Early Experience with the Talent™ Stent-Graft System for Endoluminal Repair of Abdominal Aortic Aneurysms

Endoluminal grafting for treatment of aortic aneurysms is the most exciting topic in vascular surgery today. It is anticipated that at least half of all aneurysms in the infrarenal abdominal and descending thoracic aorta will be repaired endovascularly in the near future.

Endovascular grafting procedures require a combination of surgical maneuvers and refined interventional skills. They are often difficult, and involve catheter techniques and imaging requirements that are not readily available in most vascular surgery practices today. Collaboration between surgeons and interventionists is often necessary and, occasionally, is mandated by the investigational protocol.

The most significant technological achievement to date has been the development of the modular, fully supported, bifurcated stentgraft (Fig. 1). ^1,2 This device incorporates 2 features that are currently viewed as critical components of endovascular graft technology: 1) modular design—which joins 2 or more sections of the stent-graft within the aorto-iliac lumen—optimizes deployment and exclusion by enabling the addition of extensions both cephalad and caudad; and 2) full-length support achieves the columnar strength that is necessary for stability and integrity, preserving normal channel flow even when placed across tortuous vessels. Another design feature that has recently become the focus of attention is suprarenal fixation of the uncovered stent at its proximal end, which enables secure attachment to a segment of the aorta less prone to progressive dilatation. ³

Fig. 1 Modular, bifurcated, fully supported stent-graft.

In September 1999, 2 stent-graft devices for the exclusion of abdominal aortic aneurysms received approval from the Food and Drug Administration: the Ancure® device (Guidant; Indianapolis, Ind) (Fig. 2), which is an early-design balloon-expandable, 1-piece bifurcated stent-graft; and the AneuRx™ device (Medtronic AVE; Santa Rosa, Calif), a self-expanding, modular-design, fully supported bifurcated stent-graft. Additionally, several other stent-grafts are now under clinical investigation, including the Vanguard™ (Boston Scientific Corp; Natick, Mass) (Fig. 3), Talent™ (World Medical, a division of Medtronic Vascular; Sunrise, Fla), Bifurcated EXCLUDER Endoprosthesis (W.L. Gore & Associates; Sunnyvale, Calif) (Fig. 4), and Zenith™ (Cook Inc.; Bloomington, Ind) (Fig. 5). They are all self-expanding, modular-design endoluminal grafts, made of nitinol or stainless steel stents covered by a Dacron or polytetrafluoroethylene (PTFE) fabric. A somewhat different design is being developed by Cordis Endovascular (Cordis Corporation, a Johnson & Johnson company; Warren, NJ): this is a bilateral, aortoiliac endoluminal graft configuration that may be deployed percutaneously, given its low-profile (13 F) delivery system. A clinical trial is set to begin in mid-2000.

Fig. 2 Ancure® stent-graft device.

Fig. 3 Vanguard™ stent-graft device.

Fig. 4 Bifurcated EXCLUDER Endoprosthesis.

Fig. 5 Zenith™ stent-graft device.

Endoluminal repair of aneurysms in the descending thoracic aorta is another area under active investigation at this time. ⁴ Designers of the Talent™, AneuRx™, and EXCLUDER devices have developed endoluminal grafts configured for placement in the thoracic aorta (distal to the aortic arch branches). Some forms of aortic dissection ⁵ and traumatic rupture are also being managed with endovascular approaches, but available information is only preliminary at this time; a much larger clinical experience with longer follow-up will be necessary before a definitive view can be attained concerning the performance of these endoluminal grafts for treatment of aneurysmal and nonaneurysmal thoracic aortic diseases. It is our impression today that stent-graft repair of descending thoracic aortic aneurysms will rapidly become a popular approach, given the extensive nature of conventional surgical treatment and the severe morbidity associated with it.

The Talent™ AAA Stent-Graft System

The Talent™ stent-graft is a modular, self-expanding prosthesis (Fig. 6) designed for endoluminal exclusion of aortic aneurysms. It consists of a series of serpentine nitinol stents embedded into woven Dacron fabric. The stents are spaced discontinuously along a full-length nitinol spine. The delivery system is a co-axial sheath with pusher rod and a compliant poly-urethane balloon used to maximize attachment to the vascular wall and ensure full expansion throughout the length of the device. The outer diameter of the delivery system (containing the main section) ranges from 22 to 25 F (Table I). The more recently developed thinner Dacron fabric (Talent Low Profile System, or LPS™) has significantly reduced the outer diameter (Table II). For most AAA patients today, a 22-F system is used.

Fig. 6 Talent™ stent-graft device.

Table I. Talent™ AAA Stent-Graft System (Standard Graft Material)

Table II. Talent LPS™ (Low Profile System)

Salient features of the Talent device include the proximal bare spring (uncovered nitinol stent) (Fig. 7) and custom-manufacturing to fit a wide range of aorto-iliac sizes and configurations, as determined preoperatively by computed-tomographic (CT) imaging and angiography (Table III).

Fig. 7 Note the bare spring (uncovered nitinol stent) at the top end of the Talent™ stent-graft.

Table III. Talent™ AAA Stent-Graft System: Sizes and Configurations

Device Implantation Techniques

The methods and technical principles described here are drawn from the senior author's (FJC's) personal experience with over 120 implants. Naturally, the opinion and advice of many investigators worldwide (who together have performed over 5,000 implants) and of Medtronic's engineering and technical team have had significant influence in the conception of these approaches.

