Rationale and Objectives
Studies reporting the safety of magnetic resonance imaging (MRI) in patients with a cardiac implantable electronic device (CIED) have mostly excluded examinations with the device in the magnet isocenter. The purpose of this study was to describe the safety of cardiac and thoracic spine MRI in patients with a CIED.
Materials and Methods
The medical records of patients with a CIED who underwent a cardiac or thoracic spine MRI between January 2011 and December 2014 were reviewed. Devices were interrogated before and after imaging with reprogramming to asynchronous pacing in pacemaker-dependent patients. The clinical interpretability of the MRI and peak and average specific absorption rates (SARs, W/kg) achieved were determined.
Results
Fifty-eight patients underwent 51 cardiac and 11 thoracic spine MRI exams. Twenty-nine patients had a pacemaker and 29 had an implantable cardioverter defibrillator. Seventeen percent ( n = 10) were pacemaker dependent. Fifty-one patients (89%) had non-MRI-conditional devices. There were no clinically significant changes in atrial and ventricular sensing, impedance, and threshold measurements. There were no episodes of device mode changes, arrhythmias, therapies delivered, electrical reset, or battery depletion. One study was prematurely discontinued due to a patient complaint of chest pain of which the etiology was not determined. Across all examinations, the average peak SAR was 2.0 ± 0.85 W/kg with an average SAR of 0.35 ± 0.37 W/kg. Artifact significantly limiting the clinical interpretation of the study was present in 33% of cardiac MRI studies.
Conclusions
When a comprehensive CIED magnetic resonance safety protocol is followed, the risk of performing 1.5-T magnetic resonance studies with the device in the magnet isocenter, including in patients who are pacemaker dependent, is low.
Introduction
Magnetic resonance imaging (MRI) has been considered to be a contraindication in patients with a cardiac implantable electronic device (CIED) due to potential life-threatening interactions with incompatible CIED systems . In recent years, an increasing number of MRI-conditional pacemakers have become available . These systems contain specially developed components that are tested and approved for usage in an MRI environment. While the routine implantation of MRI-conditional devices and leads may become standard practice, there is currently a large population of patients with previously implanted cardiac devices that require MRI scanning. In addition, until recently, there was no Food and Drug Administration approved MRI-conditional device approved to be scanned in the isocenter of the magnet precluding cardiac magnetic resonance (MR) and thoracic spine MR exams .
The largest, prospective multicenter data come from the recently completed MagnaSafe Registry trial, which included 1500 patients undergoing MRI with a cardiac implantable device . However, patients with a CIED undergoing cardiac and thoracic spine MRI studies were explicitly excluded from the trial due to safety concerns with the device in the magnet isocenter during scanning. In addition, exams with the CIED in the magnetic isocenter are poorly represented in the literature and the energy deposition of the specific MR protocols is rarely reported. The purpose of the present study was to describe the safety of cardiac and thoracic spine MRI in patients with a CIED, including information on the energy deposition during scanning (specific absorption rate [SAR], W/kg, and whole-body radio frequency [RF], energy J/kg) achieved during MR scanning, using a multidisciplinary MRI safety protocol.
Methods
Study Design and Data Collection
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MRI SARs
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MRI RF Energy Deposition
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Comprehensive Safety Protocol
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MRI Protocol
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Statistical Analysis
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Results
Patient and Device Characteristics ( Table 1 )
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Table 1
Patient and Device Characteristics
Variable Age, years (SD) 58.5(14.3) Male gender, n (%) 40(65) Pacemaker, n (%) 29(50) ICD, n (%) 29(50) Dual-chamber device, n (%) 38(62) Biventricular device, n (%) 7(11) MRI-conditional device, n (%) 7(11) Pacemaker dependent, n (%) 10(17)
ICD, implantable cardioverter defibrillator; MRI, magnetic resonance imaging; SD, standard deviation.
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Table 2
Mean Device Measurements
Baseline Lead Position Sensing, mV (SD) Impedance, ohm (SD) Threshold, V (SD) Right atrium 2.7(1.4) 489.3(96.0) 0.88(0.49) Right ventricle 9.1(4.2) 486.9(98.5) 0.96(0.58) Left ventricle 11.0(5.3) 618.6(221.5) 1.2(0.5)
Mean Difference Post-MRI Lead Position Sensing, mV (SD) Impedance, ohm (SD) Threshold, V (SD) Right atrium +0.03(0.22) −1.4(17.7) +0(0.1) Right ventricle +0.09(0.85) −4.1(32.7) +0(0.13) Left ventricle −0.33(0.65) −6.4(11.8) +0.02(0.04)
MRI, magnetic resonance imaging; SD, standard deviation.
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Complications
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SAR Data
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Table 3
Exam Level-Specific Adsorption Ratio Data
Exam Subjects, n Peak SAR (W/kg) SAR (W/kg) Max Average Median SD Average Median SD Brain MRI 3 0.08 0.07 0.07 0.00 0.03 0.03 0.01 Cardiac MRI 51 3.65 2.03 1.97 0.91 0.25 0.19 0.30 Cervical spine MRI 7 1.49 0.94 0.92 0.35 0.50 0.45 0.16 Thoracic spine MRI 10 2.18 1.68 1.82 0.39 0.94 0.88 0.23 Lumbar spine MRI 7 2.21 1.81 2.00 0.46 1.24 1.26 0.36 Pelvis MRI 1 2.00 N/A N/A N/A 0.93 0.66 0.74
MRI, magnetic resonance imaging; N/A, not applicable; SAR, specific absorption rate; SD, standard deviation.
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Whole-Body RF Energy
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Patients with Multiple MRI Exams
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Clinical Interpretability
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Discussion
Main Findings
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Comparison to Prior Studies
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Risks of MRI in the Presence of a CIED
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Limitations
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Conclusions
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