Re-endothelialization of microvascular carotid end-to-side anastomosis in the rat

Prevention of anastomotic thrombosis by botulinum toxin B after acute injury in a rat model

PURPOSE

Revascularized or replanted digits may fail because of vessel thrombosis. Off-label use of botulinum toxin type A injected subcutaneously has been used successfully in limited case series to treat vasospastic disorders. Botulinum toxin type B (BTX-B) is thought to have an earlier onset of action than type A in certain settings. We used a rat model to determine the ability of BTX-B to decrease vasospasm and prevent thrombosis after acute vessel division and anastomotic repair.

METHODS

We transected and immediately repaired the bilateral femoral arteries and veins of 25 rats via microscopic technique. We measured each vessel's diameter before transection. Each rat had 1 leg randomly assigned to receive BTX-B; the contralateral side received normal saline. We separated the animals into 5 groups. Each group underwent vasospastic stress at a different time point (12, 24, 48, 72, and 120 h) after the anastomoses and treatment with BTX-B or saline. Vasospastic stress included a lower extremity cold temperature challenge and systemic treatment with phenylephrine. After vasospastic stress, we reopened the wounds and recorded vessel thrombosis and diameter.

RESULTS

Vessel thrombosis rate was lower in the BTX-B-treated group of vessels compared with those receiving placebo. Thrombosis rate was 8% for BTX-B-treated arteries versus 68% for saline-treated arteries. Thrombosis rate was 20% for BTX-B-treated veins versus 76% for saline-treated veins. Overall vessel thrombosis rate was significantly lower for BTX-B at all time points except at 120 hours when no thrombotic events occurred for either group. Average increase in diameter for BTX-B-treated vessels was significantly greater than that for the controls regardless of patency.

CONCLUSIONS

BTX-B prevented or reduced the incidence of thrombosis after acute vessel anastomosis in this rat model at all time points less than 120 hours compared with placebo. The average final vessel diameter throughout the series of BTX-B-treated vessels was significantly larger than in the control group.

CLINICAL RELEVANCE

The use of BTX-B may improve the success rate of microvascular anastomoses by being protective against vasospastic stress and subsequent thrombosis.

Anastomosis with fish-mouth technique using fibrin glue

Researchers have made numerous attempts to shorten anastomosis duration since Jacobson first used the term microvascular surgery in 1960. However, none of these alternatives has its combination of facility, low cost, reliability, durability, and high success rate. This study aimed to shorten the anastomosis duration, especially in operations that require multiple anastomoses, and the authors performed experimental anastomoses with the fish-mouth technique using fibrin glue. This technique first involves 2 longitudinal incisions made 180 degrees apart in the shape of a fish mouth at each vessel end, thus creating a pair of equal-sized, full-thickness flaps on both vessels. These incisions, equal in length, were as long as the radius of the vessel. Two simple stay-sutures placed on the corners of the flap bases and vessels were approximated. Then, the anastomosis site was sealed with fibrin glue. Both control and experimental groups are consisted of 32 rats. This study assessed and statistically evaluated the groups with biopsies on days 3, 7, 14, and 21 and also assessed patency rates, microaneurysm formation, histologic healing patterns, and operation duration. The present study concluded that anastomosis with fish-mouth technique using fibrin glue takes less time, requires fewer sutures, decreases the amount of foreign materials in direct contact with the blood stream, creates less foreign-body reaction in the vessel wall, and everts contact surfaces. With these advantages, this technique provides a reliable and successful alternative, especially in operations requiring multiple anastomoses.

Long-term reendothelialization of excimer laser—assisted nonocclusive anastomoses compared with conventionally sutured anastomoses in pigs

Object. In contrast to conventional anastomosis methods, the excimer laser—assisted nonocclusive anastomosis (ELANA) technique involves a platinum ring and intima—adventitia apposition with a rim of medial and adventitial layers exposed to the bloodstream. The authors assessed the reendothelialization of porcine carotid arteries through ELANA compared with conventional anastomosis by using scanning electron microscopy.

Methods. In 28 pigs a bypass with one ELANA and one conventional anastomosis was made on the left common carotid artery. All patent anastomoses were evaluated intraoperatively with the aid of an ultrasonographic flowmeter and postoperatively by using scanning electron microscopy at 2 weeks, 2 months, 3 months, and 6 months thereafter. Twenty-four of 28 bypasses (48 of 56 end-to-side anastomoses) were fully patent at the time of evaluation. On scanning electron microscopic evaluation of the bypasses, all 48 patent anastomoses showed complete reendothelialization, including all 24 ELANAs in which the endothelium covered the rim and the laser-ablated edge completely. No endothelial difference was observed between conventional anastomoses and ELANAs, aside from the obvious anatomical differences like the platinum ring, which had been completely covered with endothelium. At 6 months postsurgery, remodeling of the ELANA was observed, leaving the ring covered with a layer of endothelium as the most narrow part of the anastomosis.

