MRI Compatibility of Implantable Loop Recorders
Modern implantable loop recorders can undergo MRI scanning, but this requires specific safety protocols and generates frequent artifacts that can mimic arrhythmias—these artifacts must not be mistaken for true cardiac events.
MRI Safety Profile
Loop recorders can be safely scanned without permanent device damage or patient harm, but the procedure requires careful preparation and monitoring. 1, 2
Key Safety Findings
No device damage occurs: Multiple studies demonstrate that ILRs maintain signal integrity, programmed parameters, battery status, and communication capability after MRI exposure 1, 2
No patient symptoms: Patients experience no sensations of device tugging, heating at the implant site, or cardiopulmonary symptoms during or after scanning 1, 2
Device functionality preserved: All ILRs remain fully functional and programmable immediately post-MRI 1, 2
Critical Artifact Problem
The most significant issue with MRI in ILR patients is the generation of artifacts that convincingly mimic both tachyarrhythmias and bradyarrhythmias—this occurs in virtually all patients undergoing MRI. 1, 3, 2
Artifact Characteristics
Mimics wide and narrow complex tachycardias: Artifacts can appear identical to true ventricular or supraventricular tachyarrhythmias 3
Mimics bradyarrhythmias: False bradycardia patterns are commonly recorded 1
Scan location matters: Artifacts are more prominent when scanning closer to the device location (e.g., shoulder MRI produces more artifacts than cranial MRI) 3
Universal occurrence: These artifacts appear regardless of the type of MRI scan performed 2
Essential Safety Protocol
Pre-MRI Preparation
Clear device memory immediately before scanning: This prevents confusion between true arrhythmias and MRI-induced artifacts 1, 2
Verify signal integrity and time-date stamp: Document baseline device function 1
Document all programmed parameters: Record baseline settings for post-scan comparison 1
Post-MRI Management
Interrogate device immediately after scanning: Check for any parameter changes (perform within minutes, not days) 1
Compare with baseline parameters: Verify lead impedance, thresholds, signal amplitude, and battery voltage remain unchanged 1
Disregard any recorded "arrhythmias" during the MRI timeframe: These are artifacts, not true cardiac events 1, 3, 2
Comparison to Other Cardiac Devices
While the European Society of Cardiology provides detailed MRI protocols for pacemakers and ICDs (requiring exclusion of patients with leads <6 weeks old, abandoned leads, or epicardial leads, plus specific programming changes), 4 loop recorders have a simpler safety profile since they lack pacing leads and therapeutic functions that could cause harm.
Key Differences
No lead heating risk: Unlike pacemakers/ICDs, ILRs lack endocardial leads that could cause radiofrequency-induced heating at lead tips 4
No pacing dysfunction: ILRs cannot cause inappropriate pacing, asynchronous pacing, or induction of tachyarrhythmias 4
No therapy delivery concerns: Unlike ICDs, there are no shock therapies to deactivate 4
Clinical Context
The American Heart Association and American College of Cardiology recommend ILRs for patients with recurrent unexplained syncope, cryptogenic stroke (particularly ESUS), and suspected paroxysmal atrial fibrillation, with detection rates significantly higher than conventional monitoring (52% vs 20%). 4, 5, 6 Given that up to 75% of patients with cardiac devices develop an indication for MRI during follow-up, 4 the ability to safely perform MRI in ILR patients is clinically essential.
Important Caveats
One older study reported irreversible device error in a non-implanted ILR exposed to MRI 7, but this has not been replicated in studies of implanted devices in actual patients 1, 2
Device migration is a rare complication that could theoretically affect MRI safety, though this is unrelated to MRI exposure itself 8
Always inform the MRI facility that the patient has an ILR to ensure appropriate protocols are followed 1