Computer Modeling for Radiofrequency Bipolar Ablation Inside Ducts and Vessels: Relation Between Pullback Speed and Impedance Progress.

Abstract

Radiofrequency (RF)-induced ablation can be carried out inside ducts and vessels by simultaneously dragging a bipolar catheter while applying RF power. Our objective was to characterize the relation between pullback speed, impedance progress, and temperature distribution. We built a numerical model including a bipolar catheter, which is dragged inside a duct while RF power is applied between a pair of electrodes. The model solved a triple-coupled electrical, thermal, and mechanical problem. Lesions were assessed by an Arrhenius model. The numerical model's thermal and electrical characteristics were chosen to obtain the same initial impedance value as in the experiments: 560 Ω at 16°C (sample temperature). The catheter initially remained still, and the impedance was falling during the application of power. When pullback speed was too slow (<0.4 mm/s) impedance continued to drop when the catheter began to move, creating deep lesions, overheating and impedance roll-off, while at the faster speed (0.4-1.0 mm/s) impedance first rose slightly and then reached a plateau. There was a strong inverse relation between pullback speed and lesion depth. The hottest point was always around the second electrode, creating a kind of hot wake. These findings confirm the close relationship between pullback speed and impedance progress, and suggest that the latter factor could be used to guide the procedure and achieve effective and safe ablations along the inner path of a duct or vessel. Lasers Surg. Med. © 2020 Wiley Periodicals, Inc.