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Biomedical subjects

D Vorwerk

Publications and source records attributed to D Vorwerk.

158 records · Page 9Linked to original sources
PubMedDate not supplied

Stent placement on fresh venous thrombosis.

PURPOSE: To report on the efficacy of fixing fresh venous thrombus to the venous wall by stent placement. METHODS: Seven patients underwent stenting to treat acute venous thrombosis. In two patients, the hemodialysis fistula was thrombosed with the thrombus extending into the brachial veins. In three patients, the hemodialysis fistula was patent but massive swelling of the ipsilateral arm was caused by proximal venous thrombosis. Two patients presented with iliac venous thrombosis within stented pelvic veins. Stent placement was preceded by other mechanical thrombectomy methods in all cases. RESULTS: Attachment of thrombus to the venous wall was successful in all cases treated. Acute rethrombosis did not occur. Follow-up patency in dialysis patients was 7.2 +/- 2.1 months. One patient had rethrombosis of the dialysis graft 3 months after primary treatment. Three patients developed restenosis within a mean period of 7.7 months. One shunt remained patent for 10 months with no event of reobstruction during follow-up. In both patients with iliac stent placement, the vein remained patent over a follow-up period of 8 and 12 months respectively. CONCLUSION: Stenting fresh venous thrombus can achieve immediate venous patency. It may be used as an alternative approach when all other percutaneous methods fail. Frequent restenosis within stented veins limits its use to very selected cases.

Aged↗
PubMedDate not supplied

In vitro evaluation of a rheolytic thrombectomy system for clot removal from five different temporary vena cava filters.

PURPOSE: To evaluate the feasibility of thrombus removal from temporary vena cava filters using a rheolytic thrombectomy device and to assess the embolization rate of this procedure. METHODS: Five temporary vena cava filters together with porcine thrombi were placed in a vena cava flow model (semitranslucent silicone tube of 23 mm diameter, pulsatile flow at a mean flow rate of 4 L/min). A rheolytic thrombectomy system (Hydrolyser) was used with a 9 Fr guiding catheter to remove the clots. The effluent was passed through filters of different size and the amount of embolized particles as well as the remaining thrombus were measured. RESULTS: Thrombus removal rates ranged from 85% to 100%. Embolization rates between 47% and 60% were calculated for the different filters. CONCLUSION: The Hydrolyser is able to remove sufficiently high amounts of thrombus from temporary vena cava filters. However, the amount of embolized particles makes it impossible to utilize this method without special precautions against embolization.

Animals↗
PubMedDate not supplied

Determination of stent stenosis: an in vivo experimental comparison of intravascular ultrasound and angiography with histology.

PURPOSE: To compare intravascular ultrasound (IVUS) and angiography with histology in determining the degree of stent stenosis in an in vivo experiment. METHODS: In 16 sheep, a total of 64 stents were implanted into the external iliac arteries. Two stents were inserted on either side. Patency was followed by angiography and IVUS. Four types of stent were used: two Dacron-covered (Cragg Endopro and heparinized Cragg Endopro) and two noncovered (Cragg and Memotherm stents). Eight animals were killed after 1 month, eight others after 6 months. Histological sections were prepared from the stented vessels. Measurements of the patent and total stent diameters determined by IVUS, angiography, and histology were compared. RESULTS: Correlation between IVUS and angiography was 0.75, between IVUS and histology 0.77, and between angiography and histology 0.85. A mean stent stenosis of 17 +/- 11% (range 0-51%) was found on angiography, of 10 +/- 11% (0-46%) on IVUS, and of 20 +/- 11% (4%-49%) on histology. In comparison with histology, IVUS underestimated the degree of stenosis by 10 +/- 8%, and angiography underestimated it by 3 +/- 6%. Resolution of IVUS was calculated to be about 0.35 mm and that of angiography to be about 0.15 mm. CONCLUSION: Under experimental conditions, IVUS was not superior to angiography in determining the degree of stent stenosis in long-segment stenoses of iliac artery stents, when measurements were correlated with histology. Angiography is sufficient for following the patency of iliac artery stents.

Angiography↗
PubMedDate not supplied

Single and tandem stents in sheep iliac arteries: is there a difference in patency?

PURPOSE: To compare patency and neointima formation of single and tandem arterial stents. METHODS: In each of six sheep, two Memotherm nitinol stents (tandem stents) were inserted into the external iliac artery on one side and a single stent into the artery on the opposite side. The size of the iliac lumen was assessed in the proximal, middle, and distal segments of the stents by intravascular ultrasound (IVUS) before, immediately after, and 1 month after implantation when the sheep were killed. Neointimal thickness was determined in the proximal, middle, and distal segments of each stent by light microscopy. RESULTS: All stents remained patent. There was no significant difference in lumen and neointimal thickness between single and tandem stents. Cranial tandem stents showed a significantly wider lumen and smaller neointimal thickness than caudal tandem stents. In the proximal and distal segments, the lumen of the stents was significantly smaller and the neointimal thickness greater than in the middle segment; differences in neointimal thickness were significant only between the proximal and the middle segment. CONCLUSION: In an experimental setting, tandem stents did not interfere with one another with regard to patency and neointima formation when compared with a single contralateral stent. Neointimal thickening after stent insertion seems to be inversely related to the original arterial diameter.

