Anatomical characteristics of infrarenal abdominal aortic aneurysms (AAA) are the most critical factors for successful endovascular repair (EVAR). The long-term durability of EVAR is highly dependent on the integrity of the proximal fixation site. Severe proximal aortic neck angulation (i.e., ≥60 degree angulation between the infrarenal aortic neck and the longitudinal axis of the aneurysm) and iliac angulation/tortuosity make it difficult to introduce the delivery system and deploy the Stent-Graft which tends to kink when encountering severe proximal neck angulation or compound curvatures of the iliac arteries. High proximal aortic neck angulation increases EVAR complexity and is associated with several postoperative complications including persistent Type Ia Endoleak, graft migration, aneurysm sac expansion with late rupture, and requirement for remedial procedures or delayed open conversion. Severe iliac artery tortuosity increases the risk of iliac limb occlusion and Type Ib endoleak.
Patients with these unfavorable anatomical features comprise a large proportion of those who eventually receive EVAR. Initial landmark clinical trials excluded up to 20% of patients with an infrarenal aortic neck angle >60 degrees from receiving EVAR since they did not meet the anatomic restrictions in the instructions for use (IFU) for the endografts available at the time of these trials. Newer generation devices have attempted to accommodate a wider range of aortoiliac anatomies. The Lombard Aorfix endograft (Lombard Medical Inc., Oxfordshire, United Kingdom) is a highly conformable nitinol/polyester device designed for transrenal fixation and accommodates highly angulated aortic necks of up to 90 degrees. Aorfix has been on the European market since late 2004 and was approved by the US Food and Drug Administration (FDA) in 2013 after initial early results of the Prospective Aneurysm Trial: High Angle Aorfix Bifurcated Stent-Graft (PYTHAGORAS) trial showed that outcomes associated with the use of the Aorfix were comparable to those of other endografts used in normal anatomy. The use of the Aorfix increased the number of patients eligible for EVAR, who were previously excluded from this type of treatment.
The Aorfix endograft remains the only on-label alternative to open repair for patients with highly angulated aortic necks. The device uses the ring stent concept and is designed to be flexible and conformable to the vessel, resistant to kinking and twisting, and able to shorten without kinking ( Fig. 9.1 ). These features make it particularly suitable when proximal and/or distal landing zones are considerably angulated, especially in larger aneurysms with elongated aorta and iliac arteries. When implanted, the Stent-Graft rings are reformed to have a saddle or “fish-mouth” shape hugging the renal artery orifice and allowing the endograft to be placed pararenally. The fish-mouth troughs are aligned with the renal arteries juxtarenally and the fish-mouth peak extends suprarenally. This provides optimum seal positioning, which might reduce endoleak risk ( Fig. 9.2 ). The Stent-Graft can also be used in patients with standard anatomy, which helps increase operator familiarity with the device. On certain occasions, namely in patients with tortuous iliac vessels and wide proximal aneurysm necks, main bodies made by other manufacturers in conjunction with the Aorfix iliac limbs have been used ( Box 9.1 ).
Care needs to be taken when sizing the proximal fish-mouth section of the graft, as gross oversizing may cause luminal distortion. An oversizing between 10% and 30% proximally in the aortic neck and 1–2 mm in the iliac component is recommended. However, it is important to note that the outside diameter of Aorfix stent grafts is 1 mm larger than the label diameter which refers to the lumen of the graft. Oversizing is calculated from this outside diameter. Moreover, some familiarity with the orientation of the proximal fish-mouth configuration of the graft is essential for a successful deployment. Once this process is mastered, the subsequent steps can be implemented with minimal difficulty.
EVAR and Device-Specific Complications
The first intraoperative difficulty that may be encountered with the Aorfix Stent-Graft is the introduction of the delivery system through the angulated neck. This problem can be solved by applying gentle external compression on the abdomen to the aneurysm via a simple hand maneuver. An additional option would be adding a stiff buddy wire to straighten the anatomy. In cases where there is difficulty in cannulating the contralateral limb, the bifurcated graft can be converted to an aorto-uni-iliac (AUI) stent graft.
In the PYTHAGORAS trial, graft deployment was unsuccessful in eight patients out of 218 patients because of iliofemoral access issues. In one case, no attempt was made to insert the endograft after failure to introduce appropriate dilators. However, in all other cases, various degrees of difficulty were encountered that resulted in failure to gain adequate access to deploy the graft ( Box 9.2 ). Notably, the low profile Intelliflex delivery system for Aorfix is not available in the United States, and PYTHAGORAS and other US experience is currently limited to early versions of the deployment device which featured a larger profile and different delivery mechanism.
