C.M. Bünger

Provisional extension to induce complete attachment after stent-graft placement in type B aortic dissection: the PETTICOAT concept.

Purpose: To report the use of a technique (PETTICOAT: provisional extension to induce complete attachment) to obliterate sustained abdominal false lumen flow and pressurization despite successful stent-graft sealing of the thoracic entry tear in patients with complicated type B aortic dissection. Methods: Of 100 initial patients subjected to stent-graft repair for complex type B aortic dissection with thoracoabdominal extension, 12 patients (10 men; mean age 58.7 years, range 44–76) demonstrated distal true lumen collapse and a perfused abdominal false lumen despite successful sealing of the proximal tears. As an adjunctive or staged procedure, a scaffolding stent was placed for distal extension of the previously implanted stent-graft. In each case, a Sinus aortic stent, Fortress stent, or a Z-stent system was customized with maximum 2-mm oversizing versus the original stent-graft diameter. Magnetic resonance or computed tomographic angiography was performed at discharge, at 3 months, and then annually to determine false channel thrombosis, true and false lumen dimensions, and re-entry flow. Results: Delivery was successful in all cases (100%). The compressed distal true lumen (mean 4±3 mm) was reconstructed to a mean width of 21±3 mm, and malperfusion was abolished without any obstruction of the abdominal side branches. At up to 1-year follow-up, there were no signs of expansion or distal progression of the scaffolded dissected aorta. All patients with complete thoracic thrombosis showed evidence of improved aortic remodeling; 1 patient with no false lumen thrombosis died at 11 months from thoracoabdominal aortic rupture. Conclusion: The PETTICOAT technique may offer a safe and promising adjunctive endovascular maneuver for patients with distal malapposition of the dissecting membrane and false lumen flow. The technique can both abolish distal true lumen collapse and enhance the remodeling process of the entire dissected aorta.

A biodegradable stent based on poly(L-lactide) and poly(4-hydroxybutyrate) for peripheral vascular application: preliminary experience in the pig.

Purpose: To assess the technical feasibility and biocompatibility of a novel stent based on poly(L-lactide) (PLLA) and poly(4-hydroxybutyrate) (P4HB) for peripheral vascular applications. Methods: A polytetrafluoroethylene aortobi-iliac graft was implanted in 5 pigs through a midline abdominal incision. After transverse graft limb incision, 5 PLLA/P4HB stents and 5 metal stents (316L stainless steel) were randomly deployed at both iliac anastomotic sites with 6-mm balloon catheters. Angiography was performed to determine patency prior to sacrifice at 6 weeks. Stented segments were surgically explanted and processed for quantitative histomorphometry. Vascular injury and inflammation scores were assigned to the stented iliac segments. Results: No animals were lost during follow-up. All PLLA/P4HB stents were deployed within 2 minutes by balloon inflation to 8 bars without rupture of the stent struts or anastomotic suture. All stents were patent on postprocedural angiography. Histological analysis showed no signs of excessive recoiling or collapse. PLLA/P4HB stents demonstrated decreased residual lumen area and increased neointimal area after 6 weeks (12.27±0.62 and 8.40±1.03 mm2, respectively) compared to 316L stents (13.54±0.84 and 6.90±1.11 mm2, respectively) as the result of differences in stent areas (PLLA/P4HB: 4.31±0.15 mm2; 316L: 2.73±0.29 mm2). Vascular injury scores showed only mild vascular trauma for all stents (PLLA/P4HB: 0.41±0.59; 316L: 0.32±0.47). Inflammatory reaction was slightly higher around PLLA/P4HB stent struts (1.39±0.52) compared to 316L (1.09±0.50). Conclusion: Rapid balloon expansion of PLLA/P4HB stents is feasible without risk of strut rupture. PLLA/P4HB stents provide adequate mechanical stability after iliac anastomotic stenting in pigs. Smaller residual luminal areas in the PLLA/P4HB stents might have been caused by tissue ingrowth into the larger strut interspaces due to higher strut thickness (stent area) in this group. This limitation needs to be addressed in future work on the stent design.

