When Heart-Device Patients Need MRI
Date: July 1, 2009
Pacemakers and implantable cardioverter defibrillators have come a long way in the past two decades, yet the debate continues regarding the safety of performing MRI in patients who have the devices.
Cardiologists Henry Halperin and Saman Nazarian say it may be time for a new perspective.
Millions of patients have had either pacemakers or ICDs implanted, and millions more will. The problem is that up to 75 percent of those patients will likely need an MRI in their lifetime.
“If you have an implanted cardiac device and you need an MRI, traditional concerns limit your options,” says Nazarian. Those concerns have included possible movement of the devices, programming changes and induced lead currents that result in heating and cardiac stimulation. Nazarian explains in a study published in Circulation that other problems have included strong electromagnetic fields that might cause asynchronous pacing, activate tachyarrhythmia therapies or inhibit a demand pacemaker.
But in that same study, Nazarian, Halperin and other colleagues concluded that MRI can be safely performed in patients with implanted cardiac devices. What’s more, they were able to answer diagnostic questions in 95 percent of cases using MRI versus 20 percent using alternatives like CT scans and nuclear imaging. “The need to be able to use MRI in these situations is significant,” says Halperin.
To prevent inappropriate device behavior, they reprogram each device so its electronics won’t mistake the MRI radiofrequency for an arrhythmia. They also turn off a defibrillator’s shocking function for the 30 to 60 minutes needed to perform the imaging test. In addition, they limit the amount of energy used at peak scanning, reducing the strength of the electromagnetic field from as much as 4 watts per kilogram to 2 watts per kilogram per patient. And during the scan, they closely monitor every patient using electrocardiography, blood pressure and pulse oximetry.
There are caveats, though. Halperin notes special protocols for patient safety and emphasizes that the procedures need to be performed at centers that follow those protocols. Plus, patients who aren’t eligible include those with “abandoned” leads not connected to the implanted device or with leads on the outside of the heart.
Halperin, Nazarian and their team have made definitive diagnoses in more than 300 patients who have been scanned so far, helping plan artery-opening procedures, measuring tumor growth, detecting strokes and brain masses, and diagnosing a blood clot in the spine that had been missed by CT scanning. They also pinpointed the cause of one woman’s seizures, allowing surgical cure.