Pacemaker interactions with transcutaneous cardiac pacing

Magnetic resonance imaging in patients with cardiac pacemakers: era of "MR Conditional" designs

Advances in cardiac device technology have led to the first generation of magnetic resonance imaging (MRI) conditional devices, providing more diagnostic imaging options for patients with these devices, but also new controversies. Prior studies of pacemakers in patients undergoing MRI procedures have provided groundwork for design improvements. Factors related to magnetic field interactions and transfer of electromagnetic energy led to specific design changes. Ferromagnetic content was minimized. Reed switches were modified. Leads were redesigned to reduce induced currents/heating. Circuitry filters and shielding were implemented to impede or limit the transfer of certain unwanted electromagnetic effects. Prospective multicenter clinical trials to assess the safety and efficacy of the first generation of MR conditional cardiac pacemakers demonstrated no significant alterations in pacing parameters compared to controls. There were no reported complications through the one month visit including no arrhythmias, electrical reset, inhibition of generator output, or adverse sensations. The safe implementation of these new technologies requires an understanding of the well-defined patient and MR system conditions. Although scanning a patient with an MR conditional device following the strictly defined patient and MR system conditions appears straightforward, issues related to patients with pre-existing devices remain complex. Until MR conditional devices are the routine platform for all of these devices, there will still be challenging decisions regarding imaging patients with pre-existing devices where MRI is required to diagnose and manage a potentially life threatening or serious scenario. A range of other devices including ICDs, biventricular devices, and implantable physiologic monitors as well as guidance of medical procedures using MRI technology will require further biomedical device design changes and testing. The development and implementation of cardiac MR conditional devices will continue to require the expertise and collaboration of multiple disciplines and will need to prove safety, effectiveness, and cost effectiveness in patient care.

Anesthetic Implications for Patients With Permanent Pacemakers

Anesthesiologists will increasingly be required to treat patients with permanent pacemakers in the periopera tive period. Careful preoperative anesthetic evaluation is mandatory and includes attention to both the initial pathology that led to pacemaker insertion as well as to coexisting disease and treatment. Specific information regarding the patient's pacemaker should be sought, including the type and model, battery state, ability to stimulate the heart, and the expected response to placement of a magnet over the device. Additional preoperative considerations are discussed. Important intraoperative considerations for patients with perma nent pacemakers are also reviewed, including issues of rate-adaptive pacing, electrical interference with pace maker function, and loss of pacing capability. Additional intraoperative anesthetic issues, including the choice of anesthetic technique and the use of invasive monitoring for patients with permanent pacemakers are addressed. Specific considerations for lithotripsy, radiotherapy, and magnetic resonance imaging are also discussed. Finally, postoperative considerations are reviewed. Although pacemaker complications are unusual during anesthe sia, it is essential that anesthesiologists be able to anticipate, recognize, and treat pacemaker dysfunction in the perioperative period.