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W Chik - One of the best experts on this subject based on the ideXlab platform.
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Circuit Impedance could be a crucial factor influencing radiofrequency ablation efficacy and safety a myocardial phantom study of the problem and its correction
Journal of Cardiovascular Electrophysiology, 2016Co-Authors: Abhishek Bhaskaran, W Chik, C Nalliah, Jim Pouliopoulos, M A Barry, Pierre QianAbstract:BACKGROUND: Circuit Impedance could affect the safety and efficacy of radiofrequency (RF) ablation. AIM: To perform irrigated RF ablations with graded Impedance to compare (1) lesion dimensions and overheated dimensions in fixed power ablations (2) and in power corrected ablations. METHODS: Ablations were performed with irrigated Navistar Thermocool catheter and Stockert EP shuttle generator at settings of 40 W power for 60 seconds, in a previously validated myocardial phantom. The Impedance of the Circuit was set at 60 Ω, 80 Ω, 100 Ω, 120 Ω, 140 Ω, and 160 Ω. The lesion and overheated dimensions were measured at 53 °C and 80 °C isotherms, respectively. In the second set of ablations, power was corrected according to Circuit Impedance. RESULTS: In total, 70 ablations were performed. The lesion volume was 72.0 ± 4.8% and 44.7 ± 4.6% higher at 80 Ω and 100 Ω, respectively, compared to that at 120 Ω and it was 15.4 ± 1.2%, 28.1 ± 2.0%, and 38.0 ± 1.8% lower at 140 Ω, 160 Ω, and 180 Ω, respectively. The overheated volume was four times larger when Impedance was reduced to 80 Ω from 100 Ω. It was absent at 120 Ω and above. In the power corrected ablations, the lesion volumes were similar to that of 40 W/120 Ω ablations and there was no evidence of overheating. CONCLUSION: The lesion and overheated dimensions were significantly larger with lower Circuit Impedance during irrigated RF ablation and the lesion size was smaller in high Impedance ablations. Power delivery adjusted to Impedance using a simple equation improved the consistency of lesion formation and prevented overheating.
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observations on attenuation of local electrogram amplitude and Circuit Impedance during atrial radiofrequency ablation an in vivo investigation using a novel direct endocardial visualization catheter
Journal of Cardiovascular Electrophysiology, 2015Co-Authors: Abhishek Bhaskaran, W Chik, C Nalliah, Jim Pouliopoulos, Tony Barry, Doan Trang NguyenAbstract:Radiofrequency Ablation with Visual Ablation CatheterAims To define the temporal characteristics of atrial lesion growth (lesion surface area), local electrogram amplitude attenuation, and Circuit Impedance decrement during in vivo radiofrequency (RF) ablation with direct endocardial visualization (DEV). Methods and Results A direct endocardial visualization catheter was used for real-time endoscopic visualization of atrial endocardial surface during RF ablation. Videos of lesion growth (surface area), Circuit Impedance, and local electrogram amplitude were recorded during ablation in 11 ovine. Fifty-two atrial ablations at 12 W, 14 W, and 16 W power for 30 seconds were analyzed. During 30-second RF ablation, the lesion matured (90% of final lesion dimension) in the first 23.0 ± 5.8 seconds. The local electrogram amplitude attenuation (80% decrement) and Circuit Impedance attenuation (20% decrement from initial) occurred 13.8 ± 8.2 seconds and 13.1 ± 7.9 seconds, respectively, before lesion maturity in a significant proportion of 30 second atrial ablations. Conclusion The DEV observations suggest that in smooth atrial surface ablations with significant local electrogram and Impedance decrement in the first 10 seconds, further extension of ablation for 10–15 seconds could deliver optimal surface dimensions; however, real-time measurement of depth was not possible.
Abhishek Bhaskaran - One of the best experts on this subject based on the ideXlab platform.
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Circuit Impedance could be a crucial factor influencing radiofrequency ablation efficacy and safety a myocardial phantom study of the problem and its correction
Journal of Cardiovascular Electrophysiology, 2016Co-Authors: Abhishek Bhaskaran, W Chik, C Nalliah, Jim Pouliopoulos, M A Barry, Pierre QianAbstract:BACKGROUND: Circuit Impedance could affect the safety and efficacy of radiofrequency (RF) ablation. AIM: To perform irrigated RF ablations with graded Impedance to compare (1) lesion dimensions and overheated dimensions in fixed power ablations (2) and in power corrected ablations. METHODS: Ablations were performed with irrigated Navistar Thermocool catheter and Stockert EP shuttle generator at settings of 40 W power for 60 seconds, in a previously validated myocardial phantom. The Impedance of the Circuit was set at 60 Ω, 80 Ω, 100 Ω, 120 Ω, 140 Ω, and 160 Ω. The lesion and overheated dimensions were measured at 53 °C and 80 °C isotherms, respectively. In the second set of ablations, power was corrected according to Circuit Impedance. RESULTS: In total, 70 ablations were performed. The lesion volume was 72.0 ± 4.8% and 44.7 ± 4.6% higher at 80 Ω and 100 Ω, respectively, compared to that at 120 Ω and it was 15.4 ± 1.2%, 28.1 ± 2.0%, and 38.0 ± 1.8% lower at 140 Ω, 160 Ω, and 180 Ω, respectively. The overheated volume was four times larger when Impedance was reduced to 80 Ω from 100 Ω. It was absent at 120 Ω and above. In the power corrected ablations, the lesion volumes were similar to that of 40 W/120 Ω ablations and there was no evidence of overheating. CONCLUSION: The lesion and overheated dimensions were significantly larger with lower Circuit Impedance during irrigated RF ablation and the lesion size was smaller in high Impedance ablations. Power delivery adjusted to Impedance using a simple equation improved the consistency of lesion formation and prevented overheating.