Conclusions. In long-term experiments, ELANA allows reendothelialization comparable to that achieved with conventional anastomosis. Considering its nonocclusive and high-flow characteristics, the ELANA technique is preferable in cerebral revascularization procedures.

Experimental animal studies of clip-induced microvascular trauma

This study was designed to evaluate microvascular clip potential for causing changes in vessel-wall tissue and the extent to which this potential is influenced by features of the clip. Light and scanning electron microscopy were used to examine vessel-wall changes after temporary clip occlusion. Vessel patency is shown to be influenced by anastomosis and clip site, changes in occlusion force due to material fatigue are described, and novel clip features to reduce vessel trauma are proposed. Evaluation of mechanical clip properties showed that material fatigue does not lead to relevant loss of precision in alpha-type clips. While the modified clip designed to reduce trauma cannot abolish trauma altogether, it significantly reduces the associated changes and hence the risk of thrombosis. Arteries were more sensitive than veins to clip-induced trauma, with increased occlusion force producing more severe damage than increased clipping time. Maximal changes were seen in the tunica media. These results indicate the paramount importance of applying modest clip pressure commensurate with the requirements of microvascular Surgery.

Comparative study of the efficacy of the common topical hemostatic agents with fibrin sealant in a rabbit aortic anastomosis model

OBJECTIVE

The purpose of this study was to compare the hemostatic efficacy of the common surgical hemostatic agents with fibrin sealant (FS) and to assess their functional strength to secure hemostasis in lieu of placing additional sutures.

METHODS

End-to-end anastomosis of transected abdominal aorta was performed in moderately anticoagulated rabbits using 4 or 6 interrupted sutures. The suture line was covered either with gauze alone ("untreated") or with gauze plus Gelfoam, Avitene, Surgicel, FloSeal, or FS, following which blood flow was restored. Blood loss was absorbed by gauze and measured. The surviving rabbits were recovered and the repaired vessel was examined histologically 4 weeks after operation. The investigators were blinded to the treatment groups. Aortic anastomoses using 8 or 12 sutures (untreated) were also performed.

RESULTS

Untreated 4-suture anastomosis of aorta resulted in a profuse hemorrhage with an average 108.0 +/- 19.2 (mean +/- SD) ml blood loss and 100% mortality (n = 4). FS application sealed the anastomoses, prevented blood loss (P < 0.01 vs untreated) and exsanguination of the rabbits (n = 4). Other hemostatic agents reduced the bleeding to varying degrees compared to the untreated animals (Gelfoam 66.4 +/- 17.6, Avitene 80.6 +/- 34, Surgicel 66.7 +/- 16.7, FloSeal 44.2 +/- 8.5 ml blood loss, n = 4/group), but the changes were not statistically significant. One to three rabbits in each group survived the operation. Six-suture aortic anastomoses, untreated, resulted in 67.7 +/- 21.8 ml blood loss and 100% survival (n = 6). Application of FS produced immediate and sustained hemostasis in all the animals (P < 0.01 vs untreated). Other hemostatic agents also reduced the bleeding (Gelfoam 42.5 +/- 10, Avitene 50.9 +/- 12.4, Surgicel 32.1 +/- 14, FloSeal 33.9 +/- 5.4 ml blood loss, n = 6/group), but the changes were not statistically significant. The 8- and 12-suture aorta repairs resulted in a moderate blood loss (43.9 +/- 19 and 21.3 +/- 14.9 ml, respectively), followed by a stable hemostasis that precluded the need to use any hemostatic agent. The aortic cross-clamping time of the 12-suture and time to hemostasis for both the 8- and the 12-suture techniques were significantly longer than those of the 4-suture plus FS application (P < 0.01, P < 0.01 and P < 0.05, respectively).

CONCLUSION

In a moderate coagulopathy, FS was proven to be the most efficacious hemostatic agent, producing immediate and sustained hemostasis at the arterial anastomotic site. This high efficacy is in part attributed to the strong tissue adhesive property of this agent. FS application may potentially ease the anastomosis and shorten the duration of timely critical vascular procedures.

