[Pulsed radiofrequency ablation using perfused needle applicators in an in vitro trial on bovine liver]

Intermittent energy application seems to have positive effects in achieving necrotic zones. We analyzed different pulse periods (PPs) to optimize this method. A radiofrequency alternating current was delivered via a triple-needle applicator (3 cm distance of each needle) introduced into freshly procured bovine liver. The open applicator system was constantly perfused with physiological NaCl solution (3×80 ml/h, power output was constant 90 W). Radiofrequency current was fed to the individual needle in turn of varying PPs (1, 2, 5, and 7 s) over 15 min. Each experimental run comprised a total of 30 applications and temperature was recorded over time. The largest necrotic diameters were found at PP 1 s (relevant: shortest axial diameter/D in the center of the lesion: 9.27 cm, SD±0.97 cm) (PP 2 s D=8.65 cm, SD±0.95 cm, p=0.021; PP 5 s D=8.35 cm, SD±0.95 cm, p=0.001; PP 7 s D=8.18 cm, SD±0.79 cm, p=0.0001). Neither doubling the perfusion rate nor raising the concentration of the perfusion liquid led at PP 1 s to increased necrotic diameters (p=0.82). Our study shows that reducing the PP to 1 s of an open perfused intermittent radiofrequency ablation system produces significantly larger coagulation volumes in explanted liver tissue reaching necrotic diameters over 9 cm. Neither doubling perfusion rates nor higher concentrated perfusion liquid increase necrotic diameters.