The Intimal Hyperplastic Response

Placement of Self-expanding Stents with Different Diameters in the Porcine Venous System: An Experimental Study

PURPOSE

To study the vascular histologic response after placement of oversized self-expanding stents in the porcine venous system.

MATERIALS AND METHODS

Twenty-four oversized stents (range of oversizing, 119.5%-216.0%) were deployed in jugular and iliac veins of six miniature pigs divided into two groups with follow-up times of 1 and 3 months. Necropsy with histologic evaluation of each stent was performed, and the areas of neointimal proliferation were calculated with slices obtained during follow-up from each stent at 5 mm from the proximal and distal edges and at the midpoint.

RESULTS

Neointimal proliferation was observed inside the stent lumen. All segments were patent in both groups. However, one jugular stent in the 1-month group and one jugular stent in the 3-month group had migrated at follow-up and were excluded from analysis. There were no significant differences in neointimal growth between the stent edges (proximal and distal) and middle segments of the stents at follow-up in the 1-month group (P = .970) or in the 3-month group (P = .694). Simple linear regression showed strong positive correlation between stent oversizing and neointimal proliferation in the 1-month model (r = 0.791; P < .001) and the 3-month model (r = 0.718; P < .001). There were no significant differences between 1-month and 3-month groups in the degree of neointimal proliferation (P = .072). Also, branched vessels showed no neointimal proliferation at their intersections with the stent-implanted segments.

CONCLUSION

Stent oversizing showed a strong positive correlation with neointimal growth in each follow-up model in this study.

Effects of external gamma radiation on femoral artery reimplantation in rats: morphometrical analyzes

PURPOSE: To investigate the effects of external gamma radiation on rat femoral artery reimplant. METHODS: Sixty-two male Wistar rats were distributed in two groups I (Control) and II (Irradiated), both formed by three observation subgroups: 2 (10 animals), 7 (11) and 21(10) postoperative days (PO). The right femoral artery of each animal was split up and reimplanted (end-to-end anastomosis), through microsurgery technique. In the first PO day group II animals were irradiated with a single dose of 15Gy, external source. The histological analysis, qualitative and descriptive analysis, was accomplished through hematoxylin and eosin (HE), Verhoeff and Masson trichromium methodology. Morphometric analysis was realized in the same slides used to histological analysis stained by HE. Computer software was used to quantify morphological alterations of the vascular wall, by processing captured images from a microscope. It was analyzed the intimal layer (intimal hyperplasia and endothelium cells formation) and the nuclei percentage of smooth muscular cell in the medium layer and in the intima hyperplasia. The data were treated applying the statistical tests: Fisher's exact, Chi-square, Mann-Whitney, Kruskal-Wallis and analysis of variance (p < .05). RESULTS: The patency graft was observed by microscope distal to the autograft in 93.5% (29/31). It was observed that the gamma-radiation reduced the degree of covering of the vascular wall for the neo-formed endothelium. The nuclei percentage of smooth muscular cells, in the media, was smaller compared to control animals, although it was no significant for the studied sample size. The irradiated group showed a significant lower luminal stenosis and the intimal hyperplasia occurrence. In this group the percentage of smooth muscular cells proliferation, in the media, were significantly lower for 7 and 21 days of observation. CONCLUSION: The external single dose of 15 Gy gamma-radiation delivered at first postoperative day may inhibit the endothelial cells regeneration and the percentage of lumen stenosis and prevents intimal hyperplasia, in the 2, 7 and 21 PO on femoral artery autograft in rats.

Modelos experimentais de hiperplasia intimal: efeitos da radiação ionizante

A hiperplasia intimal ocorre em resposta à lesão vascular, pode complicar significantemente os procedimentos vasculares abertos e endovasculares, levando a diferentes graus de estenose do lume vascular e isquemia. De certo modo, a hiperplasia intimal está presente em todos os tipos de reconstruções vasculares, incluindo enxertos autólogos, homólogos e sintéticos, após angioplastias com ou sem colocação de stent e em órgãos transplantados. Um dos maiores desenvolvimentos experimentais nos últimos anos, para prevenção da hiperplasia intimal, é a utilização da radiação ionizante. A radiação ionizante inibe a proliferação de muitos tipos celulares, incluindo fibroblastos e células musculares lisas in vitro e a síntese de colágeno em culturas de fibroblastos. Modelos animais de experimentação têm sido utilizados para o desenvolvimento de novas estratégias de tratamento e entendimento dos mecanismos fisiopatológicos básicos da hiperplasia intimal. Assim, o objetivo desta revisão e atualização da literatura é o de expor os diferentes modelos de animais de experimentação para o desenvolvimento de hiperplasia intimal, o tipo de lesão empregada, as artérias mais utilizadas e os efeitos encontrados com o uso de diferentes tipos de fontes de radiação ionizante.

Long-term effects of extraluminal dilatation with a rigid circle on arteriovenous anastomotic line in venous grafts transposed into arterial defects

Postanastomotic narrowing resulting from subintimal hyperplasia is a well-known phenomenon. In the current study the authors compared a metallic circle and conventional suture technique in anastomoses performed in two ends of external jugular vein grafts interposed in carotid arteries of rabbits. They recorded the patency rates, fluid flow rates, and histological effects of the circle on the anastomotic line and compared them with conventional suture anastomoses. In 16 rabbits (experimental group) a standard suture was used in both ends of the jugular vein graft transposed to the carotid arteries on one side. On the other side, circle anastomoses were performed on both ends of the vein graft. In an additional 8 rabbits (control group), the anterior jugular veins and carotid arteries were dissected on both sides and left. During postoperative week 12, in 8 rabbits of the experimental group, the flow rates of carotid arteries were measured in vitro, and intraluminal silicone casts were prepared. In the remaining 8 experimental rabbits, carotid angiographies were performed and anastomotic segments were harvested for histological examination. Flow rates were also measured in the control group, and artery and vein segments were harvested. The patency rates of the vein grafts with metallic circle anastomoses were 100%, whereas conventional suture patency was 75% at week 12. Flow rates were significantly higher in the metallic circle-anastomosed vein grafts (74 ml per minute vs. 123 ml per minute, mean values; p < 0.05). Histological examination revealed reduced intimal thickness in the metallic circle anastomoses compared with conventional suture anastomoses. Dilatation of the arteriovenous end-to-end anastomotic line by a rigid circle prevents anastomotic narrowing in the long term.

"No-touch" technique using saphenous vein harvested with its surrounding tissue for coronary artery bypass grafting maintains an intact endothelium

Spasm and consequent dilation of the saphenous vein (SV) for coronary artery bypass grafting (CABG) can be avoided if the vein is harvested with its surrounding tissue. Morphologic techniques, including scanning and transmission electron microscopy, were used to compare endothelial cell integrity using three SV harvesting procedures: conventional (adventitial stripping of the vein, manual distention and storing in saline); intermediate (after adventitial stripping, the vein was left in situ, covered with a papaverine-soaked compress, and stored in heparinized blood); and "no-touch" (SV dissected with its surrounding tissue was left in situ, covered with a saline-soaked compress and stored in heparinized blood). Preservation of endothelial cell integrity was greater with the "no-touch" procedure than with the other methods. Since endothelial cell integrity of SV grafts may affect the patency rate, we conclude that the "no-touch" preparation should improve the results of CABG.