The biocompound method in coronary artery bypass operations: surgical technique and 3-year patency

Adventitial Collagen Crosslink Reduces Intimal Hyperplasia in a Rabbit Arteriovenous Graft Model

BACKGROUND

Intimal hyperplasia (IH) is the initial lesion of vein graft failure after coronary artery bypass grafting. The weak venous wall is likely one of the primary reasons for IH after exposure to the arterial environment. We investigate whether adventitial collagen cross-link by glutaraldehyde (GA) reinforces the venous wall and then reduces IH.

MATERIALS AND METHODS

Adventitial collagen cross-link by 0.3% GA was performed on the rabbit jugular veins. The degree of cross-link was accessed by tensile test. The jugular vein with or without cross-link was implanted into the carotid artery of rabbit. Vein dilatation at the immediate anastomosis and pathological remodeling of vein graft after 4 wk was assessed.

RESULTS

Tensile test indicated that the mechanical property of 3-min cross-linked veins more closely resembled that of the carotid artery. In rabbit arteriovenous graft models, 3-min adventitial collagen cross-link limited overdistension (diameter: 3.24 mm versus 4.65 mm, P < 0.01) at the immediate anastomosis and reduced IH (intima thickness: 78.83 μm versus 140.19 μm, P < 0.01) of vein grafts 4 wk after implantation in the cross-link group as compared with the graft group (without cross-link). Compared with the cross-link group, the expression of proliferating cell nuclear antigen and vascular cell adhesion molecule-1 increased significantly at both the mRNA and protein levels within the graft group (P < 0.01), but the expression of smooth muscle-22α decreased significantly (P < 0.01).

CONCLUSIONS

Adventitial collagen cross-link by GA increased the vessel stiffness and remarkably reduced IH in a rabbit arteriovenous graft model.

External Stenting with a New Polyester Mesh Reduces Neointimal Hyperplasia of Vein Grafts in a Sheep Model

Objective

External stents placed around vein grafts have demonstrated effectiveness in reducing neointimal hyperplasia by preventing distension of the thin-walled vein grafts when exposed to arterial pressure. However, the ideal stent material has yet to be defined. The following study investigates the short- and long-term effects of an innovative polyester mesh stent designed with optimized adaptation of circumferential compliance.

Methods

Following in vitro definition of the ideal macro-porous polyester stent material, a total of 12 sheep underwent implantation of bilateral carotid artery vein graft bypasses. In six sheep, the short-term outcome (four weeks of implantation) was investigated by comparing the newly-designed stent to native veins, micro-porous PTFE stent grafts and metallic Biocompound® stents (BCGs). Flow volume and graft diameter were measured prior to explantation. Grafts were evaluated histologically with respect to morphometry and immunoassaying. In the long-term group (6-month implantation time), the polyester stent was compared to native veins.

Results

All stents effectively prevented dilatation of the graft. Perfused vessel diameters of the polyester veins were 8.3±0.6 mm. BCG as well as PTFE veins showed diameter reduction to 7.4±0.7mm (p<0.05) and 7.8±0.4 mm (p<0.05), respectively. Both in the short and long terms, the new polyester stent led to significantly higher reduction of neointimal hyperplasia and luminal encroachment compared to the native vessel. It proved superior to PTFE stenting, while the Biocompound® material failed to prove efficacy.

Conclusions

It was demonstrated that the new macro-porous polyester mesh stent reduced neointimal hyperplasia more effectively than other commercially available stents.

Perivascular medical devices and drug delivery systems: Making the right choices

Perivascular medical devices and perivascular drug delivery systems are conceived for local application around a blood vessel during open vascular surgery. These systems provide mechanical support and/or pharmacological activity for the prevention of intimal hyperplasia following vessel injury. Despite abundant reports in the literature and numerous clinical trials, no efficient perivascular treatment is available. In this review, the existing perivascular medical devices and perivascular drug delivery systems, such as polymeric gels, meshes, sheaths, wraps, matrices, and metal meshes, are jointly evaluated. The key criteria for the design of an ideal perivascular system are identified. Perivascular treatments should have mechanical specifications that ensure system localization, prolonged retention and adequate vascular constriction. From the data gathered, it appears that a drug is necessary to increase the efficacy of these systems. As such, the release kinetics of pharmacological agents should match the development of the pathology. A successful perivascular system must combine these optimized pharmacological and mechanical properties to be efficient.

