Heat conduction from the exceedingly hot fiber tip contributes to the endovenous laser ablation of varicose veins

Abstract

Lower-extremity venous insufficiency is a common condition, associated with considerable health care costs. Endovenous laser ablation is increasingly used as therapy, but its mechanism of action is insufficiently understood. Here, direct absorption of the laser light, collapsing steam bubbles and direct fiber-wall contact have all been mentioned as contributing mechanisms. Because fiber tips have reported temperatures of 800-1,300°C during endovenous laser ablation, we sought to assess whether heat conduction from the hot tip could cause irreversible thermal injury to the venous wall. We approximated the hot fiber tip as a sphere with diameter equal to the fiber diameter, having a steady state temperature of 800°C or 1,000°C. We computed venous wall temperatures due to heat conduction from this hot sphere, varying the pullback velocity of the fiber and the diameter of the vein. Venous wall temperatures corresponding to irreversible injury resulted for a 3 mm diameter vein and pullback velocities <3 mm/s but not for 5 mm and ≥1 mm/s. The highest wall temperature corresponded to the position on the wall closest to the fiber tip, hence it moves longitudinally in parallel with the moving fiber tip. We concluded that heat conduction from the hot fiber tip is a contributing mechanism in endovenous laser ablation.

Resultados de médio e longo prazo do tratamento endovenoso de varizes com laser de diodo em 1940 nm: análise crítica e considerações técnicas

“…Only administration of a relatively high energy per unit of length results in sufficiently high temperatures to cause denaturing of collagen. 33 During endovenous laser ablation, intraluminal temperatures can rise to over 100ºC, 28,[34][35][36][37][38][39] and these temperature profiles are independent of wavelength, i.e. use of different wavelengths does not influence the endovenous temperature profile.…”

“…33 Since the coefficient of molar extinction is similar for water and blood, when a laser with a wavelength of 1470nm or 1940nm is used, it is important to empty the vein of intraluminal blood, 33 because otherwise the majority of the energy will be absorbed by the intraluminal blood, leading to thrombotic occlusion and possible recanalization after a few months. 27,33,37,38 This statement is based on a study by Vuylsteke et al, 33,40 that assessed the role played by blood in the results of endovenous treatment with a 1500nm laser, histologically evaluating the degree of destruction of the vein wall. The study concluded that the volume of intraluminal blood results in a reduction of vein wall destruction.…”

Is a vein filled with blood a good model for studying endovenous laser ablation?

“…The formation of these steam bubbles has been confirmed by Proebstle et al [9] who have observed that they were generated in hemolytic blood by 810, 940, and 980 nm diode lasers, whereas no bubbles were produced in normal saline or plasma However, this mechanism is now considered of secondary importance for EVLA efficacy [1].…”

“…Several experimental studies were recently published in order to give a better understanding on the mechanism of action of endovenous laser ablation (EVLA) [1][2][3][4]. The experimental model is usually a human vein segment filled with heparinised blood [1,2].…”

“…The experimental model is usually a human vein segment filled with heparinised blood [1,2]. Another experimental model (hind limb of freshly slaughtered cows) has been proposed by Schmedt et al [3,4].…”