Effect of CO2 laser on the luminal surface of blood vessels in vivo

Small-Caliber Arterial Anastomosis Using a CO2 Laser

The present study was designed to determine whether the use of CO2 laser irradiation could effectively maintain long-term patency in small-caliber arteri al anastomoses less than 3 mm in diameter. A preliminary study was conducted to examine the relationship between laser energy and histologic changes. The laser output of 30 to 40 mW produced a less inflammatory response, than 50 mW did and almost normal aortic architecture one month after the exposure. Therefore, a 30 to 40 mW range, over a twenty-second period, was seen as a suitable laser energy. Arterial anastomoses using a CO2 laser were performed (12 rabbits) with a suitable laser energy. Conventional anastomoses were per formed as controls (12 rabbits). The operation times, patency rate, and histo logic changes were compared in both groups at one week and at one, three, and six months after anastomoses. The anastomotic time was shorter in the laser anastomosis group than that in the control group. The patency rate was equal in both groups. However, the conventional anastomosis group revealed slight intimal hyperplasia at six months, whereas the laser anastomosis group showed almost normal neointimal development. It was hence concluded that CO2 laser welding of the anastomosis is an acceptable alternative to conventional anastomosis.

Carotid artery anastomosis with albumin solder and near infrared lasers: a comparative study

BACKGROUND AND OBJECTIVE

Laser tissue-welding has been used for anastomosis of carotid arteries. During welding, thermal injury sustained by the vessel walls should be minimized to prevent thrombosis. Two different types of lasers were used and effects on tissue damage were studied in vitro and in vivo.

STUDY DESIGN/MATERIALS AND METHODS

End-to-end anastomosis of dog carotid arteries (n = 10) was performed by using a human albumin solder (HAS) in conjunction with Nd:YAG or diode lasers (lambda = 1.32 microm and 1.9 microm, respectively). The arteries were evaluated for patency and evidence of histologic injury after 21 days. Another group of arteries was laser soldered in vitro to measure the intimal and adventitial temperatures by using thermocouples.

RESULTS

The arteries repaired with the diode laser sustained significantly less thermal damage than those repaired with Nd:YAG laser, both in vitro and in vivo. In particular, the intimal temperature was significantly lower (P < 0.05) for the diode than for the Nd:YAG repairs (approximately 35 degrees C and approximately 50 degrees C, respectively). In the latter group, the patency rate was 75%, but thrombosis occurred in 75% of the specimens at 21 days. All diode anastomoses were patent and thrombosis developed in only 17% of the arteries.

CONCLUSION

Use of the diode laser and albumin solders may provide a means to successfully repair carotid arteries with minimal thermal damage.

Neointimal hyperplasia following argon ion laser carotid endarterectomy: with and without endothelial cell seeding

BACKGROUND AND OBJECTIVE

This study compares the development of neointimal hyperplasia following conventional and argon ion laser carotid endarterectomy and assesses the potential advantage of endothelial cell seeding.

STUDY DESIGN/MATERIALS AND METHODS

Eight dogs underwent conventional endarterectomy in one carotid artery and an argon ion laser endarterectomy in the other. After 42 days, these arteries were harvested and the intimal thickness were compared. Six additional dogs underwent bilateral argon ion laser carotid endarterectomy with endothelial cell seeding on the one side only. These arteries were harvested after 65 days and their mean intimal thickness were compared.

RESULTS

At 42 days, the mean intimal thickness in the conventional endarterectomy group was 0.070 +/- 0.007 mm; in the argon ion laser endarterectomy group it was 0.058 +/- 0.001 mm (P = 0.76, NS). At 65 days, the mean intimal thickness in the group without endothelial cell seeding was 0.125 +/- 0.003 mm vs. 0.061 +/- 0.001 mm on the seeded side (P = 0.043).

CONCLUSION

Argon ion laser carotid endarterectomy results in no more neointimal hyperplasia than conventional endarterectomy. The neointimal hyperplasia is reduced by endothelial cell seeding.

