Biomedical subjects
Publications and source records attributed to D Vorwerk.
This report describes the successful management of a long venous stenosis that resulted from intimal hyperplasia in a synthetic hemodialysis graft. The recurrent stenosis was kept patent with four overlapping, self-expanding metallic stents, which allowed coverage of the 16 cm distance from the axillary vein to the synthetic graft.
A new coaxial needle system was designed for percutaneous puncture of osteoclerotic lesions. Driven by a conventional motor unit, the instrument allows safe guidance even where difficult biopsy routes are used, and has been shown to penetrate radiopaque lesions. Preliminary clinical results from 29 patients are presented. The specimens obtained yielded a correct diagnosis in 28 cases. No major complications were observed.
A benign circumferential stenosis of the left hepatic duct was successfully treated with a self-expanding flexible metallic stent in a 70-year-old woman. Multiple intrahepatic stones were also removed percutaneously after dilatation of the tract up to a 24F diameter.
PURPOSE: To compare neointima formation following insertion of low-profile Nitinol stents, Palmaz stents, and Wallstents. METHODS: Nitinol stents, Palmaz stents, and Wallstents similar in size were transfemorally inserted into the iliac arteries of 12 sheep. Four stents per sheep were deployed; the position of the stents was varied so that each type of stent was placed in each position (right or left, proximal or distal) with equal frequency. Stent patency was followed by angiography. Six sheep were euthanized after 1 month, and the remaining six after 6 months. Iliac arteries were removed en bloc and prepared for histological examination. Neointimal and medial thickness were measured by light microscopy, and measurements were analyzed statistically. RESULTS: Mean neointimal thickness both over (NO) and between (NB) the stent struts was greater in Wallstents (NO = 0.341 mm, NB = 0.368 mm) than in the Nitinol (NO = 0.260 mm, NB = 0.220 mm) and Palmaz stents (NO = 0.199 mm, NB = 0. 204 mm), but differences were not significant (p > 0.05). Medial atrophy in the area between the stent struts was greater in Wallstents compared with Nitinol and Palmaz stents (p < 0.007 and p < 0.02, respectively); in the area under the stent struts there was a significant difference only between Palmaz stents and Wallstents (p < 0.02). CONCLUSION: Under defined experimental conditions, none of the three types of stent appears to be preferable to the others regarding neointima formation in the short- to mid-term follow-up period.
PURPOSE: To assess the efficacy of catheter fragmentation of massive caval thrombosis and of filter protection against procedure-related pulmonary embolism. METHODS: In 10 sheep, a self-expanding tulip-shaped filter made from Wallstent mesh (diameter 25 mm) was introduced from the right jugular approach into the proximal inferior vena cava. Experimentally induced massive iliocaval thrombosis was fragmented by an impeller catheter (expanded diameter 14 mm), which was advanced coaxially through the sheath of the expanded filter. Post-procedural cavography and pulmonary angiography were performed to document the extent of caval recanalization and pulmonary embolism. RESULTS: In all cases, impeller fragmentation cleared the inferior vena cava and the iliac veins of thrombi completely. Fragments washed downstream were trapped in the filter. In two of the first cases, parts of the clots caused pulmonary embolism before the filter was in place. Further events were avoided by a modification of the experimental setup. Except for some small peripheral perfusion defects in two cases, pulmonary angiograms did not show any incidence of pulmonary embolism. CONCLUSION: Our preliminary results suggest that impeller fragmentation of iliocaval thrombi under tulip filter protection is effective and does not cause significant pulmonary embolism.
Primary stenting of common iliac artery occlusions was complicated by dislodgement of occluding material to the contralateral common iliac artery in 2 of 59 patients following successful stent placement. In both patients, the complication occurred after balloon dilatation of the inserted self-expanding stent. In the first patient the embolus dislodged to the tibioperoneal trunk and required surgical embolectomy. In the second patient, percutaneous insertion of a self-expanding stent into the contralateral common iliac artery prevented distal embolization.
As an alternative approach to thrombectomy in peripheral arteries, a miniaturized Dormia basket was designed which is attached to a 0.021 inch guidewire and can be introduced coaxially by a 3F thin-walled catheter. The device was applied successfully in 6 patients: for percutaneous thrombectomy in 5 patients with peripheral embolization during angioplasty and as a protective filter during thrombectomy in 1.
Self-expandable endoprostheses were used in 18 failing arteriovenous shunts after unsuccessful balloon dilatation. Technical success was satisfactory with an early patency in 17 of 18 shunts. Thrombosis right after stenting occurred in three shunts but was successfully treated in two. Follow-up history revealed recurrent events of reobstruction due either to stent or shunt stenoses or thrombosis. Restenosis within the stented segment was responsible for reobstruction in about half the cases. Although patency was low with 27% at 18-month follow-up, repeated intervention established a shunt survival rate of 77% at 18-month follow-up. Stent placement in AV shunts is useful for overcoming acute problems of balloon dilatation but does not prevent restenosis.
In 2 patients, an aortic stenosis failed to respond adequately to balloon dilatation but was successfully treated by implantation of a self-expandable large caliber endoprosthesis and subsequent balloon angioplasty. Intravascular ultrasound helped to classify the characteristics of the lesion in preparation for intervention.
Our experience with percutaneous transluminal angioplasty for treatment of stenoses and occlusions in surgically created arteriovenous fistulas (Brescia-Cimino) is reported. Methodological aspects are emphasized. Forty-nine PTAs were performed in 36 patients, in 3 combined with the use of a vascular metallic endoprosthesis (Wallstent). The initial success rates for stenoses and occlusions were 91% and 77%, respectively. Long stenoses and occlusions (greater than 4 cm) showed significantly worse initial results (55%) as compared to short ones (95%). Of the primarily successfully treated shunts, 90% are still functioning after a mean follow-up time of 8 months. The results indicate that PTA may replace surgical intervention as the primary method for treatment of insufficient flow for internal arteriovenous shunts, provided fresh thrombi are not the cause of the occlusion. Metallic endoprostheses and the use of atherectomy catheters were shown to be a valuable adjunct to classical PTA in selected cases.
