Sulkin, Matthew S.

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.

Abstract Catheter-tissue coupling is crucial for effective delivery of radiofrequency (RF) energy during catheter ablation. Force sensing catheters provide a metric of mechanical tissue contact and catheter stability, while local impedance has been shown to provide sensitive information on real-time tissue heating. The complementary use of force and local impedance during RF ablation procedures could provide an advantage over the use of one metric alone. This study evaluates a prototype ablation catheter that measures both contact force (CF) using inductive sensors and local catheter impedance (LI) using only catheter electrodes. The complementary nature was assessed with discrete lesions in vitro and an intercaval line in vivo. A force-sensing catheter with LI was evaluated in explanted swine hearts (n=14) in an in vivo swine model (n=9, 50–70kg) using investigational electroanatomical mapping software. In vitro, discrete lesions were created in ventricular tissue at a range of forces (0–40g) controlled externally. RF energy was applied at a range of powers (20W, 30W, and 40W), durations (10s-60s), and catheter orientations (0°, 45°, and 90°). Lesions were stained with TTC and measured. LI drop relative to baseline during RF in the bench studies was used to inform the in vivo study. In a separate subset of animals in vivo, an intercaval line was created in three experimental groups: LI blinded, 20Ω ΔLI, and 30Ω ΔLI. CF was maintained between 15 and 25g in all groups. All ablations were performed with a power of 30W. In the LI blinded group, all lesions were delivered for 30s. In the 20Ω ΔLI group, the investigator ablated until a 20Ω drop or 30 seconds was achieved. Likewise, in the 30Ω ΔLI, the investigator ablated until a 30Ω drop or 30 seconds was achieved. In vitro, 137 discrete ventricular lesions were created. LI drop during ablation correlated strongly with lesion depth using a monoexponential fit (R=0.84) while force time integral (FTI) did not correlate as strongly (R=0.56). In the intercaval LI blinded group, starting LI ranged from 126–163Ω with a median of 138Ω. LI drops ranged from 13Ω-44Ω, with a median of 26Ω. In the 20Ω ΔLI group, starting LI ranged from 137–211Ω with a median of 161Ω and LI drop ranged from 7Ω-35Ω, with a median of 22Ω. In the 30Ω ΔLI group, starting LI ranged from 130–256Ω with a median of 171Ω and LI drop ranged from 20Ω-52Ω, with a median of 31Ω. Notably, RF time for the LI blinded group was 13±0.1 minutes while RF time in the 20Ω ΔLI group was 6.4±1.9 minutes and 7.5±0.7 minutes in the 30Ω ΔLI group. A catheter incorporating CF-sensing and LI capabilities provides a powerful tool for RF ablation. Bench studies demonstrate a strong correlation between LI drop and lesion dimensions, which guided the use of LI in vivo. In vivo, the confirmation of stable mechanical contact and viewing of real-time LI drops enabled a significant reduction in RF time while creating a continuous intercaval line. Acknowledgement/Funding This study was funded by Boston Scientific.

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.