The modification of the new type of end-to-side anastomosis between carotid arteries in rats: a technical and scanning electron microscopic study

Modification of a type of end-to-side anastomosis that has been described before is studied. The recipient artery is occluded for only 3-4 minutes to complete the anastomosis by using only the running suture. The anastomotic site was studied by inspection and Scanning Electron Microscope (SEM) at different times after the operation on 30 rats.

Re-endothelialisation in autogenous vein grafts

OBJECTIVES

To clarify the course of re-endothelialisation (Re-E) in an entire graft and to establish the effect of immersion media for the preservation of endothelial cells.

METHODS

Autogenous femoral veins of dogs were immersed in heparinised saline solution (n = 18) or heparinized autogenous blood (n = 18). After immersion, the grafts were implanted into bilateral femoral artery, and were retrieved 1 day to 4-8 weeks after implantation.

RESULTS

For the grafts immersed in the heparinised saline solution, the values for % area of endothelial cell coverage before implantation, and at 1 day, 1 week, and 4 weeks after implantation were 44.9%, 6.2%, 14.5%, and 81.3%, respectively. For the grafts immersed in heparinised autogenous blood, the values were 73.5%, 20.6%, 79.2% and 95.5%, respectively. However, such relatively rapid speed of Re-E slowed down considerably after 1 week following implantation in this group.

CONCLUSIONS

The use of heparinized autogenous blood is strongly recommended as a preparation media for autogenous vein grafts. Almost all of the endothelial cells fall away in the earlier period after implantation and regenerate multifocally and irregularly. Re-E is incomplete even at 8 weeks after surgery, and we suggest that the area of incomplete Re-E may develop into intimal hyperplasia.

Use of fibrin glue to minimize bleeding of microvascular repairs in hypertensive rats

The purpose of this study is to describe our technique of applying fibrin glue at the microvascular anastomotic site and to evaluate the effect of fibrin glue on anastomotic hemostasis and patency under various high pressure states using dopamine-induced acute hypertension in rats. A total of 72 male Wistar Kyoto rats, 10 weeks old, were used in this study. Under urethane anesthesia, end-to-end anastomosis of the left femoral artery was performed using 10-0 nylon suture by the standard interrupted suture technique. Pasteurized fibrin glue was then topically applied upon the suture line of the anastomosis. Thirty-six normotensive rats were divided into three groups based on the number of sutures (4, 6, or 8) used to complete the anastomosis. Groups were subdivided, half receiving fibrin glue application and half without. Thirty-six dopamine-induced acutely hypertensive rats were divided into three groups based on the blood pressure levels of 150, 200, and 250 mmHg, respectively. These groups were again subdivided, with half receiving glue applications. Microvascular anastomosis was performed using 6 nylon sutures. Patency rates and anastomotic bleeding were evaluated. The results revealed that successful anastomoses could be performed with fewer sutures when fibrin glue was used as a reinforcement at the anastomosis. Fibrin glue was also effective at the maximum blood pressure (250 mmHg) with no anastomotic leakage and no decrease in postoperative patency rate. These results suggest that conventional microsurgical suturing technique combined with fibrin glue would be effective in the prevention of leakage in microsurgical repairs, even under conditions of high blood pressure.

A scanning electron microscopic study of arterial endothelial repair under turbulent flow conditions

In order to study the role of hemodynamic factors on the healing and native morphology of endothelium in vivo, turbulent arterial flow was created using a loop bypass model, with and without occlusion in the recipient vessel. In this model, several different patterns of turbulent arterial blood flow resulted. The scanning electron microscope (SEM) was used to evaluate endothelial morphology in the area of the anastomoses at 3 and 14 days post-operatively. Morphological changes in the native endothelium along the recipient vessel correlated well with the direction of blood flow and predicted patterns of turbulence. The morphology of the native endothelium was altered to reflect the direction and pattern (laminar versus turbulent) of blood flow by 3 days postoperatively. Based on endothelial morphology, very narrow zones of separation could be demonstrated between areas of laminar and turbulent blood flow. The degree of reendothelialization across the suture itself was greatly variable at 3 days and there seemed to be no relationship to the location of turbulent flow.

