Ann Thorac Surg 1999;67:85-88
© 1999 The Society of Thoracic Surgeons
Original Articles
Favorable scanning electron microscopic findings of stapled saphenous vein–carotid artery anastomoses
Mohammad Bashar Izzat, FRCS(CTh)a,
Anthony P.C. Yim, MDa,
Kenny C.H. Ho, BVMa,
Carmen S.Y. Chan, BHSca,
David Yew, PhDb,
Louis T.C. Chow, FRCPathc
a Surgery, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong
b Anatomy, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong
c Pathology, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong
Accepted for publication June 17, 1998.
Address reprint requests to Dr Izzat, P.O. Box 33831, Rowda, Damascus, Syria
e-mail: izzat{at}cyberia.net.lb
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Abstract
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Background. In the progress toward "off-pump" endoscopic coronary artery surgical procedures, new techniques for coronary artery anastomoses are being developed. One such approach is the use of nonpenetrating titanium clips. We evaluated the quality of anastomoses achieved using this technique in a porcine model of saphenous vein–carotid artery grafting using scanning electron microscopy.
Methods. Bilateral saphenous vein–carotid artery interposition grafts were implanted in 10 "white race" pigs, using the nonpenetrating clips in one side of the neck and conventional hand suturing on the opposite side. One week after operation, the grafts were harvested.
Results. All grafts were patent 7 days after operation, and 40 anastomoses underwent scanning electron microscopic study. In all samples, the luminal surfaces of both the carotid artery and vein graft were covered by a continuous layer of endothelial cells up to the anastomosis. Anastomotic sites in all clipped samples and most of the sutured anastomoses were completely endothelialized, and anastomotic clefts were indistinguishable. However, in 25% of sutured specimens, the suture material remained clearly visible inside the lumen of the vessel, and the subendothelial matrix remained exposed, with extensive fibrin, red blood cells, and platelet deposition on its surface.
Conclusions. Because the endothelial coverage consistently appeared to be complete and the subendothelial matrix was not exposed, it is likely that the risk of early anastomotic thrombosis is reduced by using the nonpenetrating titanium clips.
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Introduction
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Efforts to develop less invasive approaches to coronary artery operations have gained substantial interest in the past 2 years [1]. Yet, the ultimate minimally invasive coronary artery operation (ie, totally endoscopic complete revascularization without cardiopulmonary bypass) remains far from reach because of several technical difficulties [2, 3], the principal of which is the accuracy of the coronary anastomosis made difficult by the constant motion of the coronary artery during cardiac cycles. A variety of techniques that aim at reducing movements of the coronary artery have been described, with some success [4, 5]. An alternative, and perhaps more realistic, approach to overcome this obstacle is to abandon the tedious and demanding endoscopic suturing technique, hence the recent surge of interest in alternative vascular anastomosis methods, such as stapling, clipping, and coupling [6].
One technique consists of the application of arcuate-legged, nonpenetrating titanium clips in an interrupted fashion to the everted tissue edges (VCS; Autosuture, Norwalk, CT). Although recent studies have demonstrated that this method is practically suitable for performing coronary anastomoses on the beating heart, concern remains about the success of anastomoses performed with this device. In the present study, we evaluated the quality of vein–artery anastomoses performed with the VCS clips in comparison to conventional suturing, using an established porcine model of saphenous vein–carotid artery grafting.