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observations on attenuation of local electrogram amplitude and Circuit Impedance during atrial radiofrequency ablation an in vivo investigation using a novel direct endocardial visualization catheter
Journal of Cardiovascular Electrophysiology, 2015Co-Authors: Abhishek Bhaskaran, W Chik, C Nalliah, Jim Pouliopoulos, Tony Barry, Doan Trang NguyenAbstract:Radiofrequency Ablation with Visual Ablation CatheterAims To define the temporal characteristics of atrial lesion growth (lesion surface area), local electrogram amplitude attenuation, and Circuit Impedance decrement during in vivo radiofrequency (RF) ablation with direct endocardial visualization (DEV). Methods and Results A direct endocardial visualization catheter was used for real-time endoscopic visualization of atrial endocardial surface during RF ablation. Videos of lesion growth (surface area), Circuit Impedance, and local electrogram amplitude were recorded during ablation in 11 ovine. Fifty-two atrial ablations at 12 W, 14 W, and 16 W power for 30 seconds were analyzed. During 30-second RF ablation, the lesion matured (90% of final lesion dimension) in the first 23.0 ± 5.8 seconds. The local electrogram amplitude attenuation (80% decrement) and Circuit Impedance attenuation (20% decrement from initial) occurred 13.8 ± 8.2 seconds and 13.1 ± 7.9 seconds, respectively, before lesion maturity in a significant proportion of 30 second atrial ablations. Conclusion The DEV observations suggest that in smooth atrial surface ablations with significant local electrogram and Impedance decrement in the first 10 seconds, further extension of ablation for 10–15 seconds could deliver optimal surface dimensions; however, real-time measurement of depth was not possible.
Wenjuan Song - One of the best experts on this subject based on the ideXlab platform.
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design of a single phase 6 5 mva 25 kv superconducting traction transformer for the chinese fuxing high speed train
International Journal of Electrical Power & Energy Systems, 2020Co-Authors: Wenjuan Song, Zhenan Jiang, Mike Staines, Rodney A Badcock, Stuart C Wimbush, Jin Fang, Jinping ZhangAbstract:Abstract Traction transformers are critical components of Chinese high-speed-trains. We are currently building a single–phase 6.5 MVA superconducting traction transformer which can achieve targets of less than 3 tons of transformer system weight, better than 99% efficiency, and 43% short-Circuit Impedance. The proposed transformer consists of four single-phase 25 kV/1.9 kV HTS windings, operating at 65 K, each of which drives a motor. The design incorporates Roebel cable in the LV windings to cope with large current and minimize AC loss. We present 2D FEM AC loss modelling results that identify the critical parameters that contribute to AC loss. We show that the combination of winding length ≥1 m, high performance Fujikura wires, and flux diverters arranged at the end of HV and LV windings, can restrain AC loss in the HTS windings to under 2 kW. We introduce an open-loop cooling system concept with sub-cooler integrated inside the transformer cryostat that can achieve total system weight under 3 tons assuming 2.5 kW total heat load and 8 h of continuous running time. A nominal efficiency of 99.5% can be achieved for this total heat load. The entire superconducting transformer system can be readily fit in the space allocated for conventional transformers in the Chinese Fuxing trains.
Jim Pouliopoulos - One of the best experts on this subject based on the ideXlab platform.
