Vein Interposition Model: A Suitable Model to Study Bypass Graft Patency

A Novel Porcine Model of Bilateral Hindlimb Bypass Graft Surgery Integrating Transit Time Flowmetry

BACKGROUND

Bypass graft surgery is a key surgical intervention for ischemic heart disease (coronary bypass graft surgery) and critical limb ischemia (peripheral bypass graft surgery). Graft occlusion remains a significant clinical problem for both types. Further research into the pathobiological mechanisms of graft occlusion are needed in order to design targeted therapeutic strategies.

METHODS

Three Large White female pigs (mean weight 52.3 +/- 4.4 kg) received general anaesthesia prior to surgery. The external jugular vein was harvested bilaterally, and a bilateral femoral peripheral arterial bypass was performed, with the superficial femoral artery permanently ligated. The grafts were interrogated immediately post operatively on-table using Medistim MiraQ transit time flowmetry system (Medistim, Oslo, Norway) to assess graft performance. On postoperative day three, the pigs were returned to the operating room, and the grafts were interrogated once again using transit time flowmetry.

RESULTS

Six out of six (100%) successful bilateral EJV to femoral artery bypass grafts were performed. All pigs were successfully recovered, and returned to the operating room at postoperative day 3. The wounds were re-opened and the grafts were inspected. Postoperative graft assessment was performed with transit time flowmetry using the Medistim MiraQTM system (Medistim, Oslo, Norway), demonstrating all grafts were patent (100%).

CONCLUSION

This model may serve as a platform to gain further mechanistic insight into graft failure pathobiology. By combining a bilateral graft model with gold-standard transit time flowmetry, longitudinal experimentation of targeted therapeutic interventions to combat graft failure may be further studied with improved objectivity.

Bletilla striata Polysaccharide Prevents Restenosis of Vein Graft Through Inhibiting Cell Proliferation in Rat Model

Coronary artery bypass grafting (CABG) is still the most effective method for the treatment of coronary heart disease at present. However, the restenosis of vein grafts following surgery is an important complication of CABG. In this study, Bletilla striata polysaccharide (BSP), which has anti-inflammatory and antiproliferative properties, was used to prevent or delay the proliferation of venous bridge endothelial cells in a rat model. We transplanted the autogenous jugular vein to the rat carotid artery, and wrapped it with BSP. We carried out experiments in 4 groups (with 24 rats in each group): a high-BSP dose group (the HBG group, 10 mg), a low-BSP dose group (the LBG group, 3 mg), a pluronic gel group (the gel group), and a control group. Vein grafts were then harvested after 3, 14, and 28 days. Following transplantation, we used color Doppler ultrasound to assess the patency of the transplanted vein. The grafted veins were stained with hematoxylin and eosin (H&E) and Masson to measure the thickness of the intima and media of the blood vessels. Proliferating cell nuclear antigen (PCNA) and vascular cell adhesion molecule-l (VCAM-1) were assessed in vein grafts by immunohistochemistry and western blotting. We detected a significant reduction in the proliferation of endothelial cells in the BSP group compared with the control group (P < 0.05). H&E and Masson's trichrome staining showed that the extent of intimal hyperplasia in transplanted veins from the high BSP group (HBS) (67.42 ± 0.54 µm) and low BSP group (LBS) (120.83 ± 1.87 µm) groups was significantly lower than that in the control group (257.03 ± 2.74 µm, P < 0.05), and that the extent of intimal hyperplasia in the HBS group was lower than that in the LBS group (P < 0.05). We found that the effect of BSP was dose-dependent, as high-dose BSP had a more significant inhibitory effect on cell proliferation than low-dose BSP (P < 0.05). The results of immunohistochemistry and western blotting showed that PCNA and VCAM-1 were significantly downregulated in the BSP treatment group on days 14 and 28 (P < 0.05). BSP inhibits the proliferation of vascular endothelial cells and reduces the expression of VCAM-1, thereby inhibiting the restenosis of graft veins.

Rapid Self-Assembly of Bioengineered Cardiovascular Bypass Grafts From Scaffold-Stabilized, Tubular Bilevel Cell Sheets

BACKGROUND

Cardiovascular bypass grafting is an essential treatment for complex cases of atherosclerotic disease. Because the availability of autologous arterial and venous conduits is patient-limited, self-assembled cell-only grafts have been developed to serve as functional conduits with off-the-shelf availability. The unacceptably long production time required to generate these conduits, however, currently limits their clinical utility. Here, we introduce a novel technique to significantly accelerate the production process of self-assembled engineered vascular conduits.

METHODS

Human aortic smooth muscle cells and skin fibroblasts were used to construct bilevel cell sheets. Cell sheets were wrapped around a 22.5-gauge Angiocath needle to form tubular vessel constructs. A thin, flexible membrane of clinically approved biodegradable tissue glue (Dermabond Advanced) served as a temporary, external scaffold, allowing immediate perfusion and endothelialization of the vessel construct in a bioreactor. Subsequently, the matured vascular conduits were used as femoral artery interposition grafts in rats (n=20). Burst pressure, vasoreactivity, flow dynamics, perfusion, graft patency, and histological structure were assessed.

RESULTS

Compared with engineered vascular conduits formed without external stabilization, glue membrane-stabilized conduits reached maturity in the bioreactor in one-fifth the time. After only 2 weeks of perfusion, the matured conduits exhibited flow dynamics similar to that of control arteries, as well as physiological responses to vasoconstricting and vasodilating drugs. The matured conduits had burst pressures exceeding 500 mm Hg and had sufficient mechanical stability for surgical anastomoses. The patency rate of implanted conduits at 8 weeks was 100%, with flow rate and hind-limb perfusion similar to those of sham controls. Grafts explanted after 8 weeks showed a histological structure resembling that of typical arteries, including intima, media, adventitia, and internal and external elastic membrane layers.

CONCLUSIONS

Our technique reduces the production time of self-assembled, cell sheet-derived engineered vascular conduits to 2 weeks, thereby permitting their use as bypass grafts within the clinical time window for elective cardiovascular surgery. Furthermore, our method uses only clinically approved materials and can be adapted to various cell sources, simplifying the path toward future clinical translation.