Endovascular Treatment of Aneurysms of the Infrarenal Aorta




Historical Background


Volodos and colleagues performed the first stent graft repair of an aortic pathology in 1987 in Kharkov, Union of Soviet Socialist Republics, but Parodi, Palmaz, and Barone are credited with pioneering and popularizing the technique in the early 1990s. Scott and Chuter were the first to repace the early single tube structure with a bifurcated device, extending the ability to exclude more complex aortoiliac aneuryms. Numerous innovations have been subsequently introduced to improve fixation, correct early failure modes, and extend these devices to effectively treat more challenging aneurysmal anatomy. Three large, randomized prospective trials confirmed an early advantage to endovascular aneurysm repair (EVAR) in both mortality and morbidity when compared with open surgical repair. The survival benefit of EVAR is largely limited to the first 2 years after the procedure; associated comorbidities are the main cause of late deaths.


Current endovascular devices intended for EVAR come in a variety of configurations. Although most devices consist of modular components that are assembled in situ to improve ease of device delivery, some endografts are composed of a single or unibody construction. Bifurcated devices are used in most patients, but tapered aortomonoiliac devices, which would necessitate an associated femoral-femoral bypass for lower extremity revascularization, also are available for challenging iliac and distal aortic anatomy. Both passive and active infrarenal or suprarenal fixation systems are also available to improve attachment of the device to the aortic wall.




Preoperative Preparation





  • Physical examination. Most asymptomatic aneurysms are discovered incidentally on imaging studies, and 75% of aneurysms greater than 5 cm are palpable on physical examination.



  • Ultrasound screening. Ultrasound identifies aneurysms in 3% to 10% of patients in targeted screening studies. A screening ultrasound should be considered for male adults older than 65 years with a smoking history or family history of aortic aneurysm.



  • Ultrasound surveillance. Small aneurysms between 3.5 and 4.4 cm in diameter can be followed with an annual ultrasound examination. Aneurysms between 4.5 and 5.4 cm in greatest dimension should be evaluated with an ultrasound examination every 6 months. Aneurysms 5.5 cm or larger should be evaluated by contrast-enhanced computed tomography (CT) imaging for possible repair. Note that measurements in the minor axis provide a closer estimate of centerline measurements, and these are usually smaller than the greatest diameter measurements.



  • Preoperative imaging. Three-dimensional (3D) CT imaging with fine (0.6 to 2.5 mm) cuts is required for preoperative measurements and graft selection. Workstation image processing with curved linear reformats facilitates accurate diameter, angle, and centerline length measurements. The infrarenal neck length is measured from the lowest renal artery to the start of the aneurysm, and diameters at several locations should be obtained to assess the extent of tapering within the neck. The diameter of the common iliac arteries should be measured at several points before the iliac bifurcation, with special focus on the intended landing zone. The distance from the aortic bifurcation to the iliac bifurcation should be recorded on both sides.



  • Preoperative risk assessment. Preoperative risk assessment should be performed, with particular attention given to renal function. Patients with marginal renal function may be prehydrated, and sodium bicarbonate, N -acetylcysteine, and isosmolar contrast agents may be considered.



  • Preoperative vascular examination. A comprehensive pulse examination should be performed and documented before the procedure.



  • Management of anticoagulation and antiplatelet agents. Cessation of chronic anticoagulation is necessary before EVAR, but antiplatelet agents can be continued unless epidural anesthesia is planned.



  • Anesthesia. EVAR can be performed under general, epidural, or local anesthesia with sedation. If the patient is awake, sedation should be minimized to allow breath-holding during abdominal digital subtraction. Intraoperative arterial monitoring is advisable, but central venous monitoring can be used selectively.



  • Prophylaxis of infection and deep venous thrombosis. Perioperative antibiotics and subcutaneous heparin are administered.





Pitfalls and Danger Points





  • Device selection. Appropriate preoperation sizing is critical to the success of EVAR. Undersized grafts lead to endoleaks and graft migration. Significantly oversized grafts can lead to aortic injury or infolding ( Fig. 25-1 ).




    Figure 25-1


    CT scan after EVAR. The arrow denotes an infolded left iliac limb as a result of graft oversizing.



  • Arterial injury. Calcified and narrow femoral and iliac arteries are at risk for injury at the time of the introduction and removal of the device delivery system. Wire access should be maintained until the end of the procedure to allow endovascular rescue in the event of an injury. Depending upon the deployment system, an iliac conduit may be necessary when the iliac artery is deemed too small to facilitate passage of sheaths. Oversized noncompliant balloons should be avoided in the aortic neck and the iliac arteries, and balloon inflation should be confined within the fabric of the endograft.