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Circuit Impedance could be a crucial factor influencing radiofrequency ablation efficacy and safety a myocardial phantom study of the problem and its correction
Journal of Cardiovascular Electrophysiology, 2016Co-Authors: Abhishek Bhaskaran, W Chik, C Nalliah, Jim Pouliopoulos, M A Barry, Pierre QianAbstract:BACKGROUND: Circuit Impedance could affect the safety and efficacy of radiofrequency (RF) ablation. AIM: To perform irrigated RF ablations with graded Impedance to compare (1) lesion dimensions and overheated dimensions in fixed power ablations (2) and in power corrected ablations. METHODS: Ablations were performed with irrigated Navistar Thermocool catheter and Stockert EP shuttle generator at settings of 40 W power for 60 seconds, in a previously validated myocardial phantom. The Impedance of the Circuit was set at 60 Ω, 80 Ω, 100 Ω, 120 Ω, 140 Ω, and 160 Ω. The lesion and overheated dimensions were measured at 53 °C and 80 °C isotherms, respectively. In the second set of ablations, power was corrected according to Circuit Impedance. RESULTS: In total, 70 ablations were performed. The lesion volume was 72.0 ± 4.8% and 44.7 ± 4.6% higher at 80 Ω and 100 Ω, respectively, compared to that at 120 Ω and it was 15.4 ± 1.2%, 28.1 ± 2.0%, and 38.0 ± 1.8% lower at 140 Ω, 160 Ω, and 180 Ω, respectively. The overheated volume was four times larger when Impedance was reduced to 80 Ω from 100 Ω. It was absent at 120 Ω and above. In the power corrected ablations, the lesion volumes were similar to that of 40 W/120 Ω ablations and there was no evidence of overheating. CONCLUSION: The lesion and overheated dimensions were significantly larger with lower Circuit Impedance during irrigated RF ablation and the lesion size was smaller in high Impedance ablations. Power delivery adjusted to Impedance using a simple equation improved the consistency of lesion formation and prevented overheating.
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observations on attenuation of local electrogram amplitude and Circuit Impedance during atrial radiofrequency ablation an in vivo investigation using a novel direct endocardial visualization catheter
Journal of Cardiovascular Electrophysiology, 2015Co-Authors: Abhishek Bhaskaran, W Chik, C Nalliah, Jim Pouliopoulos, Tony Barry, Doan Trang NguyenAbstract:Radiofrequency Ablation with Visual Ablation CatheterAims To define the temporal characteristics of atrial lesion growth (lesion surface area), local electrogram amplitude attenuation, and Circuit Impedance decrement during in vivo radiofrequency (RF) ablation with direct endocardial visualization (DEV). Methods and Results A direct endocardial visualization catheter was used for real-time endoscopic visualization of atrial endocardial surface during RF ablation. Videos of lesion growth (surface area), Circuit Impedance, and local electrogram amplitude were recorded during ablation in 11 ovine. Fifty-two atrial ablations at 12 W, 14 W, and 16 W power for 30 seconds were analyzed. During 30-second RF ablation, the lesion matured (90% of final lesion dimension) in the first 23.0 ± 5.8 seconds. The local electrogram amplitude attenuation (80% decrement) and Circuit Impedance attenuation (20% decrement from initial) occurred 13.8 ± 8.2 seconds and 13.1 ± 7.9 seconds, respectively, before lesion maturity in a significant proportion of 30 second atrial ablations. Conclusion The DEV observations suggest that in smooth atrial surface ablations with significant local electrogram and Impedance decrement in the first 10 seconds, further extension of ablation for 10–15 seconds could deliver optimal surface dimensions; however, real-time measurement of depth was not possible.
Kamiar J. Karimi - One of the best experts on this subject based on the ideXlab platform.
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Input Impedance Modeling and Analysis of Line-Commutated Rectifiers
IEEE Transactions on Power Electronics, 2009Co-Authors: Zhonghui Bing, Kamiar J. KarimiAbstract:This paper presents the modeling and analysis of small-signal input Impedance for line-commutated rectifiers. The recently developed Impedance mapping method, which has been applied to single-phase rectifiers with sinusoidal line inputs, is generalized to single-phase rectifiers with distorted lines as well as three-phase rectifiers. The modeling method assumes known Impedance of the Circuit on the dc side of the rectifier bridge (including its output filter and the load), and determines the corresponding ac input Impedance by using a current and voltage mapping function that describes the operation of the rectifier bridge in the frequency domain. In this approach, closed-form analytical expressions are derived for the ac input Impedance as functions of the dc Circuit Impedance. The resulting models are intended for stability analysis and design of large ac power systems involving significant number of rectification loads, such as more-electric aircraft power systems and microgrids. Detailed derivation of the models is presented in this paper. Numerical simulation and experimental measurement results are also presented to validate the developed models.
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Input Impedance Modeling and Analysis of Line-Commutated Rectifiers
2007 IEEE Power Electronics Specialists Conference, 2007Co-Authors: Zhonghui Bing, Kamiar J. KarimiAbstract:This paper presents the modeling and analysis of small-signal input Impedance for line-commutated rectifiers. The recently developed Impedance mapping method, which has been applied to single-phase rectifiers with sinusoidal line inputs, is generalized to single-phase rectifiers with distorted lines as well as three-phase rectifiers. The modeling method assumes known Impedance of the Circuit on the dc side of the rectifier bridge (including its output filter and the load), and determines the corresponding ac input Impedance by using a current and voltage mapping function which describes the operation of the rectifier bridge in the frequency domain. In this approach, closed-form analytical expressions are derived for the ac input Impedance as functions of the dc Circuit Impedance. The resulting models are intended for stability analysis and design of large ac power systems involving significant number of rectification loads, such as more-electric aircraft power systems and microgrids. Detailed derivation of the models is presented in this paper. Numerical simulation and experimental measurement results are also presented to validate the derived models.