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FIGURE 403 Three-dimensional (3D) reconstruction from spiral computed tomography (CT) scan of abdominal aortic aneurysm (AAA).

Note tortuous iliac arteries (A). Degree of tortuosity may be underestimated in direct anterior-posterior view, but on a more oblique angle (B), a more significant degree of tortuosity is visible.

Many of the features necessary for an adequate aortic neck are also necessary for the distal landing zone. Presence of thrombus, calcification, and tortuosity can significantly hinder the iliac limb seal. Ectatic or aneurysmal iliac arteries obviously affect the ability of the graft to seal against the iliac limb. Most available endograft systems require at least a 15-mm segment of iliac artery to be of adequate caliber and free of significant disease to obtain a distal seal. If this is not present, adjunct interventions can be performed to assist in placing the device (i.e., iliac artery conduit placement, coil embolization of the internal iliac artery [IIA]). Management of these complicated situations is discussed in more detail later.

Endograft Design

Endograft design can greatly affect the ability of the device to be placed in patients, particularly in those with complex anatomy. Alterations in graft characteristics are what distinguish one manufacturer's device from another. Some key elements in endograft design are outlined in the following discussions.

Delivery System

Standard endograft insertion involves placement of the device through an arteriotomy in the common femoral artery, from where the graft traverses the external iliac and common iliac arteries (CIAs). The ability to deliver the endograft safely and effectively in this fashion is a prerequisite for effective repair. Three factors are important determinants of device delivery.

DELIVERY SYSTEM SIZE

With the placement of most endografts through the iliofemoral arterial system, any site along this pathway can represent a size limitation, the most common of which is the external iliac artery (EIA). Inadequate diameter or presence of extensive calcifications can exclude standard endograft placement. It is intuitive that the size of the delivery system cannot be larger than the size of the iliac arteries it traverses. Most sheaths are sized based on inner diameter, so knowledge of the outer diameter of the sheaths is necessary for safe graft placement. Different manufacturers’ devices have different size measurements for the delivery systems, so one device may be suitable for placement, whereas another is not. Most delivery systems easily traverse an iliofemoral segment of 7 to 8 mm in diameter (or a sheath that does not exceed 21 F), although several designs that provide a lowerprofile system are currently in clinical trials in the United States.

FLEXIBILITY

Tortuosity, another anatomical variant, affects the ability to adequately deliver the endograft system. Tortuous iliac vessels can be “straightened” with the use of stiff guidewires, but this is not always

possible or desirable. The ideal delivery system easily traverses these arteries on the basis of an intrinsic degree of flexibility. Again, different delivery systems have different abilities to track through tortuous iliac arteries, and some may be more successfully placed than others in this anatomical variant. Delivery systems composed of long, flexible, tapered tips pass more easily than those with short, stiff, blunt tips. In addition, other aspects of device construction, such as metallic struts that provide columnar strength, increase device rigidity and limit use in tortuous vessels.

DELIVERABILITY

A number of features have been noted to affect the deliverability of endograft devices. As stated previously, long, flexible, tapered tips pass more easily than short, blunt, stiff ones. This allows for easier maneuverability through tortuous vessels, as well as past sites of narrowing. Larger-caliber devices are also more difficult to deliver, particularly in patients with smaller-diameter arteries.

Some delivery systems allow for placement of the endograft system through alternate sheaths, whereas other systems necessitate use of the manufacturer's own delivery system. This can greatly affect placement of specific endografts in specific anatomical variants. A thorough understanding of the patient's arterial anatomy and the limitations of different endograft systems are important. The complexity of the delivery system also affects the ease with which it is placed. Some devices generally provide a simple maneuver to deploy the graft, whereas others have several complicated steps.

Endograft Features

The ideal endograft should be flexible enough to maneuver through tortuous and angulated vessels but also rigid enough to prevent kinking. It should have a low profile (having a small external diameter) that would allow it to be placed through as small an arteriotomy as possible. Two general classifications of endografts exist: unibody and modular. A unibody device is a single-piece graft—including the main body and both limbs. Although this decreases the risk of endoleaks at the graft-graft interface, the unibody design often requires a larger delivery system, and sizing can be more difficult. The modular system includes endografts that are composed of two to three pieces. Generally there is a main body that may have one attached limb and one or two docking limbs. These devices can be introduced through smaller delivery systems and offer a greater degree of flexibility with regard to placement. With multiple sites of graft-graft interface, however, there is an increased risk of endoleak, as explained later.

Graft material is variable and can range from thin-walled polytetrafluorethylene (PTFE) to polyester. The graft material is typically supported by a metal framework that is commonly stainless steel, its modified version Elgiloy, or nitinol. The graft support can be placed inside the graft material (endoskeleton) or outside the graft (exoskeleton). Grafts can be fully supported, having stent material throughout, or only partially supported, with aspects of the device composed only of graft material and no metal. The graft skeleton provides several key elements to endograft make-up. First, it assists in graft fixation and in obtaining a seal. These stents provide some degree of radial force that helps provide a seal, as well as providing a point of fixation. Some devices have hooks or barbs in the proximal aspect of the skeleton that help anchor the graft onto the aortic wall and prevent migration. In addition, some devices employ a metal framework that extends above the fabric and is used to engage the aorta in the pararenal or suprarenal location. The second function of the skeleton is to provide columnar strength, which may prevent graft migration. The skeleton can also prevent kinking and occlusion of limbs as they traverse the aortoiliac anatomy. Lack of stents, however, may allow a graft to adapt more readily to morphological changes without dislocation of attachment sites. The interplay of the stent and fabric materials can lead to eventual erosion of the fabric.

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TABLE 40-1 Description of a Variety of Commercially Available Endografts

COMPANY

Cook

(Bloomington,

Ind.)

Gore (Flagstaff, Ariz.)

Endologix (Irvine, Calif.)

Medtronic (Minneapolis,

Minn.)

Medtronic (Minneapolis,

Minn.)

ePTFE, expanded polytetrafluoroethylene; FDA, U.S. Food and Drug Administration; OD, outer diameter.