  • Unintended coverage of arterial branches. Precise angiographic imaging is mandatory throughout the procedure. The C arm should be oriented orthogonal to the branch vessel of interest to avoid parallax. For example, cranial angulation should be used to image the aortic neck, and caudal angulation should be used when imaging the iliac arteries. Right or left oblique projections should be used to visualize the ostia of the renal arteries and the iliac artery bifurcation.



  • Embolization and thrombosis. Device and wire manipulation should be kept to a minimum to limit the risk of embolization. Postdeployment imaging should ensure that limbs are not kinked to avoid subsequent limb thrombosis.



  • Endoleak. Types I and III endoleaks at the aortic and iliac attachments sites and graft component junctions, respectively, are associated with a persistent risk of aortic rupture. A neck that has an angulation greater than 60 degrees, is less than 15 mm in length, or is lined with substantial thrombus and calcification is associated with an increased risk of a type IA endoleak. An aortic extension piece or a balloon-expandable Palmaz stent may be needed to treat a proximal type IA endoleak. Junctional type III leaks are avoided by ensuring that optimal component overlap is achieved.





Endovascular Strategy


Graft Sizing or Selection


Endograft diameters at seal zones are typically oversized by 10% to 20%. Endograft length should be selected to extend from the most caudal renal artery to the iliac bifurcations, with best estimates obtained from line of flow measurements. It is important to anticipate the potential need for alternative or additional sizes, including proximal and distal extensions. For bifurcated, modular grafts with single docking limbs, such as Excluder (W.L. Gore and Associates, Newark, Del.), the ipsilateral side of deployment should be chosen to assure the appropriate graft length and iliac diameter. Additional flexibility exists when using a bifurcated device with bilateral iliac docking limbs, such as in the Zenith device (Cook Medical, Bloomington, Ind.). In the case of severe unilateral, external iliac artery occlusive disease, an aortouniiliac graft, with planned occlusion of the common iliac artery on the contralateral side and femoral-femoral bypass, is an alternative option.


Percutaneous Deployment


Percutaneous EVAR can be performed in more than 90% patients, with a success rate exceeding 95%, shorter operative times, and fewer wound complications compared with open surgical repair. However, access vessel diameters less than 5 mm are at greater risk for percutaneous failure. Maintaining wire access while assessing hemostasis allows reintroduction of the sheath after EVAR in case femoral artery exposure is required. The most widely used approach uses the preclose technique with suture-mediated closure devices (Prostar XL or Perclose ProGlide, Abbott Vascular, Redwood City, Calif.). Contraindications to percutaneous closure include circumferential or anterior wall calcification of the common femoral artery, stenosis or small-caliber femoral artery, and high femoral bifurcation.


Adjunctive Iliac Angioplasty


A stenotic external or common iliac artery may prevent introduction of a large endograft sheath, which can be pretreated by balloon angioplasty at the time of EVAR. Although the presence of a dissection in the external iliac artery requires stent placement after the completion of endograft deployment, if noted within the common iliac artery, stenting is not necessary because it will be covered by the endograft iliac limb. Stent deployment for iliac occlusive disease before endograft introduction should be avoided.


Iliac Artery Conduit


Small-caliber external iliac arteries, severe calcification, and occlusive disease or excessive tortuosity may impede device delivery. As an alternative, an iliac artery conduit provides direct access to the common iliac artery. Iliac conduits can be performed either 1) via open surgical anastomosis of a prosthetic graft to more proximal healthy iliac artery, or 2) via endoluminal placement of covered stent graft or iliac limb followed by balloon angioplasty. Planned conduits have a lower complication rate than emergency conduits performed after a failed attempt to introduce an endograft.




Endovascular Technique


Arterial Access


Open Femoral Artery Exposure


A short oblique incision parallel to the inguinal ligament is made 1 to 2 cm above the inguinal crease on both sides. Dissection to the femoral sheath is performed with ligation of lymphatics and venous branches. The common femoral artery is dissected for a short segment distal to the inguinal ligament and controlled with vessel loops. In the presence of significant occlusive disease, the distal external iliac artery is exposed, because it may provide a less calcified point of access. An anterior wall puncture needle is inserted into a disease-free portion of the artery, and a 0.035-inch J wire is advanced into the proximal aorta. A short 6- to 8-Fr femoral sheath is placed over the wire into the common femoral artery. In tortuous iliac arteries or large aneurysm sacs, an angled 5-Fr catheter, such as a Kumpe (KMP; Cook Medical) or Berenstein catheter (Infiniti Medical, Menlo Park, Calif.) may help direct the wire into the proximal aorta. On the ipsilateral side, the wire is replaced with an exchange-length, stiff Amplatz or Lunderquist wire. A pigtail angiographic catheter with multiple 1-cm marks is introduced from the contralateral side and placed into the aorta, and heparin is administered.


