Aortic endograft technology has evolved significantly since the initial U.S. commercial release in late 1999. Second- and third-generation endografts have come to market, providing improvements in fixation, sizing, versatility, tractability, and delivery profile. These device improvements have made it possible to treat challenging anatomy that would not have been feasible in the early days of endovascular aneurysm repair (EVAR). However, anatomic limitations continue to persist despite the improvements that have been incorporated among currently available endografts. Thus the ability to safely “push” the anatomic envelope is predicated on the ability of the experienced operator to make wise decisions with regards to patient and device selection.
Detailed examination of computed tomography (CT) angiography imaging is critical to evaluate concerns regarding the aortic neck, iliac access, or maintenance of hypogastric perfusion.
All measurements related to selection of the size of the endograft should be made by the operator.
The presence of anatomic constraints should anticipate the potential need for adjunctive techniques.
A stock of ancillary devices (stents, wires, catheters, and sheaths) that could be required should be available.
Pitfalls and Danger Points
Persistent type IA endoleak may occur from poor patient selection, inaccurate endograft placement, or both.
Iliac perforation and hemorrhage can occur from overly aggressive attempts at treating challenging iliac anatomy.
Iliac limb occlusion from kinking, external compression, or excessive oversizing may be observed, particularly if endografts extend into the external iliac arteries.
Colonic ischemia can result from atheroemboli or simultaneous bilateral hypogastric occlusion.
Endovascular Strategy for Unfavorable Anatomy
Severe iliac occlusive disease, calcification, and tortuosity can combine to make access for EVAR difficult. Although these challenges can frequently be overcome with adjunctive techniques when only a single anatomic problem is present, the combination of multiple anatomic access issues may make EVAR difficult or impossible to perform. Commercially available endografts are 14 to 20 Fr and thus require a minimum 5- to 7-mm iliac diameter for passage. Although focal areas of iliac occlusive disease can be readily treated to gain access to the aorta, a diffusely diseased iliac artery can be more problematic. Use of longer angioplasty balloons or hydrophilic Coons dilators (over a stiff wire) can sometimes be helpful in these situations. The placement of uncovered stents in the iliac vessel should be avoided before EVAR. Finally, a surgically placed iliofemoral conduit can be considered if the patient is anatomically suitable. Placement of the proximal iliac artery anastomosis typically is performed at the iliac bifurcation, allowing deployment of the ipsilateral endograft limb in the common iliac artery.
An alternate method of obtaining access in a patient with extensive iliac occlusive disease is to create an “internal endoconduit” by placing a covered stent in the external iliac vessel, which is then aggressively angioplastied to the required diameter. The covered stent protects against extensive dissection, free rupture of the native vessel caused by the aggressive angioplasty, or both. There must be a sufficient proximal and distal seal zone for the covered stent for this approach to be safe. Although these techniques have been anecdotally reported with successful outcomes, larger series are needed to establish the safety of this approach.
Significant iliac tortuosity can often be straightened with use of a very stiff guidewire, such as the Lunderquist or Amplatz (Cook Medical, Bloomington, Ind.) guidewires. Severe circumferential calcification in association with tortuosity must be approached cautiously, because even the stiffest guidewire may not straighten the vessel. Rarely, a second “buddy wire” may be helpful in this situation. Superstiff wires should be exchanged for a soft J wire before completion arteriography. Otherwise, an apparent high-grade stenosis may be seen in the external iliac artery that is caused by the vessel “accordioning” on the wire. These pseudolesions disappear with replacement of the stiff wire for a more flexible wire and thus do not require intervention.
“Through and through” access or brachial-femoral access was commonly used in the early period of EVAR to manage tortuous and challenging access vessel anatomy. It is rarely needed today given the development of smaller hydrophilic delivery systems.
Aortic necks that are less than 15 mm in length, highly angulated (>60 degrees), and conical are considered suboptimal for EVAR using current commercial devices. Aortic necks with multiple adverse anatomic features have a substantially higher risk of poor immediate and long-term outcome.
Proximal limb diameters range from 12 to 16 mm, so placing two limbs in a small terminal aorta with an aortic bifurcation diameter of less than 20 mm can significantly constrict the limbs of a bifurcated endograft. After placement of the limbs, bilateral “kissing” angioplasty with noncompliant balloons usually ameliorates this issue. If there is significant residual stenosis, the placement of kissing balloon-expandable stents should be considered.
Bifurcated endografts such as Endurant (Medtronic, Minneapolis), Excluder (Gore, Flagstaff, Ariz.), Ovation (Trivascular, Santa Rosa, Calif.), Powerlink (Endologix, Irvine, Calif.), or Zenith (Cook Medical) are used in more than 95% of EVARs. An aortouniiliac configuration may be preferable in the presence of a small calcific terminal aorta, severe unilateral iliac occlusive disease, treatment of a displaced shortbodied endograft, or when there is a need to preserve hypogastric flow using a retrograde approach.
Type I Endoleak Treatment
Initial treatment of a type IA endoleak should be guided by the position of the endograft to the lowest renal artery. If this distance is less than 3 mm, the seal zone should be angioplastied with a compliant molding balloon such as Coda (Cook Medical) or Reliant (Medtronic). If the distance is more than 5 mm, placement of an aortic cuff should be considered to increase the seal zone. Compliant balloon angioplasty of the aortic neck should be performed after cuff placement. It is essential that proper fluoroscopic gantry position is used to accurately assess the distance between the endograft and the renal arteries before these adjunctive treatments are employed. Frequently, significant cranial tilt and left or right obliquity are required to achieve a perpendicular axis to the aortic neck and lowest renal artery. The gantry position should be adjusted until the radiopaque markers on the proximal edge of the stent graft are in alignment.
Giant Palmaz Stent Placement
If a type IA endoleak persists despite these maneuvers, placement of a giant Palmaz (Cordis Corp., Bridgewater, N.J.) stent is indicated ( Fig. 26-1 ). Placement of this stent provides greater radial strength in the seal zone and eliminates the type I endoleak in most cases. A 3010, 4010, or 5010 Palmaz stent is hand-mounted on an appropriately sized valvuloplasty balloon (Z-Med, B. Braun Interventional Systems, Bethlehem, Pa.) in a slightly asymmetric manner, such that the more proximal (cranial) extent of the balloon inflates first. Choose a balloon size to match the diameter of the aortic neck. The choice of stent length depends on the diameter of the neck and the length of the main body of the endograft. The stent foreshortens significantly as it is expanded. Although the Palmaz 5010 is 5 cm in length at 10 mm of expansion, it shortens to about 33.8 cm at 28 mm. We typically use a Palmaz 5010 length for a long-body device such as Zenith. If this technique is used with a short-body bifurcated device (Endurant, Excluder, Ovation), a shorter stent (Palmaz 4010 or 3010) and balloon may be required so as not to intrude on the iliac flow divider distally.