## 3 Results
### Performances of Multielectrode Unipolar (MEU) and Multielectrode Bipolar (MEB) Modes
The outer side of each electrode was occupied by more extensive areas of current density that formed a fan-shaped region. Owing to the gap in current density between adjacent electrodes on the tissue surface, the temperature at the two sides, especially the four corners of the electrode, was weak in the MEU mode. The MEB mode had a continuous distribution of current density along the circular catheter. The current density field vastly expanded at the inner edge of the CMC. Adjacent electrodes shared a connection between current density fields, responding to continuous lesions. The joint between the electrode and the catheter body was characterized by a higher current density in both modes. Furthermore, the current density of electrode 1 was cut off at the edge of the catheter body. Because the catheter body had extremely low electrical conductivity, it functioned as a barrier blocking the current flow. Electrode 10 had a broader distribution of current density along the catheter body without electrodes in the MEU mode. Figure 7 displays the maximum lesion depth, temperature, and time required for effective lesion generation by each electrode, as well as the total lesion volume in the myocardium in the MEU and MEB modes. Electrodes 1 and 10 were the first two electrodes to generate effective lesions in the MEU mode but the last two electrodes in the MEB mode. Under the same RFCA period, faster heat generation of the electrode led to higher temperatures in both ablation modes. In the MEB mode, the lesion deepened with the increase in temperature. In the MEU mode, however, this finding was only established during the first 30 s of RFCA. For the subsequent 30 s, the electrode that previously  
Figure 5: (**a**) Concave of the lesion between the adjacent active electrodes in the MEU mode. The minimum distance between adjacent lesions on the tissue surface is defined as \(d\). The depth of the concave is defined as \(D\). (**b**) The values of \(d\) and \(D\) at 30 s and 60 s of RFCA. generated a lower temperature produced deeper lesions. The lesion depth in the MEU mode at 60 s was \(6.35\pm 0.87\) mm, which is almost twice that in the MEB mode (\(3.39\pm 0.29\) mm). Although the applied RF power in the MEB mode was half of that in the MEU mode, the average temperature of the MEB mode was \(88.6\pm 5.8\)\({}^{\circ}\)C, which was nearly 20 \({}^{\circ}\)C higher than that of the MEU mode. A notable phenomenon was captured in the MEU mode, where the lesion depth increased by approximately 3.80 mm during the subsequent 30 s of RFCA. For both modes, the maximum lesion depth, and generation time presented by 10 electrodes appeared to be a symmetric combination. The maximum temperature under each electrode fluctuated in the MEB mode. The lesion volume at 60 s of RFCA reached 831.36 mm\({}^{3}\) and 479.59 mm\({}^{3}\) in the MEU and MEB modes, respectively, as shown in Figure 7d. The MEB mode presented a rapid initial increase in lesion volume, but the rate of increase progressively decayed over time. For the MEU mode, a turning point appeared around 50 s at which the lesion volume started to increase sharply, which is probably the outcome of the aforementioned boost in lesion depth. Figure 6: Top view of the current flow and voltage distribution in (**a**) the MEU mode with a side view of the entire model and (**b**) the MEB mode. (**c**) Distribution of current density on the surface of the myocardium at 60 s of RFCA. We also measured the surface lesion area, the maximum sectional lesion area of the myocardium, and the corresponding depth to approach the section at 30 s and 60 s of RFCA in Table 3. The results reflect that lesions spread principally from electrode to electrode as opposed to spreading in depth.