Feasibility study of sutureless distal coronary anastomoses with degradable Y-shunt and tissue adhesives in a porcine off-pump model
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a Department of Cardiothoracic Surgery, University Hospital Cologne, Kerpener Str. 62, 50937 Cologne, Germany
b Department of Cardiothoracic Surgery, University Hospital Jena, Germany
c Heart Center Brandenburg, Bernau, Germany
Abstract
The purpose of this study was to examine the feasibility of the combined use of intraluminal biodegradable shunts and surgical adhesives for sutureless distal coronary anastomosis. Eighteen LITA-LAD anastomoses were created in a porcine beating heart model. In group I (n=9) a custom-made silicone Y-shunt provided internal stability, while three different adhesives, N-butyl-2-cyanoacrylate-glue (CYAC); albumin-glutaraldehyde-glue (AG); fibrin-glue (FIB), were applied externally. In group II (n=9) biodegradable polydioxanone (PDS) shunts were used. All anastomoses were examined intraoperatively by flow measurement, blood leakage was quantified and physical strength was tested. In all pigs anastomoses could be created successfully at first attempt, but anastomotic leaks requiring additional sutures occurred in 6 animals. LITA-flow significantly decreased in both groups. A patency rate of 89.9% (8/9) was found in group I while it was 66.6% (5/9) in group II. The lowest amount of blood-loss was measured when CYAC adhesive was used while tensile strength was lowest in the FIB-anastomoses. Preliminarily we could demonstrate the feasibility of performing sutureless distal coronary anastomosis by means of a combination of adhesives and temporary intraluminal shunts. PDS-shunts, however, resulted in a high graft-occlusion rate, so that potentially less thrombotic materials need to be investigated.
Key Words: Sutureless coronary anastomosis; Degradable biomaterial; Tissue adhesive
1. Introduction
In the last 10 years, the unanimously accepted surgical approach to coronary vessels has been replaced by a wider range of measures such as off-pump coronary artery bypass grafting (OPCAB) and minimally invasive approaches (MIDCAB, TECAB). While proximal anastomotic devices exhibited clinical potential distal anastomotic devices were not successful in clinical routine. Endoscopic anastomoses with telemanipulators have also been introduced clinically but have failed to demonstrate feasibility in daily clinical practice. Therefore, three goals of truly minimally invasive coronary artery bypass grafting have not been established yet: (1) entire accomplishment of the anastomosis through small ports; (2) avoidance of the use of cardiopulmonary bypass (CPB); and (3) achievement of patency rates being superior to current stent technology. A sutureless anastomosis constructed with biological or synthetic glue utilizing an absorbable intraluminal shunt, which stabilizes the anastomotic region and guarantees unimpeded and stable flow, would greatly facilitate minimal-invasive or endoscopic approaches. We therefore performed a feasibility study of in vivo application of this technique in an acute large animal model.
2. Materials and methods
2.1. Study
All experiments were performed using juvenile white domestic pigs (40±2 kg). The study was approved by the Animal Care and Use Committee of the Friedrich-Schiller University Jena. All animals received humane care in compliance with the ‘Guide for the Care and Use of Laboratory Animals’ as revised by the National Institute of Health in 1985. Eighteen pigs underwent end-to-side OPCAB with intraluminal stabilization by different Y-shunts and glue application over the anastomotic line. Animals were divided into two groups. In group I, nine pigs (n=9) underwent left internal thoracic artery (LITA) to left artery descending (LAD) bypass with an intraluminal silicone Y-shunt for stabilizing the anastomosis. In three animals each of the following types of glue were used: fibrin glue ((FIB), Tissucol, Baxter BioSience, Heidelberg, Germany), albumin-glutaraldehyde (AG) sealant (Bioglue, Cryolife, Atlanta, GA, USA), and n-butyl-2-cyanoacrylate glue ((CYAC), Glubran2, Dahlhausen, Halberstadt, Germany). In group II (n=9) the same types of glue were applied, but the LIMA-LAD anastomoses were stabilized by a biodegradable polydioxanone (PDS) Y-shunt. All animals received 500 mg aspirin orally one day before surgery. Fig. 1 shows a schematic drawing of the experiment.
