Computed tomography arteriography (CTA) is the cornerstone of preoperative imaging for EVAR. The maximum recommended slice diameter is 2.5 mm for standard devices, whereas sizing for fenestrated or branched devices requires 1 mm or less cuts. Intravenous contrast should be routine unless the patient has severe renal insufficiency. The axial, coronal, sagittal, and three-dimensional reconstructions (Fig. 90-1A) should all be reviewed. Postprocessing software allows further image interrogation by generating centerline reconstructions. This allows for more precise length and diameter measurements, which are essential with custom fenestrated devices. Depending on institutional capabilities, these reformatted images may be routinely available. Access to dedicated work stations that allow the end user to personally postprocess and manipulate the images is ideal. Alternately, such image processing is available by third parties.

Measurement of the aortic neck diameter should be taken at the level of the lowest renal artery and 15 mm caudal. These measurements should be made from the minor axis of axial cuts or from reformatted slices that allow a plane perpendicular to the centerline. The key here is not to overestimate diameter based on tortuosity that is frequently present in the aortic neck. Using electronic calipers, these measurements are generally made from adventitia to adventitia to size the aortic neck for most devices. Intima-to-intima measurements were used in the U.S. pivotal studies of the Excluder endograft and are recommended for use with this device.

Failure to adhere to precise sizing guidelines will predictably increase the risk of both immediate- and long-term failure. The dangers of inadequate oversizing is intuitive; if there is no full apposition of the endograft to the aortic wall, the risk of a type I endoleak is substantial. The risks of excessive oversizing are less obvious, however. Bench testing has demonstrated that oversizing more than 20% creates pleats in the fabric (Fig. 90-2). This pleating of the fabric may contribute to an increased risk of a type I endoleak, and possibly decreased fixation. The deleterious effects of excessive device oversizing for EVAR are not device-specific. In a single series study with the AneuRx device (Medtronic), oversizing greater than 20% was associated with an increase in late aortic neck dilation and device migration.¹⁷ In a multicenter study utilizing the Zenith endograft, oversizing more than 30% was associated with a marked increase in the risk of aneurysm expansion and migration.¹⁸ No effects on late aortic neck dilation were observed.

Situations that typically require longer iliac limbs than the measurements suggest include extreme iliac tortuosity, “balleting” of the limbs (Endurant and Excluder) (Fig. 90-3), and the need to extend to the external iliac arteries. It these anatomic circumstances, it is prudent to choose a longer length when in doubt. Modular devices will also allow some degree of flexibility at the time of implant by adjusting the amount of overlap between the components.

Limbs for the iliac arteries should be sized 10% to 20% greater than their minor axis diameter. For nonectatic iliac arteries, this generally translates into an iliac limb diameter 1 to 3 mm larger than the vessel. Particular care should be made to correctly size the iliac limb if extension to the external iliac is required. Excessive oversizing may increase the risk of limb thrombosis.

Open

With open access, either a vertical or oblique skin incision can be utilized. The advantages of a vertical incision include the ease of gaining additional exposure to the femoral vessel. If preoperative imaging suggests significant femoral artery occlusive disease that might require an extended endarterectomy and patch angioplasty, this may be the preferred incision. Postoperative wound problems can be minimized by keeping the incision above the femoral crease, which is possible in most patients. The oblique skin exposure is favored by many operators because wound problems may be less frequent. After the superficial fat is divided in the plane parallel to the oblique skin incision, vertically oriented deeper dissection is then performed. This open exposure may be particularly useful in morbidly obese patients. If the angle into the femoral vessel is too acute, a small counter incision can be made inferior to the skin incision, just large enough for the needed sheaths.

