Jörg Schmehl

Thrombogenicity of Various Endovascular Stent Types: An In Vitro Evaluation

PURPOSE The aim of this study was to evaluate the thrombogenicity of different peripheral stent types in a standardized in vitro model with fresh human whole blood. MATERIALS AND METHODS Different stents (N = 77; n = 7 of each of 11 types) were implanted in polyvinyl chloride tubing loops and filled with donor blood samples. After 120 minutes of blood circulation, the thrombin-antithrombin III complex (TAT) levels, beta-thromboglobulin (beta-TG) levels, and platelet counts were assessed. RESULTS After 2 hours, significant differences were seen. TAT values (+/- SD) with the investigated stents were 31 micro g/mL +/- 20 (control, no stent), 328 micro g/mL +/- 206 (Saxx stent, peripheral medium CrNi31 L), 651 micro g/mL +/- 760 (Palmaz Corinthian Stent, 316 L stainless steel, electropolished), 1,609 micro g/mL +/- 1,264 (Palmaz Corinthian Stent, 316 L stainless steel, not electropolished), 810 micro g/mL +/- 578 (Palmaz Schatz long medium stent), 569 micro g/mL +/- 347 (Smart Nitinol stent), 1,037 micro g/mL +/- 577 (Megalink peripheral stent), 543 micro g/mL +/- 487 (peripheral stent, electropolished), 1,674 micro g/mL +/- 2,057 (peripheral stent, not electropolished), 3,128 micro g/mL +/- 1,812 (SelfX Nitinol stent, polished), 5,897 micro g/mL +/- 2,380 (SelfX Nitinol stent, unpolished), and 1,458 micro g/mL +/- 887 (bridge stent). The platelet count (x1,000/ micro L +/- SD) was 218 +/- 35 (control, no stent), 188 +/- 22 (Saxx stent), 187 +/- 20 (Palmaz Corinthian stent, electropolished), 135 +/- 37 (Palmaz Corinthian stent, not electropolished), 170 +/- 24 (Palmaz Schatz stent), 180 +/- 36 (Smart Nitinol stent), 159 +/- 26 (Megalink peripheral stent), 173 +/- 17 (peripheral stent, electropolished), 133 +/- 51 (peripheral stent, not electropolished), 123 +/- 37 (SelfX Nitinol stent, polished), 52 +/- 27 (SelfX Nitinol stent, unpolished), and 130 +/- 31 (bridge stent). CONCLUSION This standardized study showed a wide range of platelet activation after stent implantation. Electropolishing clearly reduced the thrombogenicity of the stents.

Silicon carbide coating of nitinol stents to increase antithrombogenic properties and reduce nickel release.

BACKGROUND The use of stents in the superficial femoral artery is still limited by the number of restenoses. Influencing factors include thrombus formation and smooth muscle cell proliferation as well as motion stress. A reduction of thrombogenicity can be achieved by passive coating with silicon carbide, which induces less thrombus formation due to its semiconducting properties. METHODS AND MATERIALS Self-expanding peripheral stents with and without silicon carbide coating were examined in a chandler loop model. Assessed parameters included thrombocyte count, beta-thromboglobulin (TG), thrombin-antithrombin (TAT) III complex, and polymorphonuclear elastase. Nickel release was quantified at Days 1, 3, and 223 using graphite furnace atomic absorption spectrometry. To visualize thrombus formation on the surface, scanning electron microscopy was conducted. RESULTS The tests showed a superiority of the coated stents regarding beta-TG (484.0+/-180.2 IU/l vs 2189.1+/-898.9 IU/l) as well as formation of TAT III complex (16.0+/-19.1 microg/l vs 458.3+/-761.0 microg/l). Scanning electron microscopy revealed a nearly absent thrombus formation on the coating. Nickel release was reduced by more than 90% at all time points. CONCLUSIONS In the provided in vitro setting, silicon carbide coating applied to self-expanding peripheral stents showed an advantage regarding thrombogenicity. The passive barrier resulted in a limited release of nickel from the alloy itself. These features seem promising for the use in the peripheral vasculature.

