Dierk Vorwerk

Results of a multicenter study of the retrievable Tulip vena cava filter: Early clinical experience

PurposeTo evaluate clinically a new, retrievable vena caval filter in a multicenter study.MethodsThe 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.ResultsAn 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.ConclusionPrecise 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.

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.

Stent placement in iliac arterial lesions : three years of clinical experience with the wallstent

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.

New retrievable percutaneous vena cava filter: Experimentalin vitro andin vivo evaluation

A new retrievable percutaneous vena cava filter was testedin vitro andin 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.

Improvement of haemocompatibility of metallic stents by polymer coating

An alternative to open heart surgery in treating arterial diseases causing restricted blood flow is the implantation of intracoronary metallic stents. In spite of the advances in implantation and in spite of the excellent mechanical properties of metallic stents, there are still limitations because of the thrombogenicity of the metal. We have, hence, directed our attention to the coating of metallic stents with an ultrathin polymer layer by chemical vapor deposition (CVD) polymerization of 2-chloroparacyclophan. In a second step of surface modification the poly(2-chloroparaxylylene) layer is modified by treatment with a sulfur dioxide plasma in order to obtain a more hydrophilic surface with new functional groups. The results demonstrate the stable polymer coating of the stents and the improvement of haemocompatibility after treatment with sulfur dioxide plasma. Platelet adhesion is decreased from 85% for the metal surface to 20% for the CVD-coated and sulfur-dioxide-plasma treated surface.

Interventional magnetic resonance. Initial clinical experience with a 1.5-tesla magnetic resonance system combined with c-arm fluoroscopy.

RATIONALE AND OBJECTIVES The authors evaluate the feasibility of performing magnetic resonance (MR) procedures on a 1.5-tesla (T) system combined with conventional c-arm fluoroscopy. METHODS A 1.5-T MR imaging system was combined with a conventional c-arm fluoroscopy unit in one room. The two systems were connected via a floating table top. Twenty-six interventional procedures (biopsies, MR-portography, percutaneous alcohol injection, laser ablation, fluid aspiration, and breast marking) were performed in 22 patients under MR, fluoroscopic control, or both. For MR guidance, fast gradient echo sequences were used, initiated from a panel at the front of the magnet. Images were displayed on an liquid crystal display screen positioned on the magnet. RESULTS All MR-guided procedures were performed successfully without complications. The addition of c-arm fluoroscopy was useful for bone interventions and MR-portography. All diagnostic biopsies yielded sufficient amounts of tissue for histologic diagnosis. In breast lesions, the target identified on dynamic MR imaging was marked correctly in each case. In interstitial laser thermotherapy the laser effect could be visualized, and in percutaneous ethanol injection the distribution of the alcohol could be seen. Both imaging systems worked without image distortions and high-quality MR images were obtained. CONCLUSIONS The combination of a 1.5-T MR imager with a c-arm fluoroscopy system seems to be a promising technical solution for performing interventional MR procedures.

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.

Neointimal hyperplasia in low-profile nitinol stents, palmaz stents, and wallstents: A comparative experimental study

PurposeTo compare neointima formation following insertion of low-profile Nitinol stents, Palmaz stents, and Wallstents.MethodsNitinol 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.ResultsMean 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 andp<0.02, respectively); in the area under the stent struts there was a significant difference only between Palmaz stents and Wallstents (p<0.02).ConclusionUnder 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.

Neointima formation following arterial placement of self-expanding stents of different radial force: Experimental results

AbstractPurpose: Radial force delivered by self-expanding stents has been discussed as a factor affecting thickness of neointima formation. Methods: Two types of Wallstents were studied experimentallyin vitro andin vivo. Due to an altered braiding angle of the stent filaments, one stent type (LS type) delivers half the radial force to the vascular wall than the conventional type. The radial force was evaluated in a compression-expansion test which related changes in stent length to the compressing force. Fourteen LS and 16 conventional stents were implanted into 15 femoropopliteal arteries of 10 dogs. Autopsy was performed after 4 weeks (14 stents) or 6 months (16 stents). Results: All stents remained patent over the follow-up period with no evidence of stenosis. Neointimal overgrowth was complete and smooth in all. Medial atrophy was a constant finding after placement of both types. Neointimal thickness did not exceed 100μm after 4 weeks and 6 months and did not significantly differ between LS stents and conventional stents. Conclusion: It is concluded that in normal dogs self-expanding stents of the Wallstent type do not induce neointimal buildup that exceeds 100μm in the femoropopliteal artery. A reduced radial force was not found to result in reduced neointima formation.

Use of a cutting balloon for dilatation of a resistant venous stenosis of a hemodialysis fistula.

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.