INITIAL FDA

DEVICE

Zenith May 2003 Self-expanding Dacron Stainless steel Modular 21F-26F Suprarenal

Excluder November

Powerlink October 2004 Self-expanding High-density

AneuRx September

Talent June 2008 Self-expanding Dacron Nitinol Modular 22F-24F Suprarenal

APPROVAL

DAT E

2002

1999

DEPLOYMENT

TYPE

Self-expanding ePTFE Nitinol Modular 20F-23F Infrarenal

Self-expanding Dacron Nitinol Modular 21F Infrarenal

GRAFT

MATERIAL

ePTFE

STENT

MATERIAL

Cobalt chromium

alloy

BIFURCATED

DEVICE DESIGN

Unibody 21F Anatomical (with

MAIN BODY

SHEATH SIZE

OD

FIXATION

either suprarenal or infrarenal proximal orientation)

Specific Grafts

Various endografts are currently commercially available or in clinical trials in the United States. A brief description of the currently commercially available endograft systems (in the United States) is outlined in

Table 40-1 and depicted in Figure 40-4.

Graft Placement and Postoperative Management

Once the patient is deemed an endograft candidate, the best graft has been chosen, and the device properly sized, the patient can undergo implantation. The majority of endografts are placed through the femoral arteries that have been operatively exposed. The majority of surgeons prefer the use of the transverse incision as it associated with a lower rate of wound complications (12.7% in transverse incision vs. 47.5% in vertical incisions). access for EVAR is growing in popularity, and its use will become even more widespread with the further development of lowprofile devices. Suture-mediated closure devices facilitate this process, and using a “preclose” technique has been described to allow closure of sheaths as large as 24 F.27 Use of this procedure has been associated with 70% to 100% technical success, and immediate failures mandate surgical exploration of the femoral artery. Prospective analysis has demonstrated that use of a percutaneous approach may shorten operating times and reduce the rate of wound-related complications, without a significant increase in overall procedural cost.

27–29

The aorta is then cannulated with a guidewire and catheter. Small boluses of contrast agent are delivered to further define the anatomy and localize the renal arteries. With an angulated aorta, it is important to remember that the best view of the renal arteries and visualization of the fixation zone may not be in a direct anterior-posterior plane but at a more cranialcaudal angle. The device is then generally advanced over a stiff guidewire and correctly positioned to allow the most extensive coverage within the aortic neck without intruding on the orifice of the renal arteries. Each device has its own unique instruction for actual deployment. Once the main body and ipsilateral limb have been placed, the contralateral limb has to be placed. The sequence of events for this varies depending on graft design—whether unibody or modular.

Recovery following EVAR is generally rapid and uncomplicated, and most patients are discharged home on the first or second postoperative day. Return to activities of daily living has been shown to be quicker following endovascular repair than open surgery. In addition, most patients report less postoperative pain. Aortic remodeling following EVAR, however, is a slow process that

Percutaneous

continues for several years. Anatomical changes in the native vessel, particularly at the proximal neck, can cause conformational changes in the implanted device that mandate close follow-up. In addition, late failures have been identified that have required reintervention.

Given these facts, routine surveillance following EVAR is universally recommended, although there are no standard regimens, and the requirements of a standard intensive regimen are debated. Nordon et al. performed a meta-analysis evaluating secondary intervention rates based on contemporary graft implants.

Their findings demonstrated that surveillance imaging alone initiated the secondary intervention in 1.4% to 9% of cases. Over 90% of EVAR cases, however, received no benefit from surveillance scans. Based on these findings, the group recommended that surveillance should be directed toward those patients identified as having a high risk for postoperative complications. Identification of this group, however, is not obvious but may be necessary in patients with complicated aortic neck anatomy or in patients in whom the device was used outside of the indications for use (IFU).

Contrast-enhanced CT is the most widely used modality for follow-up after EVAR. It is widely available, has rapid data acquisition, reproducibility, and is uniform across institutions. The major concerns associated with this modality are use of a contrast agent and the potential associated nephrotoxicity, radiation exposure, and cost. It is considered the gold standard for assessing aortic diameter, with nearly 100% sensitivity and specificity. Sensitivity and specificity rates for endoleak detection with CT are better than those with conventional angiography: 92% and 90% for CT vs. 63% and 77% for angiography, respectively.

32–34

Triphasic CT (noncontrasted phase, arterial phase, and delayed phase) results in the greatest amount of information but at the cost of increased radiation exposure. Unenhanced CT imaging is useful for differentiation of endoleaks from calcifications from the metallic portion of a stent graft, and can help detect small perigraft leaks better than arterial-phase images. Use of arterial phase alone has a lower diagnostic value than combined arterial and delayed-phase scanning.

Repeated CT scanning subjects the patient to potential carcinogenic risks associated with ionizing radiation exposure. The estimated lifetime attributable risk of death from cancer following an abdominal CT scan in a patient older than 50 years of age is 0.02%.

31,36

Although this effect in itself is small, the cumulative effects over time with repeat imaging can be significant. Repetitive use of iodinated contrast can have a cumulative deleterious effect on renal function, especially in the elderly and those patients with preexisting renal impairment.

Given this, as well as the expense,

the use of alternate modes of surveillance has been evaluated.

Magnetic resonance imaging (MRI) and MRA provide much of

the same imaging information that can be acquired by CT scanning.

497

Multiple format MR images (T1, T2, gadolinium-enhanced) can be viewed in 2D and be reformatted into 3D volumes, allowing dimensional measurements, assessment of luminal patency, device positioning, and detecting the presence of an endoleak. Limitations of MRA/MRI include potential magnet-induced heating or motion, which may prevent imaging in the immediate postimplant time period. In addition, postimplant artifacts, in particular with ferromagnetic metallic stents, will limit morphological assessments. Furthermore, there is a risk of nephrogenic systemic fibrosis associated with gadolinium contrast use in patients with

renal insufficiency. sure to ionizing radiation and low nephrotoxicity of MR contrast

Benefits of MRI are related to the lack of expo-

medium. Disadvantages of MRI are its lack of wide availability, longer procedure time than CT, patient claustrophobia, and contraindications for patients with cardiac pacemakers.

