Endovenous laser ablation: an experimental study on the mechanism of action

Objectives: The aim of this experimental study was to investigate the mechanism of action of endovenous laser ablation (EVLA) using an 810-nm diode laser. Methods: We compared intermittent and continuous delivery of laser energy and studied the absorption of laser light by blood, intravascular temperatures in ex vivo human vein segments using an intravascular thermography catheter and heat dissipation in a model tissue using the Schlieren technique. Results: Laser light is absorbed by blood and converted to heat leading to coagulation, vaporization and carbonization, and forming an isolating layer at the fibre tip. Laser energy is then absorbed into the isolating layer forming black patches that burned on the laser fibre. Intravascular temperature increased rapidly above carbonization temperatures (300 degrees C) after the fibre tip reached the thermocouple, stayed at this temperature for a few seconds and decreased gradually to around 30 degrees C, 10 s after the fibre tip passed the thermocouple. Schlieren techniques revealed that heat spread from the laser was locally distributed and closely around the laser fibre tip while heat dissipation is minimal and comparable for both exposures. Compared with intermittent exposure, continuous exposure results in more carbonization, higher mean maximum intravascular temperature (128 +/- 7 vs. 75 +/- 4 degrees C), and long-lasting temperature of 100 degrees C (1.2 +/- 0.4 vs. 0.1 +/- 0.1 s). Conclusion: In this experimental study, application of endovenous laser shows to be dominated by carbonization at the fibre tip. Although intraluminal laser-induced heat was heterogeneously distributed, with laser tip temperatures up to 1200 degrees C, heat dissipation was minimal. Continuous exposure of laser light appears to be better suited in EVLA than intermittent.