Stent-Graft Fabrics Incorporating a Specific Corona Ready to Fenestrate.

In situ fenestration of endovascular stent-grafts has become a mainstream bailout technique to treat complex emergent aneurysms while maintaining native anatomical visceral and aortic arch blood supplies. Fabric tearing from creating the in situ fenestration using balloon angioplasty may extend beyond the intended diameter over time. Further tearing may result from the physiologic pulsatile motion at the branching site. A resultant endoleak at the fenestrated sites in stent-grafts could ultimately lead to re-pressurization of the aortic sac and, eventually, rupture. In an attempt to address this challenge, plain woven fabrics were designed. They hold a specific corona surrounding a square-shaped cluster with a plain weave fabric structure, a 2/2 twill, or a honeycomb. The corona was designed to stop potential further tearing of the fabric caused by the initial balloon angioplasty and stent or later post-implantation motion. The cluster within the corona was designed with relatively loose fabric structures (plain weave, 2/2 twill weave, and honeycomb) to facilitate the laser fenestration. Two commercial devices, Anaconda (Vascutek, Terumo Aortic) and Zenith TX2 (Cook), were selected as controls for comparison against this new design. All the specimens were characterized by morphology, thickness, and water permeability. The results demonstrated that all specimens with a low thickness and water permeability satisfied the requirements for a stent graft material that would be low profile and resistant to endoleaks. The in situ fenestrations were performed on all fabrics utilizing an Excimer laser followed by balloon angioplasty. The fabrics were further observed by light microscopy and scanning electron microscopy. The dimension of the fenestrated apertures was smaller than the balloon's diameter. The tearing was effectively confined within the corona. The clinical acceptability of this concept deserves additional bench testing and animal experimentation.

Optimal In Situ Fenestration Technique With Laser Perforation and Balloon Dilation for Aortic Stent-Grafts.

PURPOSE: To evaluate the response of various stent-grafts after laser fenestration and dilation with noncompliant balloons to determine the optimal therapeutic combination for this treatment technique. MATERIALS AND METHODS: Five aortic stent-grafts were evaluated ex vivo: the Bolton RelayPlus, Jotec E-vita Thoracic 3G, Medtronic Valiant, Cook Zenith Alpha, and Vascutek Anaconda. Small holes were created using an excimer laser with the grafts submerged in saline. Five rows of 5 fenestrations were created, 4 holes in each row were dilated once with a 6-, 8-, 10-, or 12-mm-diameter noncompliant balloon to the specified nominal pressure (one hole served as the control). The saline solution from each stent-graft was collected and qualitatively analyzed for debris. The fenestrations were evaluated under light and scanning electron microscopes. The maximum diameter and area for each fenestration were measured. The direction and length of tears were assessed. RESULTS: The fenestration was feasible and reproducible in all the stent-grafts. The mean area of fenestration ranged from 7.63±1.63 to 14.75±0.73 mm2 when using balloons of 6- and 8-mm diameter, respectively. The 10- and 12-mm-diameter balloons caused a significant increase in area, variability, and tearing. The Anaconda graft tended to tear in the weft direction, while the other devices tore in the warp direction when using the 10- and 12-mm-diameter balloons. Dilation of the RelayPlus and Anaconda grafts with 6- and 8-mm-diameter balloons provided minimal tearing and precise fenestrations. Melted fiber remnants were observed after filtration of the saline solution for all devices. CONCLUSION: Laser fenestration and dilation with noncompliant balloons is a relatively simple and reproducible option for revascularization in urgent, complex aortic endovascular repairs. In our model, large balloons (ie, >10 mm) increased the destruction and tearing of the fabric. The maximum dilation recommended is 6 to 8 mm to avoid significant tears. Development of stent-grafts or novel fabrics designed explicitly for fenestration is needed to reduce potential complications.

Innovative textile structures designed to prevent type III endoleaks in endovascular stent-grafts.

