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Endovenous laser ablation: mechanism of action

Objectives The objective of this study is to review the basics of laser and established tissue response patterns to thermal injury, with specific reference to endovenous laser ablation (EVLA). This study also reviews the current theories and supporting aspects for the mechanism of action of EVLA in the treatment of superficial venous reflux. Methods The method involves the review of published literature and original investigation of histological effects of 810 nm and 980 nm wavelength EVLA on explanted blood-filled bovine saphenous vein in an in vitro system. Results The existing histological reports confirm that EVLA produces a transmural vein wall injury, typically associated with perforations and carbonization. The pattern of injury is eccentrically distributed, with maximum injury occurring along the path of laser contact. Intravenous temperature monitoring studies during EVLA have confirmed that the peak temperatures at the fibre tip exceed 1000°C, and continuous temperatures of at least 300°C are maintained in the firing zone for the majority of the procedure. Steam production during EVLA, which occurs early in the photothermolytic process when temperatures reach 100°C, accounts for only 2% of applied energy dose, and is therefore unlikely to be the primary mechanism of action of thermal injury during the procedure. Conclusion EVLA causes permanent vein closure through a high-temperature photothermolytic process at the point of contact between the vein and the laser.