Twelve-Month Results of a Randomized Trial Comparing Mono With Dual Antiplatelet Therapy in Endovascularly Treated Patients With Peripheral Artery Disease

Purpose To present the 12-month results of a trial investigating the effects of dual antiplatelet therapy on target lesion revascularization (TLR) after balloon angioplasty ± stenting in the femoropopliteal segment. Methods A prospective, randomized, single-center, double-blinded and placebo-controlled clinical trial randomly assigned 40 patients to receive pre- and postinterventional therapy with aspirin and clopidogrel. Another 40 patients received the same doses of aspirin and placebo instead of clopidogrel. Clopidogrel and placebo were stopped after 6 months, and patients remained on aspirin only. At 12 months after the intervention, 36 clopidogrel patients and 37 placebo patients were reevaluated. Results At 6 months, clopidogrel patients had significantly lower rates of TLR compared to placebo patients [2 (5%) vs. 8 (20%), p=0.04]. After stopping clopidogrel/placebo after 6 months, there was no significant difference in TLR at 12 months after treatment [9 (25%) clopidogrel vs. 12 (32.4%) placebo, p=0.35]. Mortality was 0 vs. 1 in the placebo group at 6 months (p=0.32) and 0 vs. 3 at 12 months (p=0.08). Conclusion In contrast to the first report of a reduction in the TLR at 6 months, this advantage of dual antiplatelet therapy does not persist after stopping clopidogrel. Prolonged dual therapy (>6 months) should be considered in patients who are at high risk for restenosis.

Comparison of Digital Flat-Panel Detector and Conventional Angiography Machines: Evaluation of Stent Detection Rates, Visibility Scores, and Dose-Area Products

OBJECTIVE The objective of this study was to compare the performance and radiation doses of a flat-panel detector (FPD) angiography machine with an image intensifier (II) angiography machine. MATERIALS AND METHODS Images of four nitinol stents (Sinus-SuperFlex, SMART, Luminexx, and Zilver stents) in a phantom of a human pelvis were acquired on an FPD system (Axiom Artis) and an II system (Fluorospot TOP) using the following modes: spot-film, continuous fluoroscopy (4, 7.5, 15, and 30 pulses/s), and three amplification modes. Objective stent detection rates and subjective radiopacity scores (scale: 0 [not visible] to 4 [excellent visibility]) were calculated. The radiation doses evaluated by the respective machines were compared. RESULTS Over all modes and stents, the mean objective correct stent detection rates and mean subjective radiopacity scores were 89.49% and 1.81, respectively, for the Axiom Artis and 91.00% and 2.26 for the Fluorospot TOP. The stent detection rates over all modes for the SMART and Luminexx stents were better using the Axiom Artis machine (97.61% vs 93.55% and 98.28% vs 90.41%, respectively) and those for the Sinus-SuperFlex and Zilver stents were better using the Fluorospot TOP machine (90.83% vs 83.56% and 89.29% vs 80.50%). The subjective radiopacity scores of stent visibility were worse for the Axiom Artis than the Fluorospot TOP for all stents except the Luminexx stent (mean score, 2.34 vs 2.21, respectively). The objective stent detection rates and subjective radiopacity scores improved using the spot-film mode and with raising amplification, whereas increases in the fluoroscopy pulsing frequency did not improve stent detection rates or radiopacity scores for either machine. The radiation doses at continuous fluoroscopy were approximately 90% higher for the Axiom Artis than for the Fluorospot TOP (2.60 vs 1.41 μGy/m(2) at 30 pulses/s, respectively). CONCLUSION The objective correct stent detection rates were similar for both machines with differences in detection for the respective stents. The subjective radiopacity scores were almost always better for the Fluorospot TOP machine. Also, the Axiom Artis machine generated approximately 90% higher radiation doses in fluoroscopy. For both machines, using a higher fluoroscopy pulsing frequency had no positive effect on objective correct stent detection rates or subjective radiopacity scores.

Superficial femoral artery: current treatment options

Treatment of the superficial femoral artery (SFA) has been among the least effective of all endovascular procedures in terms of long-term patency. The relatively small vessel lumen, in conjunction with a high plaque burden, slow flow, and a high frequency of primary occlusions, contributes to a considerable rate of acute technical failures. Because of these technical limitations a much effort has been made during the past years. This manuscript should summarize the hopes and limitations of different approaches such as brachytherapy, cutting balloons, stents and stent grafts, drug-eluting stents, and drug-coated balloons.

Epithelioid Angiosarcoma With Metastatic Disease After Endovascular Therapy of Abdominal Aortic Aneurysm

Malignancies of the aortic wall represent a rare condition, and only a few reports have covered cases of sarcomas arising at the site of a prosthesis made of Dacron. A coincidence with endovascular repair has only been reported in one case to date. We report a patient with epithelioid angiosarcoma and metastatic disease, which was found in an aneurysmal sac after endovascular aortic repair for abdominal aortic aneurysm.

