Lumped Element Electrical Model based on Three Resistors for Electrical Impedance in Radiofrequency Cardiac Ablation: Estimations from Analytical Calculations and Clinical Data

[EN] The electrical impedance measured during radiofrequency cardiac ablation (RFCA) is widely used in clinical studies to predict the heating evolution and hence the success of the procedure. We hypothesized that a model based on three resistors in series can mimic the total electrical impedance measured during RFCA. The three resistors or impedances are given by: impedance associated with the tissue around the active electrode (myocardium and circulating blood) (Z-A), that associated with the tissue around the dispersive electrode (Z-DE) and that associated with the rest of the body (Z-B). Our objective was to quantify the values associated with these three impedance types by an analytical method, after which the values obtained would be compared to those estimated from clinical data from previous studies. The results suggest that an RFCA using a 7 Fr 4-mm electrode would give a Z-A of around 75 ohms, a Z-DE around 20 ohms, and Z-B would be 15±10 ohms (for body surface area variations between 1.5 and 2.5 m^2). Finally, adaptations of the proposed model were used to explain the results of previous clinical studies using a different electrode arrangement, such as in bipolar ablation of the ventricular septum.This work received financial support from the Spanish “Plan Nacional de I+D+I del Ministerio de Ciencia e Innovación” Grant No. TEC2011-27133-C02-01.Berjano, E.; D Avila, A. (2013). Lumped Element Electrical Model based on Three Resistors for Electrical Impedance in Radiofrequency Cardiac Ablation: Estimations from Analytical Calculations and Clinical Data. 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Hoboken: Wiley 2006; pp. 1-14.Saito M, Nakayama K, Hori M, Fujimori Y. “A fundamental study on the electrodes for cardiac pacemakers” Jpn J Med Electron Biol Eng 1967; 5 : 192-8.Nsah E, Berger R, Rosenthal L, et al. “Relation between impedance and electrode temperature during radiofrequency catheter ablation of accessory pathways and atrioventricular nodal reentrant tachycardia” Am Heart J 1998 November; 136 : 844-51.Wen Z C, Chen S A, Chiang C E, et al. “Temperature and impedance monitoring during radiofrequency catheter ablation of slow AV node pathway in patients with atrioventricular node reentrant tachycardia” Int J Cardiol 1996 December; 57 : 257-63.Strickberger S A, Hummel J, Gallagher M, et al. “Effect of accessory pathway location on the efficiency of heating during radiofrequency catheter ablation” Am Heart J 1995 January; 129 : 54-8.Strickberger S A, Vorperian V R, Man K C, et al. “Relation between impedance and endocardial contact during radiofrequency catheter ablation” Am Heart J 1994 August; 128 : 226-9.Cao H, Tungjitkusolmun S, Choy Y B, Tsai J Z, Vorperian V R, and Webster J G. “Using electrical impedance to predict catheter-endocardial contact during RF cardiac ablation” IEEE Trans Biomed Eng 2002 March; 49 : 247-3.Rodriguez L M, Nabar A, Timmermans C, and Wellens H J. “Comparison of results of an 8-mm split-tip versus a 4-mm tip ablation catheter to perform radiofrequency ablation of type I atrial flutter” Am J Cardiol 2000 January; 85 : 109-12.Sacher F F, O'Neill M D, Jais P, et al. “Prospective randomized comparison of 8-mm gold-tip, externally irrigated-tip and 8-mm platinum- iridium tip catheters for cavotricuspid isthmus ablation” J Cardiovasc Electrophysiol 2007 July; 18 : 709-13.Jackman W M, Wang X Z, Friday K J, et al. “Catheter ablation of atrioventricular junction using radiofrequency current in 17 patients. Comparison of standard and large-tip catheter electrodes” Circulation 1991 May; 83 : 1562-76.Nath S, DiMarco J P, Gallop R G, McRury I D, and Haines D E. “Effects of dispersive electrode position and surface area on electrical parameters and temperature during radiofrequency catheter ablation” Am J Cardiol 1996 April; 77 : 765-7.Santoro I, Xunzhang W, McClelland J, et al. “Effect of skin-patch location and surface area on impedance during radiofrequency catheter ablation” Pacing Clin Electrophysiol 1992; 15 : 580.Borganelli M, el-Atassi R, Leon A, et al. “Determinants of impedance during radiofrequency catheter ablation in humans” Am J Cardiol 1992 April; 69 : 1095-7.Park J K, Halperin B D, Kron J, Holcomb S R, and Silka M J. “Analysis of body surface area as a determinant of impedance during radiofrequency catheter ablation in adults and children” J Electrocardiol 1994 October; 27 : 329-32.Wang D, Hulse J E, Walsh E P, and Saul J P. “Factors influencing impedance during radiofrequency ablation in humans” Chin Med J (Engl) 1995 June; 108 : 450-5.Koruth J S, Dukkipati S, Miller M A, Neuzil P, d'Avila A, and Reddy V Y. “Bipolar irrigated radiofrequency ablation: a therapeutic option for refractory intramural atrial and ventricular tachycardia circuits” Heart Rhythm 2012 December; 9 : 1932-41