2.2. Manufacturing of the shunts
Y-silicone shunts were constructed from 2.0 mm diameter commercially available coronary shunt (AnastaFLO, Research Medical, Inc., Oxford, UK and Medtronic GmbH, Düsseldorf, Germany) yielding a Y-shunt with 12 mm length with the Y-arm protruding at an angle of 35° [1]. The Y-connection was secured with polythene adhesive. For the manufacturing of biodegradable intraluminal shunts we reviewed the literature. Fibers of linear poly-alpha-hydroxy acids have been already used successfully in providing temporary scaffolds for tissue regeneration. In some surgical applications, degradation rates for poly-glycolide are too high, but implants of poly-lactide fibers may degrade too slowly [2]. In contrast, PDS appears to exhibit adequate stiffness while it completely degradates by action of hydrolysis within 40 days [3]. A Y-shunt aluminum mold was fabricated and filled with polydioxanone (Sola.r GmbH, Jena, Germany) (Fig. 1). After polymerization the two halves of the mold were opened and the Y-shunt removed. Prior to implantation, the ends were polished and the free passage of the lumen was tested in all groups by water injection. The inner diameter was 1.0 mm, whereas the outer diameter was 2.2 mm.
2.3. Operative technique
The anesthetized animals were placed in a supine position, full median sternotomy was performed and the LITA was harvested in a pedicled fashion. Before the mammary artery was severed 400 U/kg heparin were given. The mid-portion of the left anterior descending (LAD) artery far distal to the first diagonal branch was dissected and prepared for anastomosis in all animals. The distal segment of the LAD was dissected, prepared for anastomosis and immobilized by a CTS tissue stabilizer (CTS, Cupertino, CA, USA) in all animals. The LIMA was cut at an angle of approximately 45° and the LAD was temporarily snared with monofilament suture (4-0 Prolene), while the shunt was placed in the LAD through a 3.5-mm longitudinal incision (Fig. 2a). In all cases the shunt diameter was slightly oversized in order to achieve a tight fit thereby avoiding glue-contamination of the coronary lumen. The LIMA was pulled downward over the free side of the Y-shunt until the gap of the two vessels virtually disappeared. Immediately thereafter, either fibrin-glue; Albumin-glutaraldehyde-glue (Fig. 2b) or N-2-butyl-cyanoacrylate-glue were applied externally surrounding the entire anastomosis, while an air-blower was used to remove excessive blood immediately prior to application. After construction of the end-to-side anastomosis, protamin was given and patency was controlled by measurement of LITA-flow (MediStim AS, Oslo, Norway) subsequently and 20 min later. The total blood loss was assessed by measuring the suction content in a calibrated reservoir. At the end of the observation period all animals were scarified by injection of pentobarbital.
2.4. Mechanical testing
To characterize the biomechanical properties of the glue-assisted anastomoses we used a simple test with loads of a letter scale. In every animal, LAD segments of 30–40 mm length were harvested in which the anastomosed regions were located. The LAD was fixed on a cork plate, positioned upside-down and the free LIMA side was pulled by loads, beginning with 5 g, 10 g and 20 g up to the maximum load of 40 g. The anastomotic site was macroscopically observed. Separation of the interface between graft and coronary artery was recorded as functional tensile strength, whereas the complete uncoupling of the anastomosis was defined as maximum tensile strength. While the intraluminal shunt provided a continued apposition of the graft artery to the coronary artery, even in the case of an entire pullout, we decided the latter value as less precise and focused our testing on the functional tensile strength.
2.5. Statistical analysis
All operative data of both groups were compared by analysis of variance. The frequency of the respective gradual values was compared with Pearson's chi-square test. A two-sided exact significance was assumed if P was <0.05.
