NEW YORK (Reuters Health) – While magnetic resonance imaging is contraindicated for patients with most implanted cardiac devices because of safety concerns, MRI can in fact be performed safely with appropriate precautions in some cases, according to a report in the October 4th issue of the Annals of Internal Medicine.

Nonetheless, the authors advise, “The decision to perform MRI in each patient with an implantable device should be made by balancing the potential benefit of MRI against the attendant risks.”

Dr. Saman Nazarian, with Johns Hopkins Hospital in Baltimore, Maryland, and colleague developed a protocol for reducing the risk of MRI in patients with implanted devices. The protocol included device selection, based on previous studies, and device programming designed to minimize the chance of inappropriate activation or inhibition of device-delivered therapies.

For example, the pacing mode was programmed to asynchronous for pacemaker-dependent patients while an inhibited pacing mode was used for patients with a stable intrinsic rhythm; and all other pacing and tachyarrhythmia functions were disabled. The complete pre-MRI protocol is outlined in an algorithm in the paper.

For the current study, 438 patients with cardiac devices (54% with pacemakers and 46% with defibrillators) underwent 555 MRIs at the commonly used magnetic strength of 1.5 T, after the protocol precautions were taken.

“Blood pressure, electrocardiography, oximetry, and symptoms were monitored by a nurse with experience in cardiac life support and device programming who had immediate backup from an electrophysiologist,” the authors note.

During MRI, three patients experienced acute power-on reset events – one with an ICD, which led to discontinuation of the MRI exam, and two with pacemakers who were not pacing-dependent and were able to complete their MRI exams. In some pacemakers, MRI triggered transient asymptomatic asynchronous pacing, but no rapid activation of pacing was observed.

Appropriate device function was determined before and after the MRI studies. Typical measures included sensing, lead impedance, and capture threshold. “No immediate or long-term change in variables in any patient was large enough to require lead or system revision or device reprogramming,” the researchers report.

“In conclusion, using a protocol based on device selection and programming, MRI can be performed safely in patients with certain pacemaker and ICD systems,” Dr. Nazarian and colleagues write.

But they add a note of caution: “It is vital, however, to emphasize the need for appropriate programming of the device to an asynchronous mode, monitoring by qualified personnel, and availability of external pacing backup for such patients.”

Ann Intern Med 2011;155:415-424.