A new retrievable percutaneous vena cava filter was tested in vitro and in vivo in 15 foxhounds. In vitro, the new vena cava filter was compared with the standard Kimray-Greenfield filter and the Günther basket filter. The new filter is a stainless steel half-basket filter and is suitable for percutaneous antegrade or retrograde insertion through a 8.5 Fr introducer sheath. In vitro testing showed the filter causing no significant flow alterations and being highly effective in capturing medium- and large-sized thrombi; furthermore, fatigue testing revealed no breakage of the new filter, whereas the Günther basket filter showed breakage of the struts. In vivo studies showed no occlusion, major perforation, or filter migration during follow-up of 2 weeks to 6 months. Tilting of the filter postimplantation occurred in two out of 28 filters. Ten of 11 filters were successfully retrieved by the transjugular approach 2 weeks after implantation. The device seems to be suitable for temporary or permanent protection against pulmonary embolism.
A new catheter system for rapid percutaneous fragmentation of pulmonary emboli was tested in nine dogs. The system consisted of a high-speed rotating impeller, placed within the center of a self-expandable basket. Preformed radiopaque emboli were introduced via the right external jugular vein. In nine tests in five dogs, a single embolus was launched after the right pulmonary artery had been balloon occluded and the impeller-basket catheter had been positioned into the left pulmonary artery. Seven of nine emboli were completely fragmented, each within less than 10 s. In two tests, performed in two different dogs, the catheter was positioned after complete embolization of the left pulmonary artery. In both cases, the central pulmonary arteries could be fully, and the segmental arteries partly, recanalized. Mobility of the system within the pulmonary arteries was limited. There was no evidence of wall damage at the rotation site of the impeller. Free serum hemoglobin did not increase after treatment. We conclude that the device can be safely operated in the left pulmonary artery system of dogs. It causes no significant hemolysis, and is able to accomplish rapid recanalization of the central arteries. Due to limited steerability, occluded side branches cannot be treated consistently.
Within a 3-year period, 125 patients with 63 iliac occlusions and 62 complex iliac stenoses underwent stent placement using self-expandable vascular endoprostheses. Early technical success rate was 98%, with a total complication rate of 4%. Major complications were seen in 1.6%. Early reobstruction occurred in 4 patients with previous occlusions. Late reobstruction due to a clinically relevant restenosis or reocclusion occurred in 10 patients and required 12 repeat interventional procedures. Cumulative patency, excluding early technical failure, was 100% at 6 months and 89.4% at 24 months. Stenting of iliac arteries using self-expandable endoprostheses is a safe and effective treatment of complex iliac lesions.
A system for three-dimensional (3D) presentation of intravascular ultrasound (US) images was designed. A standard hardware configuration based on personal computer equipment was used for acquisition and processing of image data. Pullback imaging with the US catheter was controlled by a specially designed motor assembly and performed either in equidistant 1-10 mm steps or at a constant retraction speed. Curvature of the vessel was documented on biplane digital subtraction angiograms and the US images were arranged according to the vessel shape in the angiograms. 3D reconstruction appears essential for spatial orientation of intravascular US and may be helpful in the planning of vascular interventions for a better appreciation of the extent and morphology of vascular lesions.
A 47-year old male patient presented with claudication from a right-sided aortoiliac dissection secondary to transfemoral cardiac angiography. Placement of two self-expanding stents led to immediate compression of the false channel. The patient has been free of symptoms for 18 months.
In a 71-year-old patient with a Brescia-Cimino hemodialysis fistula, high-pressure balloon dilatation failed to open the stenosis completely and a constant waist of the balloon was found. The use of a 3.5-mm coronary cutting balloon (Barath balloon) was helpful in preparing the stenosis for subsequent successful dilatation.
PURPOSE: To evaluate clinically a new, retrievable vena caval filter in a multicenter study. METHODS: The Tulip filter is a stainless steel half-basket that is suitable for antegrade or retrograde insertion via an 8.5 Fr introducer sheath. The filter can be retrieved via the jugular approach using an 11 Fr coaxial retrieval system. Forty-eight filters were implanted via the femoral approach and 38 via the jugular approach in 83 patients. Follow-up examinations (plain films, colorcoded duplex sonography) were performed up to 3 years after filter insertion (mean 136 days) in 75 patients. Twenty-seven patients were screened by colorcoded duplex sonography for insertion site thrombosis. RESULTS: An appropriate filter position was achieved in all cases. Insertion problems occurred in 3 cases; these were not due to the filter design but to an imperfect prototype insertion mechanism that has now been modified (n = 2) or a manipulation error (n = 1). In 2 of these cases the filters were replaced percutaneously; 1 patient required venotomy for filter removal. No further complications due to filter insertion occurred. Two filters were used as temporary devices and were successfully removed after 6 and 11 days, respectively. There was 1 fatal recurrent pulmonary embolism (PE) and 2 non-fatal PE, 5 complete and 3 partial caval occlusions, and 3 caudal migrations of the filter. Insertion site venous thrombosis was not seen in the 27 patients monitored for this complication. CONCLUSION: Precise placement of the Tulip filter is feasible by either access route and the device appears mechanically stable. Further observations are needed to confirm that safe filter removal is practical up to 10 days after its insertion.
A simple technique of performing a circular subcutaneous suture that helps to stop bleeding after cannulation of hemodialysis grafts and fistulas following percutaneous revision is described.