3. Results
LITA-LAD anastomoses were successfully constructed in 18 animals without the need for cardiopulmonary bypass. No animal died during the operation, while one animal suffered from ventricular fibrillating burt could be successfully defibrillated. The mean time taken to perform the anastomosis was 11.8 min (range: 7 to 19 min). Immediate hemostasis was obtained in 4 pigs (22%) in which CYAC adhesives were used. Six anastomoses showed minor oozing (4 (22%) FIB; 2 (11%) AG), which ceased within a few minutes after an additional 7/0 Prolene suture was placed. All 18 anastomoses were patent after the release of the LITA bull-dog clamp. After 20 min, however, LITA-flow significantly decreased in all groups while 5 anastomoses (27.8%) were already occluded. Four of these animals belonged to group II (Polydioxanone-shunt). The highest amount of anastomotic bleeding was observed in both groups when fibrin-glue was used to secure the co-adpatation line (group I: 350±50 ml; group II: 347±66 ml), whereas the lowest rate of bleeding was found when anastomoses were surrounded with n-butyl-2-cyanoacrylate (group I: 273±68 ml; group II: 267±42 ml). The pulling test revealed that the maximal sustained load in our experiment was 40 mg. Fibrin-glue exhibited the lowest adhesive power. Although there was no significant difference in functional tensile strength between all groups, separation of the artery-graft bonded interface occurred at much lower loads in the fibrin sub-group (Table 1). Macroscopical examination revealed that none of the adhesives applied outside the approximated vessels had entered the coronary lumen.
4. Discussion
The most important milestone for coronary bypass surgery, however, was marked by the invention of monofile non-absorbable suture material with integrated needle paving the avenue for small-caliber anastomoses. No other surgical technique has thrived at such a pace and magnitude as the hand-sewn coronary bypass anastomosis, cumulatively performed in the millions worldwide ever since. With the pursuit of beating heart surgery through smaller incisions, a renewed interest in simplified, timesaving, but nonetheless reliable coronary artery anastomosis technique has again emerged. In a sutureless scenario it is mandatory to stabilize the connection with an adequate inner lumen for the time period until the externally applied adhesive guarantees a tight and secure connection. Additionally, it was considered mandatory preventing adhesive leaking into the coronary lumen. Finally, we arrived at the conclusion that removal of the temporary shunt would require secondary application of sutures or clips over a considerable portion of the entire anastomosis. For those reasons, a temporary, degradable intraluminal Y-shunt was developed which could remain in place. In order to facilitate insertion through a reasonably small incision elasticity of the material was also mandatory.
In a recent study [4], we could demonstrate that the use of temporary intraluminal shunts in a chronic off-pump model caused only minor endothelial alterations on coronary vessels wall with completely ‘restitutio ad integrum’ over a short period of time. In this study we first tested the new absorbable anastomotic device for end-to-side anastomoses. We assumed that absorbable material would equal nonabsorbable materials such as silicone or polyethylene regarding elasticity and lumen patency [5]. In previous in-vitro experiments physically degradable agents such as gelatine were tested by us. A very rapid degradation, however, was observed. Y-shunts fabricated from gelatine were therefore not considered suitable for subsequent in-vivo testing. Therefore, we concentrated on absorbable fibers of linear poly-alpha-hydroxy acids in providing a temporary Y-shunt-scaffold. Polydioxanone had been identified to be absorbed by action of hydrolysis within 3 to 6 weeks [6] and was deemed to be the ideal material for constructing a Y-shunt. To maintain a successful anastomosis in our experiment the connected and stabilized blood vessels required adequate bonding. Adhesives used in humans require several properties such as sterility, quick yet strong adhesion, no toxicity, no foreign body reaction and the potential for use under wet conditions. We therefore investigated the pre-presented adhesives while meeting the requirements. In our current experiment the adhesive action of the FIB was weak after application while continuous bleeding had to be controlled by additional stitches in four cases. Tensile strength test also revealed weak adhesive forces demonstrating early separation of the graft-artery connection. As a consequence, FIB did not appear to serve as an adequate adjunct for the construction of a sutureless anastomosis in a high pressure field such as the coronary system. AG is a development of previous adhesives utilizing gelatine and resorcine as well as formaldehyde as active components. Gundry [7] looked at AG on sutureless coronary anastomoses in pigs and suggested excellent patency and minimal inflammation at 3 months. His findings were in contradiction to our attempts, which resulted in significant rates of early occlusion. However, we could indeed demonstrate that AG was effective in producing nearly leakage-free sutureless coronary artery ananstomoses capable of withstanding stronger pulling forces. CYAC is a new tissue adhesive, designed to improve previously available cyanoacrylates, which hardened to a glass-like, brittle structure. It contains plasticizers and forms a strong, but flexible bond with a greater breaking strength than previous cyanoacrylate adhesives. It hardens even under wet conditions. As a one-component adhesive it is easy to handle and takes only a short time to solidify entirely. Consequently, a reduction of total anastomotic time was observed. The functional load of the anastomosis was comparable to those encountered with albumin-glutaraldehyde-adhesive. Bleeding, however, was reduced so that additional stitches to control oozing were not necessary. Therefore, according to our experiment the most appropriate adhesive for a sutureless coronary anastomosis appeared to be CYAC. In our acute model histologic reaction of the vessels and surrounding tissue in order to verify the important issue of intraluminal inflammation as well as toxicity and scarring could not be evaluated.
