MagnaSafe

In Review

Russo RJ, et al. "Assessing the Risks Associated with MRI in Patients with a Pacemaker or Defibrillator". New England Journal of Medicine. 2017. 376(8):755-764.
PubMed • Full text

Clinical Question

In patients with non-MRI-conditional pacemakers or implantable cardioverter-defibrillators, what are the risks of nonthoracic MRI at a field strength of 1.5 tesla?

Bottom Line

The risks associated with nonthoracic MRI imaging in patients with non-MRI-conditional pacemakers or ICDs when adhering to a strict programming and monitoring protocol are rare and often not clinically significant.

Major Points

Several smaller case series and prospective studies had suggested that MRI imaging in patients with MRI-non-conditional pacemakers and ICDs could be performed safely. The MagnaSafe Registry was a multicenter, prospective study and the largest of its kind with 1,500 cases that demonstrated that patients with MRI-non-conditional pacemakers and ICDs could undergo 1.5 tesla nonthoracic MRI imaging without death, device failure, lead replacement, loss of capture, or ventricular arrhythmia. Atrial arrhythmia and partial electrical reset occurred less than 1% of the time. Generator replacement was required in one instance when the ICD had not been programmed correctly prior to scanning.

Guidelines

2017 HRS Expert Consensus Statement on Magnetic Resonance Imaging and Radiation Exposure in Patients with Cardiovascular Implantable Electronic Devices

• It is reasonable for patients with an MR nonconditional CIED system to undergo MR imaging if there are no fractured, epicardial, or abandoned leads; the MRI is the best test for the condition; and there is an institutional protocol and a designated responsible MR physician and CIED physician (Class IIa Recommendation).
• It is reasonable to perform an MR scan immediately after implantation of a lead or generator of an MR nonconditional CIED system if clinically warranted (Class IIa Recommendation).
• For patients with an MR nonconditional CIED, it is reasonable to perform repeat MRI when required, without restriction regarding the minimum interval between imaging studies or the maximum number of studies performed (Class IIa Recommendation).
• It is recommended for the patient with an MR nonconditional CIED that device evaluation be performed immediately pre- and post-MRI with documentation of pacing threshold(s), P- and R-wave amplitude, and lead impedance using a standardized protocol (Class I Recommendation).
• A defibrillator/monitor (with external pacing function) and a manufacturer-specific device programming system should be immediately available in the holding area adjacent to the MR scanner room while an MR nonconditional CIED is reprogrammed for imaging (Class I Recommendation).
• It is recommended that continuous MR conditional ECG and pulse oximetry monitoring be used while an MR nonconditional CIED is reprogrammed for imaging (Class I Recommendation).
• It is recommended that personnel with the skill to perform advanced cardiac life support, including expertise in the performance of CPR, arrhythmia recognition, defibrillation, and transcutaneous pacing, accompany the patient with an MR nonconditional CIED for the duration of time the patient’s device is reprogrammed, until assessed and declared stable to return to unmonitored status (Class I Recommendation).
• For patients with an MR nonconditional CIED who are pacing-dependent (PM or ICD), it is recommended that: a) Personnel with the skill to program the CIED be in attendance during MR scanning. b) A physician with the ability to establish temporary transvenous pacing be immediately available on the premises of the imaging facility. c) A physician with the ability to direct CIED programming be immediately available on the premises of the imaging facility (Class I Recommendation).
• For patients with an MR nonconditional CIED who are not pacing-dependent, it is recommended that: a) Personnel with the skill to program the CIED be available on the premises of the imaging facility. b) A physician with the ability to direct CIED programming be available on the premises of the imaging facility (Class I Recommendation).
• It is recommended that for the patient with an MR nonconditional CIED who is pacing-dependent to program their device to an asynchronous pacing mode with deactivation of advanced or adaptive features during the MRI examination, and the pacing rate should be selected to avoid competitive pacing (Class I Recommendation).
• All tachyarrhythmia detections for patients with an ICD should be disabled prior to MRI (Class I Recommendation).
• For a patient with an MR nonconditional CIED who is not pacing-dependent, it is reasonable to program their device to either a nonpacing mode (OVO/ODO) or to an inhibited mode (DDI/VVI), with deactivation of advanced or adaptive features during the MRI examination (Class IIa Recommendation).

Design

• Multicenter, prospective, non-randomized, non-blinded, cohort study
• N=1,500 cases
  • 1,000 cases with pacemakers
  • 500 cases with ICDs
• Setting: 19 centers in the United States
• Enrollment: April 2009 to April 2014
• Follow-up: 93% of patients by 6 months
• Analysis: Intention-to-treat
• Primary end points:
  • Death during the MRI examination
  • Generator failure requiring immediate replacement
  • Lead failure requiring immediate replacement
  • Loss of capture during the MRI examination
  • Observed atrial arrhythmia
  • Observed ventricular arrhythmia
  • Electrical reset
• Secondary end points:
  • Decrease in battery voltage ≥0.04 V
  • Increase in pacing threshold ≥0.50 V at 0.4 ms or and increase at a wider pulse width
  • Decrease in P-wave measurement ≥50%
  • Decrease in R-wave measurement ≥25%
  • Increase or decrease in pacing lead impedance ≥50 ohm
  • Increase or decrease in shock lead impedance ≥3 ohm