Current status of bare and drug-eluting stents in infrainguinal peripheral vascular disease

Currently, the use of endovascular therapies including stent application is increasingly becoming the treatment of choice for superficial femoral and below-the-knee lesions. Primary stenting of even longer lesions is supported by favorable results of mid- to long-term evaluations. However, issues such as the long-term patency of these devices, optimal design of the stents used, and the role of coating with drugs for infrainguinal disease are under investigation. With more widespread use, problems such as fractures become evident and further developments will have to address these issues. Currently, a number of studies are being conducted, which will help to clarify the role of patient and lesion selection, choice of device, design of the stent and the question of whether or not to use drug-eluting stents for this application. Furthermore, endovascular therapy of below-the-knee lesions is becoming an increasingly interesting area for interventional procedures.

Effects of MRI contrast agents on human embryonic lung fibroblasts.

Rationale and Objectives:The objective of this investigation was to evaluate 6 magnetic resonance contrast media (CM) with regard to their different effects on human embryonic lung fibroblasts (HEL-299). Methods:Human embryonic fibroblasts (HEL-299) were incubated with 1×, 5×, 10×, and 20× of the normal molar blood concentration (1×, 5×, 10×, 20× conc.) reached through routine contrast media applications for MRI examinations. Four gadolinium-based CM, ie, Gadovist, Magnevist, Multihance, Omniscan, Teslascan (Manganese-based), and Resovist (Iron-based), with incubation periods over 4 hours and 24 hours were investigated. Proliferation kinetics, colony formation, and viability assays were performed after 4 and 24 hours of treatment. Apoptotic cells were quantified after tetramethylrhodamine ethyl ester staining following 24 hours of CM media incubation (20× conc.) by fluorescence activated cell sorting cytometry. Furthermore, immunofluorescence images with vimentin staining were obtained (20× conc., 24 hours treatment). Cell cycle analysis was performed after 24 hours of incubation and 20× conc. directly after incubation and 24 hours later (fluorescence activated cell sorting cytometry). Results:The proliferation kinetics performed with 20× conc. revealed a persistent increase in cell numbers until day 11 for all CM without significant differences after 4 hours of incubation. A significant reduction in initial cell numbers was recorded in the 24-hours-group after 4 days of CM incubation with Magnevist, Multihance, Omniscan, and Teslascan. Solely cells incubated with Resovist and Gadovist failed to show decreased cell numbers when compared with the control group. However, a considerable cell regain occurred afterward reaching control-group levels on day 21. Colony numbers were significantly reduced (about 20%, respectively) with Magnevist at 10× and 20× conc., as well as Omniscan and Multihance at 20× conc. when compared with all other groups, P < 0.05. Cell-cycle distribution showed a reduction of S-phase cells for Magnevist, Omniscan, and Multihance (2.9%–10.5%) when compared with Gadovist, Resovist and Teslascan (16.7%–21.0%). Twenty-four hours after incubation, the percentiles of cells in S-phase were significantly increased for Magnevist, Omniscan, and Multihance (31.4%–38.5%) when compared with Gadovist, Resovist, and Teslascan (18.6%–26.8%), P < 0.05. Viability was not impaired by administration of any CM and no apoptosis was seen after tetramethylrhodamine ethyl ester staining at 24 hours of incubation. Cell morphology remained unchanged in vimentin-staining for all CM and conditioning regimens. Conclusions:No toxic effects on embryonic fetal lung fibroblasts were detectable after 4 and 24 hours of incubation in 6 MRI CM and 10× to 20× conc. in our setting. Antiproliferative effects, initially detected with Magnevist, Omniscan and Multihance, were rapidly compensated for.

Delayed endovascular treatment of renal artery dissection and reno-vascular hypertension after blunt abdominal trauma.

As a rare complication of blunt abdominal trauma, dissection of the renal arteries can be observed among other severe complications [1, 2] and necessitates immediate surgical or endovascular intervention to prevent significant ischemic organ damage. If successful intervention cannot be performed immediately, patients are prone to develop renovascular hypertension over time through the activation of the renin-angiotensin-aldosterone system (RAAS). However, they still may benefit from a delayed surgical reconstruction of the vessel or percutaneous endovascular treatment. If recovery of kidney function and reversal of renovascular hypertension before the intervention is in doubt due to prolonged delay of revascularization, percutaneous endovascular treatment may be the first option because complication rates can be kept reasonably low. We report a case of a successful but delayed endovascular treatment of a traumatic renal artery dissection and reversal of consecutive renovascular hypertension after blunt abdominal trauma.

Endovascular repair of infrarenal abdominal aortic aneurysm associated with a horseshoe kidney and graft thrombosis in early follow-up

Endovascular aneurysm repair (EVAR) is a well-established alternative to open surgery. The presented case underwent endovascular therapy of an abdominal aortic aneurysm (AAA) with the anatomical prerequisite of a horseshoe kidney. We describe the technique used, including the embolization of aortic side branches, to avoid endoleaks, and the management of thrombotic complications during follow-up.