Imaging method safe for cardiac implants

A study conducted by cardiologists at Hopkins shows that patients with implanted cardiac devices are able to undergo magnetic resonance image (MRI) examination under the proper precautions and monitoring.

Patients with devices like pacemakers and implantable cardioverter-defibrillators (ICDs) made to regulate heart rhythms and to stop unexpected cardiac death, respectively, have traditionally been advised against these diagnostic tests by the device manufacturers as well as the U.S. Food and Drug Administration (FDA) because of safety concerns.

However, 75 percent of patients with these implants develop a needs for an MRI exam due to medical co-morbidities, diseases which occur in addition to the primary disease. Thus, the results of this study have major implications for over two million people in the United States who have implanted cardiac devices.

MRIs can enable early detection of cancers and other diseases. They are the most accurate technique for brain and spinal cord imaging are sometimes essential in directing surgeons through procedures.

In fact, other exams like CT scans and ultrasounds have failed to locate problems in Hopkins patients, which were later revealed with an MRI. With the spread of this new safety protocol, a whole new set of at-risk patients will now be able to get the more accurate MRI exam.

The study aimed to test the safety of a specific MRI protocol of its patient audience using the common magnetic strength of 1.5 tesla (T). The protocol involved the preparation of the implant device before the scan and close monitoring during the exam by a nurse with cardiac life support and device programming training.

To be considered for the study, a patient's pacemaker had to have been implanted after 1998 (or 2000 for an ICD) and any leads, the connectors between the heart and the device, had to be implanted at least six weeks before. These newer pacemakers and ICDs have electromagnetic interference protection, which allow them to withstand the MRI unaffected.

Before the scan, all pacemakers were set to asynchronous mode, a fixed mode which is be safer for patients. Periodic blood pressure, electrocardiography (electrical heart activity), oximetry (oxygen saturation) and any other abnormal symptoms were recorded.

After the MRI, patients' implants were reset and checked for proper function. They were checked again after three to six months had passed, though 10 percent of patients in the study were unavailable for this second confirmation.

In all but three patients, the scans went smoothly and the post-MRI checks were clear. The three patients (1.5 % of those tested) experienced a power-on reset of their implant during the scan, which meant that the device went to its default settings, but this was easily fixable. Thus, with the proper implant model (not all were tested), programming before the test and close electrophysiological monitoring throughout the scan, this research shows that MRIs are very unlikely to cause complications like device malfunction, heating or movement because of the magnetic and radiofrequency energy produced by the test.

The study examined the responses of 438 patients to a total of 555 MRI tests between February 2003 and April 2010. Similar experiments have been conducted before, but Saman Nazarian, lead author of the study which was published in Annals of Internal Medicine on Oct. 4, believes this is the largest study of its kind to date.

It was a nonrandomized trial: 54 percent of those studied had pacemakers and 46 percent had ICDs. 94 percent of the trials were conducted at Hopkins Hospital and the rest took place at Rambam Medical Center in Haifa, Israel. The institutional review boards of both establishments approved the procedures and the National Institutes of Health provided the primary funding.