5. Conclusion
The simultaneous use of adhesives and intraluminal graft connectors is feasible and instead of preliminary high occlusion rates we believe that the idea of using biodegradable Y-shunts and tissue adhesives for sutureless anastomoses in coronary surgery is attractive enough to further investigate other shunt materials, such as Poly-4- Hydroxybutyrat or Magnesium, as potential alternatives.
References
Krueger U, Zanow J, Scholz H. Comparison of two different arterio-venous anastomotic flows by numerical 3 D simulation of blood flow. Int J Angio 2000; 9:226–231.
Andriano KP, Pohjonen T, Tormala P. Processing and characterization of absorbable polyactide polymers for use in surgical implants. J Appl Biomater 1994; 5:133–140.
Bourne RB, Bitar H, Andrea PR, Martin LM, Finlay JB, Marquis F. In-vivo comparison of four absorbable sutures: Vicry, Dexon, Plus, Maxon and PDS. Can J Surg 1988; 31:43–45.
Wippermann J, Albes JM, Bruhin R, Hartrumpf M, Vollandt R, Kosmehl H, Wahlers T. Chronic ultrastructural effects of temporary intraluminal shunts in a porcine off-pump model. Ann Thorac Surg 2004; 78:543–548.
Daniel RK, Olding M. An absorbable anastomotic device for microvascular surgery: experimental studies. Plast Reconstr Surg 1984; 74:329–336.
Hawkins JA, Minich LL, Tani LY, Ruttenberg HD, Sturtevant JE, McGough EC. Absorbable polydioxanone suture and results in total anomalous pulmonary venous connection. Ann Thorac Surg 1995; 1:55–59.
Gundry SR, Black K, Izutani H. Sutureless coronary artery bypass with biologic glued anastomoses: preliminary in vivo and in vitro results. J Thorac Cardiovasc Surg 2000; 120:473–477.(Jens Wippermann, Christo )
b Department of Cardiothoracic Surgery, University Hospital Jena, Germany
c Heart Center Brandenburg, Bernau, Germany
Abstract
The purpose of this study was to examine the feasibility of the combined use of intraluminal biodegradable shunts and surgical adhesives for sutureless distal coronary anastomosis. Eighteen LITA-LAD anastomoses were created in a porcine beating heart model. In group I (n=9) a custom-made silicone Y-shunt provided internal stability, while three different adhesives, N-butyl-2-cyanoacrylate-glue (CYAC); albumin-glutaraldehyde-glue (AG); fibrin-glue (FIB), were applied externally. In group II (n=9) biodegradable polydioxanone (PDS) shunts were used. All anastomoses were examined intraoperatively by flow measurement, blood leakage was quantified and physical strength was tested. In all pigs anastomoses could be created successfully at first attempt, but anastomotic leaks requiring additional sutures occurred in 6 animals. LITA-flow significantly decreased in both groups. A patency rate of 89.9% (8/9) was found in group I while it was 66.6% (5/9) in group II. The lowest amount of blood-loss was measured when CYAC adhesive was used while tensile strength was lowest in the FIB-anastomoses. Preliminarily we could demonstrate the feasibility of performing sutureless distal coronary anastomosis by means of a combination of adhesives and temporary intraluminal shunts. PDS-shunts, however, resulted in a high graft-occlusion rate, so that potentially less thrombotic materials need to be investigated.
Key Words: Sutureless coronary anastomosis; Degradable biomaterial; Tissue adhesive
1. Introduction
In the last 10 years, the unanimously accepted surgical approach to coronary vessels has been replaced by a wider range of measures such as off-pump coronary artery bypass grafting (OPCAB) and minimally invasive approaches (MIDCAB, TECAB). While proximal anastomotic devices exhibited clinical potential distal anastomotic devices were not successful in clinical routine. Endoscopic anastomoses with telemanipulators have also been introduced clinically but have failed to demonstrate feasibility in daily clinical practice. Therefore, three goals of truly minimally invasive coronary artery bypass grafting have not been established yet: (1) entire accomplishment of the anastomosis through small ports; (2) avoidance of the use of cardiopulmonary bypass (CPB); and (3) achievement of patency rates being superior to current stent technology. A sutureless anastomosis constructed with biological or synthetic glue utilizing an absorbable intraluminal shunt, which stabilizes the anastomotic region and guarantees unimpeded and stable flow, would greatly facilitate minimal-invasive or endoscopic approaches. We therefore performed a feasibility study of in vivo application of this technique in an acute large animal model.
