Mechanism Of In-stent Restenosis After Stent Implantation For Iliac Vein Stenosis:An Animal Experiment

Part I: Design of a novel special stent for iliac vein and evaluation of radial mechanical propertiesObjective: To introduce the structure design of a novel domestic special stent for iliac vein and evaluate its radial mechanical properties.Methods: Using a radial supporting force tester,radial supporting force of the experimental stent and control stent was measured and compared.The radial mechanical properties of the novel special stent for iliac vein were evaluated.Then,a finite element model of the stent was constructed,and the accuracy of the above results was analyzed by the finite element method.Results: The novel special stent for iliac vein was a self-expanding Ni Ti alloy bare-metal stent,including "Corolla" location area and support area.Radial supporting force showed a statistically significant difference between the experimental stent and the control stent(P < 0.0001).Conclusion: Compared with the control stent,radial supporting property of the novel special stent for iliac vein with different diameters presents obvious superiority.The location of the "corolla" location provides loci for intraoperative location,which may affect the blood flow of the contralateral iliac vein and the occurrence of adverse events.Part II: Establishment and evaluation of a model of iliac vein stenosisObjective: To provide a simple,reliable and stable animal model of iliac vein stenosis.Methods: A model of iliac vein stenosis was established in experimental pigs.Thirty days after the establishment,changes in imaging and histopathology were observed before and after coarctation of iliac veins.The quality of the model was evaluated.Results: There were 3 experimental pigs in the experimental group.No death occurred after the operation.The angiography showed that the iliac vein was unobstructed in the narrow side.Before and after coarctation,blood of the subjects was collected for the detection of routine blood,hepatic and renal function and coagulation function,which showed no statically significant differences.Mean diameter of left iliac vein was 7.48 ± 0.40 mm,postoperative diameter was 4.87 ± 0.23 mm,and the percentage of coarctation was 47.43% ± 4.55%.Preoperative mean cross-sectional area of left iliac vein was 41.90 ± 4.25mm2,postoperative mean value was 18.67 ± 1.76mm2,and the percentage of coarctation was 55.23 ± 4.97%.Diameter and cross-sectional area of iliac vein presentedstatically significant differences before and after coarctation(P < 0.001).Mean intima-media thickness at coarctation site of left iliac vein was 212.33 ± 25.13 μm in the experimental group and 37.76 ± 12.62 μm in the control group,presenting statically significant differences(P = 0.0005).Conclusion: The establishment of iliac vein stenosis model in experimental white pigs is characterized by simplification,stability and reliability,and is an ideal choice for simulating human iliac vein compression syndrome.After the establishment of the iliac vein stenosis model,local vascular intimal hyperplasia,VSMCs proliferation,migration and proliferation of extracellular matrix were found.Part III: Verification of radial mechanical properties and investigation on biocompatibility of the novel special stent for iliac veinObjective: To evaluate the radial mechanical properties and biocompatibility of the novel special stent for iliac vein.Methods: Balloon dilatation angioplasty + stent implantation was conducted in the iliac vein model with stenosis.Angiography for bilateral iliac vein was performed at the 30 th and 60 th day after surgery and the 90 th day after the end point of the experiment to observe the properties of stent,in-stent thrombosis,thrombosis in the contralateral iliac vein,the loss of in-stent lumen and the loss rate of in-stent lumen.At the end point of the experiment,target vessel samples were collected.After staining,change in tissue structure and inflammatory reactions of the venous wall with stent were observed.Intima-media thickness of vessels,lumen area,area of inner elastic plate,and rate of in-stent restenosis were measured.The results in the 2 groups were compared,to evaluate the radial mechanical properties and biocompatibility of the novel special stent for iliac vein.Results: Before and after the experiment,there was no death event in the two groups of experimental pigs,and there was no obvious mental,appetite and other abnormal events.Success rate in both groups was 100%.Each group was implanted with 6 stents,respectively.No statistical significance was found in the percentage of stent diameter enlargement(P > 0.05).The diameter of iliac vein and various indexes of blood samples showed no statistical significance between the 2 groups before and after surgery(P > 0.05).There was no significant displacement of stents and the occurrence of stent fracture.In the control group,an old thrombus was detected at the opening of the contralateral iliac vein,and the rest was unobstructed.The loss of in-stent lumen,the loss rate of in-stent lumen,inflammatory reactions,the intima-media thickness of vessels,lumen area,the area of inner elastic plate and the rate of in-stent restenosis presented no obvious statistical significance(P > 0.05).There were a small number of inflammatory cells around the stents in the two groups of specimens,and no severe inflammatory reaction was observed.The differences between the two groups