Novel Measure of Local Impedance Predicts Catheter-Tissue Contact and Lesion Formation.

Abstract

Coupling between the ablation catheter and myocardium is critical to resistively heat tissue with radiofrequency ablation. The objective of this study was to evaluate whether a novel local impedance (LI) measurement on an ablation catheter identifies catheter-tissue coupling and is predictive of lesion formation. LI was studied in explanted hearts (n=10 swine) and in vivo (n=10; 50-70 kg swine) using an investigational electroanatomic mapping system that measures impedance from an ablation catheter with mini-electrodes incorporated in the distal electrode (Rhythmia and IntellaNav MiFi OI, Boston Scientific). Explanted tissue was placed in a warmed (37 °C) saline bath mounted on a scale, and LI was measured 15 mm away from tissue to 5 mm of catheter-tissue compression at multiple catheter angles. Lesions were created with 31 and 50 W for 5 to 45 seconds (n=90). During in vivo evaluation of LI, measurements of myocardium (n=90) and blood pool (n=30) were guided by intracardiac ultrasound while operators were blinded to LI data. Lesions were created with 31 and 50 W for 45 seconds in the ventricles (n=72). LI of myocardium (119.7 Ω) was significantly greater than that of blood pool (67.6 Ω; P<0.01). Models that incorporate LI drop (ΔLI) to predict lesion size had better performance than models that incorporate force-time integral (R2=0.75 versus R2=0.54) and generator impedance drop (R2=0.82 versus R2=0.58). Steam pops displayed a significantly higher starting LI and larger ΔLI compared with successful radiofrequency applications (P<0.01). LI recorded from miniature electrodes provides a valuable measure of catheter-tissue coupling, and ΔLI is predictive of lesion formation during radiofrequency ablation.