Commentary: Honing the Technique of In Situ Stent-Graft Fenestration

In Situ Laser Fenestration Technique: Bench-Testing of Aortic Endograft to Guide Clinical Practice

PURPOSE

In situ laser fenestration (ISLF) is a recently introduced technology that offers the potential to perform total endovascular treatment of aortic arch and thoracoabdominal aortic pathologies in the acute setting. This experiment's aim was to assess ISLF in some currently common aortic endografts and bridging stent-grafts.

MATERIALS AND METHODS

Three different aortic endografts were evaluated: (1) Zenith Alpha, (2) Zenith TX2, and (3) Conformable GORE TAG. Each endograft was submerged in 37°C saline to create fenestrations using the 308 nm CVX-300 Excimer Laser System fitted with a 2.3 mm diameter Turbo-Elite laser atherectomy catheter compatible with a 0.018″ guidewire. Three different 8 mm bridging stent-grafts were evaluated: (1) BeGraft peripheral, (2) BeGraft peripheral plus, and (3) GORE VIABAHN VBX Balloon Expandable. All bridging stent-grafts were deployed and exposed to different balloon sizes and pressures. The ISLFs and bridging stent-grafts were then evaluated for any tears, stenoses, and seal.

RESULTS

A laser fenestration was consistently rapidly obtained in the Zenith Alpha and the Zenith TX2 endografts while it proved difficult to achieve a timely fenestration in the C-TAG. No fabric tears were noted in the Zenith Alpha and Zenith TX2 when inflating Armada (Abbott) 8 mm balloon in the fenestrations with pressures up to 15 atmospheres (rated burst pressure) nor when flaring bridging stent-grafts with balloons up to 12 mm in diameter at 10 atmospheres, while major tears were frequently noted in the C-TAG when the Armada 8 mm balloons were inflated. BeGraft Peripheral and BeGraft Peripheral Plus were all firmly attached to the fenestrations showing good seal on manual testing, while every sixth VBX bridging stent-graft displayed poorer attachment to the fenestration before dilatation at high pressure. Commonly, significant stenoses remained in the bridging stent-grafts after dilatation at nominal pressure, which could only be eradicated with high-pressure balloons.

CONCLUSION

In this limited bench-test, Dacron endografts responded well to the ISLF technology. Satisfactory deployment of the bridging stent was noted only after inflation and/or flaring with high-pressure balloons. Further work with different types of commercially-available bridging stent-grafts and endografts to assess the durability of in situ fenestration (ISF) and bridging stents in ISF is recommended.

CLINICAL IMPACT

This report on experimental in situ laser fenestration provide important insights for clinicians considering using in situ laser fenestration of aortic stentgrafts in vivo. In particular, different laser settings were tested together with a selection of aortic stentgrafts. Also, the target pressure needed in PTA balloons to dilate the fenestrations and any subsequent tears in the fabric were noted. This was followed by deployment of assorted balloon-expandable stentgrafts with estimation of residual stenosis and seal.

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.

Parallel grafts and physician modified endografts for endovascular repair of the aortic arch

Aortic arch aneurysms are a challenging clinical problem especially in high-risk patients. Open aortic arch replacement, even in the best of centers, carries significant risk of stroke or death in this high-risk population. Many high-risk patients are deemed inoperable and not offered repair. Branched and fenestrated thoracic endografts are currently undergoing clinical trials in the United States but are not yet commercially available. Many elderly and frail patients have significant brachiocephalic occlusive disease or anatomy excluding them for consideration for such clinical trials. These patients also present with acute aortic syndromes requiring urgent or emergent repair and are unable to participate in clinical trials due to the time required to have such devices available. Alternative endovascular therapies, including parallel stent grafts (including Chimneys, Snorkels and Periscopes) and physician modified thoracic endografts, have been used to treat such high-risk patients combined with commercially available thoracic endovascular aneurysm repair (TEVAR) devices. This paper aims to review the techniques and current reported outcomes from parallel stent grafts and physician modified devices used to treat high risk patients undergoing repair for aortic arch pathologies.