Color duplex ultrasonography (US) is a convenient, noninvasive, inexpensive portable means of postimplant surveillance. Its reliability as a useful surveillance tool, however, is still debated. Grayscale US is accurate for measurement of aortic aneurysm diameter. Endoleak detection by US requires color duplex. The reported specificity rates of color duplex US for endoleak detection are high (89%-97%), but the sensitivity and diagnostic power of color duplex US for endoleak detection compared with CT is still debated.

use of duplex US to detect an endoleak has a sensitivity of approximately 77%, with a specificity approaching 94%. US contrast agents increases sensitivity to 98%, with no significant change in specificity.

Contrast agents are useful in identifying slow leaks that are not readily discernible on CT. direction of the endoleak is also an advantage of US that is not easily discernable with CT.

Presence of a “to-and-fro” flow pattern is associated with spontaneous closure of the endoleak, whereas a monophasic or biphasic waveform is consistent with endoleak persistence.

Limitations of color duplex US include its operator dependence, variation based on patient physical size, and the need for optimal patient preparation. The substitution of duplex US imag-

ing for CT, however, may result in long-term cost savings.

in vivo metallic

The addition of

41,42

Detection of flow

The

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FIGURE 404 Several endograft systems illustrating different features. A, Zenith endograft (Cook Inc., Bloomington, Ind.) represents a three-piece modular

system with a main body and separate bilateral limbs. This graft design uses a bare suprarenal stent and internal stents at the sealing zones and is otherwise supported by a stainless steel Z-stent exoskeleton. B, Powerlink graft (Endologix, Irvine, Calif.) constructed of expanded polytetrafluoroethylene (ePTFE) and a cobalt alloy skeleton. C, AneuRx stent graft system (Medtronic AVE, Santa Rosa, Calif.) composed of nitinol exoskeleton. D, Excluder endograft (WL Gore and Associates, Flagstaff, Ariz.), which represents a two-piece modular system. Graft is constructed from ePTFE and is fully supported by a nitinol exoskeleton. E, Talent endograft system (Medtronic AVE, Santa Rosa, Calif.) represents a two-piece modular system composed of a suprarenal bare stent and then a nitinol endoskeleton.

Problems with Endografting and Management

Various problems can arise in the planning and placement of abdominal aortic endografts. Once the grafts are in place, several complications can arise over time that may require intervention to prevent subsequent expansion and possible rupture of the previously excluded aneurysm. In the following section, several of the more common problems that occur following endograft placement are outlined.

Iliac Artery Disease

When iliac artery disease is present, whether it be aneurysmal disease, atherosclerotic disease, or severe tortuosity, the use of an iliac conduit can provide a safe route to deliver the endograft. In cases of iliac artery lumen narrowing resulting from atherosclerotic disease or increased vessel tortuosity, advancement of the device, despite the presence of resistance, can result in rupture of the iliac artery. Iliac artery rupture has been reported in 1% to 2% of cases.

46,47

To circumvent prohibitive iliac artery anatomy, an iliac conduit can be used. An iliac conduit involves suturing a prosthetic graft (generally 8-10 mm in diameter) to the mid–CIA even if it is aneurysmal. This can be done in an endto-end or end-to-side fashion, although the latter often provides a greater lumen for passage of the device. The device is placed through the prosthetic graft, and the iliac limb of the endovascular graft traverses the CIA and anastomosis and seals within the conduit. The distal end of the graft is tunneled along the natural course of the iliac artery and anastomosed to the femoral artery. The distal end of the CIA is oversewn to allow retrograde flow through the EIA to supply the ipsilateral hypogastric artery. Alternatively, the hypogastric artery can be anastomosed directly to the conduit.

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Iliac artery ectasia or aneurysms can present a problem in obtaining a distal seal. Enlarged CIAs are present in up to 30% of patients presenting for endovascular aneurysm repair. available endografts do not allow for ectatic or aneurysmal common iliac arteries, so the distal seal may have to be obtained within the external iliac artery, which is often of normal caliber. If the distal

seal occurs in the external iliac artery, the hypogastric artery is gen-

erally sacrificed using coil embolization. Presence of a hypogastric artery aneurysm would necessitate the same approach. Rarely, bilateral hypogastric artery embolization is required. Hypogastric artery embolization can occur before aneurysm repair or concurrently. If bilateral embolization is planned, it is generally performed in a staged fashion, although its occlusion is not always planned. Hypogastric artery embolization is not without risk, and side effects can occur in up to 50% of patients. the predominant complaint after hypogastric artery occlusion. This occurs in 12% to 50% of patients, but in most it generally resolves after several months. onset erectile dysfunction (ED).

48–53

Some 5% to 25% of men complain of new-

51,52

ischemia requiring resection are of theoretical concern, but they have not been described in any of the larger series. Patients requiring embolization in the more distal branches of the hypogastric artery (as might be done with the presence of an IIA aneurysm) and those in whom coil placement was not adequately controlled are at higher risk of developing pelvic symptoms. gastric artery embolization has not been associated with increased symptoms when compared with unilateral occlusion. embolization of the IIA is not necessary if it is not aneurysmal. In the face of CIA aneurysms, Wyers et al.54 have shown that if there is a 5-mm neck of iliac artery proximal to the hypogastric artery in addition to a 15-mm neck in the external iliac artery, coil embolization of the hypogastric artery is not necessary to obtain a distal seal. This may be possible in up to two thirds of patients requiring coverage of the hypogastric artery.

Buttock claudication is

Buttock ischemia and bowel

Bilateral hypo-

48–51

49,50,52

Many

FIGURE 405 Angiogram demonstrating a type 1 endoleak. Contrast can be seen leaking around proximal part of graft and filling aneurysm sac. Patient subsequently had a giant Palmaz stent placed in the aortic neck, and this ameliorated the endoleak.

