Every year in Canada over 25,000 pacemakers and internal defibrillators are implanted in Canada and according to the Canadian Journal of Cardiology over 200,000 Canadians have permanent pacemakers or implantable defibrillators. Demand for these devices is only expected to grow given the link between aging and the indications necessitating these devices, such as bradycardia, combined with our shifting demographics in Canada.
Until 2012, pacemaker and MRI manufacturers instructed physicians not to scan patients with pacemakers, as this exposure could disrupt a pacemaker’s electronic system and burn surrounding tissue.
As a result, an MRI was not usually considered for patients with a pacemaker. However, a study published in The Japanese Heart Journal showed that an MRI procedure is requested by a physician for 17 per cent of pacemaker patients within 12 months of device implant.
Four years ago, the landscape changed when Medtronic introduced Advisa, the first MRI conditional pacemaker that had been designed, tested, and licensed by Health Canada for use as labeled with MRI machines. Patients with the Advisa pacing system have access to full body scans, without positioning limitations in the MRI scanner.
Since then, physicians such as Dr. Vikas Kuriachan, cardiologist and cardiac electrophysiologist at the Libin Cardiovascular Institute of Alberta, and University of Calgary are faced with deciding which patients are the more likely candidates for an MRI conditional pacemaker or implantable defibrillator.
The statistics provide a strong argument for MRI conditional devices. Dr. Kuriachan reports that up to 10 per cent of the population in Canada might get an MRI every year. “If you specifically look at patients with cardiac implantable devices, the estimate is 50 to 75 per cent of them will need an MRI in their lifetime. And the reasons can be quite variable. MRIs are a crucial test for diagnosing problems in the neurological, muscular skeletal and even cardiac systems. These include things like stroke, brain tumours and sometimes more common problems such as investigating back or joint pain. So we want to be prepared for that.”
In addition, MRIs are the preferred option for soft tissue imaging as they provide more detail than modalities such as CT or ultrasound. “An MRI can give images that cannot be found with other imaging, especially for certain brain tumours, certain strokes that you couldn’t see, as well as certain spine, joint and cardiac muscle problems,” Dr. Kuriachan says.
The historic concern of scanning a patient with a pacemaker was indeed a legitimate safety concern, he adds “I think the first thing to keep in mind is these devices are designed to be MRI conditional. And we have lots of studies now including clinical studies that show that they’re safe to use in the appropriate MRI environment and condition.” He also stresses that the Canadian Heart Rhythm Society and the Canadian Association of Radiologists have a joint consensus statement published in 2014 that specifies the appropriate procedures to be followed when scanning a patient with a MRI conditional pacemaker. Ultimately Dr. Kuriachan believes that beyond the diagnostic benefits, MRI conditional devices improve efficiency and patient care. “The MRI scan can offer advantages that other testing cannot so there are certain conditions where the diagnosis can be reached with an MRI scan but not necessarily by some of the other tests. So if you have a patient with an MRI conditional device, they can get the MRI scan and have the answer with the one test. Otherwise they may need multiple tests and still not have the answer.”
Alan, a patient from Calgary is a case in point. A recently retired government employee, he suffered a mini-stroke. When sent for an echocardiogram and carotid artery ultrasound, it was discovered he had atrial fibrillation. Further checking revealed that his pulse had been dropping into the 30s, a problem that could be resolved with a pacemaker.
He notes that when the decision was made, “I had no idea at that point that there was anything that was even compatible with an MRI. It never occurred to me that there were different kinds of pacemakers. I just trusted my cardiologist to pick the right one for me.”
The decision was a fortuitous one. A stress test and CT scan picked up anomalies on his liver. A subsequent ultrasound also indicated something was wrong in his pancreas which could only be diagnosed with an MRI.
“I’d never thought my pacemaker could prevent me from getting an MRI,” Alan says. “But my family doctor knew I had a pacemaker that was compatible with the MRI. With a different pacemaker that wasn’t MRI conditional I would probably have felt cheated because I know that the MRI is so important in diagnosing some conditions.”
Given the advances in pacemaker technology and the diagnostic capabilities of MRIs, the hope for patients like Alan is that more physicians, cardiologists, and MRI technicians will become more knowledgeable about MRI conditional devices so that their patients can also access the benefits of both pacemakers, and MRI scans.