Endovascular Aneurysm Repair Techniques

Introduction

Current commercially available systems have a wide variety of configurations that are capable of treating the majority of infrarenal aortoiliac aneurysms. Various options exist for stent-graft fixation, sealing, patency, sizing, and durable exclusion of aortic aneurysms. Radiopacity, deployment precision, ease of use, and sheath size and flexibility are additionally important characteristics. Current commercially available infrarenal endografts and their respective US Food and Drug Administration (FDA) approval dates can be seen in Table 74.1 .

TABLE 74.1

Current Commercially Available FDA-Approved Infrarenal Aortic Stent Graft Devices

Device	Manufacturer	FDA Approval Date	Implants Worldwide (Approx.)
Excluder	Gore	2002	350,000
Zenith Flex	Cook	2003	200,000
Endurant	Medtronic	2010	400,000
AFX	Endologix	2011	83,000
Ovation	Trivascular	2011	15,000
Aorfix	Lombard	2013	N/A ∗
Treo	Terumo	2020	9000

FDA , Food and Drug Administration.

∗ Updated implant number undisclosed by Lombard Medical.

Fixation

An essential feature of all stent grafts is a method of fixation to the surrounding aortic intima to inhibit distal migration from the intended seal zone after deployment, as systolic blood flow delivers constant force against the stent graft. In tortuous aortic anatomy, augmented vector forces increase the risk of component separation and migration of graft components. Aortic remodeling after endovascular aneurysm repair (EVAR) can also result in morphologic changes of the excluded aorta, resulting in loss of seal, stent graft migration, component separation, and limb kinking or thrombosis.

Positive Fixation, Column Support, and Friction

Multiple endograft features are designed to prevent graft migration and consequent complications. Positive fixation describes the use of metal hooks, barbs, anchors, or supplemental staples to attach the graft to the aortic wall and prevent migration. In endografts designed to straddle the aortic bifurcation with proximal extension of graft components, columnar support helps maintain the position of the cranial aspect of the device with buttressed support from the bifurcation component. The outward radial force of the stents themselves creates friction with the vessel wall that reduces the risk of migration. Increased risks of long-term migration in first generation devices without active fixation have led to near universal incorporation of active fixation in current endograft designs. Some devices have polyester fuzz or other prosthetic material that induces a fibrotic reaction in the aortic neck and aids in graft fixation, and several devices include a combination of these characteristics.

Infrarenal Versus Suprarenal Fixation

Infrarenal fixation describes active sealing at the proximal most aspect of the endograft in the infrarenal aortic neck. Endografts with suprarenal fixation employ a bare metal stent that is separated from the sealing component of the infrarenal portion of the stent graft, extending the fixation component into the pararenal and suprarenal aorta. The suprarenal aortic neck is typically more uniform and resistant to late dilation, and long-term fixation with this suprarenal fixation may be improved. If open conversion and complete graft explantation become necessary, removal of endografts with suprarenal fixation requires a comparatively more complex surgical approach, and a variety of techniques have been utilized in this situation.

Sealing

Currently approved endografts are designed to seal aortic aneurysms with ideal infrarenal aortic morphology, which includes a straight, cylindrical, 10 to 15 mm long neck without significant thrombus or calcification. Seal zone adjuncts include anchoring screws or endoanchors, covered flares that expand beyond the nominal diameter of the main graft, polyester fuzz, sealing cuffs, and off-label stent utilization. The basic stent pattern of the proximal portion of the device impacts sealing and conformability, both critical factors for treating angulated or shorter necks.

Iliac Limbs

The unsupported limbs of first generation EVAR devices were often plagued by kinking and limb occlusion, which prompted frequent off-label use of additional stents within the originally unsupported limbs to maintain adequate patency. Late fabric erosion with subsequent type III endoleak and aneurysm enlargement or rupture is one complication of this approach that illustrates a late pitfall of off-label component use. Although most current, fully supported endograft limbs provide excellent long-term patency, there is sufficient space between stents or stent rings in some devices to allow potential limb kinking, compression, and occlusion in cases with challenging anatomy. Concomitant iliac arterial injury during EVAR, heavy circumferential distal aortic or iliac calcification, severe iliac tortuosity, and excessive graft limb oversizing are additional factors that increase the degree of difficulty and associated risk of limb occlusion with EVAR.

