MRI Safe for Patients with Implanted Legacy Devices

Patients with a legacy pacemaker or implantable cardioverter-defibrillator (ICD) system that need to undergo a magnetic resonance imaging (MRI) scan have nothing to fear, according to a new study.

Researchers at the University of Pennsylvania (Penn; Philadelphia, USA) and Johns Hopkins University (JHU; Baltimore, MD, USA) conducted a prospective, nonrandomized study to assess the safety of MRI at a magnetic field strength of 1.5 Tesla in 1,509 patients who had a pacemaker (58%) or an ICD (42%) that was not considered to be MRI-conditional (also known as a legacy device). Overall, the patients underwent 2,103 thoracic and non-thoracic MRI examinations that were deemed to be clinically necessary.

The pacing mode was changed to asynchronous mode for pacing-dependent patients, and to demand mode for other patients, with tachyarrhythmia functions disabled. Outcome assessments included adverse events and changes in device parameters indicating lead and generator function and interaction with surrounding tissue. The results showed no reports of long-term clinically significant adverse events. Following the MRI scan, the patient's device reset to a backup mode in nine cases (0.4%), of which eight were transient. One pacemaker reset to ventricular inhibited pacing and could not be reprogrammed.

A decrease in P-wave amplitude was the most common notable change in device parameters (occurring in one percent of patients) immediately after MRI. At long-term follow-up, the most common notable changes from baseline were decreases in P-wave amplitude (4%), increases in atrial capture threshold (4%), increases in right ventricular capture threshold (4%), and increases in left ventricular capture threshold (3%). The study was published on December 28, 2017, in the New England Journal of Medicine (NEJM).

“Patients who have pacemakers or defibrillators are often denied the opportunity to undergo magnetic resonance imaging because of safety concerns, unless the devices meet certain criteria specified by the FDA, termed MRI-conditional devices,” concluded lead author Saman Nazarian, MD, PhD, of the University of Pennsylvania, and colleagues. “No long-term clinically significant adverse events were reported, and the observed changes in lead parameters were not clinically significant, and did not require device revision or reprogramming.”

Until now, patients with ICD systems have been contraindicated from receiving MRI scans because of potential interactions between the MRI and device function, which might result in risk to patients. The restriction has resulted in a critical unmet need as data have shown that within four years, 36% percent patients with ICDs in the United States are likely to need an MRI.

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