Thermal Latency adds to Lesion Depth after Application of High-Power Short-Duration Radiofrequency Energy: Results of a computer-modeling study

[EN] Introduction: The use of ultra-short RF pulses could achieve greater lesion depth immediately after the application of the pulse due to thermal latency. Methods and results: A computer model of irrigated-catheter RF ablation was built to study the impact of thermal latency on the lesion depth. The results showed that the shorter the RF pulse duration (keeping energy constant), the greater the lesion depth during the cooling phase. For instance, after a 10-second pulse, lesion depth grew from 2.05 mm at the end of the pulse to 2.39 mm (17%), while after an ultra-short RF pulse of only 1 second the extra growth was 37% (from 2.22 to 3.05 mm). Importantly, short applications resulted in deeper lesions than long applications (3.05 mm vs. 2.39 mm, for 1-and 10-second pulse, respectively). While shortening the pulse duration produced deeper lesions, the associated increase in applied voltage caused overheating in the tissue: temperatures around 100 degrees C were reached at a depth of 1 mm in the case of 1-and 5-second pulses. However, since the lesion depth increased during the cooling period, lower values of applied voltage could be applied in short durations in order to obtain lesion depths similar to those in longer durations while avoiding overheating. Conclusion: The thermal latency phenomenon seems to be the cause of significantly greater lesion depth after short-duration high-power RF pulses. Balancing the applied total energy when the voltage and duration are changed is not the optimal strategy since short pulses can also cause overheating.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) and by the National Scientific and Technical Research Council - Argentina "Proyecto de Investigacion Orientado" (PIOCONICET-UNAJ 0001).Irastorza, RM.; D Avila, A.; Berjano, E. (2018). Thermal Latency adds to Lesion Depth after Application of High-Power Short-Duration Radiofrequency Energy: Results of a computer-modeling study. Journal of Cardiovascular Electrophysiology. 29(2):322-327. doi:10.1111/jce.13363S32232729

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

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

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

Radiofrequency Ablation Using a Novel Insulated-Tip Ablation Catheter Can Create Uniform Lesions Comparable in Size to Conventional Irrigated Ablation Catheters While Using a Fraction of the Energy and Irrigation

[EN] Introduction: During radiofrequency ablation (RFA) using conventional RFA catheters (RFC), similar to 90% of the energy dissipates into the bloodstream/surrounding tissue. We hypothesized that a novel insulated-tip ablation catheter (SMT) capable of blocking the radiofrequency path may focus most of the energy into the targeted tissue while utilizing reduced power and irrigation. Methods: This study evaluated the outcomes of RFA using SMT versus an RFC in silico, ex vivo, and in vivo. Radiofrequency applications were delivered over porcine myocardium (ex vivo) and porcine thigh muscle preparations superfused with heparinized blood (in vivo). Altogether, 274 radiofrequency applications were delivered using SMT (4-15 W, 2 or 20 ml/min) and 74 applications using RFC (30 W, 30 ml/min). Results: RFA using SMT proved capable of directing 66.8% of the radiofrequency energy into the targeted tissue. Accordingly, low power-low irrigation RFA using SMT (8-12 W, 2 ml/min) yielded lesion sizes comparable with RFC, whereas high power-high irrigation (15 W, 20 ml/min) RFA with SMT yielded lesions larger than RFC (p < .05). Although SMT was associated with greater impedance drops ex vivo and in vivo, ablation using RFC was associated with increased charring/steam pop/ tissue cavitation (p < .05). Lastly, lesions created with SMT were more homogeneous than RFC (p < .001). Conclusion: Low power-low irrigation (8-12 W, 2 ml/min) RFA using the novel SMT ablation catheter can create more uniform, but comparable-sized lesions as RFC with reduced charring/steam pop/tissue cavitation. High power-high irrigation (15 W, 20 ml/min) RFA with SMT yields lesions larger than RFC.Sirona Medical Technologies, Inc; The Proyecto UNAJ Investiga 2017, Grant/Award Number: 80020170100019UJ; The Spanish Ministerio de Ciencia, Innovacion y Universidades/Agencia Estatal de Investigacion (MCIN/AEI/10.13039/501100011033), Grant/Award Number: RTI2018-094357B-C21Aryana, A.; Irastorza, RM.; Berjano, E.; Cohen, RJ.; Kraus, J.; Haghighi-Mood, A.; Reddy, VY.... (2022). Radiofrequency Ablation Using a Novel Insulated-Tip Ablation Catheter Can Create Uniform Lesions Comparable in Size to Conventional Irrigated Ablation Catheters While Using a Fraction of the Energy and Irrigation. Journal of Cardiovascular Electrophysiology. 33(6):1146-1156. https://doi.org/10.1111/jce.154611146115633

