How should LI be used with PEF ablation?
Impedance metrics have been useful clinical tools in monitoring
resistive heating and predicting lesion transmurality for RF
ablation22–24. When used in a clinical RF workflow,
targeting a >20Ω LI drop effectively predicted lesion
efficacy and durability25,26. For PEF ablation, LI is
a useful way to measure CTC and confirm optimal catheter placement for
lesion formation. However, LI may be limited in informing real-time PEF
lesion formation. PEF ablation does not rely on electrode-tissue
coupling to conduct current to tissue and cause resistive heating for
cell death7. Therefore, starting impedance as an
indicator of resistive potential or electrode coverage is not critical
in PEF ablation. Once contact was established, no correlation was
observed between starting impedance and treatment size in this study.
Additionally, inconsequential impedance drops immediately post-PEF
delivery (1-3Ω) indicate negligible resistive heating is occurring from
energy delivery (Figure 6 ). These PEF-specific differences
limit the utility of impedance drop as an acute metric of therapy
success. The effects of the induced electric field cause a cascade of
cellular activity which impacts cell homeostasis and viability over the
course of hours to days. LI, a wholistic measurement of tissue
properties (e.g., temperature and relative health), changes with the
evolution of myocardial damage and fibrosis27. In
previous RF studies, tissue impedance was reduced in more fibrotic
tissue compared to healthy myocardium28. Similarly, in
this study, there was a substantial decrease in LI response on treated
myocardium that presented evidence of transmural fibrosis at 30 days.
When considering LI as an indicator of CTC, the decrease in feedback on
scar tissue poses a potential shortcoming. Determining contact with
previously treated myocardium or in fibrotic tissue will be challenging
with LI and warrants further investigation.