Efficacy of a Paclitaxel-Eluting Nitinol Stent on the Inhibition of Pseudointimal Hyperplasia in a Transjugular Intrahepatic Portosystemic Shunt: An Experimental Study in a Swine Model

PURPOSE: To evaluate the efficacy of a paclitaxel-eluting nitinol stent on the inhibition of pseudointimal hyperplasia in a transjugular intrahepatic portosystemic shunt. MATERIALS AND METHODS: Twelve pigs were used in this study. Two types of 10-mm diameter and 60-mm long nitinol stents were made for a transjugular intrahepatic portosystemic shunt by coating them with a polyurethane solution, with and without paclitaxel. Each transjugular intrahepatic portosystemic shunt was created successfully in the 12 swine with 7 paclitaxel-eluting stents and 5 polyurethane stents. Five swine in each group were followed-up for 14 days due to the death of 2 swine given the paclitaxel-eluting stents. The proliferation of the pseudointima was evaluated on both follow-up portograms and histopathology examinations. The mean maximum pseudointimal hyperplasia is expressed as the percentage of the stent radius. RESULTS: On the portograms, all the transjugular intrahepatic portosystemic shunts using the paclitaxel-eluting stents maintained patency despite there being a complete occlusion of the polyurethane stents in all the animals. The histopathology analysis revealed the mean maximum pseudointimal hyperplasia to be 25% and 76% in the paclitaxel-eluting and control stents, respectively. CONCLUSION: A transjugular intrahepatic portosystemic shunt with a paclitaxel-eluting nitinol stent appears to significantly inhibit the formation of pseudointimal hyperplasia.

Reduction of Tissue Hyperplasia with a 188Re-MAG3-filled Balloon Dilation: Experimental Study with a Rabbit Esophageal Model

PURPOSE: The purpose of this study was to evaluate the feasibility and efficacy of beta-radiation therapy with a rhenium-188-mercaptoacetyltriglycine ((188)Re-MAG(3)) filled balloon to prevent tissue hyperplasia secondary to stent placement in a rabbit esophageal model. MATERIALS AND METHODS: Fifteen rabbits were divided into the three study groups. The ten rabbits having the radioactive balloon dilation performed immediately after stent placement were scheduled to be sacrificed at six weeks; the 20 Gy (Group I, n=5) or 40 Gy (Group II, n=5) at 1 mm away from the balloon surface were also sacrificed at six weeks. The remaining five rabbits that had conventional balloon dilation done immediately after stent placement were scheduled to be sacrificed six weeks later; this was the control group (Group III). At follow-up, we obtained esophagography and the histologic findings (epithelial layer thickness, degree of destruction of the muscularis propria, and degree of submucosal inflammatory cell infiltration) at both the normal area and the mid-stent area for each esophageal specimen after sacrificing each rabbit. The differences among the three groups were statistically assessed using Kruskal-Wallis and Mann-Whitney U tests. RESULTS:There were no complications such as migration after stent placement. Nine of the rabbits died 1-3 weeks after stent placement and the stents were partially obstructed with a lot of residue, so it was impossible to compare the esophagographic findings among the three groups. Esophageal perforation (n=6) and mucosal reddish changes (n=5) of the esophagus adjacent to the stent were observed only for rabbits of group I or II. The esophageal mucosa displayed smoothness in group I and II, and the esophageal mucosa displayed nodularity in group III. The degree of destruction of the muscularis propria was significantly higher in group I or II when compared to group III (p<0.05). CONCLUSION: Beta-irradiation using a (188)Re-MAG(3)-filled balloon dilation has the potential for preventing tissue hyperplasia secondary to stent placement in a rabbit esophageal model.

Glue Embolization of Aneurysm after Stenting in Canine Carotid Arteries - Technical Feasibility

