Keywords

Introduction

Endovascular aortic aneurysm repair (EVAR) has now been used for almost 30 years and has changed the treatment of abdominal aortic aneurysms (AAA) [1]. A basic limitation of standard EVAR includes the necessity for an adequate infrarenal sealing zone in order to exclude the aneurysm sufficiently. Thus, aneurysms that present with a short neck or no neck were initially not amenable to endovascular treatment with standard EVAR.

The evolution of endovascular technology led gradually to advanced endovascular options that enabled sealing in the suprarenal or paravisceral segment of the aorta with the use of fenestrations on the aortic endograft in order to preserve perfusion of the renal and visceral arteries [2]. Fenestrated stent-grafts enabled endovascular treatment of short-neck AAA, pararenal AAA, and some type IV thoracoabdominal aortic aneurysms (TAAA). Fenestrations are stented with a covered stent in order to secure a complete alignment of the fenestration with the respective target vessel. A further evolution of fenestrations led to the introduction of branched endografts [3] (Fig. 52.1). Branched endografts have a tubular protrusion arising from the main lumen of the endovascular graft. This tubular protrusion (directional branch) is connected with the respective target vessel with a balloon-expandable or self-expanding bridging covered stent. The rationale for using a branch instead of a fenestration is that such a construction provides a longer surface for the bridging stent to seal within the main body of the endograft compared to the ring of a fenestration. This may be particularly important in larger aneurysms, where the gap between the aortic endograft and the orifice of the target vessel is large and may lead to bridging stent-graft instability. Another important factor is that directional branches can direct the bridging stents toward the target vessel in a direction that matches native anatomy. Directional branches were first developed to preserve the internal iliac artery when sealing has to be achieved in the external iliac artery during endovascular aortic or iliac aneurysm repair. Directional branches were also developed for the visceral arteries in extensive TAAAs. Later on, branches were also used to preserve the supra-aortic branches in arch-branched devices [4].

Fig. 52.1
An illustration of the bulging aorta with a branched endograft secured.

Branched endograft for the treatment of type III TAAA

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The present chapter describes the development and use of branched endografts, focusing on indication, planning, and procedure execution to treat different aortic segments if anatomically suitable, starting from the aortic arch to the external and internal iliac arteries.

Historical Aspects of Evolution of Branched Endografts

The idea of endovascular aortic aneurysm repair (EVAR) has been introduced in the mid-1980s when Blako et al. [5] used stent-grafts based on self-expanding nitinol stents and polyurethane to treat abdominal aortic aneurysms (AAA) in canine. In 1987, Volodos et al. [6] performed the first endovascular repair of a post-traumatic aneurysm in the distal thoracic aorta by advancing a stent-graft, while in 1989 they unsuccessfully attempted the endovascular use of a bifurcated stent-graft for the treatment of an AAA. The first successful EVAR was reported by Parodi et al. in 1991 when he combined his straight tubular polyester stent-graft with the balloon-expandable Palmaz stent as a proximal fixation [1]. The technique gained early recognition and acceptance, whereas in 1992 Frank Veith used the first tubular stent-graft in the USA to treat a patient with AAA [7].

The next evolution was the development of bifurcated stent-grafts in order to involve the iliac arteries and secure distal sealing zone. Timothy Chuter in 1993 was the first to introduce a unibody bifurcated stent-graft system for the treatment of an AAA [8].

As experience grew, it was realized that successful endovascular repair required good sealing in healthy aorta proximally and healthy iliac arteries distally to provide a long-term durable repair.

Despite the development and constant improvement of endovascular stent-grafts for AAA, there was still a significant portion of patients with anatomy not suitable for standard EVAR. This included patients with suprarenal, juxtarenal, short-neck infrarenal aneurysms, or thoracoabdominal aortic aneurysms (TAAA). Gradually, it became obvious that incorporating critical vessels (visceral, renal arteries) into the proximal sealing zone was mandatory in order to treat this group of patients with endovascular techniques.

