A study published in the Annals of Internal Medicine, the largest published experience of MRI in standard, contemporary cardiac rhythm management devices (CRMDs) to date, shows that MRI can be done safely, with appropriate precautions, in patients with selected cardiac devices. As a result, according to an editorial also published in the Annals of Internal Medicine, MRI should no longer be considered an absolute contraindication in the presence of a CRMD.
MRI is considered an absolute contraindication in the presence of CRMD for a variety of reasons, including the concern that its electromagnetic field will interact with a pacemaker or implantable cardioverter defibrillator and potentially cause them to malfunction. However, the development of the first FDA-approved, specifically designed, MRI-safe pacemaker and increasing reports of the safe use of MRI with conventional CRMDs has started to challenge this view.
In their study, Saman Nazarian, assistant professor of Medicine, Johns Hopkins Hospital, Baltimore, USA and his co-authors examined the use of MRI in 438 patients with either an implantable cardioverter defibrillator (ICD) or a pacemaker (consisting of 555 MRI examinations overall). Prior to the MRI, the settings of the devices were adjusted to try to avoid the potential negative consequences that could occur as a result of the MRI interacting with a device. In patients with ICDs, the pacing and tachyarrhythmia functions were disabled and those who were pacemaker-dependent were excluded from the study. The pacing mode of patients with pacemakers who were pacemaker dependent was switched to asynchronous mode and inhibited in pacemaker patients who were not pacemaker dependent. After the MRI, the devices were return to their original settings.
Only three patients in the study had acute power-on-reset events, which is a device returns to its back-up programming mode. This is potentially hazardous: in pacemakers, the back-up mode is inhibited pacing and this has obvious risks for a patient who is pacemaker-dependent: in ICDs, the back-up mode is to enable tachycardia therapies and thus put the patient at risk of inappropriate shocks. One of these patients had an ICD and the power-on-reset event caused him to feel a “pulling sensation” in his chest, but the ICD did not attempt to deliver tachyarrhythmia therapy. The other two patients had pacemakers and did experience, on occasion, inhibited pacing. However, neither of them were pacemaker dependent and both were able to complete their MRI examinations. None of three patients experienced device dysfunction during long-term follow-up. Immediately after MRI, right ventricular sensing, atrial and right and left ventricular lead impedances were reduced in some patients. At long-term follow-up, in some patients, right ventricular sensing was reduced, right ventricular lead impedance was decreased, right ventricular capture was increased, and battery voltage was decreased. However, none of these changes required device revision or reprogramming.
Nazarian et al reported: “In conclusion, using a protocol based on device selection and programming, MRI can be performed safely in patients with certain pacemakers and ICD systems. Given the potential changes in device variables and programming, monitoring by device experts is necessary.” They stressed that they only investigated certain devices (ie, just ICDs and pacemakers) and numbers of each individual model were small. They reported: “Given the public health importance of this issue, device manufacturers should continue efforts to design permanent pacemaker and ICD systems with improved safety in the MRI environment.”
Writing in their editorial, Matthew Reynolds and Peter Zimetbaum, Beth Israel Deaconess Medical Center, Harvard Medical School, say that Nazarian et al‘s data, alongside other studies, suggest that the risks of MRI in the presence of CRMDs, although potentially serious, have “probably been overestimated” and probably can effectively managed in many cases. They add: “In our opinion, the presence of CRMD should no longer be considered an absolute contraindication to MRI. Rather, the risks and benefits of MRI in a patient with CRMD should be assessed on an individual patient basis, as with any important medical decision.”