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We thank Dr. Rozner and colleagues for their interest in our work (1). They found that a Medtronic Thera DR 7960ipacemaker demonstrated an elective replacement indicator upon interrogation of the device immediately after magnetic resonance imaging (MRI). This phenomenon is neither unexpected nor alarming. Many pacemakers will respond with this warning after an exposure to intense electromagnetic interference. Examples of this exposure include direct current cardioversion, radiofrequency ablation, electrocautery, and MRI. This response is unrelated to the battery voltage or impedance but rather occurs because of a brief power interruption. Magnetic resonance imaging can cause this behavior when the telemetry coil or leads themselves are driven by the radiofrequency output of the MRI, which can result in a parasitic capacitance for brief instances. The solution, when this occurs, is to reset the pulse generator. Newer pacemakers are more resistant to such interference but also can demonstrate this problem.
With respect to their comments, several observations are relevant. The statement that a “pacemaker-facile physician” be present rather than available is consistent with our practice and our recommendations. During all MRI examinations involving pacemaker and implantable-cardiovertor defibrillator patients at Oklahoma Heart Institute, an electrophysiologist is present and observing all available data from the start of the scan through completion of the post exam interrogation. We concur wholeheartedly that this extra step is mandatory to the performance of these studies.
Since the publication of our article (1), we have had the opportunity to expand our pacemaker/MRI database to include a total of 87 patients with 156 leads. We have continued to observe similar but subtle threshold changes in a portion of leads subjected to the levels of electromagnetic interference found at 1.5-T, but none of these threshold changes have been beyond the safe programming limits of the pulse generators.
We stand by our original conclusions. Performance of MRI in appropriately selected, nonpacemaker-dependent patients can be accomplished with an acceptable safety profile. Precautions must include continuous monitoring of the patient with ECG and intermittent voice contact, resuscitation equipment on standby, adequate personnel to move and resuscitate the patient should the need arise, and the presence of a person facile in pacemaker interrogation and programming.
- American College of Cardiology Foundation