First in Human Validation of Impedance-Based Catheter Tip-to-Tissue Contact Assessment in the Left Atrium

Background: In this study, a new method of contact assessment based on the measurement of the local electrical properties at the catheter tip‐to‐tissue interface was validated in a blinded fashion in vivo in the human left atrium. Methods: Using a 3‐terminal circuit model, local resistance and reactance between catheter tip and tissue surface were measured and combined in an electrical coupling index (ECI). Twelve patients undergoing atrial fibrillation (AF) catheter ablation were included in this study. The catheter was placed in the left atrium at various levels of contact. Blinded to the physician, measurements of electrogram amplitudes, pacing thresholds, and impedances at the catheter tip‐to‐tissue interface were performed. Results: As the catheter went from noncontact to contact, ECI increased from 118 ± 15 to 145 ± 24 (P < 0.0001), electrogram amplitudes increased from 0.14 ± 0.16 to 2.0 ± 1.9 mV (P < 0.0001), and pacing thresholds decreased from 13.9 ± 3.1 to 3.1 ± 2.0 mA (P < 0.0001). ECI was significantly higher in vascular tissue as compared with trabeculated and smooth myocardium. Patch orientation, operator, body mass index, or clinical type of AF had no influence on ECI values. On a patient‐by‐patient analysis, true contact/noncontact locations showed a mean ECI difference of 32.7 ± 11.6 units (95% CI 25.8–39.6). A cut‐off value of 5 ECI units was able to separate contact from noncontact with 97% sensitivity and 95% specificity. Conclusion: Measurement of local impedances between catheter tip and tissue is feasible to reproducibly describe electrical catheter contact within the left atrium in a clinical setting of AF catheter ablation.