Endovascular aortic repair (EVAR) has become the standard of care in the treatment of infrarenal abdominal aortic aneurysm (AAA), with low perioperative morbidity and mortality and comparable long-term outcomes to open surgical repair. Successful EVAR requires meticulous intraoperative execution and careful consideration of a variety of anatomic factors during preoperative planning. Of these anatomic features, perhaps the most important are the characteristics of the infrarenal aortic neck. Hostile proximal neck anatomy, in the form of severe angulation, copious thrombus or calcification, or short overall length, is associated with worse short- and long-term outcome after EVAR. In order to improve these outcomes, continuous technological innovation in EVAR has focused on broadening the anatomic applicability of currently available devices and improving endograft performance in the infrarenal neck. These advances and a steadily increasing comfort level with EVAR among vascular specialists have led to an increasing number of aortic stent grafts placed over the past 10 years, with a significant percentage placed outside device specific indications for use (IFU). Given this trend of EVAR application in cases with challenging anatomy, the use of a repositionable stent graft offers several potential advantages, including increased deployment accuracy, potentially reduced procedure and fluoroscopy time, and a potential cost reduction by reduced need for aortic cuffs following inaccurate initial deployment or to treat proximal endoleak. With these potential advantages novel complications also emerge, specific to intraoperative repositioning of the device. This chapter will examine the unique attributes and potential complications of the only commercially available, repositionable device for EVAR, the Gore Excluder with its C3 delivery system (W.L. Gore & Associates, Flagstaff, AZ).
Evolution of the Gore Excluder AAA Endoprosthesis
Since the introduction of EVAR, technological innovation has focused on increased anatomic applicability of respective stent grafts and on improved short- and long-term outcomes following aortic repair. The Gore Excluder, now in its third iteration, has been implanted in over 300,000 patients and has undergone several design modifications and improvements since its initial FDA approval in 1997. The first major improvement, in 2004, was the modification of the original ePTFE (expanded polytetrafluoroethylene) microstructure, reducing porosity and subsequent fluid transmigration. The newer, low permeability Excluder was shown not only to reduce the incidence of sac enlargement and associated endotension, but also to promote early aneurysm sack shrinkage. Although known for its inherent overall flexibility and performance in challenging iliac anatomy, accurate proximal deployment of the Excluder still remained a concern among clinicians.
A critical second modification to the Excluder was the complete redesign of the traditional “rip-cord” mechanism or sim-pull technology of proximal graft deployment, which was occasionally imprecise in the setting of severe proximal neck angulation, to a repositionable deployment system. The modified C3 delivery system allows the operator to reconstrain the proximal aspect of the stent graft twice and reposition the device before final deployment. This novel feature means the graft can be repositioned when the proximal aspect of the main body graft fabric lands either too far proximally or too far distally with respect to the lower renal artery. The proximal aspect of the stent graft is constrained to approximately 30% of its full diameter, withdrawing the proximal anchors away from the aortic wall and allowing proximal or distal adjustment. In addition, when contralateral gate catheterization is challenging, the proximal aspect of the stent graft can be reconstrained and the graft rotated to allow a more favorable orientation.
Excluder with C3 Delivery System Deployment
Deployment of the Excluder with C3 delivery system occurs with three sequential steps: (1) opening of the main body and contralateral gate; (2) removal of the constraining wire and loop; and (3) deployment of the ipsilateral limb.
First, to initiate the deployment sequence after the usual maneuvers to establish access and perform diagnostic aortography are accomplished, the outer white deployment knob is rotated 90 degrees counter-clockwise, then slowly and steadily pulled ( Fig. 5.1 ). This maneuver will deploy the main body of the endograft and spring the contralateral gate. If the proximal position of the stent graft is acceptable, the procedure continues with cannulation of the contralateral gate. If the endograft requires adjustment to maximize proximal seal, the main body can be reconstrained and the endograft moved cephalad or caudad for ideal positioning. In order to reposition, the gray dial is rotated clockwise to reconstrain the proximal end, until the handle stops turning, moving the black nut toward the trailing end of the catheter handle, as seen through the transparent aspect of the manifold. While the main body of the endograft is reconstrained, the entire device can be manipulated proximally or distally to improve the position of the proximal landing zone, or along its rotational axis to improve the position of the contralateral gate. When the desired position of the proximal graft and gate is achieved, redeployment of the main body is accomplished by turning the same gray dial counterclockwise as far as possible. The black nut will be seen to move proximally. Fig. 5.2 displays these constrainment maneuvers and corresponding graft behavior ( Boxes 5.1 and 5.2 ).
Do not rotate the device delivery catheter while the endoprosthesis is inside the introducer sheath. Catheter breakage or premature deployment may occur.
Do not continue advancing any portion of the delivery system if resistance is felt during advancement of the guidewire, sheath, or catheter. Arterial or catheter damage may occur. Instead, stop and assess the cause of resistance.
After the main body and contralateral gate are optimally positioned and proximal position is verified, the graft is released from the constraining wire and loop by pulling back and holding in place the red safety lock. The entire transparent knob is then rotated 90 degrees counterclockwise and pulled completely out of the catheter handle ( Fig. 5.3 ).
Ipsilateral limb deployment is completed by loosening the gray deployment knob, then pulling it straight out of the catheter handle using a slow, steady motion ( Fig. 5.3 ). The contralateral limb can then be placed to complete the procedure.
Critical Technical Considerations, Potential Pitfalls, Troubleshooting
The C3 deployment system offers a number of options for repositioning and readjustment of both the proximal main body and the contralateral gate of the main body Excluder device, which are useful in a variety of clinical scenarios. The ability to deploy, recapture, and reposition the proximal aspect of the endograft relative to the lower renal artery is advantageous for both the inexperienced operator in cases with routine anatomy and for the experienced operator in cases that feature hostile proximal neck anatomy. Recapturing the proximal aspect of the main body for rotational adjustment of the endograft along its longitudinal axis also allows for reorientation of the contralateral gate to a more favorable position to facilitate cannulation.
Several critical technical points should be considered by the operator when repositioning is undertaken:
The endoprosthesis should not be constrained and reopened more than two times during a procedure, because device or catheter damage may occur.
Repositioning should not be performed with the endoprosthesis while the trunk is at its maximum diameter. Vessel damage or device misplacement may result.
The endoprosthesis should be repositioned only when fully constrained.
The IFU for the Excluder recommends a maximum of two reconstrain/reposition maneuvers, and there are fundamental risks involved with excessive repositioning ( Box 5.3 ). Reconstraining the stent graft with subsequent upward force applied to move the endograft proximally can be difficult in severely angulated, heavily calcified, short, narrow, or otherwise hostile necks. The increased friction generated with cranial force on the delivery system in these anatomic conformations can limit trackability during reorientation or, with excessive force, potentially result in aortic dissection or rupture. With this type of challenging proximal anatomy, Verhoeven and colleagues in reviewing the 1-year experience of C3 Excluder in the GREAT (Global Registry for Endovascular Aortic Treatment) recommend aggressive deployment of the stent graft at the level of the renal arteries or even a few millimeters higher, with the option to withdraw the endograft to a slightly lower position if needed.