Coil

Endoleaks

An endoleak is the persistence of blood flow outside the endograft, but in the aneurysm sac. Endoleaks are classified according to their etiology, and currently five types have been described (

Table 40-2). A type 1 endoleak (Fig. 40-5) arises from inadequate

sealing at either the proximal aortic (allowing antegrade flow) or distal iliac (allowing retrograde flow) attachment sites. Type 2 endoleaks (

Fig. 40-6) arise from patent branch vessels off of

the aortic sac that allow for retrograde flow into the aneurysm. Such branches may include a patent lumbar or inferior mesenteric artery (IMA). Type 3 endoleaks develop from defects in the fabric of the graft or at the junction zone between modular components. Type 4 endoleaks develop secondary to diffuse “leaking” of blood between the interstices of the fabric or where the graft is sutured to a stent. Type 5 endoleaks describe a scenario in which the aneurysm sac remains pressurized and the aneurysm enlarges, but no demonstrable flow of blood into the sac can be visualized on current imaging modalities. These may be due to imaging that is not sophisticated enough to discern these leaks

TABLE 40-2 Endoleak Classification

ENDOLEAK

Type 1 Inadequate seal at aortic or

Type 2 Patent branches off aneurysm

Type 3 Fabric defects or component

Type 4 Leak at fabric interstices Antegrade

Type 5 Endotension No clear leak

CAUSE

iliac attachment sites

sac

junctions

BLOOD FLOW INTO

SAC

Antegrade or

retrograde

Retrograde

Antegrade

47,48

FIGURE 406 Computed tomography (CT) scan representative of a type 2 endoleak. There is contrast within aneurysm sac but outside limbs of

endograft. This aneurysm had continued expansion until patient underwent embolization of inferior mesenteric artery (IMA).

or due to intermittent episodes of leakage. to the aneurysm sac causing it to continue to expand in this situation, has been termed endotension.

The pressure applied

50,51

Controversy with regard to this concept exists, in particular with the ability of the thrombus to transmit pressure to the aneurysm wall. It is argued that these merely represent a type 1, 2, or 3 endoleak in which the defect is large enough to allow blood to flow into the sac and transmit pressure to the sac, but the exit site is not present or too small to be detected.

Type 1 and type 3 endoleaks are associated with significant risks of aneurysm enlargement and possible rupture, and these should be treated.

55,56

This may be accomplished with placement of an extension cuff limb over the site of the leak. If the leak is a type 1 and the graft is juxtaposed to the inferior border of the renal arteries, a large balloon-expandable stent can be placed in the proximal aspect of the endograft. This provides increased radial force, causing better juxtaposition of the graft and aortic wall, thus ameliorating the leakage. If this is unsuccessful, open repair and graft explantation are generally indicated. Fabric tears are easily managed if the site of the leak is localized. In these situations, the tear can be covered with a cuff or extension. When it is more

diffuse, the entire endograft can be relined with a second endograft, or the device can be removed and the aneurysm repaired in an open fashion.

Type 2 endoleaks are rarely associated with aneurysm rupture. At least 10% to 15% of patients are identified with a type 2 endoleak during follow-up.

58–61

Warfarin treatment is not associated with an

increased incidence of early or delayed postoperative endoleak, but type 2 endoleaks are less likely to undergo spontaneous resolution in these patients.

Type 2 endoleaks are generally observed unless they are associated with an increase in aneurysm size or aortic pulsatility on physical examination. In these situations, arteriography is the next step to identify the source of the endoleak. Superior mesenteric artery injection reveals retrograde IMA flow as the source, whereas selective hypogastric artery injection demonstrates a lumbar artery filling the aneurysm. Super-selective arterial canalization can then be performed with embolization of the feeding vessels. Another approach is through direct aneurysm sac puncture.

With direct sac puncture, one can measure sac pressure and inject the sac directly with contrast agent to precisely identify the leak. The systolic sac pressure is related to the size of the leak, and the pulse amplitude is related to the resistance of the outflow vessels and sac compliance. vessels can be directly accessed and embolized.

After localization of the leak, feeding

In addition, the sac can be filled with substances such as coils, glue, or gel foam to further prevent flow. Differences in outcomes between these two different approaches has not been realized.

Measurement of intrasac pressures may help determine whether an endoleak is present at the time of the original surgery or if an endoleak has been adequately treated if it has been approached through direct sac puncture. In an ex vivo model of endoleaks, Parodi et al.67 evaluated pressure changes in the aortic sac with various types and sizes of endoleaks. In this model, sac pressures were significantly higher than systemic pressures in the presence of all endoleaks. This obviously places the aneurysm at significant risk for rupture. Presence of patent side branches significantly reduced the pressure within the sac, particularly the mean pressure and diastolic pressure. Clinically, persistent side branches augment the development of type 2 endoleaks and influence early sac behavior.

68,69

Gawenda et al.70 evaluated the use of sac pressure monitoring and found it helpful in the detection and treatment of endoleaks. They noted, however, that intrasac pressure measurements did not correlate with AAA size change over ensuing followup. This may be an effective modality for monitoring aneurysms after endograft exclusion once less invasive methods of pressure measurement are developed.

Structural Failure

Material failure represents one of the most concerning problems for potential failure of endograft placement. This is a difficult event to identify because patients are often asymptomatic and may not present with any acute changes in their endograft evaluation. Three modes of structural failure have been described in aortic endografting and involve fabric erosion, suture disruption, and metal fracture.

Development of endoleaks secondary to graft erosion has been documented with some first-generation endograft devices (

Fig. 40-7). It has been speculated that the areas of graft erosion

are secondary to friction between the stent material and the fabric, which can be confounded by pulsation of the aorta. Predicting the incidence of fabric fatigue is difficult, and although this does occur in grafts placed by conventional open aneurysm repair, it occurs much more rapidly and more commonly in the endograft systems.

74,75

In several device designs, the graft fabric is attached to the metal skeleton through the use of sutures. Disruption of these sutures is believed to explain graft failure in some instances. mechanism for suture failure is believed to be the same as for fabric erosion—namely, motion of the stents with aortic pulsations causes friction and wear of the sutures, with subsequent suture fracture.

