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Funding Acknowledgements Study was funded by Boston Scientific The effective delivery of RF energy is dependent on transmural tissue heating, with irreversible tissue necrosis occurring at a tissue temperature ≥ 50°C.  While multi-input lesion indexing algorithms can provide some value in predicting lesion durability, no clinically available metric measures tissue heating under the endocardial surface.  Temperature measured from the catheter at the tissue surface is a surrogate for intra-lesion heating, but variables such as intra-cardiac flow and catheter irrigation have the potential to make this measure unreliable.  A metric that assesses volumetric tissue heating would provide a superior method of predicting RF ablation in clinical practice. This study evaluated a prototype catheter that measures local catheter impedance (LI) using ring and tip electrodes and contact force (CF) using inductive sensors with an electroanatomical mapping system.  In vitro, 51µm thermocouples were placed in explanted cardiac ventricular swine tissue to measure the temperature profile during RF delivery.  The correlation between the LI drop during RF and intra-lesion temperature was assessed.   A total of 44 lesions were created.  Intra-lesion temperature was measured using 3 51µm thermocouples placed 0mm, 2mm, and 4mm from the surface of the tissue. The probes were placed in-line, 0.5-1mm lateral to the catheter tip. Lesions were created at a constant force of 15 ± 3g at standard powers of 25W and 30W and high power of 50W for durations of 10s and 30s. LI drop correlated strongly with lesion depth (R = 0.81) while force time integral (FTI) did not correlate as strongly (R = 0.58).  As seen in Figure 1A (temperature traces inverted), a characteristic temperature increase was observed, with the greatest increase at the probes located in the lesion core (2mm).  Lower temperatures were observed in the probes exposed to irrigation flow/ bloodpool (0mm).  Notably, the LI drop (33Ω) demonstrated a similar slope to the 2mm temperature probe recordings (maximum 78°C).  There was a strong linear relationship between maximum intra-lesion temperature and LI drop (R = 0.74) (Figure 1B), while there was a very weak relationship between temperature and FTI (R = 0.36). There was a strong relationship between LI drop and maximum temperature in the first 5s across all powers (R = 0.81).  At 50W, both LI drop (22 ± 5Ω) and maximum temperature (66 ± 9°C) were greater than standard power.  For 30W, LI drop was 14 ± 6Ω and maximum temperature was 52 ± 7°C in the first 5 seconds.  In this study, LI drop was highly correlated to intra-lesion temperature at standard and high power, demonstrating the sensitivity of the metric to volumetric heating under the tissue surface. A LI drop greater than 20Ω results in a tissue temperature >50°C, and a 30Ω LI drop likely results in a transmural temperature profile in 2mm tissue. The correlation of LI to the core lesion temperature provides a powerful, biophysical measure of tissue heating during RF ablation. Abstract Figure 1

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.