were not statistically significant(P > 0.05).Vascular intima hyperplasia was significant in the 90 th day after stent implantation.Endothelial cells lining surface basic neatly arranged,are arranged monolayer of columnar,owe neatly,below the endothelium are a large number of VSMCs proliferation,extracellular matrix was significantly increased,a small lymphocytes,monocytes infiltration;In some areas,the film is atrophic or unclear;There are many VSMCs and fibroblasts and collagenous fibers around the mesh.The outer membrane connective tissue thickens.Conclusion: The radial supporting properties of the novel special stent for iliac vein is good and biocompatibility is stable,showing no obvious differences from stents in the control group.The "corolla" positioning area of NIVS is used to provide locus for intraoperative stent implantation and may reduce the effects of the ipsilateral iliac vein blood flow and thrombosis and other adverse events.90 th day after surgery after stent implantation in iliac vein,the surface of the stent is covered with endothelial cells completely.Intimal hyperplasia of vessels leads to the occurrence of ISR.Intimal hyperplasia is due to that migration of vascular smooth muscle cell,the proliferation of extracellular matrix.The inflammatory response may be involved in the hyperplasia of intima and the ISR process in the vein after stent implantation.Part IV: Mechanism of in-stent restenosis after metal stent implantation for iliac vein stenosis: an animal experimentObjective: To investigate the mechanism of in-stent restenosis after metal stent implantation for iliac vein stenosis.Methods: Balloon dilatation angioplasty + stent implantation was conducted in the iliac vein model of the animal model.Target vessel samples were collected at the 14 th,30th,90 th and 180 th day after surgery,respectively,to observe intimal hyperplasia of vessels and inflammatory reactions,as well as measure intima-media thickness of vessels,lumen area,area of inner elastic plate and rate of in-stent restenosis.The expression of IL-8,CD11 b,FGF,PDGF,MCP-1 and α-SMA was detected using immunohistochemical staining.The results in each group were compared and analyzed.Results: Except 2 experimental animals with in-stent thrombosis,the success rate of each group was 100%.A total of 17 stents were implanted,and the percentage of stent diameter enlargement showed no remarkable statistical significance between each group(P > 0.05).No statistical significance was found in the diameter of iliac vein and various indexes of blood samples between each group before and after surgery(P > 0.05).After HE staining and Masson staining,intimal hyperplasia was obviously,accompanied by VSMCs proliferation and migration and extracellular matrix hyperplasia after stent implantation.Within 90 days after surgery,intimal hyperplasia reached its peak.Thirty days after surgery,vascular endothelialization was basically completed.The intima-media thickness of vessels was 354.45 ± 61.84 μm in the d14 group,725.61 ± 144.45μm in the d30 group,1041.49 ± 135.35 μm in the d90 group and 512.5 ± 25.2 μm in the d180 group,with statistically significant differences(P < 0.0001).Lumen area was 64.07 ± 4.31 mm2 in the d14 group,48.16 ± 3.3 mm2 in the d30 group,41.09 ± 7.51 mm2 in the d90 group and 58.91 ± 5.04 mm2 in the d180 group,showing statistically significant differences(P < 0.001).No statistical significance was detected in area of inner elastic plate among each group(P > 0.05).Intimal area was 7.19 ± 1.14 mm2 in the d14 group,19.11 ± 3.51 mm2 in the d30 group,31.21 ± 5.39 mm2 in the d90 group and12.35 ± 0.45 mm2 in the d180 group,presenting statistically significant differences(P < 0.0001).The rate of in-stent restenosis was 10.04 ± 0.96% in the d14 group,28.62 ± 4.77% in the d30 group,43.34 ± 7.56% in the d90 group and 17.39 ± 1.27% in the d180 group,with statistically significant differences(P < 0.0001).Immunohistochemical staining revealed positive expression of MCP-1,IL-8,CD11 b,PDGF,FGF and α-SMA in different degrees in each experimental group.The positive expression of MCP-1 showed statistically significant differences among each group(P = 0.0002),and presented an increasing trend in the d180 group.The positive expression of CD11 b in each group showed statistically significant differences(P = 0.001),and reached its peak at the 30 th day after surgery.No statistical significance was found in the positive expression of IL-8 among each group(P = 0.1949).Comparison in the positive expression of PDGF,FGF and α-SMA showed statistically significant differences among each group(P = 0.0089,0.0007 respectively),and their expressions reached their peak at the 90 th day after stent implantation,followed by a decreasing trend.Conclusion: Thirty days after stent implantation in iliac vein,the surface of the stent is covered with endothelial cells completely.With 90 days after stent implantation,intimal hyperplasia reaches its peak,and then is weakened.Intimal hyperplasia leads to the occurrence of venous ISR,and mainly caused by the proliferation and migration of VSMCs and the proliferation of ECM.PDGF and FGF play an important role in the intimal hyperplasia and the occurrence of venous ISR after intravenous stent implantation.PDGF and FGF are closely related to VSMCs proliferation and migration.MCP-1,IL-8 and CD11 b are involved in the occurrence of venous intimal hyperplasia,which may be related to the proliferation and migration of VSMCs.