As a Jackson area cardiologist who implants and cares for people with pacemakers and defibrillators, one of the most vexing clashes of technologies in my 38 years of practice has arisen when people with these devices need magnetic resonance imaging (MRI). This is the story of “No, you cannot have an MRI” to “Yes, you can.”
MRI employs a large, powerful magnet and sophisticated electronics to create images using radio frequency waves. For the most common MRI scanners (the 1.5 Tesla), the primary radio wave frequencies used for imaging are centered around that of old television channel 2 (63.87 MHz, for those interested). Not only are the images of most internal body structures far superior to CT images, the MRI uses no ionizing radiation (X-rays) avoiding a small but real cancer risk. Unfortunately, we told people with pacemakers or defibrillators for five decades that they absolutely could not have MRI because of several potentially dangerous interactions and early reports of patient injury. Placing our patients in these strong electrical and magnetic fields was considered simply too dangerous. As recently as 2010, the 2 million Americans with pacemakers and defibrillators, an estimated 50-75% of whom would at some point “need” an MRI, were excluded. That was my story to hundreds of my own patients.
In little over a decade, two developments have dramatically diminished this prohibition for the widely available 1.5 Tesla machines. First, in 2011, manufacturers introduced design changes that make pacemaker and defibrillator systems safer for MRI. This involved testing and satisfying safety criteria for an entire system (the device itself plus all attached lead wires). Regulatory agencies such as the Food and Drug Administration designated these systems “MRI conditional,” and many radiology departments began making MRI available to these patients. The small, implantable ECG monitors and the entirely subcutaneous defibrillator devices are among the conditional group. Logistical hurdles are not insignificant and include evaluating device function and making changes in the settings prior to imaging, monitoring the patient during the scan, checking the device for changes after the scan, and finally restoring the original settings. The MRI facility must be in-hospital, have cardiac resuscitation capability available, and coordinate device management with a technical representative of the pacemaker or defibrillator manufacturer. Because of these requirements, some hospitals still opt out of offering MRI to these patients.
While a growing percentage of systems are MRI conditional, most patients have non-conditional systems because of some lack of conformity to the strict criteria required for being labeled conditional. For example, many older non-conditional devices and lead wires are still in service. One manufacturer’s device attached to lead wires from another, leads placed by a surgeon on the outside of the heart (epicardial leads), temporary pacing leads abandoned after cardiac surgery, fractured lead wires, or older leads that were abandoned in place make a system non-conditional. What about these folks? That brings us to the second development. Fortunately, for 1.5 Tesla scanners most non-conditional variations have now been studied sufficiently to permit scanning when MRI is essential. Each case must be evaluated with patient safety paramount. Unlike MRI conditional systems, scanning requires the presence of a cardiologist or other provider with expertise in pacemakers and defibrillators and cannot be supervised only by a manufacturer’s representative adding further logistical burden. The complete requirements are enumerated by CMMS (Centers for Medicare and Medicaid Services) and pertinent professional societies. Because of these complexities, only a few larger hospitals currently have protocols for scanning non-conditional device patients.
So, for people with these devices, what we once knew for sure just isn’t true any longer. If you or someone you know has a pacemaker or defibrillator device and needs an MRI, talk to your cardiologist. We can now almost always get an MRI done safely. For the newer 3 Tesla machines, demonstrating safety remains a work in progress. The good news is that many devices implanted today are by design MRI conditional for 3 Tesla scanners.
Dr. F. Earl Fyke III is a Northsider.