Laser-induced stimulation of thromboxane B2 synthesis in human blood platelets: role of superoxide radicals

Exposure of platelet-rich plasma to laser radiation at 3.5 W for 30 seconds reduced the threshold concentrations of adenosine diphosphate and L-epinephrine needed from complete platelet aggregation by 20% to 60% and by 30% to 50%, respectively. The irradiation of platelet-rich plasma with laser also increased the basal level of thromboxane A2 from < 0.5 pmol/10(8) platelets for each second of exposure. In contrast, the exposure of gel-filtered platelets to laser produced no effect on the prostanoid formation. However, the addition of laser-exposed platelet-free plasma to gel-filtered platelets stimulated the synthesis of thromboxane A2 in these cells. The effect of laser was completely blocked by adding superoxide dismutase or catalase to the platelet-rich plasma, indicating that the radiation-induced stimulation of thromboxane A2 production was mediated through the generation of superoxide radicals. Electron microscopic studies indicated that the laser-induced stimulation of thromboxane A2 production in platelet can occur without any noticeable damage in the cellular structure.

Initial results of endothelial cell seeding following argon laser carotid endarterectomy

This study evaluates the initial results of endothelial cell (EC) seeding following argon laser carotid endarterectomy. Venous endothelial cells were harvested from 12 dogs and cultured. A laser endarterectomy was performed on both carotids of each dog. One side was seeded with endothelial cells. Six dogs had both carotids harvested 1 hour after restoring blood flow. The others were harvested in 24 hours. The percentage of lumen covered with EC was evaluated by scanning electron microscopy. At 1 hour, the seeded arteries demonstrated 35 +/- 3 percent EC coverage, whereas the unseeded arteries had no EC coverage (P = 0.0002). At 24 hours, the seeded arteries had 58 +/- 15 percent EC coverage, whereas the unseeded arteries had no coverage (P = 0.01). Significant gross thrombus developed only in unseeded arteries (P = 0.047), two of which were occluded at 24 hours. EC seeding is beneficial following argon laser carotid endarterectomy resulting in improved patency and less surface thrombogenicity.

The effects of laser energy on the arterial wall

Laser energy has been proposed as a method of resecting atherosclerotic plaque since the mid 1960s. However, only over the past several years have we come to understand some of the unique interactions of the laser with cardiovascular tissue. In laser angioplasty a major challenge has been choosing the optimal laser and duration of laser exposure to achieve adequate resection of plaque, while minimizing such complications as thrombosis, perforation, embolization, aneurysm formation, and accelerated atherosclerosis. Ultimately we must develop a more selective laser that resects plaque while leaving adjacent arterial wall uninjured. This review describes the physics of laser energy, the different lasers available for use in the cardiovascular system, laser-arterial wall interactions, and some of the limitations of laser angioplasty.

A fiberoptic compatible midinfrared laser with CO2 laser-like effect: application to atherosclerosis

In theory, pulses of laser light in the 2-microns range should ablate tissue in a manner similar to that of the 10.6-microns CO2 laser with the added advantage of efficient transmission through flexible quartz fibers. Using 200-microseconds pulses of 2.15-microns thulium-holmium-chromium:YAG (THC:YAG) laser light, we were able to create 700-microns-diameter holes through calcific atherosclerosis in vitro. In vivo evaluation of thrombogenicity and healing was accomplished by exposing the luminal surface of rabbit aortas to the THC:YAG laser. Serial histologic examinations of laser-treated rabbit aortae revealed a time course of resolution of the lesions which was very similar to that observed with like-sized lesions created with the same amount of continuous wave CO2 energy. No significant differences in thrombogenicity nor healing response were noted. The excellent in vivo response observed is due in part to the pulsed nature of the THC:YAG laser output as well as to the efficient tissue absorption at the 2.15-microns wavelength. We feel that excellent ablative effects with minimal collateral thermal damage can be obtained through fiberoptic delivery systems by taking advantage of laser wavelengths corresponding to the infrared absorption peak of water in the 2-microns region and pulsed delivery of the laser energy.

The CO2 laser as an intraluminal repair tool

The CO2 laser can weld vessels together and vaporize plaque. This study evaluates its use as an intraluminal reparative tool. In 17 dogs, a 1-cm circumferential intimectomy with a 1-mm distal intimal flap was performed in both carotids. In each dog, one carotid (CON, control) underwent suture flap repair. On the contralateral side (LR, laser repair), the flap was tacked with 20 250-mW 1-sec pulses and the denuded medium was g-lased for 90 sec (250 mW continuous). Animals were randomized into five groups and sacrificed on the day of surgery (Group I, n = 3), at 3 days (Group II, n = 3), at 1 week (Group III, n = 4), at 2 weeks (Group IV, n = 4), or at 4 weeks (Group V, n = 3). Vessel patencies were 88.2 and 82.4% for CON and LR, respectively. Flap repair appeared similar. No aneurysms were noted. Histology revealed a relative absence of platelet adherence to the g-lased surfaces in Groups I and II when compared to that of mechanical methods (CON). The ratio of the thickness of the regenerated surface to the total wall thickness demonstrated hyperplasia in LR vessels (0.54 +/- 0.12) when compared to that in CON (0.30 +/- 0.15) at 2 and 4 weeks (ANOVA, P less than 0.001). Coverage with endothelial-like cells appeared complete at 4 weeks in both methods. The CO2 laser can effectively repair intimal flaps. However, our results demonstrate a significant increase in medial hyperplasia following g-lasing even in the face of minimal early platelet adherence. This may prove detrimental to the long-term patency of intraluminal CO2 laser-treated vessels.