2. Materials and methods
2.1. Study
All experiments were performed using juvenile white domestic pigs (40±2 kg). The study was approved by the Animal Care and Use Committee of the Friedrich-Schiller University Jena. All animals received humane care in compliance with the ‘Guide for the Care and Use of Laboratory Animals’ as revised by the National Institute of Health in 1985. Eighteen pigs underwent end-to-side OPCAB with intraluminal stabilization by different Y-shunts and glue application over the anastomotic line. Animals were divided into two groups. In group I, nine pigs (n=9) underwent left internal thoracic artery (LITA) to left artery descending (LAD) bypass with an intraluminal silicone Y-shunt for stabilizing the anastomosis. In three animals each of the following types of glue were used: fibrin glue ((FIB), Tissucol, Baxter BioSience, Heidelberg, Germany), albumin-glutaraldehyde (AG) sealant (Bioglue, Cryolife, Atlanta, GA, USA), and n-butyl-2-cyanoacrylate glue ((CYAC), Glubran2, Dahlhausen, Halberstadt, Germany). In group II (n=9) the same types of glue were applied, but the LIMA-LAD anastomoses were stabilized by a biodegradable polydioxanone (PDS) Y-shunt. All animals received 500 mg aspirin orally one day before surgery. Fig. 1 shows a schematic drawing of the experiment.
2.2. Manufacturing of the shunts
Y-silicone shunts were constructed from 2.0 mm diameter commercially available coronary shunt (AnastaFLO, Research Medical, Inc., Oxford, UK and Medtronic GmbH, Düsseldorf, Germany) yielding a Y-shunt with 12 mm length with the Y-arm protruding at an angle of 35° [1]. The Y-connection was secured with polythene adhesive. For the manufacturing of biodegradable intraluminal shunts we reviewed the literature. Fibers of linear poly-alpha-hydroxy acids have been already used successfully in providing temporary scaffolds for tissue regeneration. In some surgical applications, degradation rates for poly-glycolide are too high, but implants of poly-lactide fibers may degrade too slowly [2]. In contrast, PDS appears to exhibit adequate stiffness while it completely degradates by action of hydrolysis within 40 days [3]. A Y-shunt aluminum mold was fabricated and filled with polydioxanone (Sola.r GmbH, Jena, Germany) (Fig. 1). After polymerization the two halves of the mold were opened and the Y-shunt removed. Prior to implantation, the ends were polished and the free passage of the lumen was tested in all groups by water injection. The inner diameter was 1.0 mm, whereas the outer diameter was 2.2 mm.
2.3. Operative technique
The anesthetized animals were placed in a supine position, full median sternotomy was performed and the LITA was harvested in a pedicled fashion. Before the mammary artery was severed 400 U/kg heparin were given. The mid-portion of the left anterior descending (LAD) artery far distal to the first diagonal branch was dissected and prepared for anastomosis in all animals. The distal segment of the LAD was dissected, prepared for anastomosis and immobilized by a CTS tissue stabilizer (CTS, Cupertino, CA, USA) in all animals. The LIMA was cut at an angle of approximately 45° and the LAD was temporarily snared with monofilament suture (4-0 Prolene), while the shunt was placed in the LAD through a 3.5-mm longitudinal incision (Fig. 2a). In all cases the shunt diameter was slightly oversized in order to achieve a tight fit thereby avoiding glue-contamination of the coronary lumen. The LIMA was pulled downward over the free side of the Y-shunt until the gap of the two vessels virtually disappeared. Immediately thereafter, either fibrin-glue; Albumin-glutaraldehyde-glue (Fig. 2b) or N-2-butyl-cyanoacrylate-glue were applied externally surrounding the entire anastomosis, while an air-blower was used to remove excessive blood immediately prior to application. After construction of the end-to-side anastomosis, protamin was given and patency was controlled by measurement of LITA-flow (MediStim AS, Oslo, Norway) subsequently and 20 min later. The total blood loss was assessed by measuring the suction content in a calibrated reservoir. At the end of the observation period all animals were scarified by injection of pentobarbital.