Iliac Anastomotic Stenting with a Sirolimus-Eluting Biodegradable Poly-L-Lactide Stent: A Preliminary Study after 6 Weeks

Purpose: To assess technical feasibility and biocompatibility of a new biodegradable sirolimus-eluting poly-L-lactide (PLLA) vascular anastomotic stent. Methods: A polytetrafluoroethylene bifurcated graft was implanted in 9 pigs through a midline abdominal incision. After transverse graft limb incision, 6 unloaded PLLAs, 6 sirolimus-loaded PLLAs, and 6 unloaded stainless steel (316L) stents were randomly implanted at both iliac anastomotic sites. Stents were deployed with a 6-mm balloon under direct vision without the use of angiography. Prior to sacrifice after 6 weeks, contrast-enhanced computed tomography (CT) was performed to determine patency of the target vessels. Stented segments were surgically explanted and processed for histology to measure the mean luminal diameter and intimal thickness and to assign vascular injury and inflammation scores. Results: No animals were lost during the study period. All stented graft limbs were patent on CT and histology. At the anastomotic sites and iliac arteries, the mean luminal diameter of SIR-PLLA stents (4.11±0.15 and 4.08±0.13 mm, respectively) were comparable to metal stents (4.23±0.35 and 4.21±0.26 mm, respectively), but significantly higher compared to unloaded PLLA stents [3.32±0.56 mm (p<0.001) and 3.29±0.39 mm (p=0.013), respectively]. At the iliac arteries, the mean intimal thickness was significantly lower with SIR-PLLA stents (0.09±0.02 mm) compared to unloaded PLLA stents (0.31±0.15 mm, p<0.001) and metal stents (0.19±0.04 mm, p=0.004). Vascular injury scores demonstrated only mild vascular trauma for all stents (SIR-PLLA: 0.42±0.63, PLLA: 0.51±0.62, metal: 0.50±0.62). Only mild inflammatory reaction was noted around SIR-PLLA stent struts (1.14±0.46), which was comparable to metal stents (1.27±0.45) but significantly lower than PLLA stents (1.79±0.56, p<0.001). Conclusion: SIR-PLLA stents showed comparable luminal diameter compared to metal stents, so incorporating sirolimus could reduce the inflammatory and neointimal response to PLLA stents. These findings need to be assessed with longer follow-up to confirm maintenance of efficacy.

Iliac Anastomotic Stenting with a Biodegradable Poly-L-Lactide Stent: A Preliminary Study after 1 and 6 Weeks

Purpose: To assess the technical feasibility, thrombogenicity, and biocompatibility of a new biodegradable poly-L-lactic acid (PLLA) anastomotic stent. Methods: A polytetrafluoroethylene bifurcated graft was implanted in 17 pigs through a midline abdominal incision. After transverse graft incision, 17 316L stainless steel stents and 17 PLLA stents were randomly implanted at both iliac anastomotic sites and deployed with a 6-mm balloon under direct vision without angiography. Intended follow-up was 1 week in 6 pigs receiving oral acetylsalicylic acid (ASA) and in 7 pigs receiving ASA/clopidogrel; 4 pigs receiving ASA/clopidogrel were followed for 6 weeks. At the end of the study, the segments containing the stents were surgically explanted and processed for histology to measure the mean luminal diameter, intimal thickness, and the vascular injury and inflammation scores. Results: Initial technical success of stent placement was achieved in all animals without rupture of the suture. Two pigs died (unrelated to the stent) at 3 days after operation (1 in groups A and B). At 1 week, all PLLA stents showed thrombotic occlusion with the use of ASA alone. In contrast, all PLLA stents remained patent with concurrent administration of ASA/clopidogrel. All metal stents were patent regardless of the antiplatelet regimen. The mean luminal diameter of patent PLLA stents (4.13±0.17 mm) was comparable to metal stents (4.27±0.35 mm, p=0.78) at 1 week, but significantly diminished at 6 weeks (3.21±0.44 versus 4.19±0.18 mm, p=0.005). Histological analysis showed no signs of excessive recoil. PLLA stents induced a higher inflammation score (1.79±0.56) and more intimal hyperplasia (0.34±0.11 mm) compared to metal stents [1.27±0.44 mm (p<0.001) and 0.18±0.04 mm (p=0.006), respectively] at 6 weeks. Vascular injury was comparable between PLLA and metal stents. Conclusion: Biodegradable PLLA stents showed higher thrombogenicity and reduced patency compared to metal stents during early follow-up. Although ASA and clopidogrel prevented thrombotic occlusion, the increased inflammatory response and neointima formation remain major concerns of PLLA stents. A solution to this problem might be the incorporation of anti-inflammatory drugs into the PLLA stent.

Enhanced visualization of biodegradable polymeric vascular scaffolds by incorporation of gold, silver and magnetite nanoparticles:

Due to improved tissue regeneration and the enabling of post-operative minimally invasive interventions in the same vessel segment, biodegradable polymeric scaffolds represent a competitive approach to permanent metallic stents in vascular applications. Despite these advantages some challenges, such as the improvement of the scaffold mechanics and enhancement of scaffold visibility during the implantation procedure, are persisting. Therefore, the scope of our studies was to investigate the potential of gold, silver and magnetite nanoparticles incorporated in a polymeric blend of poly(L-lactide)/poly(4-hydroxybutyrate) for image enhancement in X-ray, magnetic resonance or near-infrared imaging. Their impact on mechanical properties of such modified scaffold materials was also evaluated.

