Mixed-brand cardiac implants fall outside MRI safety labeling because MRI safety is assessed for complete implanted systems, not just connectors. Research shows that measuring electrical properties like generator impedance could help determine whether cross-manufacturer combinations are MRI-safe, though this approach requires extensive testing and validation before broad application.
- Cardiac leads and pulse generators use standardized connectors (IS-1, IS-4, DF-4), allowing components from different manufacturers to work together mechanically.
- MRI safety assessment evaluates the complete implanted system under ISO/TS 10974, including interactions between generators and leads, not just connector compatibility.
- When a generator is replaced with one from another manufacturer, the system may lose its MR-conditional labeling status even if the physical MRI risk hasn't changed.
- Research found that when generator impedance is less than 5% of total system impedance, substituting generators did not meaningfully alter RF-induced heating at lead electrodes.
- Before applying cross-manufacturer equivalence criteria broadly, additional testing across diverse device combinations, frequencies, and MRI hazards is needed to establish validated safety standards.
Cardiac leads and pulse generators use standardized connectors, allowing components from different manufacturers to be combined. Yet a mixed-brand system may fall outside MR-conditional labeling because MRI safety is assessed for the complete implanted system, not simply the connector.
Abdou Khadir Fall, PhD, senior MRI safety engineer at TÜV SÜD America, has investigated whether measurable electrical properties could help determine how replacing a generator affects MRI-related heating. His research found no meaningful change in RF-induced lead heating in the devices tested when generator impedance was small relative to the overall system impedance.
AuntMinnieEurope: Cardiac leads and pulse generators use standardized connectors that can allow components from different manufacturers to be connected. Why does this technical interoperability not extend to MR-conditional labeling?
Fall: Most cardiac leads and pulse generators use standardized connectors, such as IS-1, IS-4 and DF-4. These standards allow clinicians, where clinically appropriate, to connect components from different manufacturers. However, a connector standard does not establish how the complete lead-generator system responds to MRI.
MRI safety assessment under ISO/TS 10974 considers the implanted system, including interactions between the generator and leads. Historically, manufacturers have mainly established MR-conditional claims for combinations within their own portfolios.
Our research examined whether measurable electrical properties could help assess generator substitution. For the leads and generators we tested, changing the generator did not meaningfully alter the predicted RF-induced power deposited at the lead electrodes. This suggests a possible route to evaluating mixed-manufacturer combinations, but connector compatibility or a favorable RF-heating result alone does not establish MR-conditional status.
AME: When a patient receives a replacement generator from another manufacturer, the leads may remain unchanged while the complete system loses its MR-conditional status. Has the MRI risk necessarily changed, or only its regulatory classification?
Fall: Generators are often replaced when their batteries reach the end of service, while implanted leads may remain in place because replacing them can involve additional risks. If the new generator comes from another manufacturer, the resulting combination may fall outside the system configurations covered by existing MR-conditional labeling.
That change in labeling does not, by itself, prove that the physical MRI risk has increased. The risk depends on how the replacement generator and retained leads actually respond together during MRI. Our study found that, for the devices we tested, substituting the generator did not produce a meaningful change in predicted RF-induced power at the lead electrodes.
Other combinations could behave differently, and RF heating is only one part of MRI safety. Until the new combination has appropriate supporting evidence, its previous MR-conditional claim cannot simply be assumed to apply.
AME: Your study raises the possibility of assessing generator substitution through measurable electrical properties. Could MRI compatibility eventually be determined by engineering criteria rather than lists of manufacturer-approved combinations?
Fall: Yes. If a generator and lead each belong to an MR-conditional system but have not been evaluated together, measurable electrical properties could help identify which interactions need further testing.
In our 64 MHz study, changing among three generators produced similar predicted RF power deposition for the two tested leads when generator impedance was small relative to lead impedance. Jeong and colleagues later investigated cross-manufacturer substitutions at 64 and 128 MHz.
These results support developing targeted engineering tests, although RF-heating equivalence alone would not establish an MR-conditional claim for the complete system.
AME: Your study tested different technological platforms and lead designs from MicroPort CRM. What cross-manufacturer testing would be required before the approach could be applied to combinations involving devices from different companies?
Fall: Our study tested two different pacing lead designs with three MicroPort CRM generators: two pacemakers and one CRT-D. That introduced variation in generator technology, but it did not establish equivalence across manufacturers.
A 2026 study published by Jeong and colleagues took the next step, testing generator substitutions across three manufacturers at 64 and 128 MHz. Its results were consistent with our central finding: when the generator’s RF impedance was small relative to the lead-generator system impedance, substitution did not substantially change the measured RF-heating response under the conditions tested.
Before applying this approach broadly, I would test a larger, deliberately varied set of cross-manufacturer combinations. For each lead, we should compare its response with the original generator and replacement generators under the same RF exposures. That means measuring generator impedance and the system transfer function, then checking RF power deposition at the electrodes across relevant lead designs, lengths, implant paths and MRI frequencies.
We would also need to assess RF-induced voltage, device function and other applicable MRI hazards before making a claim for the complete combination. The aim is to define and validate an equivalence criterion, rather than assume that one favorable cross-brand result applies to every system.
AME: The generators you tested contributed less than 5% of the total system impedance. Should this be regarded as a possible equivalence criterion, or is it too early to interpret it as a generally applicable threshold?
Fall: The less-than-5% result is a starting point for developing an equivalence criterion, not a threshold that can already be applied to other devices. In our study, the generators’ RF impedances were small compared with the lead impedances. Substituting one tested generator for another did not change the predicted RF power at the lead.
Abdou Khadir Fall, PhD is a senior MRI safety engineer at TÜV SÜD America, where he works on MRI safety assessments of medical devices. He previously worked at MicroPort CRM on MRI safety of cardiac rhythm management devices.
