Radiofrequency cardiac ablation with catheters placed on opposing sides of the ventricular wall: Computer modelling comparing bipolar and unipolar modes

Purpose: The aim of this study was to compare the efficacy of bipolar (BM) vs. unipolar (UM) mode of radiofrequency ablation (RFA) in terms of creating transmural lesions across the interventricular septum (IVS) and ventricular free wall (VFW). Materials and methods: We built computational models to study the temperature distributions and lesion dimensions created by BM and UM on IVS and VFW during RFA. Two different UM types were considered: sequential (SeUM) and simultaneous (SiUM). The effect of ventricular wall thickness, catheter misalignment, epicardial fat, and presence of air in the epicardial space were also studied. Results: Regarding IVS ablation, BM created transmural and symmetrical lesions for wall thicknesses up to 15 mm. SeUM and SiUM were not able to create transmural lesions with IVS thicknesses >= 12.5 and 15 mm, respectively. Lesions were asymmetrical only with SeUM. For VFW ablation, BM also created transmural lesions for wall thicknesses up to 15 mm. However, with SeUM and SiUM transmurality was obtained for VFW thicknesses <= 7.5 and 12.5 mm, respectively. With the three modes, VFW lesions were always asymmetrical. In the scenario with air or a fat tissue layer on the epicardial side, only SiUM was capable of creating transmural lesions. Overall, BM was superior to UM in IVS and VFW ablation when the catheters were not aligned. Conclusions: Our findings suggest that BM is more effective than UM in achieving transmurality across both ventricular sites, except in the situation of the epicardial catheter tip surrounded by air or placed over a fat tissue layer.This work received financial support from the Spanish 'Plan Nacional de I+D+I del Ministerio de Ciencia e Innovacion' (TEC2011-27133-C02-01), and from the Universitat Politecnica de Valencia (PAID-06-11 Ref. 1988). A. Gonzalez-Suarez is the recipient of a Grant VaLi+D (ACIF/2011/194) from the Generalitat Valenciana, Spain. The authors alone are responsible for the content and writing of the paper.González Suárez, A.; Trujillo Guillen, 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. https://doi.org/10.3109/02656736.2014.949878S372384306SIVAGANGABALAN, G., BARRY, M. A., HUANG, K., LU, J., POULIOPOULOS, J., THOMAS, S. P., … KOVOOR, P. (2010). Bipolar Ablation of the Interventricular Septum is More Efficient at Creating a Transmural Line than Sequential Unipolar Ablation. Pacing and Clinical Electrophysiology, 33(1), 16-26. doi:10.1111/j.1540-8159.2009.02602.xNagashima, K., Watanabe, I., Okumura, Y., Ohkubo, K., Kofune, M., Ohya, T., … Hirayama, A. (2011). Lesion Formation by Ventricular Septal Ablation With Irrigated Electrodes. Circulation Journal, 75(3), 565-570. doi:10.1253/circj.cj-10-0870D’ Avila, A., Houghtaling, C., Gutierrez, P., Vragovic, O., Ruskin, J. N., Josephson, M. E., & Reddy, V. Y. (2004). Catheter Ablation of Ventricular Epicardial Tissue. Circulation, 109(19), 2363-2369. doi:10.1161/01.cir.0000128039.87485.0bDukkipati, S. R., d’ Avila, A., Soejima, K., Bala, R., Inada, K., Singh, S., … Reddy, V. Y. (2011). Long-Term Outcomes of Combined Epicardial and Endocardial Ablation of Monomorphic Ventricular Tachycardia Related to Hypertrophic Cardiomyopathy. Circulation: Arrhythmia and Electrophysiology, 4(2), 185-194. doi:10.1161/circep.110.957290Sosa, E., Scanavacca, M., d’ Avila, A., Oliveira, F., & Ramires, J. A. F. (2000). Nonsurgical transthoracic epicardial catheter ablation to treat recurrent ventricular tachycardia occurring late after myocardial infarction. Journal of the American College of Cardiology, 35(6), 1442-1449. doi:10.1016/s0735-1097(00)00606-9Nagashima, K., Watanabe, I., Okumura, Y., Sonoda, K., Kofune, M., Mano, H., … Hirayama, A. (2012). Epicardial Ablation With Irrigated Electrodes. Circulation Journal, 76(2), 322-327. doi:10.1253/circj.cj-11-0984Berjano, E. J. (2006). BioMedical Engineering OnLine, 5(1), 24. doi:10.1186/1475-925x-5-24Abraham, J. P., & Sparrow, E. M. (2007). A thermal-ablation bioheat model including liquid-to-vapor phase change, pressure- and necrosis-dependent perfusion, and moisture-dependent properties. International Journal of Heat and Mass Transfer, 50(13-14), 2537-2544. doi:10.1016/j.ijheatmasstransfer.2006.11.045Jo, 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.2010.02.004HAINES, D. E., & WATSON, D. D. (1989). 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International Journal of Hyperthermia, 29(4), 262-280. doi:10.3109/02656736.2013.786140Doss, J. D. (1982). Calculation of electric fields in conductive media. Medical Physics, 9(4), 566-573. doi:10.1118/1.595107Watanabe, I., Nuo, M., Okumura, Y., Ohkubo, K., Ashino, S., Kofune, M., … Hirayama, A. (2010). Temperature-Controlled Cooled-Tip Radiofrequency Ablation in Left Ventricular Myocardium. International Heart Journal, 51(3), 193-198. doi:10.1536/ihj.51.193Yokoyama, K., Nakagawa, H., Wittkampf, F. H. M., Pitha, J. V., Lazzara, R., & Jackman, W. M. (2006). Comparison of Electrode Cooling Between Internal and Open Irrigation in Radiofrequency Ablation Lesion Depth and Incidence of Thrombus and Steam Pop. Circulation, 113(1), 11-19. doi:10.1161/circulationaha.105.540062Kumar, P., Mounsey, J. P., Gehi, A. K., Schwartz, J. D., & Chung, E. H. (2013). Use of a closed loop irrigated catheter in epicardial ablation of ventricular tachycardia. 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Feasibility study of an internally cooled bipolar applicator for RF coagulation of hepatic tissue: Experimental and computational study

Purpose: To study the capacity of an internally cooled radiofrequency (RF) bipolar applicator to create sufficiently deep thermal lesions in hepatic tissue. Materials and methods: Three complementary methodologies were employed to check the electrical and thermal behaviour of the applicator under test. The experimental studies were based on excised bovine (ex vivo study) and porcine liver (in vivo study) and the theoretical models were solved by means of the finite element method (FEM). Results: Experimental and computational results showed good agreement in terms of impedance progress and lesion depth (4 and 4.5 mm respectively for ex vivo conditions, and approximately 7 and 9 mm respectively for in vivo conditions), although the lesion widths were overestimated by the computer simulations. This could have been due to the method used to assess the thermal lesions; the experimental lesions were assessed by the white coagulation zone, whereas the tissue damage function was used to assess the computational lesions. Conclusions: The experimental results suggest that this applicator could create in vivo lesions to a depth of around 7mm. It was also observed that the thermal lesion is mainly confined to the area between both electrodes, which would allow lesion width to be controlled by selecting a specific applicator design. The comparison between the experimental and computational results suggests that the theoretical model could be usefully applied in further studies of the performance of this device. © 2012 Informa UK Ltd All rights reserved.This work received financial support from the Spanish Plan Nacional de I+D+I del Ministerio de Ciencia e Innovacion TEC2011-27133-C02-(01 and 02), from Universitat Politecnica de Valencia (INNOVA11-01-5502; and PAID-06-11 Ref. 1988). 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