Hemodynamics-based treatment of varices: A therapeutic concept counteracting the intrinsic tendency of varicose veins to recur

Varicose vein disease is characterized by tenacious tendency to recur. Measures recommended to prevent recurrences (flush ligation at the saphenofemoral junction, removal of incompetent great saphenous vein in the thigh, and insertion of mechanical barriers in the fossa ovalis) did not succeed in preventing recurrence. Reflux recurrence is triggered by the hemodynamic phenomenon called hemodynamic paradox. Abolition of saphenous reflux removes the hemodynamic disturbance of any degree of severity but at the same time it releases the pathological process leading to recurrent reflux. This process is induced by drainage of venous blood from incompetent superficial thigh veins into deep lower leg veins during calf pump activity, which evokes the development of ambulatory pressure gradient between the femoral vein and incompetent segments of the saphenous system in the thigh. The pressure gradient sets off biophysical and biochemical events inducing recurrent reflux. The designed therapeutic strategy consists of reliable abolition of saphenous reflux and of hindering the pathological drainage of venous blood at the knee level in order to preclude development of the hemodynamic preconditions for reflux recurrence. In this way, the dividing line of the ambulatory pressure gradient would be kept below the knee, as is the case with healthy people.

Saphenofemoral Junction Ligation Supplemented by Postoperative Sclerotherapy: A Review of Long-Term Clinical and Hemodynamic Results

This review article summarizes information found in the literature concerning long-term results following high ligation supplemented in the postoperative period by sclerotherapy. Subjective complaints, recurrent reflux, and recurrent varicose vein rates as well as changes in venous hemodynamics are reviewed and compared with results after high ligation and stripping. The fate of the greater saphenous vein trunk after high ligation, the question whether it could actually be used as a graft in arterial and coronary artery reconstructions, and the relevance of saphenous vein saving surgery are discussed. The trunk of the greater saphenous vein, when incompetent preoperatively, continues to be patent and incompetent after surgery in most cases. It is not diffusely degenerated and could be used as an arterial substitute. However, ligation of the saphenofemoral junction alone provokes a higher recurrence rate in comparison with high ligation and stripping. The excellent hemodynamic improvement achieved immediately after high ligation deteriorates progressively during the follow-up owing to recurrent reflux. Sclerotherapy can compensate this undesirable feature, because it is itself capable of reducing or even abolishing reflux and improving venous hemodynamics, although only transitorily, but repeated sclerosing injections can restore improvement at any time, if necessary, during the follow-up period. The improvement of venous hemodynamics and subjective symptoms achieved with the combined procedure (high ligation plus sclerotherapy) is comparable with that after high ligation and stripping.

External support in preventing vein graft failure

Saphenous vein remains a widely used conduit in coronary surgery. However, the long-term success of surgical myocardial revascularization is largely limited by the development of neointimal hyperplasia and superimposed atherosclerosis in vein grafts. Although strategies for preventing vein graft failure have been constantly explored, few therapeutic interventions to date have shown sustained benefits in the clinical setting. The application of external support has emerged as a promising strategy for modulating the overall biomechanical responses in venous wall. Nonetheless, clinical translation of this intervention has been formerly challenged, primarily due to several technique limitations. The purpose of the current review is to summarize the possible mechanisms involved in the external support strategy for preventing vein graft failure. Furthermore, several previously tested biomaterials and delivery techniques are also highlighted.

