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

Abstract

Background and objectivesA 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. MethodsA 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√2 V (AC voltage). The frequency of the sine signal (fAC) varied from 0.5 Hz to 50 Hz. ResultsSine wave thermal oscillations (at twice the fAC 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 °C for very low fAC values (0.5 Hz); and (3) was reduced at higher fAC 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. ConclusionsAlthough reducing fAC reduces the computation time, thermal oscillations appear at points near the electrode, which suggests that a minimum value of fAC should be used. Replacing DC voltage by low-frequency AC voltage does not appear to have an impact on the lesion depth.