Initial impedance decrease as an indicator of good catheter contact: insights from radiofrequency ablation with two different force sensing catheters

Background: Good catheter-tissue contact force (CF) is critical for transmural and durable lesion formation during radiofrequency (RF) ablation, but difficult to assess in clinical practice. CF-sensing catheters have been developed recently. Tissue heating during RF-application results in an impedance decrease at the catheter tip. Methods: We correlated initial impedance decreases with the achieved CF during RF applications in atrial fibrillation ablations with a CF-sensing RF-catheter with stable catheter position and CF during the first 20 seconds. We analyzed 642 RF-applications in 12 patients undergoing ablation with the Tacticath catheter (Endosense) and 562 RF-applications in 21 patients undergoing ablation with the SmartTouch catheter (Biosense-Webster). Results: When RF-applications were analyzed according to an achieved average CF of <10g, 10-20g, and >20g, starting impedance levels were 152Ω, 150Ω and 155Ω with the Tacticath catheter (p=0.12), and 124Ω, 126Ω and 131Ω with the SmartTouch catheter (p=0.001). The initial impedance decreases were significantly larger when greater CF was achieved. The corresponding median values were 3Ω (IQR -3-7), 7Ω (4-11) and 11Ω (7-16) at 10 seconds, and 4Ω (-4-10), 8Ω (4-12) and 13Ω (7-18) at 20 seconds with the Tacticath (p<0.001 between categories), and 6Ω (IQR 3-9), 9Ω (6-13) and 11Ω (7-16) at 10 seconds, and 7Ω (3-11), 10Ω (7-16) and 14Ω (10-19) at 20 seconds with the SmartTouch (p=0.001 between categories). Figure 1 Conclusions: The initial impedance decrease during RF-application is larger when greater catheter contact is achieved, with findings very consistent between two CF-sensing catheters. Monitoring of the initial impedance decrease is a widely available indicator of catheter contact and may help to improve formation of durable ablation lesions.