The damage caused to the fabric of endovascular stent-grafts most often occurs at the contact zones between the fabrics where they are attached to the apices of Z-shaped stents as a result of normal physiologic pulsatile movement within angulated vessels in vivo. Although design improvements were made over the years, the risks were not fully eliminated even with the newer M-shaped stent reconfiguration. In this study, we proposed to create and manufacture a novel fabric for stent-grafts with specifically designed reinforced zones to enhance resistance to fabric abrasion. These reinforced zones are set at the vicinity of the apices of the Z-shaped stents and between two adjacent Z-shaped stents where folding and pleating are commonly observed to occur in angulated vessels. Three innovative weaving structures with two different types of yarns and two controls were designed and prepared. Two commonly used commercial devices supported, respectively, with ringed stents, and Z-shaped stents were selected as the references for comparison. Textile structures including thickness, water permeability, mechanical properties, (more specifically tensile and bursting stress, as well as fatigue simulation) were tested on all fabrics. Compared to commercially available plain weaves, the fabrics with locally reinforced zones showed improved mechanical characteristics and fatigue resistant properties. A fabric designed with specifically reinforced zones has now clearly been shown to effectively reduce the abrasion caused by the apices of Z-shaped stents. However, further optimization may still be possible.

Laser Fenestration of Aortic Stent-Grafts Followed by Noncompliant vs Cutting Balloon Dilation: A Scanning Electron Microscopy Study.

PURPOSE: To examine the effects of in situ laser fenestration and subsequent balloon dilation (noncompliant vs cutting) on the graft fabric of 4 aortic stent-graft models. METHOD: In an in vitro setup, the Zenith TX2, Talent, Endurant, and Anaconda aortic stent-grafts (all made of polyester graft material) were subjected to laser fenestration with a 2.3-mm-diameter probe at low and high energy in a physiologic saline solution followed by balloon dilation of the hole. For the first series of tests, 6-mm-diameter noncompliant balloons were used and replaced for the second series by 6-mm-diameter cutting balloons. Each procedure was performed 5 times (5 fenestrations per balloon type). The fenestrations were examined visually and with light and scanning electron microscopy. RESULTS: Each fenestration demonstrated various degrees of fraying and/or tearing regardless of the device. The monofilament twill weave of the Talent endograft tore in the warp direction up to 7.09±0.46 mm at high energy compared with 2.41±0.26 mm for the Endurant multifilament device. The fenestrations of the 3 endografts with multifilament weave (Zenith, Anaconda, and Endurant) showed more fraying; fenestration areas in the multifilament Endurant were >10 mm2 at low and high energy. The fenestrations were free of melted fibers, but minor blackening of the filaments was observed in all devices. Overall, the cutting balloons resulted in worse tearing and damage. Of note, the edges of the dilated laser-formed fenestrations of the Talent and the Endurant grafts demonstrated evidence of additional shredded yarns. CONCLUSION: In situ fenestration does not cause any melting of the polyester; however, the observed structural damage to the fabric construction must be carefully considered. Cutting balloons caused various levels of tearing compared to the noncompliant balloons and cannot be recommended for use in this application. Rather, noncompliant balloons should be employed, but only with endografts constructed from multifilament yarns. The use of in situ fenestration must be restricted to urgent and emergent cases until long-term durability can be determined.

An in Vitro Twist Fatigue Test of Fabric Stent-Grafts Supported by Z-Stents vs. Ringed Stents.

Whereas buckling can cause type III endoleaks, long-term twisting of a stent-graft was investigated here as a mechanism leading to type V endoleak or endotension. Two experimental device designs supported with Z-stents having strut angles of 35° or 45° were compared to a ringed control under accelerated twisting. Damage to each device was assessed and compared after different durations of twisting, with focus on damage that may allow leakage. Stent-grafts with 35° Z-stents had the most severe distortion and damage to the graft fabric. The 45° Z-stents caused less fabric damage. However, consistent stretching was still seen around the holes for sutures, which attach the stents to the graft fabric. Larger holes may become channels for fluid percolation through the wall. The ringed stent-graft had the least damage observed. Stent apexes with sharp angles appear to be responsible for major damage to the fabrics. Device manufacturers should consider stent apex angle when designing stent-grafts, and ensure their devices are resistant to twisting.

In Vitro Laser Fenestration of Aortic Stent-Grafts: A Qualitative Analysis Under Scanning Electron Microscope.