The popularity of percutaneous access for EVAR and TEVAR has increased over the last 5 years. A recent systematic review of percutaneous access for EVAR cites the potential for a shorter procedure time, less postoperative pain, and a lowered risk of wound issues.²³ Disadvantages include increased hospital cost and the occasional need for urgent conversion to open repair. Access is possible percutaneously for sheath sizes up to 24F. The reported success rates for percutaneous closure of ≥18 to 20F sheaths are 78% to 95%, increasing to as high as 95% to 99% with sheaths of 12 to 16F.^24,25 A substantial learning curve for the technique has been observed.²⁶ Because of the 5% to 10% rate of failure in closure of larger arteriotomies, immediate availability of surgical closure is essential. Prudent patient selection and careful study of the preoperative imaging of the femoral arteries will maximize the success rate of percutaneous access for EVAR. Box 90-2 lists relative contraindications for this procedure. Preoperative imaging should be closely scrutinized for anatomic information regarding the common femoral artery, including its diameter, associated occlusive disease (particularly anterior calcification), and the location of the femoral bifurcation relative to the inguinal ligament.

This technique utilizes off-label use of suture-mediated closure devices in a “pre-close” fashion. The common femoral artery is ideally accessed 1 to 2 cm proximal to its bifurcation but below the inguinal ligament. Some operators routinely employ a micropuncture set with a 21-gauge needle and 3F introducer rather than a standard 18-gauge needle. Routine use of ultrasound guidance has been recommended to increase the accuracy of puncture placement.²⁷ Verification of the wire entry location should be routine, done through a small retrograde arteriogram with the appropriate ipsilateral oblique to better define the superficial femoral artery (SFA) and/or profunda origins.

A 0.035-inch guidewire is then advanced into the aorta and a 7F sheath placed. The “preclose” technique may be performed with either a single 10F Prostar or two 6F Proglide devices (Abbott Laboratories, Abbott Park, Ill). Utilizing the Proglide devices,²⁴ the first device is deployed with a 30-degree medial rotation. Maintaining wire access, the second device is deployed with a 30-degree lateral rotation. These devices place a single monofilament suture proximal and distal to the puncture site. These sutures are exteriorized as the delivery device is removed and then tagged for later use. The 7F sheath is then replaced for hemostasis. Alternately, a single 10F Prostar device may be employed.²⁵ Some operators have suggested the routine use of serial “coons” dilators to predilate the tract and arteriotomy after the “preclose” sutures are placed, but before delivery of the sheath for endograft delivery. This maneuver may decrease the chance of the “lip” of the dilator and/or sheath interface catching on the subcutaneous tissue or the arteriotomy itself.

After completion of the EVAR, the delivery sheath is removed while retaining guidewire access. Hemostasis is maintained with manual compression until the preformed knots (Proglide) are cinched down with the knot pusher. After hemostasis is confirmed, the guidewire is removed and manual compression is reapplied. Reversal of heparin with protamine is suggested at this time. If there is pulsatile bleeding after the two Proglide sutures are tied, a third Proglide can be placed over the existing wire and deployed. If there is continued pulsatile bleeding, an open surgical repair should be performed. Replacement of an appropriate sized dilator over the existing wire facilitates this exposure by providing a nonhemorrhagic field.

Iliac Occlusive Disease

The iliac vessels should be carefully studied preoperatively with CTA so any potential difficulties in access can be anticipated. Angioplasty can be used for focal iliac occlusive disease immediately before endograft insertion. Bare metal stents should not be initially placed because the large sheath for the endograft will need to be placed through them, increasing the possibility of stent migration. If an iliac lesion warrants a stent placement and is not covered by the endograft, place the stent at the completion of the EVAR. Hydrophilic coons dilators can be effective in dilating longer segments of occlusive disease, and can also act as a guide as to whether the endograft sheath will pass. These should only be placed over very stiff wires. A word of caution, however, is in order here. Sometimes, a larger sheath can be negotiated into the aorta with significant pressure, only to have catastrophic bleeding from iliac disruption upon removal of the sheath or with repeated placement. This reality should be considered when planning the repair to minimize the need for repeat traversal of a diseased iliac artery.

