Effect of external stenting and systemic hypertension on intimal hyperplasia in rat vein grafts

Aneurysmorrhaphy is an Easy Technique for Arteriovenous Fistula Salvage

The life-saving procedures for patients in chronic renal failure (CRF) are hemodialysis (HD) or successful kidney transplantation. HD requires a properly placed and functioning vascular access, most often obtained by creating an arteriovenous fistula (AVF). The long-term patency of AVFs is limited, in addition to other factors, by the development of intimal hyperplasia and the process results in venous wall thickening and progressive fistula occlusion. Another problem is limited patency, due to the development of pseudoaneurysm, which is associated with an increased risk of thrombosis, infection and bleeding, difficult cannulation for dialysis, pain and cosmetic defects. Treatment is focused on rapidly progressing pseudoaneurysms, which can predispose to rupture, technical problems during cannulation because of pseudoaneurysm size or a growing intraluminal thrombus. Most of these patients are scheduled for pseudoaneurysm removal and new fistula construction or, occasionally, an endovascular procedure involving stent graft implantation. This paper describes a simple and inexpensive technique of managing an AVF pseudoaneurysm, i.e. aneurysmorrhaphy. To offset the weakening of the venous wall by suture following aneurysmorrhaphy, an external polyethylene terephthalate (PET) prosthesis was implanted in the vein to prevent the development of intimal hyperplasia in the de novo created AVF.

Accelerated intimal hyperplasia in aortocoronary internal mammary vein grafts in minipigs

Background

More than 50% of aortocoronary saphenous vein grafts are occluded 10 years after surgery. Intimal hyperplasia is the initial critical step in the progression toward occlusion. Internal mammary veins, which are physiologically prone to less hydrostatic pressure, may undergo an accelerated progression to intimal hyperplasia and thus be suitable for investigation of the mechanisms of aortocoronary vein graft disease.

Methods

Six minipigs underwent aortocoronary bypass grafting using standard cardiopulmonary bypass and cardioplegic arrest. Mammary vein were grafted in a reversed manner from ascending aorta to left anterior descending coronary artery (LAD). The proximal LAD was ligated, rendering the anterior left ventricle vein graft-dependent. Minipigs were killed after 4 weeks, and vein grafts were harvested. Histological and immunohistological investigation were performed with respect to morphometric analysis, endothelial damage/dysfunction (v-Willebrand-factor (vWF)), smooth muscle cells (α-smooth actin) and proliferation rate (proliferation marker Ki 67).

Results

Mean intimal area of vein grafts was increased compared to ungrafted mammary veins. Intimal hyperplasia in vein grafts was characterized by massive accumulation of smooth muscle cells with a high proliferation rate and endothelial perturbation. Significant (p = 0.001) intimal hyperplasia of the grafted mammary vein compared to the ungrafted mammary vein was found. These changes were absent in ungrafted mammary veins.

Conclusion

The present study demonstrates a pig model of aortocoronary vein graft intimal hyperplasia which is characterized by an accelerated progression within internal mammary veins. The model is suitable to investigate the pathophysiology of aortocoronary vein graft intimal hyperplasia as well as therapeutic approaches.

A Novel Time-Varying Poly Lactic-Co Glycolic Acid External Sheath for Vein Grafts Designed under Physiological Loading

Changes in dimensional and mechanical properties of degradable sheaths in poly lactic-co glycolic acid (PLGA) have been researched extensively. Composite PLGA having variable resorption rates in multiple layers under physiological loading has not been reported. Our novel design of a PLGA sheath is composed of 3 layers with different degradation rates (i.e., the innermost layer degrades the fastest, followed by the middle, while the outer layer degrades the slowest). In the presence of physiological luminal pressure, diameter is greater, thickness is less, resorption rate is greater, pore size is greater, and incremental modulus is greater than in nonpressurized sheaths. Furthermore, the ratio of the pore size to the sheath radius affects the dimensional changes of the sheath in the radial direction. In addition to changing the pore size-to-sheath radius ratio, the dimensional changes can be manipulated by choosing different glycolic and lactic acid ratios for the different layers. The application of this novel PLGA design for gradual arterialization of vein grafts is contemplated.

Increased venous proinflammatory gene expression and intimal hyperplasia in an aorto-caval fistula model in the rat

We hypothesized that the venous limb of an arteriovenous (AV) fistula would evince up-regulation of genes relevant to vascular remodeling along with neointimal hyperplasia and relevant histological changes. Using the aorto-caval model of an AV fistula model in the rat, we demonstrate marked up-regulation in such proinflammatory genes as monocyte chemoattractant protein-1, plasminogen activator inhibitor-1, and endothelin-1, 2 weeks after the creation of the fistula. Neointimal hyperplasia occurred in variable degrees by 5 weeks after establishing the fistula, and by 16 weeks, such neointimal hyperplasia was progressive and pronounced; at this time point, abundant extracellular matrix was also observed. Smooth muscle cells were present in the hyperplastic neointima as evidenced by staining for alpha-smooth muscle actin; ultrastructurally, smooth muscle cells with a synthetic as well as a contractile phenotype were readily observed. Accumulation of extracellular matrix in the model at 16 weeks was accompanied by increased expression of transforming growth factor-beta1 mRNA, the latter finding contrasting with the suppression of transforming growth factor-beta1 mRNA observed in this model at 2 weeks. In summary, we describe marked up-regulation in proinflammatory genes and progressive neointimal formation in the venous vasculature in an AV fistula model in the rat. We suggest that such alteration in gene expression and histological injury, in conjunction with the relative simplicity of this model, offer a new approach in the study of such timely biological and clinically relevant phenomena as differential gene expression in response to hemodynamic forces, processes involved in vascular remodeling, mechanisms of injury in venous bypass grafts, and mechanisms of dysfunction of AV fistulae used in hemodialysis.