An Expanded Evaluation of the Safety of Clinically Indicated Magnetic Resonance Imaging (MRI) in Patients With Pacemakers and Implanted Cardioverter Defibrillators

Pilot studies of approximately 1500 patients, RPN #03-08-12-11 and 00051707 (manuscript submitted) demonstrated the safety of most contemporary implanted rhythm management devices in the MRI environment given appropriate precautions.

When pilot studies were developed, there was a theoretical concern that there may be an increased risk associated with some device and device circumstances including: 1) PPM's or leads implanted prior to 1996; 2) ICD's implanted prior to 2000; 3) abandoned or endocardial leads; 4) leads implanted <6 weeks; 5) ICD's where patient is pacemaker dependent.

While it was reasonable to be hyper vigilant when initiating pilot studies by including restrictive inclusion criteria, the natural evolution of the devices and device related technologies coupled with a lack of objective scientific data to support investigator's early safety concerns has caused investigators to reevaluate their necessity. For example, older pacemakers and ICD's that previously excluded potential participants are now obsolete; all have expired batteries and have been explanted. Similarly, the technological evolution of ICD's includes ICD's that are now capable of providing ongoing asynchronous pacing including in the MRI environment. Despite some concern that abandoned, epicardial and newly implanted leads may be at increased risk of heating or subject to torque, when investigators evaluated 15 participants with these lead issues and exposed them to MRI (off protocol in life threatening situations) there were no adverse problems seen.

The vetting procedures investigators implemented in pilot studies required that a registered nurse obtain all patient device information and chest xrays (when indicated) from referring physicians, review them in advance of allowing participants to schedule an MRI, and exclude any patient who did not meet inclusion criteria. Investigators found that these procedures were time consuming and expensive (as they required a part time Registered Nurse (RN) salary). In addition, in some cases, patients who might have derived considerable benefit from an MRI were excluded from obtaining one and the time it took to adhere to the vetting procedures needlessly delayed the MRI in some participants, causing them unnecessary stress and frustration and even adversely affecting their clinical care.

MRI's will be done in participants who require a clinically indicated MRI without implementing the vetting procedures investigators included in pilot studies. Participants with implanted pacemakers and ICD's will only be eligible for MRI at Johns Hopkins Hospital (JHH) if they agree to participate in this study. All studies will be done in the 1.5 Tesla MRI unit. Since the first 100 participants were scanned in investigator's initial protocol 03-08-11-12, MRI scan sequences, field intensity and fields of exposure have been given no special consideration given the presence of the pacemaker or ICD and there have been no adverse or unanticipated problems. For this reason, investigators do not feel it is necessary to impose any special restrictions (related to field intensity or scan sequences/exposure) in this protocol. In the event that any device manufacturer indicates the need for including additional safety precautions investigators will amend the protocol immediately to include them.