PURPOSE: Coiling or infusion of embolic materials into a wide necked aneurysm can be performed with stenting. The purpose of our study is to assess the technical feasibility of aneurysm treatment with glue embolization after stenting. MATERIALS AND METHODS: We used four Wallstents for surgically repairing eight canine carotid aneurysms. After confirmation of the aneurysms on the angiogram, we introduced a 6-7 F guiding catheter in order to deploy the stents. After stenting, we passed a microcatheter into the aneurysm lumen through the stent mesh. 28% glue was slowly injected until the glue cast completely filled the lumen. We evaluated the passage of a microcatheter through the stent meshwork, formation of the glue cast and the stents' ability to protection for any leakage of glue. The follow-up angiogram was obtained for two dogs, one to three times until 8 weeks, and then we sacrificed the dogs and performed pathologic examinations. RESULTS: Stenting was successful in all cases except one in which the vessel was occluded because the stent was not completely expanded within the lumen. The microcatheter could not pass through the stent mesh in one aneurysm. The two week follow-up angiogram showed complete occlusion of the aneurysm and a patent carotid lumen in a case after successful stenting and glue embolization without distal migration of glue. Tungsten in the glue was noted to migrate out of aneurysm into the soft tissue of the neck. Histopathologic examination showed successful obliteration and stable organization of the aneurysmal lumen with ingrowth of fibroblasts and a foreign body reaction. In contrast, the aneurysms without the glue embolization being performed showed partially thrombosed aneurysmal lumens that became smaller and indistinct on the 8 week follow-up angiograms. Histopathologic examination showed a disorganized thrombus with numerous recanalizations. CONCLUSION: Glue embolization after stenting could be performed for aneurysm without distal migration of the glue or gluing of the catheter. This concept appears to be useful for applications to the further research and the treatment of aneurysm.

Radiofrequency Ablation of the Gastrointestinal Tract with a Stent-Like Electrode: Experimental Study

OBJECTIVE: To assess the technical feasibility of a newly designed stent-like electrode in rabbits. MATERIALS AND METHODS: A stent-like electrode was knitted from a single thread of nitinol wire and interconnected to a generator using similar wire. In order to gauge the extent of radiofrequency ablation (RFA), we measured the depth of the ablated area in cow liver using a combination of 180-sec time intervals and 20-watt power increments. For data processing, Cox regression analysis was used. RFA was also applied to the small intestine of rabbits using this stent-like electrode under six different sets of conditions: 10 watts for 1 min, 10 watts for 2 mins, 20 watts for 1 min, 20 watts for 2 mins, 30 watts for 1 min, and 30 watts for 2 mins. To determine the gross and microscopic findings, six animals were sacrificed immediately after the procedure and the results obtained under the different sets of conditions were correlated. Eight rabbits were monitored for 4 weeks prior to sacrifice. RESULTS: For both ex-vivo and in-vivo ablations, the depth of the thermal lesion showed linear correlation with both the duration of RFA and the power applied. RFA of the duodenum was technically successful in all 14 rabbits. The acute changes occurring in the rabbits' small intestine included color change, cytoplasmic denaturation, fibrin deposition and hemorrhage, among which hemorrhage of the mucosal layer was the earliest finding. RF ablation for 2 mins at 30 watts caused serosal hemorrhage. The gross and histologic changes occurring showed close correlation under all six sets of conditions. CONCLUSION: Use of the stent-like electrode proves technically feasible but to determine the nature of the chronic change occurring in the gastrointestinal tract after RF ablation, further investigation and long-term follow-up in animals are required.

Transluminal Radio-Frequency Thermal Ablation Using a Stent-Type Electrode: an Experimental Study

PURPOSE: To assess the feasibility of transluminal radiofrequency thermal ablation using a stent-type electrode and to determine, by means of in-vitro and in-vivo animal studies, the appropriate parameters. MATERIALS AND METHODS: In vitro: The radiofrequency electrode used was a self-expandable nitinol stent with 1cm insulated ends. A stent was placed in the portal vein of bovine liver, and ablations at target temperatures of 70, 80, 90, and 100degrees C were performed. Ablated sizes were measured longitudinally. In vivo: Four mongrel dogs were anesthetized, and a stent was inserted in the common bile duct under fluoroscopic guidance through an ultrasound-guided gall bladder puncture site. The ablation temperature was set at 80 degrees C, and each dog underwent proximal and distal esophageal ablations lasting 12 minutes. They were sacrificed immediately. RESULTS: In-vitro: Ablated sizes showed significant correlation with target temperatures (r>0.04; p<0.05). Although most lesions were fusiform, dumbbell-shaped lesions with central thinning were found in two cases in the 70degrees C group. In all cases in the 70 degrees C and 80 degrees C group, the length of the insulated segment was less than 1 cm. In-vivo: At microscopy, tissues at the center of the biliary stent showed more prominent pathological change than those at the periphery while those remote from the stent showed minimal or no change. In esophageal ablations, the mean highest temperature was 48.6 degrees C. Microscopy demonstrated the destruction and shedding of mucosa, edema, and coagulation necrosis of submucosa, but in muscle layers no abnormalities were apparent. CONCLUSION: Transluminal radio-frequency thermal ablation using a stent-type electrode may be useful for elongating patency. The appropriate target temperature for biliary ablation is 80 degrees C.