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.