Friday, September 22, 2006

Heart Devices and MRI's

Finally, it might just me okay to order an MRI for a patient with a pacemaker or an implantable cardiac defibrillator.

In two recent reports from this week's medical journal Circulation, researchers from Johns Hopkins University, Univeristy of Pennsylvania, and Germany have outlined a protocol that permits safe MRI scans (references below). The devices are first reprogrammed to a "pace only" mode (so they cannot be inhibited by outside noise interference), shock therapy is suspended for the brief time of imaging, and the MRI signal intensity is reduced to about one-half its usual intensity (from 4 Watts/kg to 2 Watts/kg). Only pacers from 1996 and later and defibrillators from 2000 and later were tested sucessfully ini 1.5 Tesla MRI scanners in both studies. Once the scan was completed, the device was reprogrammed back to its original setting.

There were some important exclusions as mentioned in this editorial from the FDA:
Meaningful exclusion criteria included pacemaker dependency and the need for a thoracic MR scan for the Sommer et al study and the presence of an epicardial, nonfixated, or abandoned lead for the Nazarian et al study.
There were some important findings. 7 of 115 patients switched to a "noise reversion mode" or factory reset setting, and 21 of 47 patients had the magnetic reed switch fail to close during the MRI (a means to prevent detection of arrhythmias or revert to pace-only mode in pacemakers). Hence, pacemaker-dependent patients might lose pacing output in such circumstances. A slight change in pacing threshold was also noted in several patients.

Although not yet endorsed by the Heart Rhythm Society, FDA, or manufacturers, this work demonstrates that such MRI imaging can be performed safely in appropriately-selected patients under careful observation.


References: Clinical Utility and Safety of a Protocol for Noncardiac and Cardiac Magnetic Resonance Imaging of Patients With Permanent Pacemakers and Implantable-Cardioverter Defibrillators at 1.5 Tesla.
Nazarian, Saman MD; Roguin, Ariel MD, PhD; Zviman, Menekhem M. PhD; Lardo, Albert C. PhD; Dickfeld, Timm L. MD, PhD; Calkins, Hugh MD; Weiss, Robert G. MD; Berger, Ronald D. MD, PhD; Bluemke, David A. MD, PhD; Halperin, Henry R. MD, MA

Strategy for Safe Performance of Extrathoracic Magnetic Resonance Imaging at 1.5 Tesla in the Presence of Cardiac Pacemakers in Non-Pacemaker-Dependent Patients: A Prospective Study With 115 Examinations.
Sommer, Torsten MD; Naehle, Claas P. MD; Yang, Alexander MD; Zeijlemaker, Volkert PhD; Hackenbroch, Matthias MD; Schmiedel, Alexandra MD; Meyer, Carsten MD; Strach, Katharina MD; Skowasch, Dirk MD; Vahlhaus, Christian MD; Litt, Harold MD, PhD; Schild, Hans MD

Food and Drug Administration Perspective: Magnetic Resonance Imaging of Pacemaker and Implantable Cardioverter-Defibrillator Patients.
Faris, Owen P. PhD; Shein, Mitchell MS[Editorial]

1 comment:

Dr. A said...

Interesting. If a definite protocol can be developed, that's one less imaging barrier for my patients.