The most common structural problem identified in aortic endo-

graft systems has been metallic stent fractures.

Stent and hook

76–78

72,73

The

FIGURE 407 Angiogram revealing a type 3 endoleak that developed at site of a tear in graft fabric. This was a “homemade” aorto-uniiliac graft that

had been in place for approximately 5 years. Patient presented with new-onset abdominal pain and had a computed tomography (CT) scan that revealed an aneurysm sac that had significantly expanded in diameter. Tear was sealed by placement of a new endograft.

fractures in the phase 1 trial of the Endovascular Technologie's graft resulted in suspension of the program and redesign of the metallic attachment system.

In a review of 686 patients who underwent endovascular aneurysm repair, Jacobs et al. identified 60 patients who had material failure.75 Forty-three (72%) of these failures were due to metallic stent fractures and occurred in various different endografts with different stent composition. The cause of metal failure has been attributed to stress fatigue and metal corrosion, particularly in nitinol stents. generation endografts and may reflect improved nitinol process-

81–83

ing.

Tortuosity of the arterial system can also stress the stent

Corrosion has not been seen in next-

graft system and lead to metal fracture. This has been reported in the longitudinal bar of the Talent and Gore stent graft devices.

Limb Thrombosis

Endograft limb thrombosis after endovascular repair of infrarenal AAA is a recognized complication occurring in up to 11% of patients. place patients at increased risk for limb thrombosis. One reported risk factor is the lack of device support. Although Carroccio et al.85 reported on the results of 351 bifurcated grafts with no significant association between use of unsupported devices and graft thrombosis, others have suggested there is a significant relationship. Baum et al.91 specifically evaluated the rates of graft limb kinking and thrombosis between supported and unsupported abdominal aortic stent grafts. In total, 12% of the limbs in their series required an intervention for kinking. In the supported limbs, 5% required subsequent placement of arterial stents; 2% required these for evidence of kinking at the time of the initial operation, and 3% required stenting in the postoperative period after the patients presented with limb thrombosis. In the unsupported grafts, there was an intervention rate of 44%. About half of these had an additional stent placed at the time of the initial procedure, and the remainder had a subsequent stent placed in the postoperative follow-up period, owing to limb thrombosis or severe stenosis.

84–90

Various underlying factors have been purported to

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Another factor increasing the risk of limb thrombosis is oversizing of the iliac limb. Oversizing causes the graft material to have a significant amount of infolding, reducing the intraluminal dia meter.87 Along these lines, significant intraluminal vessel narrowing from underlying atherosclerotic disease or tortuosity can result in flow abnormalities and eventually cause

graft limb thrombosis.

has also been described as a risk factor for developing limb thrombosis.

It was believed that transition into the EIA caused

Extension of the graft limb into the EIA

both a significant reduction in arterial diameter and a kink in the graft due to acute angulation of the limb as it passed through the pelvis. Damage to the distal iliac or femoral artery, such as dissection during graft placement, can subsequently cause outflow obstruction and graft limb thrombosis.

Management of patients presenting with limb thrombosis depends on the severity of the patient's symptoms. In the series by Carroccio et al.,85 nearly a third of the patients presenting with symptoms had such mild symptoms that no intervention was required. Most patients, however, underwent a femoral-femoral bypass to restore flow to the affected extremity. Few patients are successfully treated with thrombolysis or graft thrombectomy followed by endovascular repair of the underlying problem. In most series, patients with limb problems generally present early, within the first 6 months following endograft repair.

84,91–95

In fact, Sampram et al.93 reported that no limb occlusions presented after 30 months of follow-up.

Migration

Distal stent graft migration after abdominal aortic endografting has been reported to occur in 9% to 45% of patients. certainly has been identified as a risk for development of a type 1 endoleak and delayed aneurysm rupture or late conversion to open repair. The pathophysiology behind aortic endograft migration is complex, and various factors contribute to its occurrence. A number of forces are at play within the aortic endograft, but blood flow acts as the main displacing force. As the tube of the aortic graft curves, there is a change in the velocity of the blood, resulting in an increased displacement force. For many endografts, the forces providing protection against migration are friction forces of the graft against the aortic wall and the columnar strength of the graft. The friction forces depend on the apposition of the graft fabric and the aortic wall and obviously can be affected by aortic wall composition (thrombus, calcifications), size of the aorta, radial force of the stent, and the nature of the graft fabric. It has been suggested that the presence of barbs or hooks in the proximal portion of the stent graft may provide additional protection.

The infrarenal aortic neck length and its maximum diameter, shape, and angulation have all been implicated as causes of stent graft migration.

96,102,103

All of these work to decrease the friction between the stent graft and aortic wall. Albertini et al. the development of proximal perigraft endograft leak and device migration following endovascular aneurysm repair. Fifteen patients had graft migration, and 31 of 184 repairs developed a proximal endoleak. Neck angulation was the only factor found to be significant in the development of device migration, whereas neck angulation and neck diameter were the two factors important in developing a proximal perigraft endoleak.

102

were unable to identify any specific anatomical correlate and device migration. They did observe that any device that migrated distally by more than 1 cm subsequently required an intervention.

Other hypotheses as to the cause of device migration have focused on morphological changes in the aneurysm and aortic neck after endovascular AAA repair. Specifically, aortic neck dilation, longitudinal sac shrinkage, and graft shortening have been described.

96,97,105,106

One of the more widely accepted hypotheses is aortic neck dilation following aortic endografting. After endovascular aneurysm repair, the aneurysm neck has been documented to dilate significantly, mostly in the first 2 years after graft place-

107

ment.

In a review by Cao et al.,99 17 (15%) of 148 patients had

61,96–99

101

Lee et al.,

Migration

102

evaluated

104

however,

an episode of device migration. The only two independent risk factors for device migration were neck dilation postoperatively and an AAA diameter of greater than 55 mm. Others have argued that neck dilation is not a significant event, provided adequate graft oversizing was performed at initial endograft placement. The amount the aortic neck dilated did not exceed the size of the original aortic endograft placed. Larger aneurysms have also been noted to have increased risks of developing type 1 endoleak, graft migration, and the subsequent need for open surgical conversion compared with larger aneurysms.

