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Fenestrated Stent-Grafting of Juxtarenal Aortic Aneurysms
Continuous development in endovascular treatment of ab-dominal and thoracic aortic aneurysms, together with growing experience and encouraging results, have paved the way for a new generation of stent-grafts, to treat those previously unsuitable for conventional endovascular repair. One such advancement is the fenestrated graft, which allows extension of the proximal landing zone and preservation of the renal and visceral arteries.
Since the first reported fenestrated endovascular repair of an aortic aneurysm (FEVAR) by Park et al. in 1996, several large published studies and data from registries (including the Global Star Registry), have demonstrated high technical success rates, and promising short- and mid-term results. Nevertheless, FEVAR still presents unique challenges to the endovascular interventionalist. These include appropriate patient selection, graft selection, accurate endograft planning, and demanding technical skills.
Indications and Anatomic Suitability
Clinical and radiologic (usually based on computed tomographic angiography, CTA) indications for FEVAR include an aneurysm diameter of 5.5 cm or more, a rapidly enlarging aneurysm at a rate of 5 mm over 6 months or 1 cm over 1 year, an aneurysm neck length of 15 mm or less, and when patients are deemed unfit for open surgery. High-risk patients for major open vascular surgery include patients who have significant pulmonary disease, poor renal function, severe cardiac disease, as well as a hostile abdomen.
It is generally accepted that the ideal anatomy for FEVAR includes an aortic diameter of 20 to 32 mm at the level of the renal arteries, neck angulation of less than 45 degrees, iliac artery diameter of 7 mm or more, and iliac angulation of 85 degrees or less. Additionally, the renal arteries should be equal or greater than 4 mm in diameter to avoid early stent thrombosis. Renal artery or superior mesenteric artery (SMA) ostial stenosis is considered an adverse anatomic feature and should be handled with great care. Mendes et al. analyzed renal artery anatomy in 520 patients with abdominal aortic aneurysms and suggested that 1 in 5 patients may have unsuitable renal anatomy for good endovascular repair, including early bifurcation, small diameter, presence of an accessory artery (supplying a significant parenchymal volume but needing to be sacrificed) or simply poor iliofemoral access. These statistics should not discourage the interventionalist to proceed, but to do so with appropriate informed patient consent, and with good preparation, as discussed below.
Occasionally, the celiac artery is stented. Although catherization of this vessel is not usually different from other branches, the presence of median arcuate ligament compression (MAL) could create significant technical difficulties. Wattez et al. reported on 18-month outcomes of 45 patients with MAL treated with fenestration or branches and stenting. In this series, a complex procedure, defined as additional stenting, complex maneuvering, and/or longer procedure time, is noted in 36% of patients. However, there was no statistically significant difference in stent patency in comparison with those without MAL compression on follow-up imaging.
Contraindications
Although there is no absolute contraindication, the presence of an adverse anatomic feature could make the procedure difficult and increase procedural comorbidity. If there are three or more adverse anatomic features, the procedure could be extremely difficult or impossible. A symptomatic or ruptured aneurysm is not suitable for this technology because stent-graft manufacture could take at least 6 weeks and the procedure could also be unacceptably long in an unstable patient. Using data on predictable aortic and visceral arterial anatomy, “off-the-shelf” fenestrated devices are designed to eliminate the 6-week delay in custom manufacturing, enabling their use for symptomatic aneurysms. However, in the authors’ opinion, it is hard to envisage that within an emergency situation, a ruptured aneurysm would be suitable.
Stent-Grafts on The Market
Custom-Made Fenestrated Zenith Device
The first commercially available fenestrated stent-graft was the Cook device (Cook Medical, Bloomington, IN). Thus it has the largest evidence base, at present. It is a composite system that consists of a proximal custom-made component, a bifurcated component, and two iliac limbs. The system is based on the original Zenith platform (Cook Medical), which is made of woven polyester fabric sutured to stainless-steel Gianturco stents.
The proximal component contains two or three fenestrations and a scallop ( Fig. 21.1A–D ). Rarely, there are four fenestrations. There are two types of fenestrations, small and large. The small fenestration is 6 mm in width and 6 or 8 mm in height. It is reinforced with a Nitinol ring and should be 15 mm or more from the proximal edge of the fabric. The large fenestration is 8 to 12 mm in diameter and should be 10 mm or more from the edge of the graft. The scallop is 6 to 12 mm in depth and 10 mm wide. It is also reinforced with a Nitinol ring and has gold radiopaque markers. The bare spring (which contains fixation barbs) is located within the top cap. This, together with one or two posterior diameter reducing ties, assists device orientation until final deployment. In certain cases, double diameter reducing ties are manufactured to help partial opening of the graft in a narrow-diameter segment of the aorta, allowing room for cannulating the target vessel.
The small fenestrations and scallop have no struts across them. The small fenestrations are intended to be stented. This stenting serves two goals: migration resistance and sealing. The large fenestration can have struts crossing the fenestration.
The proximal fenestrated component has some important radiopaque markers: an anterior check mark, three anterior vertical markers, and three posterior horizontal markers.
