Repositorio Institucional Digital de la Universidad Nacional Arturo Jauretche - RID-UNAJ

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Differences in applied electrical power between full thorax models and limited-domain models for RF cardiac ablation
(2020-06-18) Irastorza, Ramiro M.; Gonzalez-Suarez, Ana; Pérez, Juan J.; Berjano, Enrique
Purpose: Most modeling studies on radiofrequency cardiac ablation (RFCA) are based on limiteddomain models, which means the computational domain is restricted to a few centimeters of myocardium and blood around the active electrode. When mimicking constant power RFCA procedures (e.g., atrial fibrillation ablation) it is important to know how much power is absorbed around the active electrode and how much in the rest of the tissues before reaching the dispersive electrode. Methods: 3D thorax full models were built by progressively incorporating different organs and tissues with simplified geometries (cardiac chamber, cardiac wall, subcutaneous tissue and skin, spine, lungs and aorta). Other 2D limited-domain models were also built based on fragments of myocardium and blood. The electrical problem was solved for each model to estimate the spatial power distribution around the active electrode. Results: From 79 to 82% of the power was absorbed in a 4 cm-radius sphere around the active electrode in the full thorax model at active electrode insertion depths of between 0.5 and 2.5 mm, while the impedance values ranged from 104 to 118 X, which were consistent with those found (from 83 to 103 X) in a 4 cm radius cylindrical limited domain model. Conclusion: The applied power in limited-domain RFCA models is approximately 80% of that applied in full thorax models, which is equivalent to the power programed in a clinical setting.
Microwave tomography with phaseless data on the calcaneus by means of artificial neural networks
(2019-12-20) Fajardo, J. E.; Lotto, F. P.; Vericat, F.; Carlevaro, C. M.; Irastorza, R. M.
The aim of this study is to use a Multilayer Perceptron (MLP) Artiﬁcial Neural Network (ANN) for phaseless imaging the human heel (modeled as a bilayer dielectric media: bone and surrounding tissue) and the calcaneus cross-section size and location using a two dimensional (2D) microwave tomographic array. Computer simulations were performed over 2D dielectric maps inspired by Computed Tomography (CT) images of human heels for training and testing the MLP. A morphometric analysis was performed to account for the scatterer shape inﬂuence on the results. A robustness analysis was also conducted in order to study the MLP performance in noisy conditions. The standard deviations of the relative percentage errors on estimating the dielectric properties of the calcaneus bone were relatively high. Regarding the calcaneus surrounding tissue, the dielectric parameters estimations are better, with relative percentage error standard deviations up to 15%. The location and size of the calcaneus are always properly estimated with absolute error standard deviations up to 3 mm.
Effect of the relative position of electrode and stellate ganglion during thermal radiofrequency ablation : A simulation study
(2021-10-21) Irastorza, Ramiro M.; Bovaira, Maite; García-Vitoria, Carles; Muñoz, Víctor; Berjano, Enrique
Purpose: Stellate ganglion (SG) block by thermal radiofrequency ablation (RFA) is frequently conducted as a therapeutic intervention for sympathetic-maintained and neuropathic pain syndromes. RFA’s partial lack of effectiveness could be partly due to the ablation zone (AZ) not completely covering the SG section and therefore preventing the ‘cutting’ of the afferent pathways. Our objective was to build a theoretical model to conduct computer simulations to assess the effect of the electrode position relative to the SG. Methods: A three-dimensional model was built including the SG and adjacent tissues (vertebrae C7T1-T2, trachea, carotid artery and vertebral artery). RFA (90-s, 80 C) was simulated considering a 22 G5 mm electrode. The AZ was computed using the 50 C isotherm. Results: An electrode displacement of 2 mm in any direction from the optimal position (centered on the SG) meant that the AZ did not fully cover the SG section. Likewise, SG size considerably affected the RFA effectiveness since the AZ fully covered the section of small but not large SGs. Conclusions: The findings suggest that the currently used SG RFA settings (i.e., 22 G-5 mm electrode, 90-s, 80 C) may not be appropriate due to their inability to achieve an AZ that fully covers the SG cross section under certain circumstances, such as a large SG and non-optimal positioning of the RF electrode with respect to the SG center.
Computer modeling of radiofrequency cardiac ablation : 30 years of bioengineering research
(2022-02) González-Suárez, Ana; Pérez, Juan J.; Irastorza, Ramiro M.; D’Avila, Andre; Berjano, Enrique
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 gaps.
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
(2022-03-23) Aryana, Arash; Irastorza, Ramiro M.; Berjano, Enrique; Cohen, Richard J.; Kraus, Jeffrey; Haghighi‐Mood, Ali; Reddy, Vivek Y.; d'Avila, André
Introduction: During radiofrequency ablation (RFA) using conventional RFA catheters (RFC), ~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.