Lasers have been widely used in the field of medicine and surgery, and satisfactory results have been obtained in the several fields.

However, laser application are very rare in the field of cardiovascular surgery throughout the world. It has been reported for a long period that it is difficult to keep long-term patency after anastomosis of the conventional fashion with suture materials especially for small-caliber vessels. For 15 years, we have tried to perform aortocoronary bypasses in treating patients with ischemic heart disease. There are some problems about obtaining favorable surgical results by conventional suture method, especially in the cases with small-caliber branches of the coronary arteries. From this standpoint, a low energy CO₂ laser was used to perform coronary artery bypass grafting (CABG).

Adult mongrel dogs were used in this study. The femoral arteries and veins were gently exposed under general anesthesia. The relationship between output and irradiation time of a CO₂ laser was analyzed as well as tissue reaction to the laser in a preliminary experiment. If a laser output of 100mW continuously irradiated on the same point more than 10 seconds, swelling disruption and vaporization of the elastic fibers of the aorta could be found in proportion to the laser output (Figure 1) [1,2].

Figure 1: Laser energy and tissue reaction of the aorta.

However, there were no remarkable tissue reactions to a laser output of 40mW. From these preliminary experiments, it could be concluded that the optimal laser output was 20-40 mW and 6-12sec?mm for vascular anastomosis of small-caliber vessels in the extremities. Side-to-side, end-to-side, end-to-end anastomosis at the site of the femoral arteries and veins or the carotid arteries and veins were carried out using a low energy CO₂ laser (Figure 2,3). Diameter of these vessels ranged from 2 to 10mm with mean of 4mm. Stay suture of 5-0 monofilamentous suture material were anchored at the incided ends of the vessels and were located to hold tightly the rim of the vessels. The posterior wall of femoral artery and its vein was sutured in the conventional fashion using 5-0 suture materials and sites of anastomosed were microscopically examined as a control. The anterior wall was anastomosis by low energy CO₂ laser(20-40mW) for 6-12sec?mm.

Figure 2: Schematic illustration of laser vascular anastomosis.

Figure 3: Important points of anastomosis.

The focused laser beam was used and moved very slowly along the anastomotic line. The distance between stay suture was maintained at no more than 5mm. Vascular anastomosis has been routinely made by CO₂ by laser and just four stay sutures on the anstomotic line. After completion of anastomosis, intravascular angioscopy was carefully carried out to observe the inside of the anastomotic portion of the vessels of which anastomotic site by laser is wide open. Vascular anastomosis between the left internal mammary artery and the LAD (left anterior descending artery) could also be performed by laser under the heart beating (Figure 4).

Figure 4: Laser vascular anastomosis between the left mammary artery and LAD (left anterior descending).

Pressure tolerance test and tensile strength test as well as histological examinations were also studied to evaluate the intensity of the laser anastomotic site of the vessels.

The number of vascular anastomosis (side-to-side, side-to-end, end-to-end) reached to 75 anastomoses. Bleeding from the anastomotic sites was found at only 3 points among 75 anastomotic sites. However, it stopped on light compression by gauze on the anastomotic line. Observation periods ranged from 6 hours to 2.5 months. There were no death caused by bleeding from vascular anastomosis and operative procedure. Anastomotic sites were picked out for histological examinations which were patent macroscopically at the time of exstirpation. Patency was also confirmrd by angiogram and pressure tolerance test, or tensile strength test at the anastomotic sites were prudently performed after surgery.

Pressure Tolerance Test

Noradrenaline was given intravenously to maintain high pressure after completion of vascular anastomosis by laser. However, there were no hemorrhages from the sites of anastomosis was effective enough for the site to tolerance high pressure without bleeding (Figure 5).

Figure 5: Pressure tolerance test.

Tensile Strength Test

Intensity of site of laser, or suture vascular anastomosis was examined by weighing. Subsequently, the laser anastomotic sites with only four stay sutures were separated in weights 1.034±103g.

Figure 6: Tensile strength test.

Histological Findings

The sites of vascular anastomosis were microscopically studied after several time of intervals. A thinned fibrous membrane was observed microscopically on the adventitia of the vessels already 6 hours after laser surgery. However, thickened fibrous membrane and proliferation of fibroblasts were recognized at the adventitia and the media of the vessels except for the intimal layer, 1week after laser anastomosis (Figure 7).

Figure 7: Hisrological findings of one week after laser Anastomosis.

Furthermore, all layers of the artery and its vein were sufficiently connected by a lot of collagen fibers 2.5months after laser anastomosis (Figure 8). Thus, good healing of sites of laser anastomosis were clearly observed histologically [5,6].

Figure 8: Histological findings of chronic stage (2.5 months) After anastomosis.

On the contrary, the suture anastomotic sites were also examined microscopically in detail. Subsequently, many giant cells as well as the infiltration of several types of cells in their early stages and marked granulations in the chronic stage were clearly observed around the suture materials. The technique of laser vascular anastomosis was very easy and good results could be obtained in hemodynamic and histological findings in comparison with conventional anastomosis using suture materials. From these favorable findings it was considered that vascular anastomosis by low energy CO₂ laser might be recommended in clinical application.

On the basis of excellent experimental results laser vascular anastomosis was employed in 111 patients with anginal, or chronic renal failure and peripheral vascular disorders (Table 1) [7,8].

Table 1: Clinical experience of laser vascular anastomosis.

Tissue Reaction of Low Energy CO₂ Laser

The diameter of arteries and veins in the extremities were no more than 10mm and the wall thickness was very thin less than 1mm. In vascular anastomosis of these vessels optimal laser output was 20-40mW and irradiation time was 6-12sec/mm. Laser beams did not reach the intimal layer in these conditions. If the output was over 50mW, a marked tissue reaction could be found such as swelling, carbonization and vaporization proportional to the irradiation time. Focused beam was convenient for making fine anastomosis on small-caliber vessels [11,12].

Important Factors in CO₂ Laser Vascular Anastomosis

There were two important points in carrying out vascular anastomosis. One of them was to close the rim of the vessels tight with some fine stay sutures. The distance between stay sutures must be less than 5mm. Another one was focus the beam on the anastomotic line. At this time the beam should be moved very slowly and repeated . Irradiation should be continued until the color along the anastomotic line changes to dark gray, or dark brown.

Intensity of the Site of Anastomosis

There is a long-term history of safety in performing vascular anastomosis with sutures. For anastomosis using many suture materials, especially for small-caliber vessels, there are some problems in their patency over the long-term period. From these standpoints a low energy CO₂ laser was employed for vascular anastomosis. Pressure tolerance was carefully tested to evaluate intensity at the site of laser anastomosis. However, no hemorrhage was observed even at the high pressure of 300mmHg. On the contrary, laser anastomotic sites were also tested for tensile strength test. However, there were no significant differences between conventional suture method and laser anastomosis. Thus, no intensity problems could be found with laser anastomosis [13,14].

Mechanism of Vascular Anastomosis by CO₂ Laser

Based on histological examinations, fibrous membrane, proliferation of fibroblasts and collagen fibers on the anastomotic line were observed by laser, as the time went on. Good healings were obviously recognized microscopically. The reason for the healing of the anastomosis site is not now clearly recognized. It is supposed that collagen fiber as well as protein components of the tissue may be changed from a sol like a paste by laser thermal energy.

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