ENHANCED RADIOFREQUENCY ABLATION OF CANINE PROSTATE UTILIZING A LIQUID CONDUCTOR - THE VIRTUAL ELECTRODE

Conventional radiofrequency (RF) ablative techniques have shown promis e for the treatment of symptomatic benign prostatic hyperplasia (BPH); however, present RF technology is limited by the small lesion size, n ecessitating several probe placements and heating cycles to achieve si zable lesions. This limitation is attributable primarily to a rapid in crease in electrical impedance secondary to tissue desiccation and cha rring at the electrode tip. We devised a hollow screw-tip needle elect rode that permits fixation to tissue, recording of temperature and imp edance, infusion of fluid, and delivery of RF energy. Infusion of elec trolyte solution (i.e., saline) into tissue prevents impedance rise by conducting RF energy away from the metal electrode and permits the cr eation of large lesions. By varying the conductivity of the perfusate (concentration and temperature), lesions of large diameter can be crea ted in a controlled manner. To determine the long-term tissue effects, we applied this new modified RF technique to the prostates of five mo ngrel dogs in a chronic (0.5 to 8-week) study. The screw-tip electrode was serially embedded into each lobe of the perineally exposed glands with 1-minute infusion of 0.9% saline (2 mL/min) followed by applicat ion of RF energy (500 KHz, 50 W, 2-18 minutes) along with continuous s aline infusion. Thermocouples were embedded 5 mm below and at the glan d capsule, and RF application was discontinued when the temperature re ached 50 degrees C at the periphery. Postoperatively, the animals were examined daily for clinical status and weekly for glandular changes u sing transrectal ultrasonography. At predetermined intervals, the anim als were sacrificed and the prostates excised, measured, sectioned, an d examined for histologic changes. Ablative tissue temperatures of 50 to 100 degrees C were produced while impedance remained stable. Four a nimals required a single catheterization for relief of urinary retenti on between days 2 and 3; otherwise, all animals demonstrated a quick a nd uneventful recovery with no edema detectable on day 7 ultrasound ex amination. The outside dimensions of the gland remained relatively con stant throughout the study (+/-0.39 cm L + W + H). Histologic examinat ion revealed coagulation necrosis (ablation) in both lobes of all pros tates (69.94% +/- 16.62% of the gland) with tissueless cavities formin g from the ablation area (28.71% +/- 8.24% of the gland) contained wit hin the capsule surrounded by healthy tissue at the periphery. Intrapr ostatic lesions were obtained without any gross damage to surrounding tissue, including the bladder and rectal wall. Utilizing a liquid cond uctor in prostate tissue allows a single electrode-placement heating c ycle for controlled ablation for the potential treatment of BPH. This new technique produces more extensive and uniform lesions than convent ional RF procedures, and lesion size is limited only by the duration o f RF energy application.