Self-covered technique for a varix on a saphenous vein graft

We describe a simple technique for eliminating a varix on a saphenous vein graft (SVG). The SVG with varix is passed through a short section of the saphenous vein, and the varix is covered by the short cylinder of the vein. Both parts are fixed by arterial pressure, which expands the SVG. This technique was used in two SVGs in 2 patients undergoing coronary artery bypass grafting. The grafts were investigated by angiography 1 year after the surgery, and the patency without varix was confirmed. This simple method is feasible to repair a varix of the SVG.

Dimensional analysis of human saphenous vein grafts: Implications for external mesh support

OBJECTIVE

Constrictive external mesh support of vein grafts was shown to mitigate intimal hyperplasia in animal experiments. To determine the degree of constriction required for the elimination of dimensional irregularities in clinically used vein grafts, a detailed anatomic study of human saphenous veins was conducted.

METHODS

In 200 consecutive patients having coronary artery bypass grafting, harvested saphenous veins (length 34.4 +/- 10.8 cm) were analyzed regarding diameter irregularities, side branch distribution, and microstructure.

RESULTS

The mean outer diameter of surgically distended saphenous veins was 4.2 +/- 0.6 mm (men, 4.3 +/- 0.6 mm vs women, 3.9 +/- 0.5 mm; P < .0001). Although the outer diameter significantly decreased over the initial 18 cm (-7.6%; P < .0001), the overall increase between malleolus and thigh was not significant (+11.2%). Smaller-diameter veins (<3.5 mm) had more pronounced diameter fluctuations than larger veins (31.8% +/- 11.0% vs 21.2% +/- 8.8%; P < .0001), with more than 71% of all veins showing caliber changes of more than 20%. There was 1 side branch every 5.4 +/- 4.3 cm, with a significantly higher incidence between 20 and 32 cm from the malleolus (P < .0001 to distal, P < .0004 to proximal). Generally, women had more side branches than men (0.30 +/- 0.15 cm(-1) vs 0.25 +/- 0.12 cm(-1); P = .0190). Thick-walled veins (565.7 +/- 138.4 mum) had a significantly higher number of large side branches (P < .0001), and thin-walled veins (398.7 +/- 123.2 mum) had significantly more small side branches (P < .0001). Pronounced intimal thickening ("cushions") was found in 28% of vessels (119.8 +/- 28.0 mum vs 40.1 +/- 18.2 mum; P < .0001).

CONCLUSION

Although the preferential location of side branches may be addressed by the deliberate discarding of infragenicular vein segments, a diameter constriction of 27% on average would eliminate diameter irregularities in 98% of vein grafts.

Adventitia contribution in vascular tone: insights from adventitia‐derived cells in a tissue‐engineered human blood vessel

Whether the adventitia component of blood vessels directly participates in the regulation of vascular tone remains to be demonstrated. We have recently developed a human tissue-engineered blood vessel comprising the three tunicae of a native blood vessel using the self-assembly approach. To investigate the role of the adventitia in the modulation of vascular tone, this tissue-engineering method was used to produce three vascular constructs from cells explanted and proliferated from donor vessel tunicae 1) an adventitia + a media, or only 2) an adventitia, or 3) a media. The vasoconstriction responses of these 3 constructs to endothelin, the most potent vasopressor known up-to-date, as well as to nonselective and selective agonists and antagonists, were compared. The adventitia contracted to endothelin-1, -2, whereas the media and the media+adventitia contracted to all three endothelins. Endothelin-induced contraction of the adventitia was dependent on ET(A) receptors, whereas that of the media and the adventitia+media was ET(A) and ET(B) receptor-dependent. RT-PCR studies corroborated these results. SNP induced a dose-dependent relaxation of the three tissue constructs. We also demonstrated that the endothelin-converting enzyme, responsible for the formation of the active endothelin peptides, was present and functional in the adventitia. In conclusion, this is the first direct demonstration that the adventitia has the capacity to contract and relax in response to vasoactive factors. The present study suggests that the adventitia of a blood vessel could play a greater role than expected in the modulation of blood vessel tone.

