In Silico Study of Local Electrical Impedance Measurements in the Atria - Towards Understanding and Quantifying Dependencies in Human

Abstract

Background: Electrical impedance measurements have become an accepted tool for monitoring intracardiac radio frequency ablation. Recently, the long-established generator impedance was joined by novel local impedance measurement capabilities with all electrical circuit terminals being accommodated within the catheter. Objective: This work aims at in silico quantification of distinct influencing factors that have remained challenges due to the lack of ground truth knowledge and the superposition of effects in clinical settings. Methods: We introduced a highly detailed in silico model of two local impedance enabled catheters, namely IntellaNav MiFi™ OI and IntellaNav Sta-blepoint™, embedded in a series of clinically relevant environments. Assigning material and frequency specific conductivities and subsequently calculating the spread of the electrical field with the finite element method yielded in silico local impedances. The in silico model was validated by comparison to in vitro measurements of standardized sodium chloride solutions. We then investigated the effect of the withdrawal of the catheter into the transseptal sheath, catheter-tissue interaction, insertion of the catheter into pulmonary veins, and catheter irrigation. Results: All simulated setups were in line with in vitro experiments and in human measurements and gave detailed insight into determinants of local impedance changes as well as the relation between values measured with two different devices. Conclusion: The in silico environment proved to be capable of resembling clinical scenarios and quantifying local impedance changes. Significance: The tool can assists the interpretation of measurements in humans and has the potential to support future catheter development.

Determinants of left atrial local impedance: Relationships with contact force, atrial fibrosis, and rhythm

“…Using the same catheter, Unger et al demonstrated how both approaching tissue and increasing CF lead to a rise in LI using an in silico model. 12 Their work produced similar results to Sulkin et al, who noted in vitro a nonlinear monotonic increase in LI when the IntellaNav MiFi catheter approached tissue, before a linear relationship following tissue contact. 8 Although these studies use catheter displacement in mm rather than measuring CF in grams, and thus a direct comparison is not possible, the relationship between CF and LIr closely resembles our findings.…”

“…The strong correlation between CF and LIr reproduces the results of laboratory models in a clinical setting. Using the same catheter, Unger et al demonstrated how both approaching tissue and increasing CF lead to a rise in LI using an in silico model 12 . Their work produced similar results to Sulkin et al, who noted in vitro a nonlinear monotonic increase in LI when the IntellaNav MiFi catheter approached tissue, before a linear relationship following tissue contact 8 .…”