The formation of a neo-intima in textile prostheses implanted in the aorta of rats and dogs

Presence of alpha-smooth muscle actin-positive endothelial cells in the luminal surface of adult aorta

Alpha-smooth muscle actin-positive endothelial cells have not been found in adult aortic endothelium except valve leaflets. Here, using en face immunostaining method, we identified alpha-smooth muscle actin-positive endothelial cells in the luminal surface of rat, mouse and human thoracic aortas. These cells express both endothelial markers and definite smooth muscle cell markers and were only occasionally observed in thoracic aorta of wild type mice and rats. Their density did not increase with aging. Given that alpha-smooth muscle actin-positive endothelial cells express low level of vascular endothelial-cadherin that is important for the maintenance of cell contact, these cells were frequently detected in the thoracic aorta of 5-week-old apolipoprotein-E deficient mice. In 20- to 24-week-old apolipoprotein-E deficient mice, marked accumulation of alpha-smooth muscle actin-positive endothelial cells was observed especially in the luminal surface of atheromatous plaques. Our findings indicate the existence of alpha-smooth muscle actin-positive endothelial cells in adult aortic endothelium and the possible association with progression of atherosclerosis.

An aortic aneurysm model for the evaluation of endovascular exclusion prostheses

PURPOSE

The purpose of this study was to develop an aortic aneurysm (AA) model with a predictable tendency for rupture for the evaluation of the efficacy of endovascular prostheses in preventing rupture and their long-term outcome after implantation.

METHODS

An infrarenal AA measuring two to three times the diameter of the proximal aorta was created in 18 dogs with a full-thickness patch of jejunum. Seven dogs were allowed to survive without aneurysm exclusion. In 11 dogs the aneurysm was immediately excluded with a stented 8 mm Dacron graft mounted in a 14F delivery system introduced through the femoral artery with aortographic guidance. The pressure differential between the aorta and the excluded aneurysm was measured, and angiography, necropsy, and histologic examination were performed at 3- and 6-month survival.

RESULTS

All animals survived aneurysm implantation. Without aneurysm exclusion, six dogs died of rupture within 1 to 6 days of surgery. In three dogs the exclusion failed because of graft-to-aorta size mismatch or misplacement demonstrated on angiography and by a low pressure differential between the aorta and the aneurysm (< 5 mm Hg); all three dogs died of rupture within 4 days. In eight dogs the aneurysm was successfully excluded on the basis of angiography results, with a mean aorta-to-aneurysm pressure differential of 51 mm Hg. Two dogs were killed at 1 and 6 days after surgery because of paraplegia produced by graft thrombosis because of kinking but without evidence of aneurysm rupture. Six dogs survived on a long-term basis, and angiography and necropsy performed at 3 and 6 months revealed patent grafts without migration, reduction in aneurysm size, no flow in the excluded lumbar arteries in five of six animals, and complete incorporation of Dacron graft and stents. No evidence of graft infection was found in any animal. The survival rate was significantly better (p < 0.023) in dogs with successfully excluded aneurysms (n = 6) compared with that in dogs without exclusion or with failed aneurysm exclusion (n = 7).

CONCLUSION

This aneurysm model demonstrates that without effective aneurysm exclusion all animals die of rupture and that successfully placed endovascular prostheses can prevent AA rupture with long-term graft patency and stability. Endovascular aortic Dacron grafts in dogs undergo complete incorporation at 3 months from implantation. This aneurysm model is useful for the evaluation of endovascular devices designed for the treatment of AAs.

Microarterial synthetic graft repair: interstitial cellular components

Although the histologic changes occurring during healing on the lumen surface of large vessel synthetic vascular grafts have been well characterized, the cells populating the interstices of microvascular grafts have not been examined in detail. Since microvascular grafts are required to provide vascular continuity under quite different physiological and hemodynamic conditions as compared with large vessel grafts, these interstitial cells within the synthetic graft material may also vary as a function of graft size. Monoclonal antibodies, light microscopy, and scanning and transmission electron microscopy were used in this study to identify the cells present within the 30-microns pores of 1-mm diameter polytetrafluoroethylene and replamineform silicone rubber grafts. Identified cells included few capillary endothelial cells enclosing erythrocytes, rare proliferating endothelial cells, few macrophages, rare foreign body giant cells, and a majority of fibroblasts. There was no evidence of smooth muscle cells or myofibroblasts within the interstices of these microvascular prostheses 12 weeks after implantation in the rabbit central ear artery. The graft types differed by the presence of foreign body giant cells and more densely packed collagen between cells in the replamineform silicone rubber graft interstices.