Patients with a pacemaker or defibrillator are often advised to undergo magnetic resonance imaging (MRI) for various health issues. However, there are potential risks to these patients that include heating of the transvenous lead tip with loss of pacing capture, and damage to the generator. The FDA has approved some pacemakers and leads as MRI-compatible under certain conditions. However, there are many patients who do not have such a device and are scheduled for an MRI. Despite evidence from Johns Hopkins and other centers that an MRI can be safely performed in most patients with cardiac implantable electrical devices when certain protocols are followed, many hospitals still do not allow patients with a device that is not labeled as MRI-compatible to undergo an MRI, and Medicare reportedly will not reimburse for it.
At the American Heart Association meeting in Chicago in November 2014, the preliminary findings were presented from the MagnaSafe Registry, which was designed to determine the real risk of MRI scans in device patients. This was a multicenter U.S. trial that enrolled 1,500 patients who had undergone implantation of either a pacemaker (n=1,000) or an implantable defibrillator (ICD; n=500) from any manufacturer after 2001, and was scheduled for a non-thoracic MRI using a standard 1.5T magnet. The patient was required to have a “strong clinical indication” for the MRI, and was excluded if he or she had an ICD and was pacemaker dependent, or had an abandoned lead, an active implanted device other than pacemaker or ICD, a device in the abdominal position, or a battery voltage at ERI. The MRI was supervised by a cardiologist, but could have been observed by a doctor or mid-level provider. Three-quarters of the MRIs were of the brain or non-thoracic spine. The protocol required that the pacemaker be programmed to an asynchronous mode (VOO/DOO) if the patient was pacemaker dependent, or to a non-pacing mode (OVO/ODO) if the patient was not pacemaker dependent, defined has having an intrinsic sinus rate >40 bpm and asymptomatic. In addition, the magnet response was programmed off, and ICD antitachycardia therapies were disabled. All devices were interrogated and reprogrammed after the MRI.
The results suggest that MRI scanning in these patients is very safe. Parameter changes were small, not clinically significant in the opinion of the investigators, and did not require reprogramming. Patients with multiple scans were not at increased risk. The only patient to have a major device malfunction had a device that was not programmed according to the protocol before the MRI. Antitachycardia therapies were not properly disabled, and so the device repeatedly charged when magnetic pulses were interpreted by the ICD as tachycardia events. The ICD could not be interrogated after the MRI, and needed to be replaced. Other adverse events included atrial fibrillation or flutter, which were likely due to asynchronous pacing rather than the MRI itself, in six patients. In addition, six pacemakers had partial electrical reset of the device that could be reprogrammed, and three patients complained of transient heating or burning at generator site.
The MagnaSafe Registry was both a great study and contribution. It was a large, multicenter study designed to ask an important clinical question about the real-world safety of performing an MRI in a patient with a pacemaker or defibrillator. The findings strongly suggest that an MRI, when done properly, is safe in these patients. The study results challenge the current stance on this topic by many doctors, hospitals, regulatory agencies, and insurance companies. Nevertheless, there are remaining questions that were not addressed by this study. These uncertainties include the safety of performing a cardiac and other non-cardiac thoracic MRI in device patients, and the safety in device patients who were not enrolled in the trial, including patients with a totally subcutaneous ICD and patients with an ICD who are pacemaker dependent. Regardless of the apparent safety of performing an MRI in a device patient, these patients should first be evaluated carefully to be sure that they understand the risks and that there is a true need for the MRI.
Bradley P. Knight, MD, FACC, FHRS
Editor-in-Chief, EP Lab Digest®
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