Bare metallic stents or covered stents may be used to bridge the gap between the fenestrations and target branch vessels. The choice of side branch stent depends on the distance of the side vessel from the aneurysm and the presence of mural thrombus. Uncovered balloon-expandable stents may be preferred over covered stents if the distance from the renal artery or the SMA to the aneurysm is 5 mm or more and/or if the mural thrombus is not severe enough to cause poor opposition of the stent to the sidewall. The Nitinol ring and overdilation of the stent after deployment of the side branch stent using an oversized balloon help seal the renal or SMA stent against the graft wall and resist future migration. However, most operators prefer to use covered bridging stents in all cases.
Newer Devices
At least three devices have been introduced to overcome certain limitations and shortfalls of the existing commercially available Cook Zenith device. Although these devices are awaiting full evaluation through multicenter studies and/or randomized trials, they clearly provide the endovascular community with a wider range of options and take endovascular treatment of challenging aneurysms a step further.
Custom-Made Fenestrated Anaconda Device
The custom-made fenestrated Anaconda device (Vascutek, Terumo, Japan) was developed on the background of the original Anaconda device. Its proximal end is positioned suprarenally. This part of the device provides the seal and fixation by means of hooks and rings. The anterior valley is oriented to cradle the SMA and/or celiac trunk. The fenestrations are usually made in the unsupported part of the fabric, which gives more flexibility to orient the fenestration according to the circumferential orientation of the renal arteries or SMA. The typical device encompasses two renal fenestrations supported by Nitinol rings and marked by four radiopaque markers ( Fig. 21.2A–D ). However, an SMA with or without celiac trunk fenestration can be added to increase the coverage length in shorter landing zones. Our experience with this device shows that potential advantages include the ability to (1) accommodate more difficult anatomy and angulation, and (2) partially reposition the top device after cannulating one vessel so that the device can be rotated and reoriented, allowing the next fenestration to face the next vessel. The device also gives the operator the option of cannulating any number of fenestrations antegradely before full device deployment, because there is no closed top cap. Furthermore, a prototype can be manufactured for each patient by the company, in conjunction with the operator’s plan from the CTA. This can then be assessed and deployed under fluoroscopy in a 3D-printed model to ensure the fenestrations are well aligned before the final device production. The delivery system profile is still relatively large, however, similar to the Cook Zenith device. Also, overmanipulation of the device to adjust the position of the fenestration could lead to shutting down one or more of the fenestrations, especially in the unsupported segment of the stent. In a recent United Kingdom multicenter study published by Colgan et al., 30-day and 1-year outcomes for mortality, freedom from sac expansion and endoleaks, as well as target vessel patency were excellent and on par with Zenith device outcomes published in the GLOBAL STAR study. The 2017 Colgan paper assessed cases from 2010 to 2014, thus the longer-term outcomes for this particular device should soon be available.
Custom-Made E-xtra Design Engineering
Custom-made E-xtra Design Engineering (JOTEC/CryoLife, Atlanta, GA) is based on the E-Vita thoracic 3G stent-graft. The main body material is woven polyester and contains individual Nitinol z-stents. A proximal stent ring is uncovered followed by three internal sealing stents. The E radiopaque markers identify the anterior and posterior orientation of the stent. Below the sealing zone, the graft is tapered to 16 mm below to include fenestrations or branches. Fenestrations (6–12 mm in diameter) are identified by four radiopaque markers and can be used for smaller-diameter aortas provided the stent-grafts have direct circumferential contact with the aortic wall. Outer branches (6–10 mm in diameter) can be incorporated for larger aortas (>30 mm). The use of inner branches is considered if the diameter of the thrombus-free lumen is 24 to 28 mm, or the stent-grafts do not have circumferential contact with the aortic wall, and/or there is not enough space for an outer branch. ( Fig. 21.3A–B ) Initial studies including more than 100 patients with mean follow-up time of 17 months show that the device is comparable with others on the market, in terms of short and medium-term safety and efficacy.
Off-the-Shelf Zenith p-Branch Device
This off-the-shelf device (Cook Medical) is based on the established Zenith platform, but is slightly different, mainly with regard to the fenestrations. The device has three fenestrations (two for the renal arteries, and one for the SMA) and a scallop for the celiac artery. The renal fenestrations are dome-shaped ( Fig. 21.4 ), effectively allowing them to pivot. The dome itself, the inner ring (6 mm diameter) and outer ring (15 mm diameter) are Nitinol-enforced. The SMA fenestration is an 8-mm-diameter standard single-ring fenestration. It is purported by the manufacturers that the device will work for 60% to 80% of aneurysm repairs. This is reflected in a single-center analysis, which reported a potential 75% compatibility rate in their series. Furthermore, the renal fenestrations have a preloaded 0.018-inch-diameter wire to obviate the need for catheterization of the fenestrations, thus helping cannulation of the target vessels. Early results of 76 patients from four high-volume centers confirm feasibility and safety of the design with 11% failure rate of target vessel catherization at the index procedure. The technical learning curve and wider availability of the stent remain limiting factors.
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