Wound healing at the site of microvascular anastomosis: fibrin-stabilizing factor XIII administration and its effects

Factor XIII has recently been recognized to play an important role as a fibrin-stabilizing factor to accelerate the wound healing process. We made an attempt to analyze the effect of how Factor XIII affects the results of the healing process at the site of a microvascular anastomosis. The strong fibrin stabilizing property of plasma Factor XIII maintained its high activity when administered intravenously and was effective for wound healing in a low-activity state made by subcutaneous administration of carbon tetrachloride. The enhanced network formation of the Factor-XIII-injected group was indicated by the accelerated maturation of the fibrin structure at the anastomotic site, exhibited both qualitatively and quantitatively. Stimulation and acceleration by Factor XIII of the healing process at the site of microvascular anastomosis were observed. It is therefore suggested that clinical use of Factor XIII may enhance the microvascular repair process. Details of the analysis using scanning electron microscopy (SEM) and a computerized graphic analyzer system (CGAS) are reported.

Re-endothelialization stages at the microvascular anastomosis

After microsurgical suturing, the wound healing process at the rat femoral artery anastomosis was studied with scanning electron microscopy. The re-endothelialization was divided into four successive stages, based on the development of a fibrin network and the rate of endothelial regrowth. Within 5 minutes of blood flow re-establishment the fibrin network formation started to cover the wound surface; it was completed by the 3rd or 4th day. The endothelial recovery started on the 2nd day and continued to the base of the suture by the 6th day. Re-endothelialization from the wound edge, which was formed between intact and injured endothelium toward the suture-restrained site, was a two-fold process: initially, a single endothelial film covered the anastomosis site, then, the singled endothelial sheet proliferated and thickened to complete the endothelialization. A better understanding of the stages involved in microvascular repair is beneficial in evaluating vascular recovery and its relationship to patency rates in microvascular surgery.

Effect of hypertension on small-vessel healing after microvascular anastomosis

Artery-to-artery microvascular anastomosis (MVA) has become an established therapeutic alternative for patients with giant intracranial aneurysms and other forms of cerebrovascular disease. Many patients afflicted with cerebrovascular disease also suffer from hypertension. To evaluate the effect of hypertension on healing of small arteries following MVA, 36 spontaneously hypertensive rats were subjected to end-to-side MVA of their common carotid arteries. At specific times after surgery the rats were sacrificed; the anastomotic site was removed and examined with light microscopy and scanning electron microscopy. All MVA's were patent, and there was no evidence of thrombus formation or stenosis at the operative site in any group. Also, there was no difference between the spontaneously hypertensive rats and the control normotensive rat group in the rate of endothelial coverage of the MVA. The presence of hypertension appears to have no effect on healing of small arteries in the rat.

Ultrastructural study of arterial wall repair after argon laser micro-anastomosis

A carotid end-to-end anastomosis was performed in 50 Wistar rats by means of a Coherent 900 argon laser. The vessel sealing was obtained with laser shots (average 19) of 300 mW power and 5-second duration, the beam being focused in a spot of 150 micron diameter (1,700 W/cm2). From day 0 to day 120, 25 specimens underwent semithin and electron microscopic examinations. The results showed the immediate sealing effect of the argon laser owing to protein denaturation and collagen fusion of the media and adventitia 100 micron in width. Re-endothelialization of the anastomotic line began by day 3, while myofibroblast proliferation was observed in the media by day 10. By day 20 media scar was still occupied by numerous myofibroblasts and surrounded by abundant collagen and elastic fibres. At long term the endothelial repair was complete and the anastomotic strength was assured by medial collagenous network.

Microvascular anastomosis in spontaneously hypertensive and stroke-prone rats

Carotid end-to-end microvascular anastomoses (MVA) were performed in 100 rats [50 spontaneously hypertensive (SHR); 30 spontaneously hypertensive stroke-prone (SHR-SP); and 20 normotensive controls (WKY)]. Animals were sacrificed at various intervals from immediately after anastomosis to 60 days after surgery, and vascular healing was studied with the scanning electron microscope. In this manner vascular healing in normotensive rats (WKY) could be compared with that in hypertensive rats (SHR and SHR-SP) with vascular disease. Results of this study suggest that vascular healing in hypertensive rats is delayed when compared with normotensive controls. Furthermore, suture material was occasionally incompletely endothelialized in hypertensive animals as long as 60 days after surgery and served as a potential source of emboli. Additionally, an increased susceptibility of hypertensive endothelium (SHR and SHR-SP) to clamp and needle injury was apparent. In spite of this, there was a 100% patency rate of all anastomoses performed, indicating that patency, per se, is unaffected by hypertensive vasculopathy.