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Outcomes

Results of Aortic Endografting

Endovascular AAA repair generally has a low mortality rate (1%-3%) compared to open repair, and subsequent rates of aneurysm rupture after endovascular repair are reduced to 1% per year. Endograft placement is not free of adverse events, however, and there is frequent need for secondary interventions. Naslund et al. reported technical complications in 26% of 34 endografts placed. Fairman et al. evaluated the occurrence of critical events during deployment of their initial 75 endografts, and patients were divided into three groups corresponding to the time period in which the graft was placed. technical difficulties that occurred during the course of operation that threatened the success of the procedure. Difficulty in obtaining access occurred in nearly one quarter of all patients. Although it would be expected that the latter 25 patients should not have experienced as great a difficulty in obtaining access, these patients had increased complexity of their aortoiliac anatomy compared with endograft patients earlier in their experience. This group had a greater frequency of iliac artery balloon angioplasty, as well as the use of iliac artery conduits. Deployment difficulties existed and

100

were composed mostly of graft foreshortening, necessitating the placement of additional distal covered extensions. Other deployment issues encountered included suprarenal graft displacement, infrarenal graft displacement, and device-related issues such as iliac limb kinking or twisting. Malplacement of the graft did not correlate with anatomical complexity.

The need for subsequent secondary procedures has been evaluated by several large series of patients who had an abdominal aortic endograft placed. results of 1023 patients with a follow-up of 12 months or longer. Overall, 186 (18%) patients required a secondary intervention. The majority of these interventions (76%) involved a transfemoral procedure, whereas the remaining patients required transabdominal (12%) or extra-anatomical (11%) surgery. The rates of freedom from intervention at 1, 3, and 4 years were 89%, 67%, and 62%, respectively. The transfemoral procedures performed most frequently were aortic or iliac limb extension for graft migration or endoleak. Late death was more frequent in those patients requiring a secondary intervention resulting in a 3-year cumulative survival of 85%, which is lower than the 90% rate (P <0.05) observed in those that did not require reintervention. In addition, death was more frequently associated with those requiring a transabdominal procedure.

The Montefiore Medical Center and the Cleveland Clinic Foundation have published their single-institution results on the durability of aortic endografting. Montefiore reported on 239 endografts placed over 9 years, with a technical success rate of 88.7%.88 The 5-year survival rate in this group was only 37%. Secondary interventions were required in 10% of the patients, with more than half of the secondary procedures being performed for presence of an endoleak. Sampram et al.93 reported the results from the Cleveland Clinic Foundation on 703 patients undergoing endovascular aortic endografting, with follow-up averaging 1 year. Survival in this group was 90% at 1 year and declined to 70% at 3 years. Overall, 128 secondary interventions were performed in 105 patients (15%). Freedom from intervention mirrored that of the Eurostar registry, with freedom from intervention rates of 88%, 76%, and 65% at 1, 2, and

Critical events were defined as unanticipated

88,93,111,112

The Eurostar registry reported the

104

56,61,93,109

110

111

3 years, respectively. Mortality related to the secondary procedure was 8% but rose to 18% in those requiring a transabdominal procedure. Univariate analysis revealed that secondary procedures were more common in patients with larger major and minor sac axes, in patients who received a large aortic stent because of a proximal endoleak present at initial aneurysm repair, and in patients who received treatment later in the course of the review. This last finding is felt to be secondary to the increased complexity of cases approached in an endovascular fashion.

The Cleveland Clinic Foundation review included the use of six different devices, which included two Zenith grafts—one that was part of the multicenter national trial and one group that was part of a sponsor-investigator investigational device exemption trial.

The overall freedom from risk of rupture was 98.7% at 2 years. Results of this review reveal that there are significant differences in outcomes between groups with different endovascular devices, in particular with regard to limb occlusion and rate of endoleak. Limb occlusion occurred most frequently with the Ancure device, at a rate of 11% at 2 years. Endoleak of any kind was most common with the Excluder device, at a rate of 64% at 1 year. Modular separations were the most frequent with the Zenith graft at 3.5%. Aneurysm sac shrinkage correlated inversely with the frequency of endo leaks, and aneurysm sac shrinkage was most common in the Zenith and Talent groups but least common in the Excluder group. There were no differences with regard to rate of secondary procedures, conversion to open repair, or migration. Sternbergh et al.

113

have reported similar findings. Outcomes were compared between the Zenith device and the AneuRx device, and it was determined that the Zenith graft was associated with fewer endoleaks and a higher rate and amount of aneurysm sac shrinkage. Bertges et al.

114

also reported similar findings in their evaluation. Regression of AAA size after endograft placement was more significant after placement of the Talent and Ancure endografts than with the AneuRx or Excluder devices. During the first 2 years of follow-up, the initial size of the AAA, presence of an endoleak, and type of graft used were significant predictors of sac shrinkage. After 2 years, however, only graft type was significant. Ouriel et al.

108

have additionally concluded that the outcome after endovascular AAA repair depends on the initial size of the aneurysm.