Angiography↗
PubMedDate not supplied

Quantification of horseradish peroxidase delivery into the arterial wall in vivo as a model of local drug treatment: comparison between a porous and a gel-coated balloon catheter.

PURPOSE: To quantify horseradish peroxidase (HRP) delivery into the arterial wall, as a model of local drug delivery, and to compare two different percutaneous delivery balloons. METHODS: Perforated and hydrophilic hydrogel-coated balloon catheters were used to deliver HRP in aqueous solution into the wall of porcine iliac arteries in vivo. HRP solutions of 1 mg/ml were used together with both perforated and hydrophilic hydrogel-coated balloon catheters and 40 mg/ml HRP solutions were used with the hydrogel-coated balloon only. The amount of HRP deposited in the arterial wall was then determined photospectrometrically. RESULTS: Using the 1 mg/ml HRP solution, the hydrogel-coated balloon absorbed 0.047 mg HRP into the coating. Treatment with this balloon resulted in a mean vessel wall concentration of 7.4 microg HRP/g tissue +/- 93% (standard deviation) (n = 7). Treatment with the hydrogel-coated balloon that had absorbed 1.88 mg HRP into the coating (using the 40 mg/ml HRP solution) led to a mean vessel wall concentration of 69.5 microg HRP/g tissue +/- 74% (n = 7). Treatment with the perforated balloon using 1 mg/ml aqueous HRP solution led to a mean vessel wall concentration of 174 microg/g +/- 81% (n = 7). Differences between the hydrogel-coated and perforated balloons (1 mg/g solutions of HRP) and between hydrogel-coated balloons (0.047 mg vs 1.88 mg absorbed into the balloon coating) were significant (p < 0.05; two-sided Wilcoxon test). CONCLUSIONS: The use of a perforated balloon catheter allowed the delivery of a higher total amount of HRP compared with the hydrogel-coated balloon, but at the cost of a higher systemic HRP application. To deliver 174 microg HRP per gram of vessel wall with the perforated balloon, 6.5 +/- 1.5 mg HRP were lost into the arterial blood (delivery efficiency range = 0.2%-0.3%). With 0.047 mg HRP loaded into the coating of the hydrogel balloon, 7.4 microg HRP could be applied to 1 g of vessel wall (delivery efficiency 1.7%), and with 1.88 mg HRP loaded into the coating of the hydrogel balloon, 69.5 microg HRP could be applied per gram of vessel wall (delivery efficiency 0.6%).

Animals↗
PubMedDate not supplied

Magnetic resonance angiography of nonferromagnetic iliac artery stents and stent-grafts: A comparative study in sheep.

PURPOSE: To compare nonferromagnetic iliac artery prostheses in their suitability for patency monitoring with magnetic resonance angiography (MRA) using conventional angiography as a reference. METHODS: In experiment 1, three Memotherm stents were inserted into the iliac arteries of each of six sheep: two "tandem" stents on one side and a single stent on the other side. In experiment 2, four prostheses (normal and low-porosity Corvita stent-grafts, Memotherm, ZA-stent) were inserted in each of 11 sheep. Patency was monitored before and 1, 3, and 6 months after insertion with 3D phase-contrast and two 2D time-of-flight sequences (TOF-1: TR/TE = 18/6.9, TOF-2: 13/2.5) with and without contrast at 1.5 T. On 206 coronal MIP images (72 pre-, 134 post-stenting), three readers analyzed 824 iliac segments (206 x 4) for patency and artifacts. RESULTS: There was no difference in the number of artifacts between tandem and single iliac Memotherm stents. The ZA-stent induced significantly fewer artifacts than the other prostheses (p < 0.00001). With MRA, patency of the ZA-stent was correctly diagnosed in 88% of cases, which was almost comparable to nonstented iliac segments (95%), patency of the Memotherm stent in 59%, and of the Corvita stent-grafts in 57% and 55%. The TOF-2 sequence with contrast yielded the best images. CONCLUSION: MRA compatibility of nonferromagnetic prostheses depends strongly on the design of the device. MRA may be used to monitor the patency of iliac ZA-stents, whereas iliac Memotherm stents and Corvita stent-grafts appear to be less suited for follow-up with MRA.

Animals↗
PubMedDate not supplied

Long-term patency of Wallstent endoprostheses in benign biliary obstructions: experimental results.

