Edward Yang

BACKGROUND: Transcatheter renal denervation (RDN) remains inconsistent despite developments in ablation technologies, due to the lack of an intraprocedural physiological end point. The aim of this study was to identify if aorticorenal ganglion (ARG) guided RDN using microwave (MW) catheter leads to more consistent denervation outcomes compared with empirical MW ablation. METHODS: Pigs underwent sham procedure (n=8) or bilateral RDN using an in-house built open-irrigated MW catheter. Before denervation, ipsilateral ARG pacing was performed leading to renal artery vasoconstriction. MW ablation group (MW-group; n=7) received 1 ablation (100–120 W for 360 seconds) in the mid-main renal artery based on artery caliber. ARG-guided-MW ablation group (ARG-MW-group; n=7) was permitted an additional ablation more distally or at higher power until a vasoconstrictive response was abolished. Animals were euthanized at 4 to 5 weeks post-procedure. RESULTS: ARG pacing caused an ipsilateral reduction in renal artery caliber from 4.67 to 4 mm; P =0.0006 in MW-group and 4.8 to 3.9 mm; P =0.001 in ARG-MW-group. Repeat ARG pacing at euthanasia led to a reduction in renal artery caliber in MW-group from 5.1 to 4.8 mm; P =0.006, but not in ARG-MW-group from 4.88 to 4.55 mm; P =0.08. There were no differences in ablation injury volumes between the groups. Compared with undenervated sham controls, ARG-MW-RDN versus MW-RDN caused median reductions in viable nerve area (antityrosine hydroxylase staining) at 4 to 5 weeks by 92.6% (interquartile range, 0.94–19.59%; P P =0.006) and median renal cortical norepinephrine content by 68.06% (interquartile range, 27.16–38.39%; P P =NS). CONCLUSIONS: ARG pacing serves as a physiological procedural end point to guide MW denervation to improve denervation outcomes.

Background: Bioimpedance method is used clinically as a surrogate measure of effective tissue heating during cardiac ablation. It does not, however provide information regarding thermal cellular destruction which is the goal of ablation procedures. Objective: This study investigated myocardial impedance (resistance and reactance) at different frequencies in response to the thermal effect and across temperatures where tissue necrosis occurs during ablation. Methods: An ex-vivo experiment bench was designed to heat heart muscle tissue blocks uniformly to different targeted temperatures. Tissue resistance and reactance were recorded at three frequencies of 5k, 50k and 250kHz. Impedance was measured in 3 phases (1) the relationship of tissue impedance with thermal effect at temperatures < 50°C, (2) impedance change at 55°C to 85°C at which cellular necrosis occurs, and (3) post-ablation impedance during restitution back to 37°C. Results: Myocardial resistance and reactance demonstrated a strong linear relationship with temperature effect within the tissue (-1.3%/°C and -1.96%/°C on average respectively, frequency dependent). At ≥ 65°C, the reactance was almost abolished (̴0Ω) and stayed flat during the restitution back to 37°C, potentially indicative of complete necrosis. Time to reactance abolishment was a few seconds for ≥ 75°C, 17 seconds for 65°C and few minutes for 55°C. Conclusion: Myocardial impedance behaviour thermal and necrotic effects were straightforward and observable. Changes in reactance can be used as a potential indicator of cellular necrosis. Significance: Data provided can be used to develop better models and solutions for monitoring the efficacy of cardiac ablation procedures, thus enhancing clinical outcomes.

Objective: To determine whether an irrigatedunbalanced antenna can create larger ablations than a conventional microwave antenna without overheating. Method: The microwave and ablation characteristics of a previously published multi-ring slot array (MRSA) ablation antenna, optimized for intravascular environments, were compared with a dielectric-insulated monopole antenna with no matching or balancing elements, creating the unbalanced monopole antenna. The two antennae were numerically simulated in an intravascular environment and tested inside a gel phantom for five repetitions for comparison. Each antenna assembly was $\text{900 mm}$ long, with a $\text{2.45 GHz}$ ablatingfrequency, with a microwave input power of $\text{60 W}$ for $\text{120 s}$ via a patient cable. Results: Gel experiments were consistent with numerical simulations, with the unbalanced monopole antenna possessing better microwave and ablative characteristics than the MRSA in a biological environment. Microwave input power to the device connector was attenuated from $\text{60 W}$ to $\text{40 W}$ due to patient cable losses. Removing matching elements improved input impedance at the test plane (Real, 52.20 $\pm$ $5.90 \;\Omega$ vs. 74.22 $\pm$ $43.25 \;\Omega$ , p = 0.05648; Imaginary, −23.50 $\pm$ $2.63 \;\Omega$ vs. 14.92 $\pm$ $51.10 \;\Omega$ , p = 0.1333) and the return loss (−12.79 $\pm$ $\text{0.45 dB}$ vs. 6.51 $\pm$ $\text{0.25 dB}$ , p = $2.521 \times 10^{-7}$ ). The unbalanced monopole antenna created wide (18.28 $\pm$ $\text{0.57 mm}$ vs. 13.38 $\pm$ $\text{0.60 mm}$ , p = $2.482 \times 10^{-5}$ ) and deeper (11.87 $\pm$ $\text{0.88 mm}$ vs. 9.41 $\pm$ $\text{0.98 mm}$ , p = $1.616 \times 10^{-2}$ ) ablation lesions than the MRSA. Clinical Impact: Removing elements from an MRSA created an unbalanced monopole antenna that creates larger ablation lesions with improved microwave characteristics.

A large resistive transition between 160–200 K has been observed in Y₅Ba₆Cu₁₁O_x thin films. The films were deposited on MgO substrates by electron‐beam evaporation and annealed through rapid thermal annealing. With 960–980 °C, 30–60 s RTA, the films showed a resistance drop about one order of magnitude around 160–200 K. This resistive transition was measured reproducibly over many samples. The preparations and measurements of the Y₅Ba₆Cu₁₁O_x films were similar to those of the YBa₂Cu₃O_7−x films. The x‐ray diffraction pattern indicated that the films mainly contain the YBa₂Cu₃O_7−x phase. The films were polycrystalline with grain sizes of a few μm and an average thickness of 0.4 μm.