In situ fenestration of stent-grafts allows patients with life threatening aortic pathologies to be amenable to emergent "off the shelf indications for use" percutaneous treatments as a bail out technique. Three types of aortic stent-grafts were subjected to laser fenestration in a physiological saline solution followed by balloon angioplasty using 8, 10 or 12 mm in diameter noncompliant balloons. The morphology and the size of fenestrations were observed under optical and scanning electron microscopy. The damage to the fabrics was analyzed and quantified. The creation of fenestrations was feasible in all devices, with varying degrees of fraying and/or tearing. The monofilament twill weave (Medtronic Valiant) tore in two directions (warp and weft) while the multifilament weave fenestrations showed more fraying (Anaconda Vascutek and Zenith TX2 Cook). The size and directions of tearing were more predictable with the 8 mm diameter balloon whereas the results obtained with the 10 and 12 mm diameter balloons were more unpredictable. The fenestrations were free of melting of the yarns and blackening of the filaments. The in situ fenestration is feasible but the observed damage to the fabric constructions must be carefully considered. This procedure must currently be limited to urgent and emergent life threatening cases because it is off indications for use for approved devices.

The Gelweave Valsalva Graft to Better Reconstruct the Anatomy of the Aortic Root.

The Bentall procedure introduced in 1968 represents an undisputed cure to treat multiple pathologies involving the aortic valve and the ascending thoracic aorta. Over the years, multiple modifications have been introduced as well as a standardized approach to the operation with the goal to prevent long-term adverse events. The Gelweave Valsalva graft provides a novel manner to more efficiently reconstruct the anatomy of the aortic root either with a valve-sparing procedure or with the implantation of a valved conduit (bioprosthesis or mechanical valve). The prosthesis holds three sections: the collar anchoring the valve; the skirt mimicking the Valsalva, which is suitable for the anastomoses with the coronary arteries; and the main body of the graft, which is designed to replace the ascending aorta. The Gelweave Valsalva graft allows the Bentall operation to be standardized, and it provides a potential for longer durability with reduced adverse events.

Stent fabric fatigue of grafts supported by Z-stents versus ringed stents: an in vitro buckling test.

Stent-grafts externally fitted with a Z-shaped stents were compared to devices fitted with ringed stents in an in vitro oscillating fatigue machine at 200 cycles per minute and a pressure of 360 mmHg for scheduled durations of up to 1 week. The devices fitted with Z-stents showed a considerably lower endurance limit to buckling compared to the controls. The contact between the apexes of adjacent Z-stents resulted in significant damage to the textile scaffolds and polyester fibers due to the sharp angle of the Z-stents. The ringed stents did not cause any fraying in the textile scaffolds.

Long-term resistance to fracture and/or corrosion of the nitinol wires of the talent stent-graft: observations from a series of explanted devices.

The biodurability of the Nitinol wires used in stent-grafts retrieved from reoperations and autopsy was analyzed to assess the possible causes of fracture and/or corrosion of the stents. The Nitinol wires of six explanted devices presented a corrosion-free surface after in vivo service. The drawing lines in the control wires were still present, but neither burrs nor flakes were observed. Pits and crevices were rare, but some shallow ones were present. Some abrasions of the surfaces of the Nitinol wires were also observed. The chemical composition of the explanted devices showed the presence of organic contamination that covered the thick layer of titanium oxide before reaching the Nitinol itself. The durability of the Nitinol employed in the manufacture of the Talent stent-grafts was confirmed; the results of this study show the Nitinol to be resistant to corrosion. We have also concluded that the fractures of the Nitinol wires in two devices were unique adverse incidents caused by compression and bending related to the sharp angle of the Nitinol wires.

Fatigue and/or failure phenomena observed in the fabric of stent-grafts explanted after adverse events.

In this study, we aimed to investigate changes to the fabric of Talent stent-grafts following implantation of aortic endografts and to determine the possible causes of fatigue and/or failure of the grafts. Six devices were explanted at reoperation (N=5) and autopsy (N=1). Selected segments were assessed nondestructively by gross observation and destructively by analyzing textile characteristics and chemical properties. All of the devices showed a 4/4 twill woven fabric of monofilament polyester. These devices, explanted at reoperation and autopsy, presented different levels of fatigue and/or failure. Numerous holes were found in the fabric of two devices. The minor damage caused by the passage of the sutures through the weave to fasten the Nitinol wires did not progress significantly over time. The sutures remained relatively intact, except for some distortions. The main failure mode was the abrasion of the yarns at the apices of adjacent Nitinol stents. In two devices, this abrasion resulted in fraying of the yarns and holes in the fabric tubes. This short series of explanted devices provides evidence of damage to polyester fabric used in aortic endografts and raises questions regarding their resistance to abrasion and the risk of endoleak associated with monofilament fabric yarn.