PURPOSE: Coated and noncoated Wallstents were implanted in dogs with experimental benign common bile duct stenoses to monitor the long-term patency of self-expanding stents in the biliary system. MATERIALS AND METHODS: Experimental common bile duct stenoses were induced with a thermal laser in 12 dogs. Three silicone-coated and 14 noncoated stents were implanted. The animals were followed up from 3 to 25 months by means of cholangiography, cholangioscopy, measurements of liver enzyme levels, autopsy, and histology. RESULTS: Silicone coated stents failed in all cases, resulting in two total occlusions and one stent dislodgment to the bowel. Noncoated stents led to marked mucosal hyperplasia and stent narrowing in most cases, but with follow-up of more than 12 months, hyperplasia underwent regression and--except in one case--neither an increase in liver enzyme levels nor stent occlusion occurred. Histologically, the extent of hyperplasia was related to the stent position within the duct wall. With stents in the mucosal layer, hyperplasia was excessive. Once the stent entered the submucosal layer, hyperplasia was decreased. CONCLUSION: In an experimental setting, mucosal hyperplasia did not compromise patency of noncoated stents in benign bile duct stenosis and regressed with late follow-up after 12 months.

Animals↗
PubMedDate not supplied

Hydrodynamic thrombectomy of hemodialysis fistulas: first clinical results.

PURPOSE: A hydrodynamic thrombectomy system was used for the treatment of recent dialysis shunt thrombosis. PATIENTS AND METHODS: Sixteen shunt thromboses in 14 patients were included in the study. There were seven polytetrafluoroethylene grafts and nine native arteriovenous fistulas. Occlusion time ranged from 6 to 48 hours, and thrombus length ranged from 4 to 40 cm. RESULTS: Thrombectomy was technically successful in 15 of 16 instances. No significant residual thrombus was found in 15 cases. In one case, half of the thrombus remained in the vessel and the procedure failed technically. One embolus to the radial artery occurred after balloon dilation following hydrodynamic thrombectomy and was removed percutaneously. Early rethrombosis within 24 hours occurred in five shunts; four more rethrombosed within 2 weeks to 3 months. Eleven shunts were available for follow-up. Cumulative patency was 41% after 6 months. CONCLUSION: Hydrodynamic thrombectomy is a promising concept for declotting of both hemodialysis grafts and native shunts and may offer an alternative to thrombolysis and surgical thrombectomy.

Adult↗
PubMedDate not supplied

Use of a temporary caval filter to assist percutaneous iliocaval thrombectomy: experimental results.

PURPOSE: To test a new filter design that allows coaxial insertion of thrombectomy devices and active clot removal. MATERIALS AND METHODS: A prototype filter system was used in animal experiments. It is a transjugularly inserted coaxial system with a 16-F outer sheath and an inner tube that is covered by a tulip-shaped meshwork with a 22-mm diameter at its inserted end. The inner tube allows insertion of instruments up to 8 F. The filter was developed to assist with percutaneous mechanical thrombectomy in the iliofemoral and caval veins. The filter has been used as an assisting tool in nine sheep and eight pigs. It was combined with an impeller system in nine sheep for caval thrombectomy and with a hydrodynamic catheter for iliac thrombectomy in eight pigs after artificial induction of iliac or caval thrombosis. RESULTS: The filters captured emboli from the intervention in six of nine sheep. The amount of captured emboli was reduced within the filter cone by the impeller instrument in five of six instances. Residual thrombus was removed by closing the filter in five of six sheep. In pigs, the filter captured emboli in three cases during hydrodynamic embolectomy. Pulmonary embolization did not occur with the filter in place. After filter removal, minor pulmonary clot embolization occurred in one case. CONCLUSION: The temporary tulip filter was effective in these animal models in capturing and removing thrombus material that may dislodge from iliocaval veins during mechanical thrombectomy.

Animals↗
PubMedDate not supplied

Comparative in vitro study of two percutaneous hydrodynamic thrombectomy systems.

PURPOSE: To test the efficacy of clot removal in small- and large-caliber vessels and determine the extent of procedure-related particle embolization for two rheolytic thrombectomy devices, the Hydrolyser and Angiojet. MATERIALS AND METHODS: Both systems were applied with and without guiding catheters in an arterial (7-mm tube diameter, wall-adherent thrombus [mean, 5.3 g], flow of 500 mL/min)and a venous (20-mm tube diameter, free-floating thrombus [mean, 12 g], flow of 1,500 mL/min) flow model. RESULTS: Particle embolization was significantly lower for the Angiojet device (mean, 1.8% +/- 2.9 [standard deviation] vs mean 4.8% +/- 6.1 for particles > 1,000 microns). When the devices were used without guiding catheters, mean clot removal rates were 65% +/- 12 with the Hydrolyser and 49% +/- 9.2 with the Angiojet in the arterial flow model and 88% +/- 15.5 with the Hydrolyser and 85% +/- 17.8 with the Angiojet in the venous flow model. Significant improvements in clot removal rates were achieved with use of guiding catheters: 81% +/- 5.4 with the Hydrolyser and 89% +/- 3.9 with the Angiojet in the arterial flow model and 95% +/- 1.4 with the Hydrolyser and 97% +/- 0.84 with the Angiojet in the venous flow model. CONCLUSION: Use of guiding catheters improved the performance of both systems significantly. Both rheolytic catheters remove sufficient amounts of soft thrombus from a large-caliber vessel, especially when applied with a guiding catheter. However, firmer thrombus is difficult to remove. The particle embolization rate is low for both systems.

Animals↗