Input Impedance Comparison of MR-Conditional Cardiac Implantable Pulse Generators at the 1.5T MR Frequency of 63.87 MHz

The MR environment poses a tissue heating hazard to patients with cardiac IPGs (implantable pulse generators), such as pacemakers and defibrillators, due to RF currents circulating in the loop formed by the IPG, a transvenous lead, and the tissue. Heating will be limited by the impedance of this loop at the MR frequency (63.87 MHz for 1.5T). The IPG input impedance (a portion of this loop) was measured in six MR-Conditional IPG’s. All have a comparable, low impedance, suggesting that device manufacturers are not intentionally adding impedance and that some interchangeability may be possible without changing RF-induced heating.