Absence of tissue ingrowth through the textile fabric in a series of explanted clinic stent-grafts.

Using the retrieved devices from one autopsy and five reoperations, the biocompatibility of explanted Talent stent-grafts was investigated to highlight the capacity of the fabric to act as an effective scaffold to regenerate a blood conduit. The autopsy device was encapsulated both internally and externally, but the capsules did not penetrate through the fabric structure. The reoperation devices showed discrete patches of compact fibrin and irregularly scattered mural thrombi. Positive staining of α-actin, tissue plasminogen activator (tPA), urokinase (uPA), urokinase receptor (uPAR), and urokinase inhibitors (PAI 1, PAI 2, PAI 3, and protease nexin), and D-dimer was more frequently identified in the autopsy sample than in the reoperation samples. This preliminary assessment shows that the stent-graft retrieved during autopsy was better healed than those explanted at reoperation.

Intra-operative fenestration of stent grafts: a note of caution based upon preliminary in vitro observations.

Intra-operative fenestrations of stent grafts make more frail and elderly patients amenable to endovascular surgery but require further assessment of the viability of currently used experimental techniques. Four types of polyester fabrics currently employed in stent grafts were exposed in vitro to various protocols of fenestration: cutting, trocaring, and cantering. The resulting fenestrations were examined by gross observation, light microscopy, and scanning electron microscopy. Blunt fenestration by scissors and sharp penetration led to unpredictable apertures, impairment of the integrity of the grafts, and damage to the filaments. The fenestrations were more likely to extend in the woven fabrics, whereas the knitted fabrics were more resistant to fraying. The use of the electric cautery demonstrated the ability to create a fenestration by simultaneously perforating/cutting and edge sealing. Any safe fenestration requires a perforating method that ensures the sealing of the edge of the graft material with a well-controlled diameter. A preoperative fenestration can be tolerated, but there are risks of damage to the stent grafts when reloading the device. More elegant methods of preoperative fenestration, particularly in situ retrograde laser fenestration, are in development and deserve clinical validation.

Detailed analysis of a series of explanted Talent AAA stent-grafts: biofunctionality assessment.

Six Talent stent-grafts were harvested at reoperations (N=5) and autopsy (N=1). The explants were observed nondestructively, including gross morphology, X-rays, CT scans and closed pressure system analysis. The Nitinol frames in three devices harvested at reoperations and another harvested at autopsy were intact. One had a stent fracture of the proximal bare stent, and one had a wire fracture of a thin proximal external supporting stent as well as a hole in the fabric just above the bifurcation. For the three devices structurally intact, reoperations were performed for a type 1A endoleak (one patient) and aorto-enteric fistulas (two patients). The healing characteristics were poor or absent. The fabric in the main body of the grafts harvested after aorto-enteric fistula was devoid of biological deposits. Two of the grafts harvested at reoperation demonstrated fabric holes of up to 4 mm 2. The device obtained at autopsy showed an almost continuous internal capsule with variable thickness. The luminal surface was smooth, but the capsule detached easily. The devices explanted at reoperations showed various levels of impaired biofunctionality associated with adverse outcomes. The stent-graft retrieved from autopsy was intact.

The marvel of percutaneous cardiovascular devices in the elderly.

Thanks to minimally invasive procedures, frail and elderly patients can also benefit from innovative technologies. More than 14 million implanted pacemakers deliver impulses to the heart muscle to regulate the heart rate (treating bradycardias and blocks). The first human implantation of defibrillators was performed in early 2000. The defibrillator detects cardiac arrhythmias and corrects them by delivering electric shocks. The ongoing development of minimally invasive technologies has also broadened the scope of treatment for elderly patients with vascular stenosis and aneurysmal disease as well as other complex vascular pathologies. The nonsurgical cardiac valve replacement represents one of the most recent and exciting developments, demonstrating the feasibility of replacing a heart valve by way of placement through an intra-arterial or trans-ventricular sheath. Percutaneous devices are particularly well suited for the elderly as the surgical risks of minimally invasive surgery are considerably less as compared to open surgery, leading to a shorter hospital stay, a faster recovery, and improved quality of life.

A branched, balloon-deployable, Aortomonoiliac stent-graft for treatment of AAA in a patient with a solitary intrapelvic kidney.

