Mark Nutley

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.

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.

Flared textile cuff to be apposed on the proximal sealing zone in fenestrated stent-grafts

Current customized fenestrated devices require a fabrication delay of 4–6 weeks and therefore cannot be considered for the treatment of emergent or urgent aortic pathology. A flared textile cuff capable of better sealing the connection between a stent-graft fenestration and a branching stent-graft could bring more flexibility in treating patients with peri- and juxta-renal abdominal aortic aneurysms. Four different flared textile cuff prototypes were fabricated by compression molding of woven fabrics having structure similar to those of commercially available devices. Each cuff comprised a flat collar as a base, an arc as a curved section, and a top as a regular fabric tube. The fabric count, density, and thickness decreased from the first to the third sections and the results differed according to the structure. The physical and mechanical properties of these flared fabric cuffs were similar to those found in commercially available stent-grafts. The flared textile cuffs showed a scope of properties adapted for easier delivery and are acceptable to various sizes and shapes of fenestration. The development of flared textile cuffs represents a considerable advancement in endovascular therapy: (1) allowing a fenestrated solution to be readily available off-the-shelf; (2) providing an adequate seal of the ancillary stent-graft to the main body of the stent-graft.

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.

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.

Commentary: nitinol stent designs need to adhere to the 3Bs: biofunctionality, biodurability, and biocompatibility.

As stated by the Clinical Device Group, the risks and benefits of implantable devices must be continuously reassessed during the lifetime of a device. An ideal cardiovascular implant should have two characteristics: first, its potential durability should exceed the life expectancy of the patient; second, it should not cause side effects likely to compromise the patient’s health. Although endovascular techniques have matured considerably during the last few decades, the fate of devices after implantation, more specifically, their biodurability, remains to be fully assessed. Thanks to multicenter trials such as EUROSTAR, during the early days of stent-grafting, device-related adverse events are less and less likely. Endovascular technology, which was, and still is, mostly driven by physicians, has matured very rapidly. The clinicians continue to require more and more sophisticated devices. Much attention is paid to the early and midterm clinical performance, as it generates new ideas that contribute to further developments of new devices. Most endovascular devices have not yet achieved the long-term durability that can exceed the life expectancy of many patients. Notably, there is a paucity of information available about the techniques of manufacturing, the characteristics of the devices (morphology, material characterization), the resistance to fatigue (accelerated cycling in ENDURATEC machines), and the biocompatibility (both in vitro and in vivo). The article by Varcoe’s team in this issue of the JEVT is therefore worthy of consideration. The authors must be congratulated for their independent and sound investigations of 5 different designs of nitinol peripheral stents. The analyses focus on stent geometry, initial stent surface quality, corrosion resistance, and X-ray photoelectron spectroscopy (XPS). The ASTM International Standard F2129-08 that they used is a precise guide for all the analyses except the XPS. Because stents have device-specific designs, there might be sites on certain stent models that are still likely to corrode, so more attention must be paid to the thickness of the titanium oxide layer that passivates the surface of the nitinol wire. Needless to say, manufacturers cannot disclose all their trade secrets because much of this information remains proprietary, but as O’Connor and Dhrura et al. pointed out, access to the reviews of the Food and Drug Administration currently remains very limited. There is an obvious need for more collaboration between industry and academia. In addition, the biocompatibility of these devices that are in direct contact with blood is rarely addressed because the term biocompatibility integrates numerous phenomena related to the continuous interactions