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Material and methods
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Surgical technique
Studies were performed with 10 "white race" pigs (weighing 25 to 30 kg), all of which received humane care according to the Home Office Animals (Scientific Procedures) Act 1986, UK (HMSO 1990). Animals were subjected to premedication, anesthesia, and autologous saphenous vein–common carotid artery bypass grafting by a modification of the method described previously [7]. Briefly, segments of saphenous vein were dissected, rinsed in isoosmotic sodium chloride solution (9 g/L) containing 2 IU/mL of heparin and 50 µg/mL of glyceryl trinitrate, and stored, without distension, in the same solution at room temperature (23°C) until needed. Both common carotid arteries of the pig were exposed. A 3-cm segment of each artery was removed and replaced with a segment of saphenous vein cut sufficiently to allow implantation without longitudinal stretching. Anastomoses were conducted end to end with reversed vein, beveled at a 45° angle. In each animal, anastomoses were performed using continuous 7-0 Prolene sutures (Ethicon, Edinburgh, UK) on one side of the neck, and using the VCS medium-sized clips on the opposite side. For clipped anastomoses, eversion and approximation of vessel walls for intima–intima apposition was accomplished with specially designed everting forceps, and clips were singly applied. The order of implantation and the use of the distal or proximal portions of the veins for sutured and clipped grafts were randomized between pigs.
Animals were allowed to recover and fed a normal chow diet, but no form of anticoagulation was given. One week after operation, each animal was anesthetized as before. The neck wound was opened, and the graft was identified and gently dissected from the surrounding tissues. The carotid artery was transected distal to the graft, and the presence of blood flow was taken to indicate graft patency.
Laboratory and scanning electron microscopy techniques
Each graft was removed, including a 2-cm segment of the proximal and distal carotid arteries at each end. The proximal carotid segment was cannulated with a syringe attached to a mercury manometer; the distal carotid segment was also cannulated, and the cannula was clamped. Fixative, consisting of 10% formalin in 0.1 mol/L sodium phosphate buffer, pH 7.3, was infused into the lumen of the vessel for 10 minutes at a pressure of approximately 100 mm Hg. Fixed grafts were dissected in two halves and further fixed, intimal surface upward, for 2 days and then postfixed in 1% osmiun tetroxide, followed by dehydration in graded alcohol. After critical point drying (in a CPD 750 critical-point dryer; Emscope, Ashford, Kent, UK), they were glued by means of a silver paste to aluminum stubs and sputter coated with gold and palladium (Edwards sputter coater S150B, UK), with special attention paid to the positioning so that the endothelial surface and blood vessel edge adjacent to the anastomotic site could be examined.
Scanning electron microscopy was performed at a magnification range from 20 to 100,000 times, using a JSM-6301F scanning electron microscope (Jeol, Colindale, London, UK). Endothelial damage and regeneration, exposure of subendothelial connective tissue, thrombus formation, and the presence of suture/clip material in the lumen were studied.
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Results
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Graft patency
All grafts were patent 1 week after operation. Therefore, two groups of 20 clipped and 20 sutured vein–artery anastomoses were available for scanning electron microscopic assessment.
Scanning electron microscopic analyses
The luminal surface of the carotid artery in both groups was covered by a single continuous layer of endothelial cells up to the anastomosis site, with no evidence of platelets, fibrin, red blood cells, or leukocytes adhering to the endothelium. Vein grafts, in agreement with previous experiments [8], also had almost complete coverage with morphologically intact endothelium. Only localized areas (about 2% of the surface) had endothelial separation or loss.
Anastomotic sites in the clipped sampled were completely endothelialized in all specimens (Fig 1), and the anastomotic cleft was indistinguishable. Furthermore, there was no evidence of platelets or fibrin adherence or thrombus formation on the endothelial surface. None of the clips were exposed to the blood stream.
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Fig 1. Scanning electron micrograph of the intimal surface of a clipped vein–artery anastomosis. The luminal surfaces of the carotid artery (CA) and the vain graft (SVG) are covered by continuous endothelium, and the anastomotic site (An) is indistinguishable. (x250 before 57% reduction.)
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Similar findings were present in most (75%) of the sutured anastomoses. However, in five specimens (25%), the suture material remained clearly visible inside the lumen of the vessel (Fig 2). Close to the site of the endothelial break at the suture exit point, significant amounts of platelets, red blood cells, and fibrin were present (Figs 3, 4). Some platelets and leukocytes were adherent to the surface of the suture material as well. Although samples showed numerous cellular elements attempting to cover the deendothelialized line of anastomosis, the subendothelial matrix remained exposed, with extensive fibrin and platelet deposition on its surface (Fig 5).
