The original Endologix endovascular graft is currently called AFX, mainly to distinguish it from the other Endologix products, Ovation and Nellix (Endologix, Irvine, California). The AFX2 is the third-generation endovascular system after the earlier Powerlink and AFX stent grafts. The AFX is a unibody, bifurcated system consisting of a self-expanding cobalt-chromium alloy stent attached to a fabric cover ( Fig. 8.1 ). The fabric is a proprietary form of polytetrafluoroethylene (PTFE), an ultra-high-density, multi-layered material referred to as Duraply, which is conformable and tear resistant. There are some unique characteristics of the AFX, differentiating it from other stent graft systems. First, AFX is the only stent graft that sits on the aortic bifurcation to provide anatomic fixation thus maintaining the native bifurcation. Second, the PTFE fabric is externally mounted and attached only to the proximal and distal ends of the stent. This allows the fabric to move independently from the stent conforming to varied shapes of the aortic neck and bifurcation achieving an ActiveSeal ( Fig. 8.2 ). The VELA proximal extension comes in two configurations, with and without suprarenal bare-metal stent, and achieves seal at the aortic neck ( Fig. 8.1 ). The iliac limb extensions come in straight, tapered, flared, and stepped configurations to treat different iliac anatomies ( Fig. 8.1 ).
The AFX2 system is delivered through a 17-French AFX Introducer sheath and a 7-French contralateral sheath. The three types of stent grafts delivered through the introducer sheath include the bifurcated main body stent graft, VELA extension, and iliac limb extensions. The AFX2 system incorporates a 0.035 contralateral wire that is fed through the ipsilateral sheath along with the main body and snared from the contralateral side ( Fig. 8.3 ). The wire is withdrawn from the contralateral sheath and the stent graft main body is delivered through the sheath over a stiff wire, ensuring that the contralateral wire is not wrapped around the inner core of the delivery system. After confirming proper alignment, the stent graft is pulled down to seat it on the aortic bifurcation, guiding each limb into its respective iliac artery ( Fig. 8.3 ). The main body, contralateral limb, and the ipsilateral limb are then sequentially deployed. The AFX main body delivery system is removed and can be followed by the VELA extension or iliac limb extensions as necessary. This novel fixation technique prevents distal migration of the graft beyond the bifurcation and allows for easy up-and-over access across the bifurcation from one femoral access to the contralateral leg. This unique design has prompted the use of the AFX main body in the treatment of aortoiliac occlusive disease, which is currently an off-label use and will not be considered further in this chapter.
Instructions for use (IFU)
The AFX stent graft system is indicated for patients with suitable abdominal aortic aneurysm morphology including:
Adequate access vessels (diameter ≥6.5 mm) compatible with the AFX delivery system.
Non-aneurysmal aortic neck between the renal arteries and the aneurysm:
≥15 mm length
diameter of ≥18 mm and ≤32 mm
neck angle of ≤60 degrees
Aortic length ≥1.0 cm longer than the body portion of the chosen bifurcated model.
Common iliac artery distal fixation site:
distal fixation length of ≥15 mm
diameter of ≥10 mm and ≤23 mm
iliac angle of ≤90 degrees to the aortic bifurcation
Extension stent grafts must have the ability to overlap the bifurcated stent graft by at least 30 to 40 mm proximally and at least 15 to 20 mm distally.
At least one hypogastric artery is preserved.
Patients with known allergy to the device materials or any condition that could result in graft infection should not be treated with the AFX stent graft system.
Like all stent grafts, the AFX device is subject to some of the same generic complications common to all devices. However, it is also subject to some unique problems, which will be discussed in this chapter.
As discussed earlier, deployment of the stent graft main body requires snaring of the contralateral wire from the contralateral femoral side ( Fig. 8.3 ). This is done prior to advancing the stent graft main body through the sheath. Wire wrap can occur if the contralateral wire takes a spiral path around the ipsilateral wire as it is advanced through the sheath. This is an extremely common event and correction of wire wrap is a routine part of AFX deployment. Nonetheless, failure to recognize and correct this can lead to problems with and even failure to successfully seat the graft on the aortic bifurcation. Steps to prevent or to minimize wire wrap include:
Insert the contralateral wire on the medial side of the sheath, medial to the ipsilateral wire.
Once the contralateral wire emerges from the end of the sheath, attempt to snare it on the medial side of the ipsilateral wire ( Fig. 8.3B,C ).
Once the wire is snared and brought out of the contralateral groin, the main body is advanced through the sheath, keeping tension on the contralateral wire. During this time, care must be taken to recognize and treat wire wrap.
The main body and its relation to the contralateral wire is carefully observed under magnified fluoroscopy as the device is advanced beyond the sheath. The wire should be on the medial side of the stent graft ( Fig. 8.3C ).
Confirm the proper orientation of the contralateral limb marker on the medial side of the sheath.
If the wire appears lateral to the main body or it appears to be crossing over the device from medial to lateral, then a wire wrap must be assumed.
Ensure that contralateral wire and limb are on the medial side of the sheath
Maintain tension on the contralateral wire as the main body is advanced
If wire wrap is identified, rotate the sheath and device as a unit in a clockwise or counterclockwise direction under fluoroscopy to unwrap
Once wire wrap is diagnosed, it must be treated appropriately. It is usually difficult to ascertain the direction in which the wire is wrapped, so correction must be done with careful fluoroscopic monitoring:
Rotate the sheath and device as a unit, in either a clockwise or counterclockwise direction, while maintaining some tension on the contralateral wire.
If the wire orientation to the device appears to be correcting, and the contralateral wire feels like it is being “reeled out”, continue rotating until the wrap is completely corrected. Both the wire at the top of the sheath and the contralateral limb marker should be on the medial side.
If the wire orientation is not correcting, or the wire feels like it is being “reeled in”, then the direction of rotation should be reversed and continued until the wrap is corrected.
Once wire wrap is corrected, the main body can be advanced and seated on the aortic bifurcation by guiding the limbs into their respective iliac arteries ( Fig. 8.3D,E ). Rarely, the wire wrap is discovered after the main body is out of the sheath. This must be corrected before the device can be seated on the bifurcation. The same technique as described earlier is used, with careful rotation of the device while maintaining mild tension on the contralateral wire. While this usually results in successful deployment, it should be noted that rotation of the unconstrained device in the aortic sac increases the risk of embolization due to dislodgment of mural thrombus.
Placement of components behind stent struts
As noted earlier, a unique feature of the Endologix AFX device and its previous versions is that the covering fabric is attached to the stent only at the proximal and distal ends. This allows a guide wire to pass between the stent strut and the fabric. While this is usually not an issue with routine use of the graft, it can lead to potential problems when wire access is inadvertently lost during deployment, or when secondary procedures are required, necessitating wire replacement through the device. It should be noted that inadvertent routing of low-profile catheters, balloons or sheaths behind the stent struts rarely cause complications. However, attempts to advance large diameter sheaths or limb extensions behind the stent can lead to disruption of the device or limb occlusion. Efforts to avoid wire placement behind a stent strut include:
Use a pigtail or similar reverse curve catheter to advance through the device, because it is less likely to find its way behind a stent strut ( Fig. 8.4A ).