Careful preoperative imaging with thin-slice computed tomography angiography (CTA) and 3D reconstruction are very valuable in determining adequate access vessels and the appropriate side for introduction of the endograft. This is helpful in preventing technical failure at this stage. In patients with highly tortuous aortic neck and iliac arteries, meticulous assessment of anatomy prior to the procedure in all three CTA planes can help choose the side with the least angulation for the introduction of the main graft delivery system. For example, in the case of severe neck angulation seen in the coronal plane toward the right, introduction from the contralateral left side will facilitate the passage at the top of the bend and allow for C-shape curve on the delivery system. The use of a super stiff guide wire, such as the Lundequist (Cook Inc., Bloomington, Indiana), is also invaluable.
For cases with small iliac diameters, extending the groin incision or a retroperitoneal exposure with placement of a conduit might be required as with any other endografts.
Do not use excessive force to advance or withdraw the delivery device when resistance is encountered.
If the delivery device kinks during insertion, do not attempt to deploy the Stent-Graft component; remove the device and replace it with a new one.
Type I Endoleak
Intraoperative proximal endoleak in the interventional suite is not a rare event in cases with hostile infrarenal necks. Their occurrence is highly associated with the learning curve for the Aorfix endograft. In preliminary single-institutional experiences with the Aorfix Stent-Graft, intraoperative Type I endoleaks were detected in 5% to 24.1% of patients. In one patient, the Stent-Graft was positioned too low beneath the lowermost renal artery and was treated successfully using proximal extension. In another patient, the Type I endoleak persisted despite positioning the proximal extender at the renal arteries and was left untreated because no Palmaz stent was available at the time and conversion to open repair could not be attempted because of the poor general condition of the patient. In two other patients, simple dilation with an aortic balloon was performed. However, it failed in one patient and a giant P4014 Palmaz stent (Cordis, Miami, Florida) was successfully deployed. On the other hand, post-operative type Ia endoleaks are quite rare with the Aorfix. The PYTHAGORAS study reported three cases of Type Ia endoleak detected on computed tomography (CT) scans. The first two occurred in the first year; one was treated by EndoAnchor and the second was left untreated. The third was diagnosed on postoperative follow-up between the third and fourth postoperative years and was treated with a fenestrated cuff.
Type II Endoleak
In Hinchliffe’s study, of 24 patients receiving the Aorfix Stent-Graft, there were only two non-graft related (Type II) endoleaks. The first was detected at completion angiography in a patient with four paired lumbar arteries and the second was detected at discharge. The endoleaks spontaneously sealed by 30 days. In the PYTHAGORAS trial, the incidence of Type II endoleaks was similar between standard-angle (<60 degrees) and highly angulated neck group at all time points (13%, 8%, and 9% at 1, 3, and 5 years respectively) ( Table 9.1 ).
|Variable||Aorfix||Aorfix, <60 degrees||Aorfix, ≥60 degrees||P value|
|( N = 218)||( N = 67)||( N = 151)|
|Sac shrinkage (>5 mm)|
|1 year||42 (69/165)||39 (20/51)||43 (49/114)||0.73|
|3 years||57 (74/129)||7 (26/43)||56 (48/86)||0.71|
|5 years||61 (52/85)||64 (16/25)||60 (36/60)||0.81|
|Sac expansion (>5 mm)|
|1 year||1 (2/165)||0 (0/51)||2 (2/114)||1|
|3 years||7 (9/129)||7 (3/43)||7 (6/86)||1|
|5 years||12 (10/85)||4 (1/25)||15 (9/60)||0.27|
|Type I or III endoleak|
|1 year||1 (2/149)||0 (0/46)||2 (2/103)||1|
|3 years||0 (0/114)||0 (0/38)||0 (0/76)||1|
|5 years||0 (0/72)||0 (0/25)||0 (0/47)||1|
|Type II endoleak|
|1 year||13 (20/149)||15 (7/46)||13 (13/103)||0.67|
|3 years||8 (9/114)||5 (2/38)||9 (7/76)||0.47|
|5 years||9 (7/75)||11 (3/27)||8 (4/48)||0.69|
|1 year||1 (2/165)||0 (0/51)||2 (2/114)||1|
|3 years||5 (6/128)||2 (1/42)||6 (5/86)||0.66|
|5 years||4 (3/85)||4 (1/25)||3 (2/60)||1|
|Fixation zone fracture|
|1 year||6 (9/159)||5 (2/43)||6 (7/116)||1|
|3 years||19 (23/123)||13 (5/39)||21 (18/84)||0.32|
|5 years||23 (17/75)||21 (5/24)||24 (12/51)||1|
|Main body fracture|
|1 year||2 (3/159)||0 (0/43)||3 (3/116)||0.56|
|3 years||1 (1/123)||0 (0/39)||1 (1/84)||1|
|5 years||1 (1/75)||0 (0/24)||2 (1/51)||1|
|1 year||10 (22/218)||8 (5/67)||11 (17/151)||0.47|
|3 years||14 (31/218)||9 (6/67)||17 (25/151)||0.21|
|5 years||17 (38/218)||12 (8/67)||20 (30/151)||0.18|