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A novel radiofrequency ablative system (40 msec-train pulses with twenty 200 msec pulses at the carrier frequency of 750 KHz and 1 Hz repetition rate) aimed at recanalizing totally occluded peripheral arteries was investigated by means of in vitro tissue ablation from human postmortem arterial wall samples. The samples were submitted to irradiation with a guidewire 150 cm long, maximum diameter of ceramic tip 0.033 inch positioned perpendicular to the tissue surface in saline, contrast medium or blood using varying generator power. Ablation efficacy was determined as the depth of vaporization per pulse delivered. Electrical current for the train duration was measured as voltage at the 1 ohm-resistor. In saline, the ablation efficacy increased from 8 to 65 mm/pulse with generator power increasing from 11 W to 27.5 W. There was no significant difference in the ablation efficacy between saline and blood. In contrast medium, the ablation efficacy was significantly lower. For the same generator power, the electrical current varied during the ablation procedure from 1.3 +/- 0.2 A at the beginning of the procedure to 1.1 +/- 0.2 A after the first pulses and to 2.0 A before artery wall perforation occurred. Neither tissue ablation nor current variations were observed when radiofrequency energy was emitted on calcified tissue. The diameter of craters was 0.89 +/- 0.1 mm (range: 0.85 - 0.96 mm). No major thermal injury such as carbonization or charring was observed. Thus, (1) radiofrequency energy emitted through a guidewire is reliable and effective for the ablation of arterial tissue; (2) the depth of penetration is related to the generator power; (3) the ablation efficacy is greater in saline and blood than in contrast medium; (4) the system is not effective in highly calcified tissue; (5) the procedure may be monitored by electrical current measurements.
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