2.4. Mechanical testing
To characterize the biomechanical properties of the glue-assisted anastomoses we used a simple test with loads of a letter scale. In every animal, LAD segments of 30–40 mm length were harvested in which the anastomosed regions were located. The LAD was fixed on a cork plate, positioned upside-down and the free LIMA side was pulled by loads, beginning with 5 g, 10 g and 20 g up to the maximum load of 40 g. The anastomotic site was macroscopically observed. Separation of the interface between graft and coronary artery was recorded as functional tensile strength, whereas the complete uncoupling of the anastomosis was defined as maximum tensile strength. While the intraluminal shunt provided a continued apposition of the graft artery to the coronary artery, even in the case of an entire pullout, we decided the latter value as less precise and focused our testing on the functional tensile strength.
2.5. Statistical analysis
All operative data of both groups were compared by analysis of variance. The frequency of the respective gradual values was compared with Pearson's chi-square test. A two-sided exact significance was assumed if P was <0.05.
3. Results
LITA-LAD anastomoses were successfully constructed in 18 animals without the need for cardiopulmonary bypass. No animal died during the operation, while one animal suffered from ventricular fibrillating burt could be successfully defibrillated. The mean time taken to perform the anastomosis was 11.8 min (range: 7 to 19 min). Immediate hemostasis was obtained in 4 pigs (22%) in which CYAC adhesives were used. Six anastomoses showed minor oozing (4 (22%) FIB; 2 (11%) AG), which ceased within a few minutes after an additional 7/0 Prolene suture was placed. All 18 anastomoses were patent after the release of the LITA bull-dog clamp. After 20 min, however, LITA-flow significantly decreased in all groups while 5 anastomoses (27.8%) were already occluded. Four of these animals belonged to group II (Polydioxanone-shunt). The highest amount of anastomotic bleeding was observed in both groups when fibrin-glue was used to secure the co-adpatation line (group I: 350±50 ml; group II: 347±66 ml), whereas the lowest rate of bleeding was found when anastomoses were surrounded with n-butyl-2-cyanoacrylate (group I: 273±68 ml; group II: 267±42 ml). The pulling test revealed that the maximal sustained load in our experiment was 40 mg. Fibrin-glue exhibited the lowest adhesive power. Although there was no significant difference in functional tensile strength between all groups, separation of the artery-graft bonded interface occurred at much lower loads in the fibrin sub-group (Table 1). Macroscopical examination revealed that none of the adhesives applied outside the approximated vessels had entered the coronary lumen.
4. Discussion
The most important milestone for coronary bypass surgery, however, was marked by the invention of monofile non-absorbable suture material with integrated needle paving the avenue for small-caliber anastomoses. No other surgical technique has thrived at such a pace and magnitude as the hand-sewn coronary bypass anastomosis, cumulatively performed in the millions worldwide ever since. With the pursuit of beating heart surgery through smaller incisions, a renewed interest in simplified, timesaving, but nonetheless reliable coronary artery anastomosis technique has again emerged. In a sutureless scenario it is mandatory to stabilize the connection with an adequate inner lumen for the time period until the externally applied adhesive guarantees a tight and secure connection. Additionally, it was considered mandatory preventing adhesive leaking into the coronary lumen. Finally, we arrived at the conclusion that removal of the temporary shunt would require secondary application of sutures or clips over a considerable portion of the entire anastomosis. For those reasons, a temporary, degradable intraluminal Y-shunt was developed which could remain in place. In order to facilitate insertion through a reasonably small incision elasticity of the material was also mandatory.