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Fig 2. Scanning electron micrograph of the intimal surface of a sutured vein–artery anastomosis. The suture material (arrows) remains clearly visible inside the lumen of the vessel. (x55 before 57% reduction.) The rectangle delineates the area further magnified in Figure 3. Abbreviations as in Figure 1.
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Fig 3. Close to the suture (Su) exit point, significant amounts of platelets and red blood cells are present (short arrows). Endothelial cells (EC) are seen attempting to cover the line of anastomosis (long arrows). (x1,200 before 57% reduction.) The rectangle delineates the area further magnified in Figure 4.
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Fig 4. Significant amount of platelets, red blood cells (arrow), and fibrin are forming microthrombi at the site of endothelial break near the suture (Su). (x5,000 before 57% reduction).
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Fig 5. The line of the anastomosis (An) in this sutured specimen is open, and the subendothelial matrix remained exposed, with extensive fibrin and platelet deposition on its surface (arrows). (x1,200 before 57% reduction.) Other abbreviations as in Figure 1.
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Comment
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Previous experiments using the same animal model have established that the endothelial coverage in a saphenous vein graft is reduced by approximately 60% during the procedure [7, 8]. This endothelial damage is caused mainly by the surgical preparation and distension of the vein graft [7]. However, almost complete repair with morphologically intact endothelium is virtually complete in the vein graft 1 week after implantation [8].
It has also been demonstrated that the principal determinant of the risk of anastomotic thrombosis and vein graft failure is the loss of endothelial coverage and exposure of the highly thrombogenic subendothelial matrix [9]. Hence, factors that can further cause or maintain endothelial damage in the vicinity of the anastomosis beyond 1 week can, theoretically at least, increase the risk of anastomotic thrombosis. Furthermore, other factors that may create a prothrombogenic environment, such as the presence of foreign materials in the lumen, may increase the risk of anastomotic thrombosis as well [9].
On the basis of this knowledge, we chose to study our vein grafts 1 week after operation. In the present experiment, anastomotic sites in the clipped samples were completely endothelialized in all specimens, and the anastomotic cleft was indistinguishable. Furthermore, there was no evidence of platelets or fibrin adherence or thrombus formation on the endothelial surface. These data are in agreement with that of Boeckx and colleagues [9], Macchiarelli and cowokers [10], and Kirsch and associates [11] in their assessments of artery–artery anastomoses.
These findings were similar to those in most of the sutured anastomoses. In some specimens, however, the picture was disquieting. The exposure of the subendothelial matrix and the protrusion of the suture material inside the lumen of the vessel with deposition of platelets, red blood cells, and fibrin close to the site of the anastomosis clearly indicate an increased risk of thrombus formation and vein graft failure.
Although our findings imply reduced risk of early failure of vein grafts when the anastomoses are performed using the VCS clips, it is unlikely that this will influence the longer term outcome of grafting using the saphenous vein because endothelial denudation is not a principal cause of smooth muscle cell proliferation, the main pathologic process underlying neointimal hyperplasia [8].
In conclusion, our data indicate that using the nonpenetrating VCS microvascular anastomosis clip system is likely to reduce the risk of early anastomotic thrombosis and improve the early results of grafting using the saphenous vein. Recent reports have also indicated that the clip technique facilitates and enhances the construction of coronary anastomosis [12]. This method as an alternative to anastomotic suturing deserves further investigation. It may be particularly applicable in minimally invasive coronary artery operations.
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Acknowledgments
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This study was supported by a grant from the Research Grants Council, The Chinese University of Hong Kong (A/C 2040581).
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References
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Abstract
Introduction
