Evaluation of an Endorectal Electrode for Performing Focused Irreversible Electroporation Ablations in the Swine Rectum

Purpose: To study the feasibility of a novel endorectal electrode for the creation of focal ablations of the rectal wall with the use of irreversible electroporation (IRE). Materials and Methods: A monopolar electrode with a grounding pad (10 ablations in five pigs) and a bipolar electrode (two ablations in one pig) were evaluated in healthy swine rectum. A two-dimensional model of the electrode in the rectum was created and used to solve the Laplace equation to determine field strength. Simulation was used to identify treatment settings for superficial ablation (mucosal layers) or transmural ablation of rectal wall. Animals were euthanized within 4 hours after treatment. Results: Treatment was successfully completed without treatment-related complications. Eleven of 12 lesions were successfully located and extracted for pathologic analysis. All lesions were characterized by necrotic cell death with mild inflammation and hyperemia, with a sharp demarcation between ablated and adjacent normal tissue. Depth of lesions corresponded with numeric simulation. Histologic,analysis and measurements indicated that lesion creation with the superficial treatment setting resulted in ablation of mucosal and submucosal layers with superficial or no injury to the muscularis propria (9.97 mm +/- 0.31 length, 3.3 mm +/- 2.92 depth), and that lesion creation with the transmural treatment setting resulted in full-thickness ablation (12.43 mm +/- 3.85 length, 4.97 mm +/- 2.89 depth) of the rectal wall. Conclusions: An endorectal electrode can be used to deliver IRE and create limited focal ablations in the rectal wall. Treatment parameters can be determined through numeric modeling to control the depth of penetration of ablation.