October 10, 2011
MRI safe for people with implanted cardiac devices
Magnetic resonance imaging, an important diagnostic test, has traditionally been off-limits to more than 2 million people in the United States who have an implanted pacemaker to regulate heart rhythms, or an implanted defibrillator to prevent sudden cardiac death. Now, in a study published in the Oct. 4 issue of Annals of Internal Medicine, cardiologists at Johns Hopkins report that a protocol they developed has proved effective in enabling patients with implanted cardiac devices to safely undergo an MRI scan.
“We believe this is the largest prospective study of MRI in patients with implanted devices,” said lead author Saman Nazarian, an assistant professor of medicine at the Johns Hopkins University School of Medicine.
“The guidelines we have published can be used to make MRI more available to people who could benefit from early detection of cancer and other diseases, and for guiding surgeons during procedures. MRI is considered superior to CT scans in many clinical scenarios, especially for brain and spinal cord imaging,” Nazarian said. To date, more than 700 patients with implanted cardiac devices have safely undergone MRI exams at Johns Hopkins.
The scientists’ prospective study followed 438 people with implanted cardiac devices who had 555 MRI scans. Ninety-four percent of the exams were conducted at The Johns Hopkins Hospital and the others at Rambam Medical Center in Haifa, Israel. The researchers found that with appropriate precautions, patients with pacemakers and defibrillators can have an MRI scan with very low risk of the device malfunctioning, moving, heating or causing abnormal heart rhythms due to the magnetic and radiofrequency energy generated by the test.
The devices implanted in three of the patients, 1.5 percent of those in the study, had a power-on reset event during an MRI scan, which means that the energy emitted from the scanner caused the devices to revert to default settings. This is a rare occurrence that warrants close expert monitoring during the test and is easily remedied after the test is completed. None of the three had device dysfunction during the long-term follow-up of between 15 and 66 weeks. One of those patients completed four repeated MRI examinations during the study without any problems.
Henry Halperin, a Johns Hopkins cardiac electrophysiologist and biomedical engineer, began researching the issue of MRI safety with implanted devices about 15 years ago, testing a range of devices. The safety protocol he developed is now being adopted by institutions around the world.
“The newer pacemakers, made after 1998, and defibrillators manufactured since 2000 come with electromagnetic interference protection,” said Halperin, who is a professor of medicine at the Johns Hopkins University School of Medicine and the senior author of the study. In addition to checking the age of the device, the Johns Hopkins team looks at the type and configuration of the leads attached to it. If, for example, a lead is disconnected and is not part of the device’s function, an MRI would not be recommended because the tip of the wire could get very hot.
Rozann Hansford, a study author and research nurse manager in Cardiology who monitors patients at Johns Hopkins during the scans, said, “We reprogram the device to a safe mode while the patient is having the MRI scan. We carefully monitor the patient’s blood pressure, electrical activity of the heart and oxygen saturation, and look for any unusual symptoms. After the test, we reprogram the device and carefully check its function.” The patients’ devices are checked again in three to six months.
The researchers conclude that with a protocol based on device selection, programming and careful patient monitoring, MRI can be performed safely in many patients who have a pacemaker or a defibrillator.
“With the advancing age of the population and the expanding indications for pacemakers and defibrillators,” Nazarian said, “this has become an increasingly important issue, and a lifesaving one for some patients.” He said that many of the patients with cardiac devices who have come to Johns Hopkins for an MRI scan have had tumors and other serious issues diagnosed and treated, problems that had been missed by a previous imaging test, such as a CT scan or ultrasound exam.
In addition to Nazarian, Halperin and Hansford, authors on the study were Menekhem M. Zivman, Albert C. Lardo, Brian S. Caffo, Kevin D. Frick, Michael A. Kraut, Ihab R. Kamel, Hugh Calkins and Ronald D. Berger, all of Johns Hopkins; Ariel Roguin and Dorith Goldsher, of Rambam Medical Center; and David A. Bluemke, of the National Institutes of Health.