Transformational features of the vein wall during a long-term period of endovenous laser ablation using 1910 nm laser radiation. Results of in-vivo experiments.

BACKGROUND: In this paper, results of in-vivo experiments on the animals of endovenous laser ablation (EVLA) using laser radiation with the wavelength 1910 nm are reported. The results of histological studies of the vein segments removed immediately after the procedure and in a long-term period (30 days and 3 months) are presented. Their structural transformation and the obliteration degree of the vein lumen using different values of the linear energy density of laser radiation (LEED=7.5; 15; 20 J/cm) are estimated. METHODS: Edilbay breed of sheep (males) were used as experimental animals. Laser radiation with a wavelength of λ=1910 nm and power of Рrad = 1.5, 3, 4 W was used for EVLA experiments, and speed of fiber traction (v) was 2 mm/s. 8 days after EVLA stitches and an elastic bandage were removed. Animals were observed for 3 months in the vivarium. Animals have duplex ultrasound scanning of coagulation veins under anesthesia, after analysis vein segments were excised for histological examination. As a result, the damage degree to the vein wall tissues (intima, media, adventitia) and peri-venous tissues was revealed. RESULTS: It is shown that in the long-time period, the intima and partial muscle layer transformed to connective tissue. EVLA using laser radiation with a higher value of LEED led to the growth of connective tissue, oedema of all vein layers and peri-venous tissue. The lumen closure occurred due to clot and the vein wall transformation, a maximum value was 25% using LEED=20 J/cm. CONCLUSIONS: The connective-tissue transformation of the coagulated vein occurs in a long-term period and more pronounced for higher LEED. However, features of vein hemodynamics of animals and differences between the clot formation process of human varicose veins and healthy animal veins lead to incomplete occlusion. These features should be taken into account during extrapolation results of experiments on animals in clinical practice.

Morphological changes of veins and perivenous tissues during endovenous laser coagulation using 2-µm laser radiation and various types of optical fibers.

OBJECTIVE: To determine the morphological changes in veins and perivenous tissues after endovenous laser coagulation (EVLC) using laser radiation with a wavelength of 1910 nm and different types of fibers (bare tip and radial). METHODS: The EVLC procedure was carried out on 22 surface veins of six sheep. The radiation source was a diode-pumped solid-state laser, which was based on a LiYF4:Tm crystal and had an emission wavelength of 1910 nm and a maximum output power of 10 W. Two types of optical fibers were used: (1) bare tip and (2) radial or radial with two rings. Histological and morphometric methods were used, and the statistical digital data were analyzed. RESULTS: The use of a linear endovenous energy density of 20 J/cm and optical bare fibers for veins with diameters of 3-4 mm resulted in a slit-shaped or wide venous wall perforation. A thermal effect was observed on the perivenous connective tissue (PVCT), which caused damage to its structures. Wide perforations were accompanied by complete destruction of the PVCT in the projection of the formed defect. The distance between the remaining vein wall fragment, located opposite to the perforation, and injured small vessels was 257.7 ± 23.6 µm. The radius of thermal damage increased to 2073.5 ± 8.0 µm near the vessel perforation. Using optical radial fibers for veins with diameters of 3.9 ± 0.5 mm did not lead to perforations. The destructive effect of the laser on small vessels of the PVCT extended to a distance of 425.7 ± 22.0 µm. CONCLUSIONS: Analysis of thermal vessel damage in perivenous tissue after EVLC with bare-tip fiber shows that in the projection of a wide perforation, the damaged vessels of the PVCT are located at a large distance from the coagulated vein wall. On the opposite side of the perforation, the distance from the coagulated vein wall to the damaged vessels of the PVCT is significantly reduced because of the minimal output of laser radiation energy through the poorly damaged part of the wall. Using an optical radial fiber facilitates the application of a uniform distribution of thermal energy to the vein wall and damage to all its layers; at the same time, it minimizes the thermal energy that extends beyond the vein wall and damages the surrounding tissue. CLINICAL RELEVANCE: The use of radiation with a wavelength of 1910 nm will make it possible to carry out endovenous laser coagulation of varicose veins at lower power values compared with radiation in the micron and one and a half micron regions of the spectrum. Understanding of morphological changes of veins and perivenous tissues after endovenous laser coagulation with 1910-nm laser radiation and different types of optical fibers (bare-tip, radial, radial 2ring) help predict possible complications and reduce their rate.

Optimization of endovenous laser coagulation: in vivo experiments.

Finding optimal parameters of endovenous laser coagulation using the radiation with a wavelength of 1910 nm. In vivo experiments have been carried out on the small saphenous veins of three sheep of Edilbay breed and the dependence of venous wall and surrounding tissue damage on the radiation power was analyzed on the basis of morphological study results, as well as ultrasound examination and clinical observation of animals in the postoperative period. As radiation source, we used the diode-pumped solid-state laser, based on the LiYF4:Tm crystal, with emission wavelength of 1910 nm. For morphological study, veins were harvested immediately and 40 days after operation. Histological analysis of the vein after treatment with 1.5-W radiation revealed asymmetric wall injury and a thrombus formation in the lumen. The blood thrombus formation and pronounced vein wall damage was observed after treatment with 3-W radiation. Perivenous tissue injury is insignificant and does not lead to postoperative complications as in the case of using 1.5-W radiation. Increasing the radiation power to 4 W results in the total vein wall destruction and the thrombus formation, which persists for 40 days after the procedure. Based on the results of clinical observations of animals with registration of skin wound healing, as well as the results of histological examination of veins harvested immediately after the EVLC and 40 days after, it was concluded that the laser power value of 3-4 W can be recommended for use in the clinic.