The warming of electrode tips depends materially on the magnetic field intensity of the MRI scanner. Critical lead length with particularly intense warming are about 50 cm for a magnetic field intensity of 1.5 tesla and about 25 cm for 3 tesla, but these depend on different parameters (1– 3). In spite of higher specific absorption rate (SAR) values of identical sequences, a lesser degree of radio frequency (RF)-induced warming was measured in vitro for 3 tesla than for 1.5 tesla (3). Combined with an transmit-receive head coil, in which RF fields are restricted to the head, patients with pacemakers can benefit from the advantages offered by MRI scans of the cerebrum at 3 tesla (2). This has been our standard procedure since 2008 in cases with an appropriate clinical indication.
The authors report on about an MRI-compatible pacemaker system and similar systems. This statement in this form is dangerous and requires clarification. The standards E-DIN 6877–1 and ASTM F2503–8, which form the basis for the CE certification, contain only the terms “MR-safe”, “MR-conditional”, and “MR-unsafe”.
The MRI-compatible pacemaker systems mentioned by the authors are all MR-conditional, which means that they should be exposed to MRI scanning only within the context of precisely defined restrictions. In this aspect, MR-conditional pacemaker systems from different manufacturers vary widely (exclusion/inclusion of thorax region, maximum permitted SAR value of MRI sequences, type of patient monitoring, and others). All these limitations have to be known for MR-conditional pacemakers, in order for MRI scans to be performed only within the limitations imposed by the manufacturers.
Even though the rates of complications in published studies have been low, MRI scans in patients with “conventional” (MR-unsafe) pacemakers or implantable cardioverter/defibrillators (ICD) should continue to be provided only at centers with proven expertise and under stringent safety precautions.
Footnotes
Conflict of interest statement
Dr Nähle has received travel and hotel expenses, honoraria for conducting commissioned clinical studies, and funding for a research project initiated by him, from Medtronic.
Dr Lüchinger has received honoraria for acting as an adviser, conference participation fees, travel and hotel expenses, and honoraria for conducting scientific medical educational events, as well as funding for a research project initiated by him from Medtronic.
References
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