Comparison with Open Surgery

Endovascular AAA repair has been shown to be associated with lower postoperative morbidity, shorter length of hospital stay, and quicker return to normal function. surgery utilizing randomized prospective trials, however, has only recently been available for evaluation. There have been three randomized prospective trials evaluating the use of EVAR compared with open surgery. The EVAR-1 trial enrolled 1082 patients with AAA who were healthy enough to be suitable candidates for surgery. They were randomized to either EVAR or open repair. Results from this trial demonstrated that the 30-day mortality rate was lower after EVAR (1.7%) than open surgery (4.7%, P <0.0001). At 4-years follow-up, the aneurysm-related mortality rate in the EVAR group was half that in the open group (P = 0.04), but there was no difference in all-cause mortality (26% for the EVAR group and 29% for the open group). The Dutch Randomized Endovascular Aneurysm Management (DREAM) trial was a prospective randomized trial that enrolled 351 patients. As in EVAR-1, the 30-day mortality rate was lower in patients who underwent endovascular repair than in those who underwent open surgical reconstruction, but the 2-year outcomes were similar between the two groups. In addition, the results of the Open versus Endovascular Repair (OVER) Veterans Affairs Cooperative Study Group results have been reported. this trial, 881 patients suitable for open or EVAR were randomized to one of the two surgical techniques. As with the other two trials, 30-day mortality was lower in the EVAR arm (0.5%) than the open surgery arm (3.0%, P = 0.004). This difference, however, resolved by 2-year follow-up time points (7.0% vs. 9.8%, respectively). Patients undergoing EVAR had shorter hospital stays, shorter operative

115

Direct comparison to open

115

116

durations, and required fewer blood transfusions, but they had increased exposure to fluoroscopy and contrast. Given its promising initial results, it is not surprising EVAR has become increasingly popular with both patients and providers over the past decade.

One of the most controversial aspects of AAA repair, however, is when to perform EVAR and when to perform conventional open surgery. Open surgical repair of AAA has long been considered the gold standard, and there is evidence this option provides good long-term durability.

117,118

Endovascular AAA repair however, given its young age, does not have similar timetested outcomes data. Recently, longer-term outcomes from both EVAR-1 and DREAM have been reported.

30,119

For EVAR-1,30 the median follow-up was 6 years (range, 5-10 years), and at followup, the overall aneurysm-related mortality was 1.0 deaths per 100 person-years in the EVAR group and 1.2 deaths per 100 person-years in the open repair group (P = 0.73). All-cause mortality was 7.2 deaths per 100 person-years (EVAR) and 7.1 deaths per 100 person-years (open surgery). Graft-related complication rates were higher in the EVAR group (12.6 per 100 person-years) compared to the open surgical arm (2.5 per 100 person-years; P <

0.001), and significantly more patients in the EVAR group required reintervention (5.1 per 100 person-years vs. 1.7 per 100 personyears; P <0.001). In fact, new graft-related complications and reinterventions were reported for as long as 8 years following EVAR. For DREAM,

119

at a median follow-up of 6.4 years (5.1-8.2 years), cumulative survival rates were 69.9% for open repair and 68.9% for EVAR. The cumulative rates of freedom from secondary interventions were 81.9% for the open repair group and 70.4% for EVAR (P = 0.03). Based on these data, it is clear that EVAR is not without its drawbacks. These factors may change as the technology improves and we gain a better understanding of the long-term implications of placing an endovascular graft in the aorta.

Initial applications of EVAR were geared toward patients considered high risk for conventional surgery, but this concept has come under some scrutiny after the results of the EVAR-2 trial. In this trial, the outcomes of 404 patients with large AAAs (≥ in diameter) who were considered to be physically ineligible for open repair were evaluated. Of this cohort, 197 patients were assigned to undergo endovascular repair, while 207 were assigned to have no intervention. The 30-day operative mortality rate for the EVAR group was 7.3%, and the overall rate of aneurysm rupture in the observation group was 12.4 per 100 person years. Aneurysmrelated mortality was lower in the endovascular repair group, but this did not provide an advantage when evaluating all-cause mortality, and during follow-up, EVAR required a considerable increase in expense. These results called into question the appropriateness of using EVAR in high-risk patients. The results, however, have been refuted by others demonstrating lower rates of perioperative mortality and better long-term survivals in these high-risk patients. These improved outcomes are likely due to an aggressive multidisciplinary approach to managing these patients’ comorbidities.

Other Considerations

EVAR for Small Abdominal Aortic Aneurysms

Randomized prospective trials have demonstrated that there is no benefit to open repair of AAA for aneurysms that are less than

5.5 cm in diameter. in these two trials raised the question of whether a procedure with lower operative mortality might provide benefit compared with observation in patients with smaller AAA. The Positive Impact of Endovascular Options for Treating Aneurysms Early (PIVOTAL) trial sought to evaluate whether endovascular repair of small AAA (4-5 cm) might provide a survival advantage compared with surveillance.

124

either EVAR (n = 366) or ultrasound surveillance (n = 362). Of the patients randomized to EVAR, 89% underwent repair, and of those assigned to surveillance, 31% subsequently underwent repair during the course of the study (mean follow-up 20 ±

122,123

Operative mortality rates of 2.7% and 5.8%

In this trial, 728 patients were randomly assigned to

12 months, range

120

5.5 cm

121

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0-41 months). The unadjusted hazard ratio (95% confidence interval [CI]) for mortality after EVAR was 1.01 (0.49-2.07; P = 0.98), with 15 deaths (4.1%) occurring in each group. No survival advantage was demonstrated with EVAR.

Endovascular Treatment of Ruptured Abdominal

Aortic Aneurysms

With the widespread application of EVAR for repair of AAA, its use in the repair of ruptured AAA has similarly expanded. Initially there were several limitations to the application of this technology to treat the devastating problem of ruptured AAA: (1) unavailability of preoperative CT in patients with ruptured AAA, (2) unavailability of a dedicated operating room and ancillary staff equipped to perform emergent EVAR at all times, (3) unavailability of off-theshelf stent grafts; and (4) lack of data from multicenter randomized trials.

125

Many large-volume centers, however, have developed protocols that allow treatment teams to overcome these hurdles and provide emergent care for ruptured AAA with endovascular devices.

125–128

Gerassimidis et al.

126

reported on the treatment of 69 patients with a ruptured AAA. Of these, 42 patients (63%) were suitable for EVAR. The in-hospital and 30-day mortality rates were 36% and 41%, respectively. Veith et al.

128

reported the worldwide experience with treating ruptured AAA with endovascular grafts. Data were collected from 49 centers at which 1037 patients were treated with EVAR for ruptured AAA. Overall 30-day mortality was 21%, which was significantly lower than the 30-day mortality rate for the 763 patients undergoing open repair (36%, P < 0.001) for ruptured AAA at these same institutions during the same time period. Given these experiences, there is a trend toward even more centers instituting a program of EVAR for ruptured AAA. Certainly, longer-term follow-up and larger series will be required to assess whether EVAR has ultimately affected outcomes from ruptured AAA.