The first stent-graft with one fenestration for the renal artery was performed by John Anderson in Adelaide, Australia, in 1998 [9], followed by Wolf Stelter in Frankfurt, Germany, who was the first to successfully use a fenestrated stent-graft to preserve a renal artery in Europe in 1999. With the advent of this technology, it became clear that more complex aneurysm could be treated with total endovascular repair. Tim Chuter was the first to suggest and implement a multibranched device for TAAAs by adding side branches to a tubular stent-graft with a reduced diameter at the level of the visceral arteries to accommodate all four branches without increasing the bulk of the multibranched stent-graft [4].

Subsequently fenestrated and branched devices were introduced also for the aortic arch. The above developments enabled gradually a total endovascular repair for anatomically suitable thoracoabdominal and aortic arch pathologies.

Preoperative Planning of Branched Endografts

Meticulous preoperative case planning and a thorough review of aneurysm anatomy are crucial in endovascular procedures, especially those using branched endografts. In addition to the measurement of lengths and diameters, a thin-slice computed tomography angiogram (CTA) determines the site of the sealing zone, target vessels’ orientation and tortuosity, the presence of thrombus and ostial stenosis, and access vessels’ quality. A successful aortic procedure with branched stent-grafts always requires a careful and accurate preoperative planning.

Sealing Zone

It is well established that endografts must seal in healthy aortic wall proximally and healthy iliac arteries distally in order to increase the durability of endovascular treatment. There is evidence that aortic disease is progressive [10, 11]; thus it is of utmost importance to assess the extent of aortic disease and carefully select the proximal and distal sealing zone.

Changes in aortic diameter or presence of arterial wall calcium, thrombus, debris, or thickening may indicate diseased aortic wall and implicate future progression of disease and failure of endovascular treatment. An aortic or iliac wall that appears diseased should not be selected for sealing zone. However, the risk of aortic disease progression must be balanced against the risk of spinal cord ischemia (SCI) by maintaining the aortic coverage to the minimum length that is considered to be safe and aiming at the same time to land if possible below major intercostal arteries.

The proximal and distal landing zones must be selected in parallel aortic wall, with minimal or no thrombus or calcification when possible. Usually, a minimum length of >2 cm is needed; however longer lengths are preferred, especially in cases of tortuous segments, ectasia, or thrombus-laden aorta [12, 13]. In cases of increased risk of paraplegia, preoperative planning should include enough overlap for future endovascular reintervention.

Selection of Fenestration/Branches

Once the sealing zone has been determined, the next step in the preoperative planning is to identify which type of incorporation will be used for the target vessels. The type of incorporation may be either fenestration or branch.

To date, there are three types of fenestrations: small, large, and scallop fenestrations. Directional branches can be internal, external, downward, or upward. Branches are either 6 or 8 mm in diameter and 18 or 21 mm in length. Routinely, 6 mm branches are used for the renal arteries and 8 mm branches for the celiac and superior mesenteric arteries.

As a general rule, fenestrations are preferred for target vessels originating from normal or only slightly dilated aortic segments, which is often the case in pararenal aneurysms or type I–III TAAA with narrow perivisceral aortic segments. On the other hand, branches are ideally suited to target vessels originating from aneurysms or large aortic lumens and, thus, are mainly used for extensive TAAA. In addition, fenestrations are ideally suited for transversely oriented vessels with a close-to-90° take-off from the aorta, while down-going vessels seem to have better alignment with branches and are also easier to catheterize via a branch from above. Fenestrations are generally placed on wide graft diameters to promote apposition to the aortic wall, while branches originate from tapered graft diameters to facilitate branch vessel catheterization [14].

The use of fenestrations is accompanied with less thoracic aorta coverage, better transverse orientation, and better patency rates of renal fenestrations [15]. Exact positioning of the main stent-graft with an alignment of the fenestration to the target vessel is mandatory or needs to be achieved by repositioning of the stent-graft, and catheterization can be tedious. Branches offer better seal and fixation for the bridging covered stent, less critical positioning and deployment of the branch, and better longitudinal alignment. On the other hand, branched endografts require a longer aortic coverage, since sealing has to be achieved above the tapered part of the graft, where the branches originate increasing therefore potentially the risk for spinal cord ischemia.