There are other potential endovascular approaches to obtaining access in the setting of small iliac arteries. It is possible to create an “internal endo-conduit” by placing a covered stent in the external iliac vessel, which then undergoes aggressive angioplasty to the needed diameter of 9 to 12 mm.^28,29 The covered stent will be protective of the extensive dissection and/or free rupture of the native vessel caused by the aggressive angioplasty. To be safe, there must be a sufficient proximal and distal seal zone for the covered stent. Such landing zones are not routinely present, however. Prudent patient selection is critical. Although these techniques have been anecdotally reported with successful outcomes,²⁹ larger series will be needed to establish the safety of these innovative access procedures before broader utilization.

Recently, a balloon-expandable sheath has become available to help in accessing smaller iliac arteries (SoloPath, Onset Medical Corp, Irvine, California). This sheath is delivered in a 14F size, and then dilated by an integrated balloon to sizes up to 24F. Its use has been reported to be successful in a small series of patients.³⁰ When removing the sheath, it is prudent to maintain wire access and perform an iliac arteriogram; treatment of secondary vessel injury may occasionally be needed with bare or covered stents.

Iliac Conduit Placement

The potential use of a surgically placed conduit should be in the “toolbox” of all operators performing endovascular aortic aneurysm repair.³¹ The need for a conduit for EVAR is now unusual, particularly with the introduction of lower profile devices. However, the larger French sizes for TEVAR and the higher prevalence of women needing this procedure have translated into a 10% to 20% usage in most larger series. Patients with diffusedly calcified and small external iliac arteries clearly need a conduit most of the time. If the operator is concerned about access, serious consideration should be made to perform a conduit without trying to access the iliac artery. Visual inspection of the common femoral and terminal external iliac arteries with open exposure can help in making this decision in equivocal cases. The worst time to perform a conduit is after the iliac vessel has been injured; the potential morbidity and mortality rates rise considerably.

An iliac conduit is performed through a right or left low retroperitoneal incision. Staying in the retroperitoneal plane, the common iliac artery is readily identified. We favor a standard end-to-side anastamosis with the distal common iliac artery. A 10-mm prosthetic conduit (Dacron or polytetrafluoroethylene [PTFE], DuPont, Wilmington, Delaware) will accommodate the largest needed sheath. The conduit should be tunneled under the inguinal ligament through a femoral counter incision. The distal end of the conduit is then clamped to the drapes and accessed in the usual fashion. After the EVAR is completed, most operators elect to anastamose the distal end of the conduit to the common femoral artery in an end-to-side fashion. Alternately, the conduit can be removed, leaving a small “stump” on the common iliac artery.

Equipment

High-quality fluoroscopy and angiographic equipment is essential to successful EVAR. A contemporary fixed-imaging unit as part of a “hybrid” operating room is increasingly utilized in many institutions. The performance of fenestrated or branched EVAR mandates this level of imaging. Portable C-arm fluoroscopy with a modern unit is acceptable for standard EVAR and/or TEVAR but cannot provide the versatility and imaging capabilities of fixed units.

Gantry Positioning

The precision of proximal endograft deployment with EVAR and TEVAR is considerably enhanced by adjusting the gantry of the fluoroscope to be perpendicular to the axis of the aortic neck. A large percentage of infrarenal aortic necks have a modest amount of anterior angulation that should be adjusted for by adding an appropriate amount of cranial tilt to the fluoroscopy unit. The amount needed can be estimated by the preoperative CTA. The majority of infrarenal aortic necks have 5 to 15 degrees of cranial angulation, but this can be as much as 30 to 40 degrees. Adjusting the left and/or right obliquity is also helpful in precisely locating the origin of the lowest renal artery. The left renal artery typically comes off the aorta a bit posterior to the centerline, whereas the right renal artery most commonly originates somewhat anterior to the centerline. An appropriate amount of left anterior oblique (LAO) angulation will give the proper orientation to the renal arteries in most cases. Frequently, this translates to approximately 10 to 20 degrees of LAO. These adjustments are particularly important in patients with shorter and angulated aortic necks.

Gantry position is also critical in the performance of TEVAR. A significant LAO of 30 to 75 degrees is routinely needed to best visualize the aortic arch and the origin of the subclavian, carotid, and innominate vessels. If the distal extent of a thoracic endograft needs to be deployed close to the celiac vessel, a true lateral (or >75 degree obliquity) is required.