Development of a sirolimus-eluting poly (l-lactide)/poly(4-hydroxybutyrate) absorbable stent for peripheral vascular intervention

Abstract Fully absorbable drug-eluting stent platforms are currently entering the clinical arena for the interventional treatment of coronary artery disease. This new technology also holds potential for application in peripheral vascular settings. Our study reports on the development of a sirolimus- (SIR) eluting absorbable polymer stent made from a blend of poly(l-lactide) and poly(4-hydroxybutyrate) (PLLA/P4HB) for peripheral vascular intervention. Stent prototypes were laser-cut from PLLA/P4HB tubes (I.D.=2.2 mm, t=250 µm), spray-coated with different PLLA/P4HB/SIR solutions, and bench-tested to determine expansion properties, fatigue, trackability and in vitro drug release kinetics. The stent prototypes were expanded with a 5.0×20 mm balloon catheter, and exhibited a recoil of 3.6% upon balloon deflation. Stent collapse pressure of 0.4 bar (300 mm Hg) was measured under external pressure load. Sustained scaffolding properties were observed in vitro over 14 weeks of radial fatigue loading (50±25 mm Hg at 1.2 Hz). Trackability was demonstrated in bench tests with an 8 French contralateral introducer sheath. SIR release kinetics were adjusted over a broad range by varying the PLLA/P4HB ratio of the coating matrix. The newly developed absorbable SIR-eluting PLLA/P4HB stent successfully fulfilled the requirements for peripheral vascular intervention under in vitro conditions.

Anastomotic stenting in a porcine aortoiliac graft model

The purpose of the study was to evaluate the feasibility of anastomotic stent application in a porcine aortoiliac graft model. In a total of 10 pigs, a polytetrafluoroethylene aortobi-iliac graft was implanted through a midline abdominal incision. The lower edge of the iliac vessel was graft-inverted about 1 mm to produce irregularities at the downstream anastomosis. After transverse graft incision, six stainless-steel stents, six poly-L-lactic acid (PLLA) stents and four PLLA stents with 10% polycaprolactone (PCL) were implanted at the iliac anastomotic site using a 6 mm balloon dilatation catheter. Four anastomotic sites were left untreated. After two weeks, the patency of graft limbs was evaluated by contrast-enhanced computed tomography (CT). Both metal and polymeric stent designs provided adequate flexibility to manoeuvre across the anastomotic site for expansion in the chosen position. After deployment, the stent–arterial wall contact was complete on a macroscopic view. On CT scan, all metal and PLLA-stented graft limbs were free of stenosis, whereas all PLLA/PCL stents were occluded. The non-stented graft limbs showed a stenosis of 50–70%. In summary, this model is feasible to assess preclinically the deployment and patency rate of an anastomotic stent and to test future stent developments.

Laparoscopic treatment of renal artery entrapment

Renal artery entrapment by the diaphragmatic crus is a very infrequent cause of renovascular hypertension. We present the case of a young man who was assigned to our hospital with arterial hypertension and stenosis of the left renal artery. Extrinsic compression was diagnosed by duplex ultrasound and magnetic resonance angiography. We performed laparoscopic decompression using the transperitoneal retrorenal approach. Antihypertensive medication could be stopped thereafter and duplex ultrasound revealed a normal blood flow to the left renal artery. We therefore propose laparoscopic treatment of left renal artery entrapment as a minimally-invasive alternative to open surgery.

Biocompatibility of biodegradable polymeric stents in an interventional porcine carotid artery model

Biodegradable polymeric stents (PLLA/P4HB) and permanent bare-metal stents (316L) were implanted interventionally into both common carotid arteries (CCA) of 6 female pigs via the left common iliac artery (8F-sheath). The stents were mounted on a balloon catheter (5.0x40 mm), and balloon-expanded with either 8 bar (PLLA/P4HB) or 9 bar (316L). The pigs were administered peroral aspirin (100 mg) and clopidogrel (75 mg) starting 5 days before the procedure until the end of the study. Stented CCA segments were explanted after 4 weeks, and processed for quantitative histomorphometry, and estimation of vascular inflammation and injury scores.

A Biodegradable Balloon-expandable Stent for Interventional Applications in the Peripheral Vasculature — In vitro Feasibility

Biodegradable polymeric stents represent an attractive approach to overcome the limitations of permanent metallic stents and current drug-eluting stents. The particular appeal of polymeric stents results from their potential for controlled biodegradation and drug incorporation. Recently, we have reported on the development and successful in vivo testing of a PLLA-based anastomotic support stent for surgical use in the porcine aorto-iliac graft model. The present study reports on the adaptation of this stent concept towards interventional application in the peripheral vasculature.