In cases of narrow aortic diameter with down-going target vessels, where neither fenestrations nor branches are suitable, inner branches can be used as a third alternative option. Until recently, inner branches were only used in the arch-branched device (Cook, Bloomington, IN, USA). Early experience demonstrates that inner branches work in selected vessels with otherwise difficult anatomy [16]. Inner branches are coupled with a diamond-shaped distal opening to facilitate branch vessel catheterization. Inner branches provide also advantages in chronic post-dissection TAAA, where the narrow true lumen can be a limitation for the planning of standard branches due to limited space. Another advantage of inner branches is that sealing can start lower in the aorta, reducing therefore the length of aortic coverage and the risk for spinal cord ischemia. This is because the graft does not need to taper down to a smaller diameter as in the case of standard branches. A typical example is two inner branches are used for the renal arteries, together with two fenestrations for the coeliac artery and the SMA. In this case the main graft remains wide in diameter at the suprarenal level, and sealing can be achieved already at this level, without the need to seal higher in the thoracic aorta (Fig. 52.2).

Fig. 52.2
A structural design of a branched endograft. It consists of two fenestrations marked by circles in the center.

Graft plan for pararenal AAA with narrow visceral aortic diameter and downward take-off of the renal arteries; two inner branches for the renal arteries; and two fenestrations for the coeliac artery and the SMA

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Implantation Techniques: Arterial Access

Down-going vessels targeted with branches are preferentially approached from above using an axillary/brachial approach [17]. Until recently, the axillary access has been considered mandatory for endovascular procedures with branched endografts. The axillary approach offers the advantage of early restoration of lower limb and pelvic blood flow, which is associated with improved spinal cord perfusion and lower rates of spinal cord ischemia. However, axillary access is combined with a stroke risk of 2–4% and a risk of median nerve neuropraxia of 1% [18]. In order to eliminate these complications, a transfemoral-only approach with the use of steerable sheaths has been applied recently in a few centers (Fig. 52.3).

Fig. 52.3
3 radiographs of the lumbar spine with an installed wire like a stent and a branched endograft.

Transfemoral access for vessels targeted with branches as an alternative to axillary approach

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The transfemoral access can result in decreased operative time, radiation exposure, and fluoroscopy time, while there are no significant differences in 30-day mortality or major adverse events [19, 20]. On the other hand, in difficult target vessel anatomies (ostial stenosis, severe calcification, or angulation), a transfemoral-only approach can be more cumbersome, and an upper approach may be preferable.

Outcomes of Branched Endografts in TAAA Endovascular Repair

Several series have reported early and mid-term outcomes of fenestrated and branched endografts for endovascular treatment of TAAA without however presenting outcomes specifically for branched stent-grafts only. Verhoeven et al. published one of the first series back in 2015 with F/BEVAR in TAAA in a total of 166 patients. Technical success was 95% with a 30-day operative mortality of 7.8%. Peri-operative spinal cord ischemia (SCI) was noted in 9%, with permanent paraplegia in 1.2%. Estimated survival at 1, 2, and 5 years was 83% ± 3%, 78% ± 3.5%, and 66.6% ± 6.1%, respectively. Estimated target vessel stent patency at 1, 2, and 5 years was 98% ± 0.6%, 97% ± 0.8%, and 94.2% ± 1.5%, respectively. Estimated freedom from reintervention at 1 and 3 years was 88.3% ± 2.7% and 78.4% ± 4.5%, respectively [21].

The group of Haulon et al. reported their experience with a total of 204 patients (42% type IV TAAA and 58% type I–III TAAA) [22]. The primary technical success rate was 92.6%, with a 30-day mortality of 6.9%. Major complications were noted in 26.5%, including SCI in 3.9%.

Oderich et al. reported recently the outcomes of F/BEVAR in 430 complex aortic aneurysms including 297 TAAAs [23]. Thirty-day mortality was 0.9%. New-onset dialysis was noted in 2% and permanent paraplegia in 2%. During follow-up there were 3 (0.7%) aortic-related deaths. Freedom from all-cause and aortic-related mortality at 5 years was 57% ± 5% and 98% ± 1%, respectively. Freedom from reintervention at 5 years was 64% ± 4%. Target vessel patency and target vessel instability at 5 years were 94% ± 1% and 89% ± 2%, respectively.