Sizing

Currently approved aortic stent grafts come in a wide range of aortic diameters, iliac limb diameters, and graft lengths that are labeled for varying anatomic configurations. The complexity of case planning varies with each system due to variability in respective indications for use (IFU), differences in sizing windows, techniques, tapering zones, and usable seal zones.

Graft Material

Widely used polyester or polytetrafluoroethylene (PTFE) graft material is similar to that used for open surgical repair. In contrast to surgical grafts that become incorporated in fibrous retroperitoneal tissue, stent grafts are suspended in aortic thrombus and may develop transudates or microfenestrations that do not close. The graft material may abrade with constant wear against metallic stent components or may be subject to weave deformation by attachment sutures. Sutures themselves may wear or break, causing subsequent increased abrasion. Some stent grafts are sutured only at the ends of the stent, whereas others use a composite bonding process without sutures.

Radiopacity

Endograft components are visible with widely available, high-quality fluoroscopy systems; however, accurate visualization with portable C-arms, particularly in obese patients, can be challenging. Respective delivery systems and endografts have a variety of radiopaque markers to facilitate rotational orientation, deployment, and gate cannulation. Such markers vary with each specific device, and not all are positioned in the same orientation with respect to the graft’s fabric edge, which is typically not radiopaque at commonly used magnifications. Some markers are circumferential, whereas others are positioned intermittently around the circumference of the device.

Deployment Precision and Ease of Use

Deployment components vary in flexibility, trackability, valve function, outer diameter of the ipsilateral and contralateral sheaths, sheath exchange requirements, and deployment precision. The labeling, torque responsiveness, need for exchange-length wires, difficulty in cannulation of the contralateral gate, and other attributes all contribute to the relative complexity of the deployment sequence with each respective graft. Ease of deployment is thus only one aspect of a device’s performance.

Graft Slection and Primary Device Characteristics

Detailed knowledge of sizing, deployment techniques, failure modes, expected outcomes, and reintervention techniques is essential to provide a durable endovascular result. There are a few anatomic situations in which one particular device may be preferred, although even in these situations a surgeon with mastery of a single specific device could probably make that device work for challenging cases ( Fig. 74.1 ). Difficult iliac anatomy can often be treated with smaller systems or those featuring deployment systems with a higher degree of flexibility and trackability. Short lengths from the lower renal artery to the aortic bifurcation can be better treated with some respective devices. Severely angulated, short aortic necks are not well treated with any approved system except the Aorfix, but more flexible investigational devices (Conformable Excluder, W.L. Gore) and off-label aortic stents can potentially overcome challenging proximal necks. Less angulated short necks may be addressed with branched endografts, fenestrated devices or parallel graft adjuncts (see Ch. 82 , Fenestrated and Branched Endograft Treatment of Juxtarenal, Paravisceral, Thoracoabdominal, and Aortic Arch Aneurysms: Device Selection and Technical Considerations).

Figure 74.1, Commercially Available Endografts.

Endograft Configurations

Bifurcated devices are currently utilized in greater than 95% of EVAR in the treatment of infrarenal aortic aneurysms. These are either modular (Endurant, Excluder, Ovation, Zenith, Aorfix, Treo) or unibody (AFX [Endologix]). While there are no commercially available devices for isolated saccular aneurysms or penetrating aortic ulcers of the infrarenal aorta, off-label use of “stacked” aortic cuffs, larger iliac components, or small diameter thoracic extensions can be utilized for this purpose when sufficient proximal and distal landing zones are present. Aorto-uni-iliac endografts (ReNu, Endurant) can be utilized in conjunction with a contralateral iliac occlusion device and a femoral–femoral bypass. The relative indications for use of this configuration are listed in Box 74.1 . Branched and fenestrated endografts and chimney or snorkel grafts can be utilized in juxta- or pararenal aneurysms with inadequate normal aorta to achieve a durable proximal seal.

BOX 74.1

Relative Indications for Aorto-Uni-Iliac Endograft Configuration

Very small (<15 mm) terminal aorta (which would not accommodate a bifurcated device)
Severe unilateral iliac occlusive disease
Secondary treatment of migration of a short-body endograft

Preoperative Sizing and Planning

Precise sizing and meticulous preoperative planning are essential for successful initial and long-term outcome after EVAR.

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