Fenestrated and Branched Aortic Endografts

The most common reason for excluding patients from EVAR is lack of a suitable proximal implantation site between the renal arteries and the aneurysm. Although commercially available devices provide a mechanism for supplementing fixation within the suprarenal aorta without detrimentally affecting renal function, a practice has not been advocated to treat juxtarenal aneurysms. Despite evidence of short-term success with treatment of short necks with devices intended to treat infrarenal aneurysms, risk of later failure remains high. stent graft technology was developed. The devices used currently are hybrids of original abdominal devices. The primary goal of treating an aneurysm with a fenestrated graft is to move the sealing and fixation region of the repair into healthy aorta with a parallel neck and without wall defects. A fenestration (hole in the graft) allows the stent graft to occupy this more proximal location while providing for transgraft flow to the renal arteries (or other significant branches) (

Fig. 40-8). It is designed to incorporate the

minimum number of visceral vessels required to achieve fixation

131

To overcome this, fenestrated

129

such

130

the

and seal within healthy aorta. The fenestrations are constructed to match the ostial diameter of the visceral vessels and maximize the sealing zone. Several large series of fenestrated endograft deployments have been reported, demonstrating the midterm safety and efficacy of fenestrated stent grafting. is reported by O'Neill et al.

132

132–134

One of the largest series

They outline a series of 119 patients with mean follow-up of 19 months. There was only one perioperative death, and survival at 12, 24, and 36 months was 92%, 83%, and 79%, respectively. The 30-day endoleak rate was 10%, and all endoleaks were type II in nature. Regression of the aneurysm sac was noted in 79% of the patients by 12 months. Complications related to the renal arteries was noted in 10 of the 231 stented renal arteries, and only one patient who did not have significant renal dysfunction preoperatively went on to require dialysis. Incorporation of the renal arteries raises questions about the effect of fenestrated stent graft repair on long-term renal function.

Application of fenestrated technology has advanced to allow for the treatment of thoracoabdominal aortic aneurysms (TAAA) in which the aneurysm involves the renal and visceral vessels. When treating TAAA with an endograft, however, use of a simple fenestration is inadequate. Unlike fenestrated grafts where a hole in the graft suffices, in more complex aneurysms such as TAAA, the branch arteries arise from the aneurysm. In this scenario, blood flow has to be carried from the endograft, across the aneurysm, and to the target vessel, without extravasation into the aneurysm ( There are two modes by which this can be assured. The first is the fenestrated branched stent graft (see

Fig. 40-8). In this style, the addition of a covered bridging stents

converts a fenestrated stent graft into a form of branched stent

137

graft.

Sealing between the covered stent and the fenestration is

135

or reinforced fenestrated graft

Fig. 40-9).

136

tenuous because there is very limited overlap of material. A nitinol ring is added to the fenestration to reinforce the site of interaction between the covered stent and the fenestration. These are termed reinforced fenestrations. The second mode of branched graft design is the cuffed branched stent graft

136

graft

(see Fig. 40-8). The cuff or branch creates an overlap zone

138

or directional branched stent

between the stent graft and the branch artery. It provides a segment of overlap that can be used to provide better sealing and fixation than the thin joint between a reinforced fenestration and mating visceral stent graft. A longer overlap affords one the ability to use a self-expanding stent graft rather than a balloon-expandable stent graft. This may provide a means to better accommodate tortuosity and diameter discrepancies and may limit type 1 endoleaks and component separation from this region.

Investigators tend to pool results of fenestrated branch grafts and cuffed branched grafts, with few series containing significant numbers of patients. has been reported by the Cleveland Clinic. Greenberg et al.

139–145

The largest single-center experience

143

performed a retrospective analysis on patients who underwent elective open surgical repair (N = 372) or endovascular repair (N = 352) of descending thoracic or thoracoabdominal aortic aneurysms. The group of patients treated with endovascular repair was older and had more comorbid conditions than those undergoing open repair. Open repair, however, was more frequently applied

A BCD

FIGURE 408 A, Example of endograft with fenestration (arrow) within endograft body to accommodate a renal artery. B, Reinforced fenestration (arrow) that allows for placement of (C) covered stent graft, creating a form of a branched endograft for treatment of a thoracoabdominal aortic aneurysm (TAAA). D, True directional branch (arrow) used to allow for continued flow to a visceral vessel when treating thoracoabdominal aortic aneurysm.

FIGURE 409 Example of thoracoabdominal aortic aneurysm (TAAA) that has been treated with a branched endograft that incorporates all of the visceral vessels.

to patients with type II or type III aneurysms and those that were associated with a chronic dissection. Despite the differences in patient age and comorbid conditions, mortality rates at 30 days (5.7% vs. 8.3%) and 12 months (15.6% vs. 15.9%) were not different between endovascular repair and surgical repair, nor was there a difference in the development of spinal cord ischemia (4% vs. 8%, respectively; P = 0.08). Bakoyiannis et al. performed a meta-analysis of all English language literature published between 2000 and 2009 on endovascular procedures using fenestrated and/or branched technology.

145

The results of this analysis demonstrated that complex endografting can be performed with a technical success rate of 94%, with a 30-day mortality of 7%. Typically these procedures were performed in patients who were deemed high risk for conventional surgery. The 1-year mortality was 1.3%. The application of fenestrated and branched technology is very much in its infancy. As the technology progresses, we will be able to better discern who will best benefit from these procedures, and ultimately replace open surgery with this less invasive option.

Summary

Abdominal aortic endografting provides a less invasive method of treating AAA. It provides a beneficial way of treating aneurysms in patients who are at high risk for conventional open surgical repair, and results of randomized trials suggest, at least in the short-term, it provides clinical equipoise with conventional surgery. The durability of this procedure is still under evaluation. It is likely, however, that the application of endovascular technology will replace current open surgical options, and ultimately the entire aortic tree will be treated with endovascular options.

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