Branched Grafts as Off-the-Shelf Devices

Customized branched endografts for each individual patient are accompanied by a waiting time for manufacturing and shipping of 6–8 weeks, exposing patients to a rupture risk during the waiting period and limiting their use only in elective cases [24]. Off-the-shelf branched stent-grafts were manufactured aiming to eliminate the waiting time and enable immediate treatment in acute (symptomatic-ruptured) or large aneurysms. Off the-shelf branched stent-grafts are immediately available and can be used to treat an important proportion of patients (60–70%) in the acute setting even if the anatomy does not match ideally. On the other hand, using a graft that is not specifically designed for each patient’s anatomy can lead to extra intraoperative difficulties that one should be prepared to handle with bail-out techniques and extra ancillary materials.

Cook t-Branch®

The Cook t-Branch® stent-graft (Cook, Bloomington, IN, USA) consists of a tapered woven polyester stent-graft sutured to a Z-stent stainless steel exoskeleton [25]. The tapered segment of the device contains four branches targeting the visceral and renal arteries. Celiac and superior mesenteric artery branches are 8 mm in diameter, 21 and 18 mm in length, and are located in the 01:00 and 12:00 positions, respectively. Right and left renal artery cuffs are 6 mm in diameter, 18 mm in length, and located in the 10:00 and 03:00 positions, respectively. The device has a diameter of 34 mm at the top and 18 mm at the bottom, with a length of 202 mm. The standard device is delivered through a 22-French system, while the lower-profile device is delivered through an 18-French system.

Gore Excluder TAMBE

The GORE® EXCLUDER® Thoracoabdominal Branch Endoprosthesis is an off-the-shelf, modular, multicomponent system composed of a proximal multibranched aortic component, a distal bifurcated component, and iliac limb extensions [26]. The TAMBE has four portals with options of either retrograde renal portals or antegrade renal portals. To date the use of this device is restricted to particular centers as investigational.

E-nside

The E-nside prosthesis (Artivion Inc., Hechingen, Germany) is a new off-the-shelf stent-graft with four inner branches for the visceral and renal arteries [27]. The stent-graft is available in two different proximal diameters (38 and 33 mm) and two different distal diameters (30 and 26 mm). The device is delivered through a 24-French system, and all inner branches are pre-cannulated. Short-term and long-term clinical results of the use of the E-nside stent-graft are lacking.

Branched Grafts for Aortic Arch Repair

Endovascular repair of the aortic arch may consist of distal extension of ascending aortic aneurysms, proximal extension of thoracic or thoracoabdominal aortic aneurysms, or isolated arch aneurysm repair. Until recently, hybrid repair with surgical debranching followed by TEVAR, parallel stent-grafts (chimney technique), and in situ fenestrations remained the alternative to open surgery in patients of high peri-operative risk. However, the significant progress of custom-made fenestrated and branched endografts gradually gained acceptance and made it possible to move the proximal sealing zone into zone 0 with total endovascular means.

Peter Mossop and Ian Nixon in Melbourne, Australia, performed the first case in 2000, using a fenestration to preserve the flow in a left subclavian artery (LSA) to extend the sealing zone proximally. Timothy Chuter and colleagues from the University of California, San Francisco, performed the first arch repair using a branched endograft in 2003 [28]. This was the first modular arch device, which was designed with a branched stent-graft to incorporate the innominate artery combined with cervical debranching of the left carotid and subclavian arteries.

The Cook A-branched arch stent-graft is a third-generation arch device developed by Cook Medical (Brisbane, Australia, and Bloomington, IN, USA). It is a custom-made design for zone 0 deployment with one or two proximal and two distal sealing stents. There are two or three internal branches (two antegrade and one retrograde for the LSA) with large diamond-shaped external openings that occupy the central narrower portion of the graft. The delivery system is equipped with a pre-curved cannula with a nitinol wire securing the outer curve of the stent-graft with the inner cannula to facilitate alignment.