Endothelialization following end-to-end and end-in-end (sleeve) microarterial anastomoses. A scanning electron microscopic study

Eighteen microvascular end-to-end and eighteen end-in-end anastomoses were performed on the central arteries (diameters 0.8-1.2 mm) of rabbit ears. Specimens taken after intervals of 1-2 hours and 3, 7, 14, 30 and 90 days were studied using a scanning electron microscope. At 1-2 hours platelets and to a minor extent erythrocytes and fibrin had accumulated in defects between the vessel ends on sutures and at the suture holes of all end-to-end anastomoses. This had also occurred at the distal end of the telescoped segment in all end-in-end anastomoses. At 3 days endothelial desquamation at anastomotic sites and clamp sites was found in both end-to-end and end-in-end anastomoses. The exposed subendothelial surface was covered with a carpet of platelets, and frequently numerous leucocytes were found. Between 3 and 7 days, new endothelial cells appeared at the junction between the vessels in end-to-end anastomoses and in all areas damaged by vascular clamps. At the ends of the sleeved segments reendothelialization was observed over platelet aggregates. Between 7 and 14 days neo-endothelialization seemed to be virtually completed in both types of anastomosis. In the vicinity of the anastomoses, the appearance of the new endothelium was frequently abnormal with irregularly formed cells. Characteristic clefts and holes were seen between these abnormal (pleomorphic) endothelial cells. Histological findings from the same vessel specimens show that areas with abnormal endothelialization correspond to segments with intimal hyperplasia. Such areas were found in specimens throughout the entire period studied.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of heparin reversal after carotid endarterectomy in the dog. A scanning electron microscopy study

The purpose of this study was to determine reversal of heparin, immediately after carotid endarterectomy would have an adverse effect on the thrombogenicity of the endarterectomized vessel wall. After systemic heparinization, unilateral common carotid endarterectomies were performed under the operating microscope on 14 dogs. Half of the animals were given protamine sulfate to reverse the heparin. Three hours after resumption of blood flow, these arteries, as well as contralateral vessels used as controls for fixation technique, were perfused with glutaraldehyde and prepared for scanning electron microscopy (SEM). Thrombin clotting times were measured throughout the experiments. Sections of the endarterectomized portions viewed by SEM showed nearly total coverage of the exposed collagen of the media with flattened platelets. There were scattered leukocytes, but few erythrocytes, little fibrin, and no true thrombus. There were no difference between the animals that received heparin reversal and those that did not. A group of five additional arteries underwent the same procedure except that no heparin was given. As expected, large amount of thrombus had formed within the lumina of these control vessels by 3 hours. Since previous studies suggest that arterial thrombosis usually occurs within 3 hours of endothelial injury, the authors conclude that total reversal of heparin does not increase thrombogenicity of the endarterectomized vessel. This suggests that heparin may be safely reversed in patients to help maintain postoperative hemostasis.

SEM evaluation of endothelial changes following end-to-side microvascular anastomoses in rats

A scanning electron microscopic (SEM) study was carried out to evaluate the endothelial changes in carotid end-to-side microsurgical anastomoses. This procedure, associated with occlusion of the brachiocephalic trunk, was performed in 24 Sprague-Dawley rats. The animals were sacrificed at time intervals ranging between 15 minutes and 14 days after surgery. The specimens were collected after perfusion-fixation in vivo and treated for SEM observations. The findings show that the first 45 minutes are the most critical time for thrombus formation. Reendothelialization could be detected at 3 days after the microsurgical procedure. Endothelial regeneration occurred earlier on the suture line than on the stitches, documented by the migration and morphological changes of the endothelial cells advancing from the normal endothelium to cover the defect and the suture material. The repair was usually completed within 14 days. Damage of the inner vascular wall, related to minor failures of the microsurgical technique, appears to be a cause of delayed reendothelialization.

Sutureless microvascular anastomosis using a neodymium-yag laser

A technique is described in which a Neodymium-YAG laser is used to anastomose arteries 0.8 to 1.0 mm in diameter. Heat generated by the laser causes fusion of the collagen of the media, making direct handling of the vessel wall unnecessary. Four variations of the technique were performed in 120 rat carotid arteries. Angiographic and scanning electron microscopic studies were carried out immediately after surgery and at intervals of 1 day to 6 months after anastomosis. Patency rates as high as 92.5% were recorded. The technique that produced the most secure anastomosis was considered to be one in which a vascular strut was used as an aid in apposition, followed by the application of a piece of vein wall to the anastomosis with tissue adhesive. The main advantages of the laser technique are speed and consistency. Complications such as disruption and aneurysm formation are considered to be rare.