Effects of Nd:YAG laser energy on the arterial wall: evaluation of a new contact delivery system

Although there has been much recent interest in the application of lasers to arterial occlusive disease, a detailed understanding of the effects of laser energy on vessel walls is lacking. This study compared the effect of a conventional, non-contact delivery system of Nd:YAG laser energy to a contact system using a 600 microns, artificial sapphire tip in eight mongrel dogs. A small section of the luminal surface of the carotid and femoral arteries was exposed to 10 or 15 joules of Nd:YAG laser power and flow was restored in the vessel. The animals were sacrificed at 0, 1, 2, 4, 7, 14, 21, and 30 days and the vessels were removed. The surface area of the laser injury for each artery was quantitated by computerized planimetry and all histologic sections were examined under light microscopy by an independent observer. Transmural necrosis occurred in 64% (20/31) of the non-contact lesions versus only 29% (9/31) of the contact lesions (P less than 0.01). Both types of laser injuries followed a predictable course with initial medial necrosis followed by formation of a fibrin erythrocyte coagulum overlying the lesions at 24 hr. The usual zones of vaporization, coagulation necrosis, and thermal damage were noted with both types of delivery systems, but the contact system resulted in more intimal vaporization. Healing of all lesions was rapid with complete endothelial coverage at two weeks. Thrombosis occurred in only 1 of 32 (3%) arteries, and there were no false aneurysms. Contact delivery of Nd:YAG laser energy produces significantly less transmural injury than does non-contact.(ABSTRACT TRUNCATED AT 250 WORDS)

Laser endarterectomy: a comparison of thrombotic potential following CO2 laser vs surgical endarterectomy

Although laser endarterectomy has recently been suggested as useful in the treatment of arteriosclerotic obstructions, the "in vivo" clotting effects have not been well delineated. In this study, the common carotid and femoral arteries of ten mongrel dogs were exposed, and alternating 1 cm segments of each artery were treated with surgical endarterectomy and low-powered CO2 laser endarterectomy. Segments were then harvested, and subjected to histologic examination and vascular prostacyclin synthesis determinations, as measured by 6-keto PFG1a radioimmunoassay. Gross examination and light and scanning electron microscopy showed increased platelet aggregation and more extensive damaging of the underlying media of the laser compared to the surgical segments. Six-keto PFG1a levels were significantly lower (p = 0.001) in the laser compared to surgical sites (mean 232 +/- 72 pg/mg vs 515 +/- 144 pg/mg), or controls (895 +/- 337 pg/mg). These findings suggest that laser endothelial evaporation leads to increased thrombotic potential in the early post-operative period in comparison to surgical endarterectomy.

Microvascular anastomosis using the milliwatt CO2 laser

The milliwatt CO2 laser was used to anastomose small vessels in a rat femoral artery model. The technique requires multiple brief applications of 60-70 mW after placement of three equidistant 10-0 nylon stay sutures. The vessel histology is described immediately and 1, 3, 7, and 21 days after the procedure. The laser effects tissue bonding through changes in the collagen of the adventitia and media. Subsequent healing consists of new collagen deposition in the adventitia and reendothelialization of the intima associated with neointimal proliferation at 3 weeks.

Argon laser coagulation of blood for the anastomosis of small vessels

A new technique is introduced in which an argon laser coagulates blood to form an adherent sleeve for the anastomosis of small vessels. The argon laser solidifies the blood into a dark tensile substance which supports the site of repair until vascular continuity is achieved. Laser pulses of 0.75 W and 0.5 seconds exposure are used, and damage to the underlying vessel wall is minimal. A histological analysis is performed and the results are examined qualitatively. The technique shows advantages of speed, reduced vascular trauma, and external protection at the site of vascular repair.