The Relay branch arch device by Terumo-Aortic (Sunrise, FL) is a custom-made branched design based on the Relay NBS Plus platform. The stent-graft comprises nitinol exoskeleton sutured to polyester fabric. It is intended for zone 0 deployment with options of one or two antegrade internal branches. The device is equipped with a dual sheath design along with a pre-curved cannula and a proximal capture mechanism to facilitate alignment. The internal branches have anchors for a locking mechanism to prevent branch migration. The device comes in diameters ranging from 22 to 46 mm. It is oriented and advanced on an aortic wire, and branches are cannulated from retrograde access via cervical carotid and/or brachial access.

Iliac Branched Grafts

Patients with aortic aneurysm and concomitant common iliac artery (CIA) aneurysm or dilatation may have unsuitable distal sealing zone in the common iliac artery (CIA). In order to achieve a distal sealing zone for the normal iliac wall, embolization of one or both internal iliac arteries with extension of the stent-graft to the external iliac artery (EIA) was initially proposed. However, a significant portion of patients may develop complications related to internal iliac artery occlusion, such as buttock or thigh claudication, erectile dysfunction, or less frequently gluteal or perineal necrosis, ischemic colitis, and spinal cord injury [29]. Evolution of endovascular repair to extend the landing zone into the external iliac artery required creation of an iliac branch device (IBD). Marcel Goodman in Perth, Australia, successfully placed the first internal iliac branched stent-graft in a patient in 2001, whereas Wolf Stelter in Frankfurt, Germany, published the first series in 2007 [3].

The Zenith (Cook Medical) endovascular iliac branch device (IBD) is a bifurcated branch vessel graft with openings to connect the common iliac to the side branch and external iliac segments. The IBD device received CE mark in 2006. The stent-graft is loaded in a 20-F hydrophilic sheath and consists of full-thickness woven polyester fabric sewn to self-expanding stainless steel and nitinol Z-stents. There are two available lengths for the CIA segment (45 and 61 mm) with a diameter of 12 mm and two available lengths for the EIA segment (41 and 58 mm) with two diameters (10 and 12 mm). The IBD is the only iliac branch graft with available long-term data [30, 31].

The Gore Excluder Iliac Branch Endoprosthesis (IBE; W.L. Gore & Associates Inc., Flagstaff, AZ, USA) consists of two modular components: the Iliac Branch Component and the Internal Iliac Component. The Iliac Branch Component is delivered through a 16F sheath over two guidewires: a stiff guidewire and a femoral-femoral through-and-through wire that passes through the pre-cannulated internal iliac gate. A 12F sheath is inserted from the contralateral femoral artery and is advanced over the through-and-through wire into the internal iliac gate. The internal iliac component is then introduced through the 12F sheath into the internal iliac artery. Several studies [32, 33] have reported favorable results of the use of the IBE; however, the long-term outcomes and durability of the IBE device remain unknown.

The newest iliac branch device, the E-liac stent-graft system, by Jotec GmbH (Hechingen, Germany), consists of a nitinol skeleton with asymmetric stents covered by woven polyester that is sutured with braided polyester. The E-liac is available with three proximal diameters of 14, 16, and 18 mm and three distal diameters of 10, 12, and 14 mm. The CIA segment length can be 53 or 65 mm, whereas the EIA segment length is 44 or 56 mm. The only available data are up to 12 months of follow-up [34], and thus long-term results data are pending.

Conclusions

Branched stent-grafts have enabled total endovascular treatment of complex aortic pathologies, providing the possibility to exclude sufficiently the aneurysm while preserving at the same time blood flow to vital aortic branches arising from the aneurysm. The technique of branched stent-graft implantation has now gradually matured, and several expert centers report very good early and mid-term outcomes given the magnitude of the treated pathology (TAAA and aortic arch aneurysms). Off-the-shelf branched stent-grafts provide an option for immediate endovascular treatment of acute cases (ruptured, symptomatic, or large aneurysms) and are also increasingly used worldwide. Future improvements include the use of dedicated bridging stent-grafts aiming to improve target vessel patency and reduce the need for reintervention.