During inpatient rounds you meet Ms. Smith, a 65-year old female with a history of sick sinus syndrome status post pacemaker placement. She was admitted overnight with fever and gram-positive bacteremia of unknown source. This morning, she reports worsening lower-back pain that “shoots” down her leg. On exam, you notice numbness in the L4 distribution. Concerned about a possible epidural abscess, you plan to order a magnetic resonance imaging (MRI) scan until you remember about Ms. Smith’s pacemaker.
The use of MRI in patients with implanted cardiac devices — whether a pacemaker or implantable cardioverter defibrillator (ICD) — may raise concerns for clinicians. This apprehension stems from the potential for MRI-induced cardiac lead heating, which hypothetically may alter pacing properties or even damage myocardium. Fortunately, the FDA has identified a subset of implanted cardiac devices that pose no known hazard under specified MRI conditions (“MRI-conditional”). However, at least two million people in the United States have pacemakers or ICDs in place that have not met these criteria (“non–MRI-conditional”). In the case of patients with a non–MRI-conditional cardiac device for whom an MRI has been recommended, in the past, clinicians had to consider the risks of removing a necessary cardiac device versus the drawbacks of utilizing an alternate and potentially less-effective imaging modality. Study results from the MagnaSafe Registry, published in this week’s issue of NEJM, may change our approach to MRI imaging in patients with non–MRI-conditional devices.
The aim of the MagnaSafe Registry was to define an appropriate protocol for screening, monitoring, and device programming for patients with non–MRI-conditional implantable cardiac devices who were undergoing a nonthoracic 1.5 tesla MRI. At 19 United States medical centers, the authors enrolled patients aged ≥18 years with a pacemaker or ICD implanted after 2001 and for whom their physician felt a 1.5 tesla non-thoracic MRI scan was clinically indicated. Study protocol dictated that all patients undergo pre-MRI device interrogation, reprogramming, intra-MRI monitoring, and post-MRI device interrogation (Click here to enlarge figure). Primary endpoints were death, generator or lead failure requiring immediate replacement, loss of capture, new-onset arrhythmia during the scan, and partial or full generator electrical reset.
Among the 1000 pacemaker cases and 500 ICD cases that underwent non-thoracic MRI, no deaths, lead failures, loss of capture, or ventricular arrhythmias were reported. Six patients (0.4%) experienced atrial arrhythmia (fibrillation or flutter) during or after the MRI; five of these had a known history of atrial arrhythmias. Six patients (0.4%) experienced a partial generator electrical reset. In one patient (0.2%) with an ICD, the study prescan reprogramming protocol was not followed, the device could not be interrogated post-MRI, and immediate generator replacement was required.
The findings from the MagnaSafe Registry demonstrate that by following an appropriate protocol, safe completion of non-thoracic MRI is possible, even in patients with non–MRI-conditional implanted cardiac devices. Although these results are encouraging, they do not obviate the need to consider (and discuss with patients) the relative risks and benefits of MRIs as they apply to each patient individually. Moreover, these results highlight the importance of a multidisciplinary approach to the implementation of the necessary safety measures detailed in MagnaSafe’s protocol. The potential for harm, as demonstrated by the patient in whom the MagnaSafe protocol was not followed, should remind us of the importance of safe implementation practices.
The Magnasafe protocol may significantly change our diagnostic approach for the two million people with non–MRI-conditional implantable cardiac devices, despite several unresolved issues. The study did not address the use of thoracic MRIs and 3 tesla MRI machines. Additionally, we cannot draw conclusions about pediatric populations or patients with cardiac resynchronization devices. Beyond these bedside dilemmas, MagnaSafe also raises questions on a health system level: Will the FDA change their approach to MRI labeling for implantable cardiac devices? Will the Centers for Medicare & Medicaid Services change their payment practices to allow for coverage of MRIs in patients with non–MRI-conditional implanted cardiac devices?
You speak with Ms. Smith’s cardiologist who tells you that her pacemaker is MRI-conditional. You coordinate with Ms. Smith and the on-call cardiologist and radiologist to arrange for an urgent MRI of her lumbar spine. As she is transported off the floor, you begin to think about how you would have approached this case if she had a non–MRI-conditional pacemaker.
Have you ever been in this situation? What did you do?
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Joshua Allen-Dicker, MD, MPH
Josh is an Instructor in Medicine and Hospitalist at Beth Israel Deaconess Medical Center in Boston, MA. He completed his residency in internal medicine at Beth Israel Deaconess Medical Center, medical degree at NYU School of Medicine, and MPH at Harvard School of Public Health.