Nrf2-dependent persistent oxidative stress results in stress-induced vulnerability to depression.

Stressful life events produce a state of vulnerability to depression in some individuals. The mechanisms that contribute to vulnerability to depression remain poorly understood. A rat model of intense stress (social defeat (SD), first hit) produced vulnerability to depression in 40% of animals. Only vulnerable animals developed a depression-like phenotype after a second stressful hit (chronic mild stress). We found that this vulnerability to depression resulted from a persistent state of oxidative stress, which was reversed by treatment with antioxidants. This persistent state of oxidative stress was due to low brain-derived neurotrophic factor (BDNF) levels, which characterized the vulnerable animals. We found that BDNF constitutively controlled the nuclear translocation of the master redox-sensitive transcription factor Nrf2, which activates antioxidant defenses. Low BDNF levels in vulnerable animals prevented Nrf2 translocation and consequently prevented the activation of detoxifying/antioxidant enzymes, ultimately resulting in the generation of sustained oxidative stress. Activating Nrf2 translocation restored redox homeostasis and reversed vulnerability to depression. This mechanism was confirmed in Nrf2-null mice. The mice displayed high levels of oxidative stress and were inherently vulnerable to depression, but this phenotype was reversed by treatment with antioxidants. Our data reveal a novel role for BDNF in controlling redox homeostasis and provide a mechanistic explanation for post-stress vulnerability to depression while suggesting ways to reverse it. Because numerous enzymatic reactions produce reactive oxygen species that must then be cleared, the finding that BDNF controls endogenous redox homeostasis opens new avenues for investigation

Orientações para Realização de Exames de Ressonância Magnética Nuclear em Pacientes com Dispositivos Eletrônicos Cardíacos

Estima-se que até 75% dos pacientes com dispositivos cardíacos eletrônicos implantáveis (DCEIs) terão indicação de exame de ressonância nuclear magnética (RNM) ao longo da vida. Pelas características dos dispositivos, esses foram excluídos historicamente do rol de pacientes considerados elegíveis ao exame

Alignment of the CMS silicon tracker during commissioning with cosmic rays

This is the Pre-print version of the Article. The official published version of the Paper can be accessed from the link below - Copyright @ 2010 IOPThe CMS silicon tracker, consisting of 1440 silicon pixel and 15 148 silicon strip detector modules, has been aligned using more than three million cosmic ray charged particles, with additional information from optical surveys. The positions of the modules were determined with respect to cosmic ray trajectories to an average precision of 3–4 microns RMS in the barrel and 3–14 microns RMS in the endcap in the most sensitive coordinate. The results have been validated by several studies, including laser beam cross-checks, track fit self-consistency, track residuals in overlapping module regions, and track parameter resolution, and are compared with predictions obtained from simulation. Correlated systematic effects have been investigated. The track parameter resolutions obtained with this alignment are close to the design performance.This work is supported by FMSR (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); Academy of Sciences and NICPB (Estonia); Academy of Finland, ME, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF (Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); PAEC (Pakistan); SCSR (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MST and MAE (Russia); MSTDS (Serbia); MICINN and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey); STFC (United Kingdom); DOE and NSF (USA)