Population

Inclusion Criteria

• Age ≥18 y
• Able to provide informed consent
• Permanent pacemaker or ICD
• Strong clinical indication for MRI without an acceptable alternative imaging modality
• Nonthoracic MRI (joint, extremity, brain, pelvis, cervical, lumbar or sacral spine)

Exclusion Criteria

• Metallic objects that represent a contraindication to MRI
• Claustrophobia unresponsive to oral preprocedural sedatives
• Morbid obesity with abdominal diameter >60 cm
• Pacemaker or ICD generator placement before 2002
• Has an ICD and is pacemaker dependent
• Device generator battery voltage at elective replacement indicated
• Presence of active implantable medical device (other then pacemaker or ICD)
• Presence of abandoned leads (with the exception of post coronary artery bypass graft temporary epicardial pacing wires)
• Presence of implanted cardiac device in the abdominal position
• Presence of MRI-conditional pacemaker or ICD

Baseline Characteristics

Reported as pacemaker cohort and ICD cohort, respectively

• Age: 72.5, 65.1
• Female sex: 42.0%, 30.7%
• BMI: 27.8, 29.1
• Coronary artery disease: 31.2%, 57.3%
• Type 1 or type 2 diabetes mellitus: 18.6%, 36.3%
• Mechanical prosthetic heart valve: 3.7%, 3.7%
• Antiarrhythmic therapy: 10.2%, 16.4%
• Leads: 1926, 997
• Pacing dependent: 28.4%, Not applicable
• Time since generator implantation (years): 3.2, 2.7
• Time since implantation of all leads (years): 4.6, 3.7
• Time since most recent lead implantation (years): 4.5, 3.6
• Duration of MRI (minutes): 45, 41
• Previous MRI with implanted cardiac device: 22.6%, 18.0%
• Specific absorption rate (SAR) limit reached: 11.9%, 8.9%
• First-level operating mode required: 0.3%, 0.4%
• MRI scans obtained:
  • Brain: 35%, 34%
  • Cervical spine: 15%, 14%
  • Lumbar spine: 27%, 24%
  • Extremity or joint: 9%, 12%
  • Abdomen or pelvis: 4%, 5%
  • Other: 10%, 11%

Interventions

For patients with pacemakers enrolled in the study:

• Device interrogation performed prior to MRI by a qualified physician
  • If pacemaker dependent: device was reprogrammed to asynchronous pacing mode and magnet response disabled
  • If not pacemaker dependent: device was reprogrammed to disable pacing and sensing functions
• Device interrogation performed after MRI and previous parameters restored or adjusted by a qualified physician
  • If parameters changed, follow up interrogation performed within 7 days, at 3 months, and at 6 months
  • If parameters did not change, follow up interrogation performed at 3-6 months when clinically indicated

For patients with ICDs enrolled in the study:

• Device interrogation performed prior to MRI by a qualified physician
  • If pacemaker dependent: No MRI
  • If not pacemaker dependent: device was reprogrammed to disable anti-tachycardia therapy and disable pacing and sensing functions
• Device interrogation performed after MRI and previous parameters restored or adjusted by a qualified physician
  • If parameters changed, follow up interrogation performed within 7 days, at 3 months, and at 6 months
  • If parameters did not change, follow up interrogation performed at 3-6 months when clinically indicated

Outcomes

Reported as pacemaker cohort and ICD cohort, respectively. Statistical comparisons were not performed between the pacemaker and ICD cohorts.

Primary Outcomes

Death during the MRI examination

0% (95% CI 0.0-0.4), 0% (95% CI 0.0-0.8)

Generator failure requiring immediate replacement

0% (95% CI 0.0-0.4), 0.2% (95% CI 0.04-1.1)

Lead failure requiring immediate replacement

0% (95% CI 0.0-0.2), 0 (95% CI 0.0-0.4)

Loss of capture during the MRI examination

0% (95% CI 0.0-1.4), Not applicable

Observed atrial arrhythmia

0.5% (95% CI 0.2-1.2), 0.2 (95% CI 0.4-1.1)

Observed ventricular arrhythmia

0% (95% CI 0.0-0.4), 0 (95% CI 0.0-0.8)

Electrical reset

0.6% (95% CI 0.3-1.3), 0 (95% CI 0.0-0.)

Secondary Outcomes

Decrease in battery voltage ≥0.04 V

0.4%, 7.2%

Increase in pacing threshold ≥0.50 V at 0.4 ms or and increase at a wider pulse width

0.7%, 0.8%

Decrease in P-wave measurement ≥50%

0.9%, 0.3%

Decrease in R-wave measurement ≥25%

3.9%, 1.6%

Increase or decrease in pacing lead impedance ≥50 ohm

3.3%, 4.2%

Increase or decrease in shock lead impedance ≥3 ohm

Not applicable, 16.4%

Adverse Events

There were no adverse events recorded other than those listed in the primary and secondary outcomes.

Criticisms

• Thoracic MRI studies were excluded
• MRI field strength was limited to 1.5 tesla, limiting generalizability to MRI with higher field strength
• Low number of left ventricular leads, limiting generalizability to patients with cardiac resynchronization devices

Funding

• Grants from St. Jude Medical, Biotronik, Boston Scientific, and the Hewitt Foundation for Medical Research
• Philanthropic gifts from Mr. and Mrs. Richard H. Deihl, Evelyn F. and Louis S Grubb, Roscoe E. Hazard, Jr., and the Shultz Steel Company