Popliteal-to-Distal Bypass for Limb Salvage

A retrospective study was carried out to examine the patency and limb salvage rates of popliteal-to-distal bypass and compare the results of diabetic to those of nondiabetic patients and elective versus emergency procedures. From January 1990 to December 2001, 71 popliteal-to-distal bypasses were performed. Indications for surgery were rest pain, tissue loss, and acute ischemia, including extensive post-traumatic tibial lesions. Survival, graft patency, and limb salvage rates were determined according to the life-table method. The log-rank test was used to compare diabetic versus nondiabetic patients, elective versus emergency procedures, and saphenous vein bypass versus PTFE bypass. Postoperative primary patency, secondary patency, and limb salvage rates at 30 days were 88.7%, 91.4%, and 87%, respectively. Postoperative mortality was 2.8%, with one case of acute myocardial ischemia and one multiorgan failure. Life-table analysis showed primary and secondary patency rates of 57% and 61%, respectively, a limb salvage rate of 64%, and survival of 77% at 5 years Log-rank testing showed no statistical difference between diabetic and nondiabetic patients, whereas a statistical difference was observed in elective versus emergency procedures (p < 0.005) and great saphenous vein versus PTFE graf (p < 0.05). These results show that popliteal-to-distal bypass is a safe and effective procedure with good long-term patency and limb salvage rates in selected cases.

External supports and the prevention of neointima formation in vein grafts

AIMS AND METHODOLOGY

the aim of this review is to provide an overview of the aetiology of neointima formation in vein grafts and to highlight the use of an external support to modulate this phenomenon. A systematic literature review was performed via computerised search on MEDLINE, OVID and the Cochrane Library. The search terms initially employed were broad-based; "vein graft", "neointima" and "external stent". Subsequently, more specific search terms were utilised; "perivenous mesh", "external prosthesis" and "varicose vein". Articles from indexed journals relevant to the objective, external venous supports, from the earliest reports in the 1960's to the latest in 2001 were included to obtain an exhaustive list. Reviews, abstracts and proceedings of scientific meetings, case reports and the results of both animal model investigations and human clinical trials in all languages were included. Articles describing an external support employed in both peripheral and aortocoronary bypass investigations were included.

Perivenous application of fibrin glue reduces early injury to the human saphenous vein graft wall in an ex vivo model

OBJECTIVES

From animal and clinical studies it is known that prevention of 'over-distention' of vein grafts by using extravascular support ameliorates the arterialization process in vein grafts with subsequent more favorable patency. The most ideal support is a biodegradable, porous, elastic graft (Biomaterials, 15 (1994) 83). However, a specific graft meeting these criteria is not available yet. Fibrin glue on the other hand, although used for other purposes in cardiac surgery, theoretically meets the criteria for ideal extravascular support. In this ex vivo study, we evaluated the possible beneficial effect of perivenous application of fibrin glue.

METHODS

Segments of human vein graft obtained during CABG procedures in 14 consecutive patients were placed in a side loop of the extracorporeal perfusion circuit. In this way the study vein grafts did meet identical circumstances as the vein grafts implanted. Perfusion in the loop was started with a flow just enough to counteract the collapse of the vein, usually about 8 mm Hg, and alternately around the segments fibrin glue was applied or no perivenous support was administered as control. After 1 min of soldification, perfusion was started with a pressure of about 60 mm Hg (non-pulsatile flow). Perfusion was maintained for 60 min, after which the grafts were collected for light microscopic and electron microscopic assessment.

RESULTS

Light microscopy and electron microscopy showed remarkable attenuation of endothelial cell loss and less injury of smooth muscle cells of the circular muscle layer of the media in the fibrin glue supported vein grafts compared to the non-supported group.

CONCLUSION

Fibrin glue is able to accomplish adequate external vein graft support, preventing overdistention, in an ex vivo model. This provides a basis for clinical application. Further investigation is necessary to evaluate long-term effects.