Percutaneous Access


Many practitioners do not routinely use ultrasound in the course of gaining percutaneous access. However, for those who advocate this approach, the ultrasound probe is used to identify the common femoral artery and the femoral bifurcation. The best location for common femoral artery puncture is determined by the extent of calcification on the anterior wall and plaque both anteriorly and posteriorly. A small stab incision is made in the skin inferior to the expected arterial puncture site. Blunt dissection with a hemostat is then carried down through the subcutaneous tissue to the anterior wall of the common femoral artery under ultrasound scan guidance. A micropuncture needle is inserted into the common femoral artery under direct visualization with the ultrasound probe. Fluoroscopy is used to confirm puncture over the femoral head.


A microsheath and a 0.035-inch wire are inserted into the common femoral artery, followed by a 7-Fr dilator. After dilation of the artery and subcutaneous tissue, a 6-Fr Perclose ProGlide device is inserted over the wire into the common femoral artery. Because the wire exits the side of the device, it is removed as soon as the ProGlide device approaches the incision to avoid arterial injury. Pulsatile blood flow from the marker lumen confirms proper positioning of the device within the common femoral artery. The ProGlide device is then fired and the wire is replaced before the device is withdrawn from the common femoral artery. The sutures are not tied down, because they are secured to the sterile drapes with a Kelly clamp. A second ProGlide device is inserted into the same artery over the wire, confirmation of intraarterial placement is obtained, the wire is removed, the device is fired, the wire is then replaced, and the sutures are secured with a Crile clamp to distinguish the second knot from the first. A 7-Fr, 25-cm sheath is then inserted into the common femoral artery.


The preceding steps are repeated on the contralateral groin, leaving two sets of untied ProGlide sutures in each groin. Two devices are deployed at 11:59 and 12:01, with the goal of slightly offsetting the devices without puncturing the sidewall of the common femoral artery to avoid narrowing the vessel or failure to puncture the vessel wall. The patient is then heparinized. If there is hemorrhage around the 7-Fr sheath, a 12-Fr sheath is inserted over an Amplatz or Lunderquist wire. Serial dilations are used with Coons dilators before placement of the large sheath and device.


Iliac Artery Conduit


An oblique lower abdominal wall incision is made between the umbilicus and the inguinal ligament. The abdominal wall muscle layers are divided until the preperitoneal fat is encountered. The peritoneum is swept medially and superiorly, exposing the iliac arteries, which are controlled at the bifurcation. An end-to-side anastomosis is fashioned using a 10-mm Dacron graft at the junction of the common and external iliac arteries. This location allows deployment into the distal common iliac artery and patching of the origin of the external, normally the most diseased portion. In thin patients the Dacron graft may be brought out directly through the retroperitoneal incision, whereas in larger patients it can be brought through a separate distal stab incision in the abdominal wall. The conduit is clamped distally, and the device sheath can then be placed through a puncture or small incision in the anterior surface of the graft. After EVAR, the conduit is either divided and oversewn near the iliac anastomosis or tunneled under the inguinal ligament and anastomosed to the common femoral artery as an iliofemoral bypass graft.


Endovascular Conduit


Alternatively, one can use a covered stent graft or iliac limb in the iliac system as an endovascular conduit. To accomplish this, once wire access across the iliac is obtained, a covered stent graft or iliac limb is deployed in the region of stenosis. This is then balloon angioplastied to profile. Larger sheaths now can be passed into the aorta through the iliacs.


Angiography


An initial aortoiliac angiogram is obtained using a marker pigtail catheter, which is placed at the level of the renal arteries using a Power injection run of 15 mL/sec for a total of 15 mL ( Fig. 25-2 ), although in smaller aortas a rate of 10mL/sec may be more appropriate. Larger volumes may be needed in the presence large aneurysm sacs or in patients with low cardiac output. The number and location of main and accessory renal arteries are identified, and the patency of the internal iliac arteries is assessed. The length of device is confirmed.


Mar 13, 2019 | Posted by in VASCULAR SURGERY | Comments Off on Endovascular Treatment of Aneurysms of the Infrarenal Aorta
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