Role of the lead structure in MRI‐induced heating: In vitro measurements on 30 commercial pacemaker/defibrillator leads

Abstract

MRI-induced heating on endocardial leads is a serious concern for the safety of patients with implantable pacemakers or cardioverter-defibrillator. The lead heating depends on many factors and its amount is largely variable. In this study, we investigated the role of those structural properties of the lead that are reported on the accompanying documents of the device: (1) fixation modality (active vs. passive); (2) number of electrodes (unipolar vs. bipolar); (3) length; (4) tip surface; and (5) tip and ring resistance. In vitro temperature and specific absorption rate measurements on 30 leads (27 pacemakers, three implantable cardioverter-defibrillator leads) exposed to the radiofrequency field typical of a 1.5 T MRI scanner are presented. The data show that each lead has its own attitude to radiofrequency-induced heating and that the information that is available in the accompanying documents of the pacemaker is not sufficient to explain such attitude. Even if combined with that of the implant geometry, this information is still not sufficient to estimate the amount of heating due to the exposure to the radiofrequency field during MRI examination. Magn Reson Med 67:925-935,

Safety and effectiveness of a 6‐French MRI conditional pacemaker lead: The INGEVITYTM clinical investigation study results

“…As described by Khan et al., the mechanism of delayed lead perforation may be related to the design of leads with a decreased diameter, leading to increased force per unit area. These concerns about increased perforation rates with decreased diameter leads was not an issue within the INGEVITY study of this 6‐French lead design, nor does the INGEVITY data suggest a higher incidence of pericarditis, cardiac perforation, tamponade, death, and lead dislodgment.…”

“…The leads have design aspects for MRI conditional safety, including unifilar coiled conductors for both the inner (cathode) and outer (anode) electrical pathways. Unifilar coils increase the inductance relative to multifilar coils which minimizes lead heating while in an MRI scanner …”

MRI interactions of a fully implantable pressure monitoring device

“…Early-stage numerical modeling results indicated the sensing catheter length would be a key determinant of resulting RF-induced heating, which is consistent with published work on leads for pacemakers, cardio defibrillators, and neurostimulators. [16][17][18] Therefore, two versions of the device were investigated for RFinduced heating, identical other than in catheter length: 1) A short catheter (SC) device, with the sensor 150 mm from the electronic unit, and 2) a long catheter (LC) device, with the sensor 420 mm from the electronic unit. These configurations represent potential implantation locations should the device be fully implanted in the head of the patient for the ICP application, if the electronic unit was required to be positioned further distal from the head, or if an alternative long-term pressure application was addressed.…”

An optically coupled sensor for the measurement of currents induced by MRI gradient fields into endocardial leads

“…The interaction between the time-varying MRI gradient field and the conductive loop formed by the implanted lead can be considered an instance of electromagnetic induction, per Faraday's law. Whereas a large body of excellent works have been published about the RF-induced heating of endocardial leads [5][6][7][8][9][10][11][12][13], few studies to date have specifically addressed the amount of the current induced by time-varying gradient fields [14][15][16].…”

“…The RF field (64 MHz for 1.5 T MRI systems; 128 MHz for 3 T systems) potentially can transfer energy into implanted electronic devices and cause thermal injury to tissue near the tissue-electrode interface. MRI gradient fields, on the other hand, have a much lower frequency (1)(2)(3)(4)(5)(6)(7)(8)(9)(10) and are used to provide spatial information. The interaction between the time-varying MRI gradient field and the conductive loop formed by the implanted lead can be considered an instance of electromagnetic induction, per Faraday's law.…”