MRI no longer off limits for pacemakers

JOHNS HOPKINS (US) — Patients with cardiac implants can safely undergo MRI scans if their doctors follow new guidelines, researchers say.

MRI—or magnetic resonance imaging—has been off limits to more than 2 million people in the United States who have implanted pacemakers to regulate heart rhythms or implanted defibrillators to prevent sudden cardiac death.

“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,” says lead researcher Saman Nazarian, a cardiac electrophysiologist and assistant professor of medicine at Johns Hopkins University.

MRI is considered superior to CT scans in many clinical scenarios, especially for brain and spinal cord imaging, says Nazarian. To date, more than 700 patients with implanted cardiac devices have safely undergone MRI exams at Johns Hopkins.

The study of the new protocol, published this week in the Annals of Internal Medicine, followed 438 people with implanted cardiac devices who had 555 MRI scans. Almost all of the exams, 94 percent, were conducted at The Johns Hopkins Hospital. The rest were performed 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 in the study had a power-on reset event during an MRI scan, which means 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, but 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.

Johns Hopkins cardiac electrophysiologist and biomedical engineer Henry Halperin 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,” says Halperin, who is a professor of medicine and the study’s senior author.

In addition to the age of the device, the Johns Hopkins team checks the type and configuration of the leads attached to the device. For example, if a lead is disconnected and not functional, an MRI would not be recommended because the tip of the wire could get very hot.

“We reprogram the device to a safe mode while the patient is having the MRI scan,” says Rozann Hansford, a nurse and study author who monitors patients at Johns Hopkins during scans. “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, this has become an increasingly important issue, and a lifesaving one for some patients,” Nazarian says.

He adds that many of the patients with cardiac devices who have come to Johns Hopkins for an MRI scan had tumors and other serious problems diagnosed and treated, whereas those problems had been missed by a previous imaging test such as a CT or ultrasound exam.

More news from Johns Hopkins University: