Current Trends in Mathematical Modeling of High-Temperature Thermal Therapies

Haemmerich, D.; Berjano, E. (2010). Current trends in mathematical modeling of high-temperature thermal therapies. The Open Biomedical Engineering Journal. 4(4):1-2. https://doi.org/10.2174/1874120701004010001S124

In-silico modeling to compare radiofrequency-induced thermal lesions created on myocardium and thigh muscle

[EN] Beating heart (BH) and thigh muscle (TM) are two pre-clinical models aimed at studying the lesion sizes created by radiofrequency (RF) catheters in cardiac ablation. Previous experimental results have shown that thermal lesions created in the TM are slightly bigger than in the BH. Our objective was to use in-silico modeling to elucidate some of the causes of this difference. In-silico RF ablation models were created using the Arrhenius function to estimate lesion size under different energy settings (25 W/20 s, 50 W/6 s and 90 W/4 s) and parallel, 45 degrees and perpendicular catheter positions. The models consisted of homogeneous tissue: myocardium in the BH model and striated muscle in the TM model. The computer results showed that the lesion sizes were generally bigger in the TM model and the differences depended on the energy setting, with hardly any differences at 90 W/4 s but with differences of 1 mm in depth and 1.5 m in width at 25 W/20 s. The higher electrical conductivity of striated muscle (0.446 S/m) than that of the myocardium (0.281 S/m) is possibly one of the causes of the higher percentage of RF energy delivered to the tissue in the TM model, with differences between models of 2-5% at 90 W/4 s, similar to 9% at 50 W/6 s and similar to 10% at 25 W/20 s. Proximity to the air-blood interface (just 2 cm from the tissue surface) artificially created in the TM model to emulate the cardiac cavity had little effect on lesion size. In conclusion, the TM-based experimental model creates fairly similar-sized lesions to the BH model, especially in high-power short-duration ablations (50 W/6 s and 90 W/4 s). Our computer results suggest that the higher electrical conductivity of striated muscle could be one of the causes of the slightly larger lesions in the TM model.This research was funded by the Spanish Ministerio de Ciencia, Innovacion y Universidades/Agencia Estatal de Investigacion MCIN/AEI/10.13039/501100011033 (Grant number: RTI2018-094357-B-C21)Pérez, JJ.; Berjano, E.; González-Suárez, A. (2022). In-silico modeling to compare radiofrequency-induced thermal lesions created on myocardium and thigh muscle. Bioengineering. 9(7):1-13. https://doi.org/10.3390/bioengineering9070329S1139

How far the zone of heat-induced transient block extends beyond the lesion during RF catheter cardiac ablation

This is an Accepted Manuscript of an article published by Taylor & Francis in International Journal of Hyperthermia on 02-01-2023, available online: http://www.tandfonline.com/ https://doi.org/10.1080/02656736.2022.2163310[EN] Purpose While radiofrequency catheter ablation (RFCA) creates a lesion consisting of the tissue points subjected to lethal heating, the sublethal heating (SH) undergone by the surrounding tissue can cause transient electrophysiological block. The size of the zone of heat-induced transient block (HiTB) has not been quantified to date. Our objective was to use computer modeling to provide an initial estimate. Methods and materials We used previous experimental data together with the Arrhenius damage index (omega) to fix the omega values that delineate this zone: a lower limit of 0.1-0.4 and upper limit of 1.0 (lesion boundary). An RFCA computer model was used with different power-duration settings, catheter positions and electrode insertion depths, together with dispersion of the tissue's electrical and thermal characteristics. Results The HiTB zone extends in depth to a minimum and maximum distance of 0.5 mm and 2 mm beyond the lesion limit, respectively, while its maximum width varies with the energy delivered, extending to a minimum of 0.6 mm and a maximum of 2.5 mm beyond the lesion, reaching 3.5 mm when high energy settings are used (25 W-20s, 500 J). The dispersion of the tissue's thermal and electrical characteristics affects the size of the HiTB zone by +/- 0.3 mm in depth and +/- 0.5 mm in maximum width. Conclusions Our results suggest that the size of the zone of heat-induced transient block during RFCA could extend beyond the lesion limit by a maximum of 2 mm in depth and approximately 2.5 mm in width.This work was supported by Spanish Ministerio de Ciencia, Innovacion y Universidades/Agencia Estatal de Investigacion IMCIN/AEI/10.13039/ 501100011033 (Grant RTI2018-094357-B-C21).Pérez, JJ.; Berjano, E.; González Suárez, A. (2023). How far the zone of heat-induced transient block extends beyond the lesion during RF catheter cardiac ablation. International Journal of Hyperthermia. 40(1):1-10. https://doi.org/10.1080/02656736.2022.216331011040

Electrical and thermal effects of esophageal temperature probes on radiofrequency catheter ablation of atrial fibrillation: results from a computational modeling study

[EN] Electrical and Thermal Effects of Esophageal Temperature Probes IntroductionLuminal esophageal temperature (LET) monitoring is commonly employed during catheter ablation of atrial fibrillation (AF) to detect high esophageal temperatures during radiofrequency (RF) delivery along the posterior wall of the left atrium. However, it has been recently suggested that in some cases the esophageal probe itself may serve as an RF antenna and promote esophageal thermal injury. The aim of this study was to assess the electrical and thermal interferences induced by different types of commercially available esophageal temperature probes (ETPs) on RF ablation. Methods and ResultsIn this study, we developed a computational model to assess the electrical and thermal effects of 3 different types of ETPs: a standard single-sensor and 2 multisensor probes (1 with and 1 without metallic surfaces). LET monitoring invariably underestimated the maximum temperature reached in the esophageal wall. RF energy cessation guided by LET monitoring using an ETP yielded lower esophageal wall temperatures. Also, the phenomenon of thermal latency was observed, particularly in the setting of LET monitoring. Most importantly, while only the ETP with a metallic surface produced minimal electrical alterations, the magnitude of this interference did not appear to be clinically significant. ConclusionTemperature rises in both the esophageal wall and the ETP seem to be primarily produced by thermal conduction, and not caused by electrical and/or thermal interactions between the ablation catheter and the ETP, itself. As such, the proposed notion of the antenna effect producing satellite esophageal lesions during AF ablation was not evident in this study.This work received financial support from the Spanish "Plan Nacional de I+D+I del Ministerio de Ciencia e Innovacion" (Grant No. TEC2011-27133-C02-01).Pérez, JJ.; D Avila, A.; Aryana, A.; Berjano, E. (2015). Electrical and thermal effects of esophageal temperature probes on radiofrequency catheter ablation of atrial fibrillation: results from a computational modeling study. Journal of Cardiovascular Electrophysiology. 26(5):556-564. https://doi.org/10.1111/jce.12630S55656426

Can Fat Deposition After Myocardial Infarction Alter the Performance of RF Catheter Ablation of Scar-Related Ventricular Tachycardia?: Results from a Computer Modeling Study

Effect of Fat Deposition on the Performance in RF Ablation IntroductionThe outcomes of catheter ablation of scar-mediated ventricular tachycardia (VT) remain far from perfect. The presence of fat as a component of the underlying substrate for scar-mediated VT could be relevant since this entity can seriously impede the passage of RF current due to its low electrical conductivity. Methods and ResultsComputer models of RF ablation were built in order to investigate the means by which the spatial heterogeneity of different tissues represented within the ventricular infarct zone, including the viable myocardium, fibrous tissue, and fat, could influence temperature distributions during RF ablation. The results demonstrated that spatial distributions of different tissue types significantly alter the density of electrical current largely as a result of fat impeding the passage of current. However, the thermal lesions appear minimally unaffected by this phenomenon, with variations in depth of approximate to 1 mm. ConclusionWhile during RF ablation of scar-related ventricular tachycardia differences in tissue characteristics may affect the density of electrical current on a small-scale, overall this does not appear to significantly impact the size of the created thermal lesions.This work was supported by the Spanish "Plan Estatal de Investigacion, Desarrollo e Innovacion Orientada a los Retos de la Sociedad" under Grant TEC2014-52383-C3 (TEC2014-52383-C3-1-R).Pérez, JJ.; D'avila, A.; Aryana, A.; Trujillo Guillen, M.; Berjano, E. (2016). Can Fat Deposition After Myocardial Infarction Alter the Performance of RF Catheter Ablation of Scar-Related Ventricular Tachycardia?: Results from a Computer Modeling Study. Journal of Cardiovascular Electrophysiology. 27(8):947-952. https://doi.org/10.1111/jce.13006S947952278Aryana, A., & d’ Avila, A. (2014). Contact Force During VT Ablation. Circulation: Arrhythmia and Electrophysiology, 7(6), 1009-1010. doi:10.1161/circep.114.002389Kottkamp, H., Hindricks, G., Horst, E., Baal, T., Fechtrup, C., Breithardt, G., & Borggrefe, M. (1997). Subendocardial and Intramural Temperature Response During Radiofrequency Catheter Ablation in Chronic Myocardial Infarction and Normal Myocardium. Circulation, 95(8), 2155-2161. doi:10.1161/01.cir.95.8.2155KOVOOR, P., DALY, M. P. J., POULIOPOULOS, J., BYTH, K., DEWSNAP, B. I., EIPPER, V. E., … ROSS, D. L. (2006). Comparison of Radiofrequency Ablation in Normal Versus Scarred Myocardium. Journal of Cardiovascular Electrophysiology, 17(1), 80-86. doi:10.1111/j.1540-8167.2005.00324.xBetensky, B. P., Jauregui, M., Campos, B., Michele, J., Marchlinski, F. E., Oley, L., … Gerstenfeld, E. P. (2012). Use of a Novel Endoscopic Catheter for Direct Visualization and Ablation in an Ovine Model of Chronic Myocardial Infarction. Circulation, 126(17), 2065-2072. doi:10.1161/circulationaha.112.112540Sasaki, T., Calkins, H., Miller, C. F., Zviman, M. M., Zipunnikov, V., Arai, T., … Zimmerman, S. L. (2015). New insight into scar-related ventricular tachycardia circuits in ischemic cardiomyopathy: Fat deposition after myocardial infarction on computed tomography--A pilot study. Heart Rhythm, 12(7), 1508-1518. doi:10.1016/j.hrthm.2015.03.041Goldfarb, J. W., Roth, M., & Han, J. (2009). Myocardial Fat Deposition after Left Ventricular Myocardial Infarction: Assessment by Using MR Water-Fat Separation Imaging. Radiology, 253(1), 65-73. doi:10.1148/radiol.2532082290Ichikawa, Y., Kitagawa, K., Chino, S., Ishida, M., Matsuoka, K., Tanigawa, T., … Sakuma, H. (2009). Adipose Tissue Detected by Multislice Computed Tomography in Patients After Myocardial Infarction. JACC: Cardiovascular Imaging, 2(5), 548-555. doi:10.1016/j.jcmg.2009.01.010Su, L., Siegel, J. E., & Fishbein, M. C. (2004). Adipose tissue in myocardial infarction. Cardiovascular Pathology, 13(2), 98-102. doi:10.1016/s1054-8807(03)00134-0Suárez, A. G., Hornero, F., & Berjano, E. J. (2010). Mathematical Modeling of Epicardial RF Ablation of Atrial Tissue with Overlying Epicardial Fat. The Open Biomedical Engineering Journal, 4(1), 47-55. doi:10.2174/1874120701004020047PÉREZ, J. J., D’AVILA, A., ARYANA, A., & BERJANO, E. (2015). Electrical and Thermal Effects of Esophageal Temperature Probes on Radiofrequency Catheter Ablation of Atrial Fibrillation: Results from a Computational Modeling Study. Journal of Cardiovascular Electrophysiology, 26(5), 556-564. doi:10.1111/jce.12630Berjano, E. J. (2006). BioMedical Engineering OnLine, 5(1), 24. doi:10.1186/1475-925x-5-24Hasgall PA Di Gennaro F Baumgartner C Neufeld E Gosselin MC Payne D Klingenböck A Kuster N 10.13099/VIP21000-03-0 www.itis.ethz.ch/databaseGonzalez-Suarez, A., & Berjano, E. (2016). Comparative Analysis of Different Methods of Modeling the Thermal Effect of Circulating Blood Flow During RF Cardiac Ablation. IEEE Transactions on Biomedical Engineering, 63(2), 250-259. doi:10.1109/tbme.2015.2451178Salazar, Y., Bragos, R., Casas, O., Cinca, J., & Rosell, J. (2004). Transmural Versus Nontransmural In Situ Electrical Impedance Spectrum for Healthy, Ischemic, and Healed Myocardium. IEEE Transactions on Biomedical Engineering, 51(8), 1421-1427. doi:10.1109/tbme.2004.82803

Computer modeling of radiofrequency cardiac ablation: 30 years of bioengineering research

[EN] This review begins with a rationale of the importance of theoretical, mathematical and computational models for radiofrequency (RF) catheter ablation (RFCA). We then describe the historical context in which each model was developed, its contribution to the knowledge of the physics of RFCA and its implications for clinical practice. Next, we review the computer modeling studies intended to improve our knowledge of the biophysics of RFCA and those intended to explore new technologies. We describe the most important technical details of the implementation of mathematical models, including governing equations, tissue properties, boundary conditions, etc. We discuss the utility of lumped element models, which despite their simplicity are widely used by clinical researchers to provide a physical explanation of how RF power is absorbed in different tissues. Computer model verification and validation are also discussed in the context of RFCA. The article ends with a section on the current limitations, i.e. aspects not yet included in state-of-the-art RFCA computer modeling and on future work aimed at covering the current gapsGrant RTI2018-094357-B-C21 funded by MCIN/AEI/10.13039/501100011033 (Spanish Ministerio de Ciencia, Innovación y Universidades/Agencia Estatal de Investigación)González-Suárez, A.; Pérez, JJ.; Irastorza, RM.; D Avila, A.; Berjano, E. (2022). Computer modeling of radiofrequency cardiac ablation: 30 years of bioengineering research. Computer Methods and Programs in Biomedicine. 214:1-16. https://doi.org/10.1016/j.cmpb.2021.10654611621

Thermal impact of replacing constant voltage by low-frequency sine wave voltage in RF ablation computer modeling

[EN] Background and objectives: A constant voltage (DC voltage) is usually used in radiofrequency ablation (RFA) computer models to mimic the radiofrequency voltage. However, in some cases a low frequency sine wave voltage (AC voltage) may be used instead. Our objective was to assess the thermal impact of replacing DC voltage by low-frequency AC voltage in RFA computer modeling. Methods: A 2D model was used consisting of an ablation electrode placed perpendicular to the tissue fragment. The Finite Element method was used to solve a coupled electric-thermal problem. Quasi-static electrical approximation was implemented in two ways (both with equivalent electrical power): (1) by a constant voltage of 25 V in the ablation electrode (DC voltage), and (2) applying a sine waveform with peak amplitude of 25 root 2 V (AC voltage). The frequency of the sine signal (f(AC)) varied from 0.5 Hz to 50 Hz. Results: Sine wave thermal oscillations (at twice the f(AC) frequency) were observed in the case of AC voltage, in addition to the temperature obtained by DC voltage. The amplitude of the oscillations: (1) increased with temperature, remaining more or less constant after 30 s; (2) was of up to +/- 3 degrees C for very low f(AC) values (0.5 Hz); and (3) was reduced at higher f(AC) values and with distance from the electrode (almost negligible for distances > 5 mm). The evolution of maximum lesion depth and width were almost identical with both DC and AC. Conclusions: Although reducing f(AC) reduces the computation time, thermal oscillations appear at points near the electrode, which suggests that a minimum value of f(AC) should be used. Replacing DC voltage by low-frequency AC voltage does not appear to have an impact on the lesion depth. (C) 2020 Elsevier B.V. All rights reserved.This work was supported by the Spanish Ministerio de Ciencia, Innovacion y Universidades under "Programa Estatal de I+D+i Orientada a los Retos de la Sociedad", Grant no. "RTI2018-094357-B-C21".Pérez, JJ.; González Suárez, A.; Nadal, E.; Berjano, E. (2020). Thermal impact of replacing constant voltage by low-frequency sine wave voltage in RF ablation computer modeling. Computer Methods and Programs in Biomedicine. 195:1-7. https://doi.org/10.1016/j.cmpb.2020.105673S17195Doss, J. D. (1982). Calculation of electric fields in conductive media. Medical Physics, 9(4), 566-573. doi:10.1118/1.595107Tungjitkusolmun, S., Haemmerich, D., Hong Cao, Jang-Zern Tsai, Young Bin Choy, Vorperian, V. R., & Webster, J. G. (2002). Modeling bipolar phase-shifted multielectrode catheter ablation. IEEE Transactions on Biomedical Engineering, 49(1), 10-17. doi:10.1109/10.972835Yan, S., Wu, X., & Wang, W. (2016). A simulation study to compare the phase-shift angle radiofrequency ablation mode with bipolar and unipolar modes in creating linear lesions for atrial fibrillation ablation. International Journal of Hyperthermia, 32(3), 231-238. doi:10.3109/02656736.2016.1145746Pérez, J. J., González-Suárez, A., & Berjano, E. (2017). Numerical analysis of thermal impact of intramyocardial capillary blood flow during radiofrequency cardiac ablation. International Journal of Hyperthermia, 34(3), 243-249. doi:10.1080/02656736.2017.1336258Keangin, P., Wessapan, T., & Rattanadecho, P. (2011). Analysis of heat transfer in deformed liver cancer modeling treated using a microwave coaxial antenna. Applied Thermal Engineering, 31(16), 3243-3254. doi:10.1016/j.applthermaleng.2011.06.005Nakayama, A., & Kuwahara, F. (2008). A general bioheat transfer model based on the theory of porous media. International Journal of Heat and Mass Transfer, 51(11-12), 3190-3199. doi:10.1016/j.ijheatmasstransfer.2007.05.030Bhowmik, A., Singh, R., Repaka, R., & Mishra, S. C. (2013). Conventional and newly developed bioheat transport models in vascularized tissues: A review. Journal of Thermal Biology, 38(3), 107-125. doi:10.1016/j.jtherbio.2012.12.003Andreozzi, A., Brunese, L., Iasiello, M., Tucci, C., & Vanoli, G. P. (2018). Modeling Heat Transfer in Tumors: A Review of Thermal Therapies. Annals of Biomedical Engineering, 47(3), 676-693. doi:10.1007/s10439-018-02177-xIasiello M., Andreozzi A., Bianco N., Vafai K. The porous media theory applied to radiofrequency catheter ablation. Int. J. Numer. Methods Heat Fluid Flow, Vol. 30 No. 5, pp. 2669–2681. 10.1108/HFF-11-2018-0707.González‐Suárez, A., Herranz, D., Berjano, E., Rubio‐Guivernau, J. L., & Margallo‐Balbás, E. (2017). Relation between denaturation time measured by optical coherence reflectometry and thermal lesion depth during radiofrequency cardiac ablation: Feasibility numerical study. Lasers in Surgery and Medicine, 50(3), 222-229. doi:10.1002/lsm.22771Irastorza, R. M., Gonzalez-Suarez, A., Pérez, J. J., & Berjano, E. (2020). Differences in applied electrical power between full thorax models and limited-domain models for RF cardiac ablation. International Journal of Hyperthermia, 37(1), 677-687. doi:10.1080/02656736.2020.1777330Seiler, J., Roberts-Thomson, K. C., Raymond, J.-M., Vest, J., Delacretaz, E., & Stevenson, W. G. (2008). Steam pops during irrigated radiofrequency ablation: Feasibility of impedance monitoring for prevention. Heart Rhythm, 5(10), 1411-1416. doi:10.1016/j.hrthm.2008.07.011González-Suárez, A., Berjano, E., Guerra, J. M., & Gerardo-Giorda, L. (2016). Computational Modeling of Open-Irrigated Electrodes for Radiofrequency Cardiac Ablation Including Blood Motion-Saline Flow Interaction. PLOS ONE, 11(3), e0150356. doi:10.1371/journal.pone.0150356Bourier, F., Duchateau, J., Vlachos, K., Lam, A., Martin, C. A., Takigawa, M., … Jais, P. (2018). High‐power short‐duration versus standard radiofrequency ablation: Insights on lesion metrics. Journal of Cardiovascular Electrophysiology, 29(11), 1570-1575. doi:10.1111/jce.13724Labonte, S. (1994). Numerical model for radio-frequency ablation of the endocardium and its experimental validation. IEEE Transactions on Biomedical Engineering, 41(2), 108-115. doi:10.1109/10.284921Babuska, I., & Oden, J. T. (2004). Verification and validation in computational engineering and science: basic concepts. Computer Methods in Applied Mechanics and Engineering, 193(36-38), 4057-4066. doi:10.1016/j.cma.2004.03.00

RF-Energized Intracoronary Guidewire to Enhance Bipolar Ablation of the Interventricular Septum: In-silico Feasibility Study

"This is an Accepted Manuscript of an article published by Taylor & Francis in International Journal of Hyperthermiaon [date of publication], available online: https://doi.org/10.1080/02656736.2018.1425487"[EN] Purpose: Although bipolar radiofrequency (RF) ablation (RFA) is broadly used to eliminate ventricular tachycardias in the interventricular septum wall, it can fail to create transmural lesions in thick ventricular walls. To solve this problem, we explored whether an RF-energised guidewire inserted into the ventricular wall would enhance bipolar RFA in the creation of transmural lesions through the ventricular wall.Methods: We built three-dimensional computational models including two irrigated electrodes placed on opposing sides of the interventricular septum and a metal guidewire inserted into the septum. Computer simulations were conducted to compare the temperature distributions obtained with two ablation modes: bipolar mode (RF power delivered between both irrigated electrode) and time-division multiplexing (TDM) technique, which consists of activating the bipolar mode for 90% of the time and applying RF power between the guidewire and both irrigated electrodes during the remaining time.Results: The TDM technique was the most suitable in terms of creating wider lesions through the entire ventricular wall, avoiding the hour-glass shape of thermal lesions associated with the bipolar mode. This was especially apparent in the case of thick walls (15mm). Furthermore, the TDM technique was able to create transmural lesions even when the guidewire was displaced from the midplane of the wall.Conclusions: An RF-energised guidewire could enhance bipolar RFA by allowing transmural lesions to be made through thick ventricular walls. However, the safety of this new approach must be assessed in future pre-clinical studies, especially in terms of the risk of stenosis and its clinical impact.This work was supported by the Spanish Ministerio de Economia, Industria y Competitividad under "Plan Estatal de Investigacion, Desarrollo e Innovacion Orientada a los Retos de la Sociedad" Grant "TEC2014-52383-C3 (TEC2014-52383-C3-1-R)". A. Gonzalez-Suarez has a "Juan de la Cierva-formacion" Postdoctoral Grant (FJCI-2015-27202) supported by the Spanish Ministerio de Economia, Industria y Competitividad, Secretaria de Estado de Investigacion, Desarrollo e Innovacion.Pérez, JJ.; González Suárez, A.; D Avila, A.; Berjano, E. (2018). RF-Energized Intracoronary Guidewire to Enhance Bipolar Ablation of the Interventricular Septum: In-silico Feasibility Study. International Journal of Hyperthermia. 34(8):1202-1212. https://doi.org/10.1080/02656736.2018.1425487S12021212348Baszko, A., Telec, W., Kałmucki, P., Iwachów, P., Kochman, K., Szymański, R., … Siminiak, T. (2016). Bipolar irrigated radiofrequency ablation of resistant ventricular tachycardia with a septal intramural origin: the initial experience and a description of the method. Clinical Case Reports, 4(10), 957-961. doi:10.1002/ccr3.648Gizurarson, S., Spears, D., Sivagangabalan, G., Farid, T., Ha, A. C. T., Masse, S., … Nanthakumar, K. (2014). Bipolar ablation for deep intra-myocardial circuits: human ex vivo development and in vivo experience. Europace, 16(11), 1684-1688. doi:10.1093/europace/euu001Koruth, J. S., Dukkipati, S., Miller, M. A., Neuzil, P., d’ Avila, A., & Reddy, V. Y. (2012). Bipolar irrigated radiofrequency ablation: A therapeutic option for refractory intramural atrial and ventricular tachycardia circuits. Heart Rhythm, 9(12), 1932-1941. doi:10.1016/j.hrthm.2012.08.001Baldinger, S. H., Kumar, S., Barbhaiya, C. R., Mahida, S., Epstein, L. M., Michaud, G. F., … Stevenson, W. G. (2015). Epicardial Radiofrequency Ablation Failure During Ablation Procedures for Ventricular Arrhythmias. Circulation: Arrhythmia and Electrophysiology, 8(6), 1422-1432. doi:10.1161/circep.115.003202Santangeli, P., Shaw, G. C., & Marchlinski, F. E. (2017). Radiofrequency Wire Facilitated Interventricular Septal Access for Catheter Ablation of Ventricular Tachycardia in a Patient With Aortic and Mitral Mechanical Valves. Circulation: Arrhythmia and Electrophysiology, 10(1). doi:10.1161/circep.116.004771Berjano, E. J., Hornero, F., Atienza, F., & Montero, A. (2003). Long electrodes for radio frequency ablation: comparative study of surface versus intramural application. Medical Engineering & Physics, 25(10), 869-877. doi:10.1016/s1350-4533(03)00125-5McLELLAN, A. J. A., ELLIMS, A. H., PRABHU, S., VOSKOBOINIK, A., ILES, L. M., HARE, J. L., … KISTLER, P. M. (2016). Diffuse Ventricular Fibrosis on Cardiac Magnetic Resonance Imaging Associates With Ventricular Tachycardia in Patients With Hypertrophic Cardiomyopathy. Journal of Cardiovascular Electrophysiology, 27(5), 571-580. doi:10.1111/jce.12948Berjano, E. J. (2006). Theoretical modeling for radiofrequency ablation: state-of-the-art and challenges for the future. BioMedical Engineering OnLine, 5(1). doi:10.1186/1475-925x-5-24Pérez, J. J., González-Suárez, A., & Berjano, E. (2017). Numerical analysis of thermal impact of intramyocardial capillary blood flow during radiofrequency cardiac ablation. International Journal of Hyperthermia, 34(3), 243-249. doi:10.1080/02656736.2017.1336258Labonte, S. (1994). Numerical model for radio-frequency ablation of the endocardium and its experimental validation. IEEE Transactions on Biomedical Engineering, 41(2), 108-115. doi:10.1109/10.284921Doss, J. D. (1982). Calculation of electric fields in conductive media. Medical Physics, 9(4), 566-573. doi:10.1118/1.595107PÉREZ, J. J., D’AVILA, A., ARYANA, A., & BERJANO, E. (2015). Electrical and Thermal Effects of Esophageal Temperature Probes on Radiofrequency Catheter Ablation of Atrial Fibrillation: Results from a Computational Modeling Study. Journal of Cardiovascular Electrophysiology, 26(5), 556-564. doi:10.1111/jce.12630Jo, B., & Aksan, A. (2010). Prediction of the extent of thermal damage in the cornea during conductive keratoplasty. Journal of Thermal Biology, 35(4), 167-174. doi:10.1016/j.jtherbio.2010.02.004Gonzalez-Suarez, A., & Berjano, E. (2016). Comparative Analysis of Different Methods of Modeling the Thermal Effect of Circulating Blood Flow During RF Cardiac Ablation. IEEE Transactions on Biomedical Engineering, 63(2), 250-259. doi:10.1109/tbme.2015.2451178WINTERFIELD, J. R., JENSEN, J., GILBERT, T., MARCHLINSKI, F., NATALE, A., PACKER, D., … WILBER, D. J. (2015). Lesion Size and Safety Comparison Between the Novel Flex Tip on the FlexAbility Ablation Catheter and the Solid Tips on the ThermoCool and ThermoCool SF Ablation Catheters. Journal of Cardiovascular Electrophysiology, 27(1), 102-109. doi:10.1111/jce.12835PÉREZ, J. J., D’AVILA, A., ARYANA, A., TRUJILLO, M., & BERJANO, E. (2016). Can Fat Deposition After Myocardial Infarction Alter the Performance of RF Catheter Ablation of Scar-Related Ventricular Tachycardia?: Results from a Computer Modeling Study. Journal of Cardiovascular Electrophysiology, 27(8), 947-952. doi:10.1111/jce.13006Haines, D. E. (2011). Letter by Haines Regarding Article, «Direct Measurement of the Lethal Isotherm for Radiofrequency Ablation of Myocardial Tissue». Circulation: Arrhythmia and Electrophysiology, 4(5). doi:10.1161/circep.111.965459González-Suárez, A., Trujillo, M., Koruth, J., d’ Avila, A., & Berjano, E. (2014). Radiofrequency cardiac ablation with catheters placed on opposing sides of the ventricular wall: Computer modelling comparing bipolar and unipolar modes. International Journal of Hyperthermia, 30(6), 372-384. doi:10.3109/02656736.2014.949878Gianni, C., Mohanty, S., Trivedi, C., Di Biase, L., Al-Ahmad, A., Natale, A., & David Burkhardt, J. (2017). Alternative Approaches for Ablation of Resistant Ventricular Tachycardia. Cardiac Electrophysiology Clinics, 9(1), 93-98. doi:10.1016/j.ccep.2016.10.006Boll, D. T., Lewin, J. S., Duerk, J. L., & Merkle, E. M. (2003). Do Surgical Clips Interfere with Radiofrequency Thermal Ablation? American Journal of Roentgenology, 180(6), 1557-1560. doi:10.2214/ajr.180.6.1801557Eung Je Woo, Tungjitkusolmun, S., Hong Cao, Jang-Zem Tsai, Webster, J. G., Vorperian, V. R., & Will, J. A. (2000). A new catheter design using needle electrode for subendocardial RF ablation of ventricular muscles: finite element analysis and in vitro experiments. 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Radiofrequency Heating of the Cornea: An Engineering Review of Electrodes and Applicators

This paper reviews the different applicators and electrodes employed to create localized heating in the cornea by means of the application of radiofrequency (RF) currents. Thermokeratoplasty (TKP) is probably the best known of these techniques and is based on the principle that heating corneal tissue (particularly the central part of the corneal tissue, i.e. the central stroma) causes collagen to shrink, and hence changes the corneal curvature. Firstly, we point out that TKP techniques are a complex challenge from the engineering point of view, due to the fact that it is necessary to create very localized heating in a precise location (central stroma), within a narrow temperature range (from 58 to 76ºC). Secondly, we describe the different applicator designs (i.e. RF electrodes) proposed and tested to date. This review is planned from a technical point of view, i.e. the technical developments are classified and described taking into consideration technical criteria, such as energy delivery mode (monopolar versus bipolar), thermal conditions (dry versus cooled electrodes), lesion pattern (focal versus circular lesions), and application placement (surface versus intrastromal)

Limitations of Baseline Impedance, Impedance Drop and Current for Radiofrequency Catheter Ablation Monitoring: Insights from In Silico Modeling

[EN] Background: Baseline impedance, radiofrequency current, and impedance drop during radiofrequency catheter ablation are thought to predict effective lesion formation. However, quantifying the contributions of local versus remote impedances provides insights into the limitations of indices using those parameters. Methods: An in silico model of left atrial radiofrequency catheter ablation was used based on human thoracic measurements and solved for (1) initial impedance (Z), (2) percentage of radiofrequency power delivered to the myocardium and blood (3) total radiofrequency current, (4) impedance drop during heating, and (5) lesion size after a 25 W¿30 s ablation. Remote impedance was modeled by varying the mixing ratio between skeletal muscle and fat. Local impedance was modeled by varying insertion depth of the electrode (ID). Results: Increasing the remote impedance led to increased baseline impedance, lower system current delivery, and reduced lesion size. For ID = 0.5 mm, Z ranged from 115 to 132 ¿ when fat percentage varied from 20 to 80%, resulting in a decrease in the RF current from 472 to 347 mA and a slight decrease in lesion size from 5.6 to 5.1 mm in depth, and from 9.2 to 8.0 mm in maximum width. In contrast, increasing the local impedance led to lower system current but larger lesions. For a 50% fat¿muscle mixture, Z ranged from 118 to 138 ¿ when ID varied from 0.3 to 1.9 mm, resulting in a decrease in the RF current from 463 to 443 mA and an increase in lesion size, from 5.2 up to 7.5 mm in depth, and from 8.4 up to 11.6 mm in maximum width. In cases of nearly identical Z but different contributions of local and remote impedance, markedly different lesions sizes were observed despite only small differences in RF current. Impedance drop better predicted lesion size (R2 > 0.93) than RF current (R2 < 0.1). Conclusions: Identical baseline impedances and observed RF currents can lead to markedly different lesion sizes with different relative contributions of local and remote impedances to the electrical circuit. These results provide mechanistic insights into the advantage of measuring local impedance and identifies potential limitations of indices incorporating baseline impedance or current to predict lesion qualitySpanish Ministerio de Ciencia, Innovación y Universidades / Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033) under grant RTI2018-094357-B-C21, and Agencia Nacional de Promoción Científica y Tecnológica de Argentina, grant PICT-2016-2303. Dr. Irastorza was the recipient of a scholarship of the Programa de Becas Externas Postdoctorales para Jóvenes Investigadores del CONICET (Argentina).Irastorza, RM.; Maher, T.; Barkagan, M.; Liubasuskas, R.; Pérez, JJ.; Berjano, E.; D Avila, A. (2022). Limitations of Baseline Impedance, Impedance Drop and Current for Radiofrequency Catheter Ablation Monitoring: Insights from In Silico Modeling. Journal of Cardiovascular Development and Disease. 9(10):1-12. https://doi.org/10.3390/jcdd9100336S11291