Can a patient with an Automatic Implantable Cardioverter-Defibrillator (AICD) undergo a Magnetic Resonance Imaging (MRI) scan?

MRI in Patients with AICDs: Current Evidence-Based Approach

MRI is no longer an absolute contraindication for patients with AICDs, but the safety and feasibility depend critically on whether the device is MRI-conditional versus conventional (non-MRI-conditional), with specific protocols required in either scenario. 1, 2

Device Classification Determines the Pathway

The first step is determining your device category, as this fundamentally changes your approach:

• MRI-conditional AICDs: Can be safely scanned at 1.5 Tesla following manufacturer-specific protocols (Class I recommendation - strong benefit-risk ratio) 2
• Conventional (non-MRI-conditional) AICDs: Can be scanned at 1.5 Tesla with appropriate precautions, though this carries a Class IIb recommendation (less favorable benefit-risk ratio) 1, 2
• MR Unsafe devices: Absolute contraindication - do not proceed 1, 2

The modern classification system eliminates ambiguous terminology and requires categorizing all devices as MR Safe, MR Conditional, or MR Unsafe before any MRI procedure. 1

Absolute Contraindications That Preclude MRI

Even if you want to proceed, these situations represent hard stops:

• Device implanted less than 6 weeks ago - risk of lead dislodgement makes this a Class III recommendation (harm or no benefit) 1, 2
• Abandoned or epicardial leads present - risk of heating creates unacceptable danger (Class III recommendation) 1, 2
• MR Unsafe classification by manufacturer - absolute contraindication 1

Mandatory Pre-MRI Protocol

Before any patient with an AICD enters the scanner, you must complete these steps:

• Verify the exact device make and model with manufacturer specifications to confirm MRI-conditional status 1, 2
• Device interrogation to document baseline parameters including impedance, capture threshold, sensing amplitude, and battery voltage 2
• Consultation with electrophysiology specialist is warranted for all cases 2
• Coordinate with device manufacturer, ordering physician, and MRI facility before proceeding 1

The American Society of Anesthesiologists explicitly states that if MRI must be performed in CIED patients, consultation with the ordering physician, patient's cardiologist, diagnostic radiologist, and device manufacturer is required. 3

Intra-Procedure Requirements

During the actual scan, these monitoring and safety measures are non-negotiable:

• Continuous ECG monitoring throughout the entire procedure by qualified personnel 2
• Peripheral pulse monitoring using pulse oximetry, arterial line, or manual palpation 2
• Temporary pacing and defibrillation equipment must be immediately available 2
• Field strength limitation to 1.5 Tesla for conventional devices (MRI-conditional devices may be safe up to 3T depending on manufacturer specifications) 2

Post-MRI Protocol

After completing the scan:

• Re-interrogate the device and compare all parameters to baseline values 2
• Restore original programming settings 2
• Monitor cardiac rate and rhythm with backup equipment available throughout the immediate postoperative period 2

Evidence Supporting Safety When Protocols Are Followed

The landmark MagnaSafe registry demonstrated that in 500 cases of patients with non-MRI-conditional ICDs undergoing 1.5 Tesla nonthoracic MRI, there were no deaths, lead failures, losses of capture, or ventricular arrhythmias when appropriate screening and device reprogramming protocols were followed. 4 The single device failure occurred in a patient whose device was not appropriately programmed per protocol before MRI. 4

This contrasts sharply with historical concerns - magnetic field strengths exceeding 0.5 mT (5 Gauss) can cause fatal device malfunction if precautions are not followed, and historical reports document sudden death in patients scanned without proper protocols. 2

Critical Pitfalls to Avoid

• Never assume a device is MRI-conditional without verifying manufacturer documentation - this assumption has led to serious adverse events 2
• Thoracic MRI carries higher risk - the MagnaSafe study specifically excluded thoracic imaging, so exercise additional caution for chest MRI 4
• Comprehensive screening is particularly critical for ICU transfers and patients unable to provide accurate history - these patients may not know their device specifications 1
• The MR Safety Expert may need time to contact the manufacturer - plan accordingly and don't rush the pre-scan verification process 1

When MRI Is Truly Necessary Despite Risks

The European Society of Cardiology acknowledges that up to 75% of patients with cardiac devices develop an indication for MRI due to medical comorbidities, and the diagnostic benefit typically outweighs minimal risks when proper protocols are followed. 1 However, the 2005 ASA guidelines state that MRI is generally contraindicated in CIED patients, reflecting the evolution of evidence over time. 3

The key distinction is that "generally contraindicated" no longer means "absolutely contraindicated" - it means you must follow rigorous protocols and have appropriate expertise available. 3, 1, 2