Johns Hopkins scientists have found that modern implanted heart devices -- such as pacemakers and defibrillators -- are safe for use in magnetic resonance imaging (MRI) machines, a diagnostic and imaging tool long ruled potentially unsafe and off-limits for more than 2 million Americans who currently have them in their bodies. The Johns Hopkins team has also developed new guidelines for their use, making MRI scans more available to people who might benefit from early detection of cancer and other diseases, when treatments are most likely to succeed, and for guiding devices during minimally invasive surgery.
During a four-month period, the Johns Hopkins team tested 18 different pacemakers and 15 implantable defibrillators previously found safe in animal experiments. In a study of 33 patients undergoing 38 separate scans, the researchers adjusted the device's pacing program and lowered MRI sequence energy levels to see if the scan affected the settings or caused any other kind of problem, such as heating of the electrical leads and surrounding tissue. All patients and devices were closely monitored during the scans, some of which lasted up to 1.5 hours, and repeat measurements weremade on average 24 days after the MRI to measure any long-term complications. No ill effects were observed. The only complaint cited was claustrophobia, which is commonly associated with the close confines of the MRI scanner.
The researchers' new guidelines caution that only modern devices, predominantly models from the past seven years, are safe in MRIs and call for low-energy-level scans, avoiding scan settings higher than 2 watts per kilogram, which might lead to overheating. The protocol also advises close monitoring by a cardiologist and a radiologist, and using MRIs only when clinically necessary and when alternative diagnostic tests are not recommended.
Evaluation of a safety protocol for clinically indicated magnetic resonance imaging of patients with permanent pacemakers and implantable defibrillators at 1.5 Tesla. Saman Nazarian, Ariel Roguin, Menekhem Zviman, Albert Lardo, Timm Dickfield, Ronald Berger, David Bluemke, and Henry Halperin.
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