PURPOSE: To report the use of a branched, balloon-deployable stent-graft to treat abdominal aortic aneurysm (AAA) in the setting of a solitary kidney. CASE REPORT: A 72-year-old man with a solitary intrapelvic kidney and multiple comorbid conditions was diagnosed with an asymptomatic 5.3-cm abdominal aortic aneurysm (AAA); the renal artery emerged from the aneurysm sac. A customized branched, balloon-deployable, aortomonoiliac stent-graft was utilized to exclude the AAA and preserve perfusion to the single renal artery. A synthetic bypass was then implanted to restore perfusion to the contralateral limb. The diameter of the aneurysm decreased from 5.3 to 2.7 cm at 18 months. The renal artery was patent without evidence of stenosis; renal function was normal. CONCLUSION: The deployment of a novel branched stent-graft represents an interesting alternative approach to the treatment of a juxtarenal aneurysm.

Fluoropassivation and gelatin sealing of polyester arterial prostheses to skip preclotting and constrain the chronic inflammatory response.

Fluoropassivation and gelatin coating have been applied to polyethylene terephthalate (PET) vascular prosthesis to combine the advantages of both polytetrafluoroethylene (PTFE) and PET materials, and to eliminate the preclotting procedure. The morphological, chemical, physical, and mechanical properties of such prostheses were investigated and compared with its original model. Fluoropassivation introduced -OCF(3), -CF(3), and -CFCF(2)- structures onto the surface of the polyester fibers. However, the surface fluorine content was only 28-32% compared to the 66% in expanded PTFE (ePTFE) grafts. The fluoropassivation decreased the hydrophilicity, slightly increased the water permeability, and marginally lowered the melting point and the crystallinity of the PET fibers. After gelatin coating, the fluoropassivated and nonfluoropassivated prostheses showed similar surface morphology and chemistry. While gelatin coating eliminated preclotting, it also renders the prostheses slightly stiffer. The original prosthesis had the highest bursting strength (275 N), with the fluoropassivated and gelatin-sealed devices showing similar bursting strength between 210 and 230 N. Fluoropassivation and gelatin coating lowered the retention strength by 23 and 30% on average, respectively. In vitro enzymatic incubation had only marginal effect on the surface fluorine content of the nongelatin-sealed prostheses. However, the gelatin-sealed ones significantly lost their surface fluorine after in vitro enzymatic incubation (by 69-85%) or in vivo 6-month implantation (by 51-60%), showing the lability of the fluoropolymer layer under the hostile biological environment.

Size of the proximal neck in AAAs treated with balloon-expandable stent-grafts: CTA findings in mid- to long-term follow-up.

PURPOSE: To determine the evolution of the proximal aortic neck diameter in mid- to long-term follow-up after endovascular aneurysm repair of abdominal aortic aneurysm (AAA) with a balloon-expandable stent-graft. METHODS: Thirty patients (27 men; average age 71 years, range 56-87) with infrarenal AAAs were treated with the SETA-Latecba balloon-expandable stent-graft (6 aortomonoiliac and 24 bifurcated configurations). Follow-up ranged from 4 to 8 years (mean 73.4 months). Computed tomography was done systematically before the procedure, after implantation (1-3 months), at 1 year, and annually thereafter. The last follow-up scan was utilized to measure the proximal neck for purposes of comparison with baseline and the initial post-implant scans. RESULTS: Five patients died during follow-up of causes unrelated to the procedure. No endoleaks or graft migrations were observed. The pre-deployment proximal neck diameter (a) averaged 23.4 mm (range 18-32), the diameter after deployment of the stent-graft (b) averaged 24.9 mm (range 18-34), and the most recent follow-up proximal neck measurement (c) averaged 23.8 mm (range 18-31). Comparing the last follow-up to the post-implant measurements (c-b), the neck diameter decreased in 15 (50%) patients [7 with short necks (i.e., <15 mm)] and remained unchanged (no variation) in 15 (50%) patients (4 with short necks). All patients treated with the SETA-Latecba balloon-expandable stent-graft showed stability of the proximal aortic neck diameter in mid- to long-term follow-up. CONCLUSION: The study showed that the diameter reached at initial deployment did not increase further in the long term, which supports the safety and reliability of this modular balloon-expandable stent-graft and illustrates that this device does not produce dilatation of the proximal neck after deployment. Future dilatation of the aortic neck is unlikely, and consequently, migration or delayed type I endoleak are also unlikely.