Shuros, Allan

AbstractBackgroundLocal impedance (LI) drop measured with microfidelity electrodes embedded in the tip of an ablation catheter accurately reflects tissue heating during radiofrequency (RF) ablation. Previous studies found 15–30 Ω LI drops created successful lesions, while more than 40 Ω drops were associated with steam pops. The objective of this study was to evaluate the safety and efficacy of LI‐guided ablation using standard (30 W) and high‐power (50 W) in a preclinical model.MethodsRF lesions were created in explanted swine hearts (n = 6) to assess the feasibility of LI‐guided ablation by targeting 10, 20, or 30 Ω (n = 20/group) drops. Subsequently, LI‐guided ablation was evaluated in a chronic animal model (n = 8 Canines, 25–29 kg, 30/50 W). During the index procedure point‐by‐point intercaval line ablation and left inferior pulmonary vein (PV) isolation were performed. RF duration was at the operators’ discretion but discontinued early if a 15–30 Ω drop was achieved. Operators attempted to avoid LI drops of more than 40 Ω. At 1‐month, durable conduction block was evaluated with electroanatomic mapping followed by necropsy and histopathology.ResultsIn explanted tissue, terminating ablation at 10, 20, or 30 Ω LI drops created statistically larger lesions (p < .05; 1.8 [1.6–2.4] mm, 3.3 [3.0–3.7] mm; 4.9 [4.3–5.5] mm). LI‐guided high‐power ablation in vivo significantly reduced RF duration per application compared to standard‐power (p < .05; intercaval: 8.9 ± 5.2 vs. 18.1 ± 11.0 s, PV: 9.6 ± 5.4 vs. 23.2 ± 10.3 s). LI drops of 15–40 Ω were more readily achievable for high‐power (90.1%, 318/353) than standard‐power (71.7%, 243/339). All intercaval lines and PV isolations were durable (16/16) at 1‐month. Necropsy revealed no major collateral injury to the pericardium, phrenic nerve, esophagus, or lungs. There was no pericardial effusion, stroke, tamponade, or PV stenosis. Vagal nerve injury was found in two 30 W animals after using 19.7 ± 13.9 and 19.5 ± 11.8 s RF applications.ConclusionLI‐guided ablation was found to be safe and efficacious in a chronic animal model. High‐power ablation more readily achieved more than 15 Ω drops, reduced RF duration compared with standard‐power, and had no major RF collateral injury.

Background: 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. Methods and Results: 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 ( R 2 =0.75 versus R 2 =0.54) and generator impedance drop ( R 2 =0.82 versus R 2 =0.58). Steam pops displayed a significantly higher starting LI and larger ΔLI compared with successful radiofrequency applications ( P <0.01). Conclusions: LI recorded from miniature electrodes provides a valuable measure of catheter–tissue coupling, and ΔLI is predictive of lesion formation during radiofrequency ablation.