some cardiac centers perform MRI on ICDs with appropriate monitoring and resuscitation support, this requires 1:

• Deactivation of all monitoring and ATP/shock therapies 1
• Immediate availability of external defibrillation equipment 1
• Same lead maturation and programming requirements as pacemakers 1

The American Society of Anesthesiologists states MRI is generally contraindicated in patients with CIEDs, requiring consultation with ordering physician, cardiologist, diagnostic radiologist, and device manufacturer if MRI must be performed 1.

Leadless Pacemakers

Leadless pacemakers are MRI-conditional at 1.5T when following manufacturer instructions 3. Key advantages include:

• Inherently less susceptible to MRI-related complications due to absence of transvenous leads 3
• No risk of lead dislodgement during MRI 3
• Reduced device-MRI interactions from smaller size and absence of pocket/lead system 3
• Still require 6-week implantation period before MRI 3

Other Implanted Devices

Passive Implanted Devices

Most passive devices are MR Conditional rather than contraindicated 1:

• Cardiovascular: Prosthetic heart valves (mechanical/bioprosthetic) and coronary stents are safe at field strengths up to 1.5T, many safe to 3T 1
• Vascular access ports and catheters: May heat during scanning—discuss with MR Responsible Person 1
• Orthopedic, ocular, penile implants: May cause image artifact or patient discomfort from movement 1
• Breast implants: RF identification tags can heat during scanning—requires manufacturer guidance 1

Programmable Hydrocephalus Shunts

Not contraindicated but require mandatory neurosurgical assessment 1:

• Pressure settings may change during MRI, causing under- or over-draining 1
• Confirm correct settings before scanning 1
• Reset device after scan if required 1
• Many newer shunts unaffected by MR scanners up to 3T, but settings must still be verified pre- and post-scan 1

Neurostimulators

Generally not recommended for MRI but may proceed under controlled conditions when benefits outweigh risks 1:

• Includes vagal nerve, deep brain, and spinal cord stimulators 1
• Risk of thermal injury from RF and magnetic field effects 1
• Increasingly available as MR Conditional devices with specific scanning time and mode recommendations 1

Essential Pre-Scan Requirements

Every patient requires comprehensive screening, particularly critical for ICU transfers and patients unable to provide accurate history 1:

• Identify exact make and model of all implants—similar devices performing the same function may behave very differently in MRI 1
• MR Safety Expert may need time to contact manufacturer or obtain current documentation 1
• Verify device has matured for minimum 6 weeks post-implantation 1, 2
• Consider alternative imaging (CT, echocardiography) before proceeding with MRI on conventional devices 2