Abstract 3028: Methods To Minimize Pacemaker Leadwire Heating During MRI Scans
INTRODUCTION: MRI scans are generally contraindicated by both pacemaker and MRI equipment manufacturers. However, MRI has become one of medicine’s most important diagnostic and clinical tools. A major concern with conducting MRI scans on a pacemaker patient is the potential for overheating of the implanted leadwires and/or distal tip electrodes. It has been reported that such overheating can cause increase in capture, loss of capture or even death in rare cases.
HYPOTHESIS: This is a continuing evaluation of whether certain combinations of leadwire geometry, lead length, position in the MRI bore, and certain scan sequences can lead to worst-case leadwire heating. We also evaluated 3.0T design refinements of a resonant inductor capacitor (L-C) bandpass filter chip at the distal tip designed to create a very high impedance at the MRI RF pulse frequency in order to reduce the flow of RF current and thereby reduce leadwire heating.
METHODS: Real time temperature rise maps were obtained by moving a human gel phantom containing a functional pacemaker with bipolar leads around inside the MRI scanner while it’s distal tip and ring were instrumented with fiber optic temperature probes. Various lead lengths, layouts and MR scan sequences were tested. Three dimensional color maps were created showing areas of maximum RF field coupling and maximum heating. Once these worst-case positions were determined, special prototype leads were built with the L-C resonant bandpass filter chip installed in the distal tip electrode and the temperature measurements were repeated at the predetermined worst-case position.
RESULTS: Temperature mapping of 1.5 and 3.0 T MRI scanners resulted in worst-case distal tip temperatures of 57°C and 95°C respectively. Identical leadwires that incorporated the L-C resonant filter were tested in the same worst-case positions and exhibited a reduction in distal tip temperature of approximately 90%.
CONCLUSIONS: Temperature mapping of pacemaker leadwires in 1.5 and 3.0 T MRI bores show that for certain worst-case lead lengths, layouts and positions excessive distal tip heating of up to 95°C can occur. The addition of a miniature L-C resonant bandstop filter chip at the distal tip reduces this worst-case heating by over 90% and provides a high safety margin.