In a recent study [4], we could demonstrate that the use of temporary intraluminal shunts in a chronic off-pump model caused only minor endothelial alterations on coronary vessels wall with completely ‘restitutio ad integrum’ over a short period of time. In this study we first tested the new absorbable anastomotic device for end-to-side anastomoses. We assumed that absorbable material would equal nonabsorbable materials such as silicone or polyethylene regarding elasticity and lumen patency [5]. In previous in-vitro experiments physically degradable agents such as gelatine were tested by us. A very rapid degradation, however, was observed. Y-shunts fabricated from gelatine were therefore not considered suitable for subsequent in-vivo testing. Therefore, we concentrated on absorbable fibers of linear poly-alpha-hydroxy acids in providing a temporary Y-shunt-scaffold. Polydioxanone had been identified to be absorbed by action of hydrolysis within 3 to 6 weeks [6] and was deemed to be the ideal material for constructing a Y-shunt. To maintain a successful anastomosis in our experiment the connected and stabilized blood vessels required adequate bonding. Adhesives used in humans require several properties such as sterility, quick yet strong adhesion, no toxicity, no foreign body reaction and the potential for use under wet conditions. We therefore investigated the pre-presented adhesives while meeting the requirements. In our current experiment the adhesive action of the FIB was weak after application while continuous bleeding had to be controlled by additional stitches in four cases. Tensile strength test also revealed weak adhesive forces demonstrating early separation of the graft-artery connection. As a consequence, FIB did not appear to serve as an adequate adjunct for the construction of a sutureless anastomosis in a high pressure field such as the coronary system. AG is a development of previous adhesives utilizing gelatine and resorcine as well as formaldehyde as active components. Gundry [7] looked at AG on sutureless coronary anastomoses in pigs and suggested excellent patency and minimal inflammation at 3 months. His findings were in contradiction to our attempts, which resulted in significant rates of early occlusion. However, we could indeed demonstrate that AG was effective in producing nearly leakage-free sutureless coronary artery ananstomoses capable of withstanding stronger pulling forces. CYAC is a new tissue adhesive, designed to improve previously available cyanoacrylates, which hardened to a glass-like, brittle structure. It contains plasticizers and forms a strong, but flexible bond with a greater breaking strength than previous cyanoacrylate adhesives. It hardens even under wet conditions. As a one-component adhesive it is easy to handle and takes only a short time to solidify entirely. Consequently, a reduction of total anastomotic time was observed. The functional load of the anastomosis was comparable to those encountered with albumin-glutaraldehyde-adhesive. Bleeding, however, was reduced so that additional stitches to control oozing were not necessary. Therefore, according to our experiment the most appropriate adhesive for a sutureless coronary anastomosis appeared to be CYAC. In our acute model histologic reaction of the vessels and surrounding tissue in order to verify the important issue of intraluminal inflammation as well as toxicity and scarring could not be evaluated.
5. Conclusion
The simultaneous use of adhesives and intraluminal graft connectors is feasible and instead of preliminary high occlusion rates we believe that the idea of using biodegradable Y-shunts and tissue adhesives for sutureless anastomoses in coronary surgery is attractive enough to further investigate other shunt materials, such as Poly-4- Hydroxybutyrat or Magnesium, as potential alternatives.
References
Krueger U, Zanow J, Scholz H. Comparison of two different arterio-venous anastomotic flows by numerical 3 D simulation of blood flow. Int J Angio 2000; 9:226–231.
Andriano KP, Pohjonen T, Tormala P. Processing and characterization of absorbable polyactide polymers for use in surgical implants. J Appl Biomater 1994; 5:133–140.
Bourne RB, Bitar H, Andrea PR, Martin LM, Finlay JB, Marquis F. In-vivo comparison of four absorbable sutures: Vicry, Dexon, Plus, Maxon and PDS. Can J Surg 1988; 31:43–45.
Wippermann J, Albes JM, Bruhin R, Hartrumpf M, Vollandt R, Kosmehl H, Wahlers T. Chronic ultrastructural effects of temporary intraluminal shunts in a porcine off-pump model. Ann Thorac Surg 2004; 78:543–548.
Daniel RK, Olding M. An absorbable anastomotic device for microvascular surgery: experimental studies. Plast Reconstr Surg 1984; 74:329–336.
Hawkins JA, Minich LL, Tani LY, Ruttenberg HD, Sturtevant JE, McGough EC. Absorbable polydioxanone suture and results in total anomalous pulmonary venous connection. Ann Thorac Surg 1995; 1:55–59.
Gundry SR, Black K, Izutani H. Sutureless coronary artery bypass with biologic glued anastomoses: preliminary in vivo and in vitro results. J Thorac Cardiovasc Surg 2000; 120:473–477.(Jens Wippermann, Christo )