The intervention often commences with percutaneous catheterization of the left brachial artery and placement of a 5-F sheath, as it has been found to be of great help during several steps of the implantation procedure (Table IV). After the guidewire has been steered along the correct pathway, the pigtail catheter is introduced and then “parked” in the proximal abdominal aorta, at the level of T12. Our own enthusiasm notwithstanding, most investigators prefer to use the brachial artery approach selectively, perhaps in less than 10% of procedures.

Table IV. Uses of Brachial Artery Catheterization

Systemic anticoagulation is induced with heparin, given intravenously in amounts adequate to prolong activated clotting time (ACT) to 300 to 400 seconds. The ACT is monitored and is maintained at this level throughout the implantation procedure by administering additional heparin as needed every 15 to 20 minutes.

Bilateral vertical groin incisions are made to surgically expose the full length of the common femoral artery (CFA) from the inguinal ligament to the femoral bifurcation.

An Amplatz Super Stiff™ (Boston Scientific) or Lunderquist (Cook) 0.035-inch guidewire, 260 cm in length, is inserted transfemorally by the exchange technique. The guidewire is advanced to the top of the aortic arch, where it is maintained until deployment has been completed. To prevent inadvertent advancement into the supra-aortic vessels or heart chambers, it is useful to have visual control of the wire's position at all times by relating it to an external reference point on the table (Fig. 8).

Fig. 8 “External control” of Super Stiff™ transfemoral guidewire.

In preparation for introducing the sheath, a transverse arteriotomy is made at the site of the puncture. If the femoral arteries are thick-walled and diseased, longitudinal arteriotomy and subsequent patch repair may be more appropriate.

The delivery sheath (containing the main body and ipsilateral limb of the endoluminal graft) is introduced over the Super Stiff wire and advanced carefully across the iliac artery into the aorta under fluoroscopic monitoring and guidance. We defer angiography until after the device has been introduced to the aorta, so that a single contrast injection will likely suffice for both anatomic definition and road-mapping. A push-pull wire technique ensures proper tension and facilitates transluminal tracking of the sheath; loss of wire access or excessive intra-luminal advancement into the right side of the heart are avoided by the precautions described above. Very tortuous (but soft) iliac arteries can be appropriately straightened with brachial-femoral (“body floss”) access, for which we prefer to use a 450-cm Glidewire® (Boston Scientific). When applying tension, we always protect the aortic arch and the left subclavian artery with a 5-F catheter over the wire (Fig. 9).

Fig. 9 Tortuous iliac artery (A) can be straightened by tensing a brachial-femoral guidewire (B).

The sheath is advanced retrograde to the level of L1, and a power-injector angiogram is obtained via the brachial catheter. The image intensifier is centered on L1-L2 in order to center the fluoroscopic field on the juxtarenal aortic segment and thereby minimize parallax.

Deployment of the device is effected by gradually withdrawing the outer sheath as the pusher rod is held frozen in place. We strongly recommend that deployment begin above the renal arteries. Once the bare spring and 1st cloth-covered stent (corresponding to the 2 uppermost metal segments on fluoroscopy) are allowed to self-expand, the entire assembly is gently brought down to the juxtarenal position. “Ideal” placement consists of transrenal fixation of the bare spring, with the top end of the Dacron fabric 2- to 3-mm below the origin of the renal arteries. The fluoroscopic road-mapping technique is adequate to determine the proper proximal attachment level; if desired, a long 20g spinal needle can be inserted through the skin of the upper abdomen to mark the position of the renal arteries. When in doubt about possible coverage of 1 or both renal artery ostia by the Dacron fabric, a “puff angiogram” (through the brachial catheter) can easily and quickly provide clues in regard to whether the device should be pulled down to a lower level. Transrenal fixation may not be necessary when a long proximal neck is present.

Once a satisfactory proximal level of attachment (“landing”) has been achieved, the outer sheath is retracted fully to allow expansion of the rest of the device. Next, the balloon is inflated sequentially, all along the length of the body and the ipsilateral limb, to ensure proper expansion and embedding. Blood pressure control is not necessary during deployment of a self-expanding stent-graft.

Following removal of the delivery system, a long 9-F sheath with a radiopaque tip is placed (over the wire) through the arteriotomy to obtain a (limited) reflux angiogram that visualizes the adequacy of seal and the level of placement of the iliac limb. If these are satisfactory, the guidewire is removed, and the arteriotomy is repaired with interrupted sutures to quickly reestablish blood flow to the lower extremity. Inadequacies in the iliac-limb landing may be corrected by further balloon dilation, or by the addition of an iliac extension graft.

Access across the short leg is easily and quickly achieved from the top by passing a 300- to 450-cm long, 0.035-inch guidewire through the left brachial catheter. The wire is advanced antegrade into the aneurysm and out the iliac artery, down to the exposed common femoral artery. It can be extracted directly through the arteriotomy, or captured intraluminally with a goose-neck snare. Alternative access techniques can be used. Most investigators prefer the retrograde or contralateral (“over the top”) approach for this maneuver. Recently, the latter has become the authors' preferred approach.

A catheter (or long sheath) is used to exchange the brachial-femoral access wire for an Amplatz Super Stiff guidewire to deliver and deploy the contralateral limb; or, as we prefer, the contralateral limb can be introduced over the brachial-femoral wire. A 300-cm or longer guidewire is required for the latter. A limited retrograde hand-injection angiogram is performed (in the same manner as described above) to verify iliac attachment.

A final antegrade aortogram is obtained to ascertain that a satisfactory technical result has been achieved (without endoleak) and to document intact renal artery flow. The femoral arteriotomy is then repaired and lower-extremity circulation is re-established.

Femoral incisions are closed in routine manner after reversal of the heparin effect with protamine sulfate. The left brachial sheath is removed when the ACT is less than 180 seconds, and hemostasis is obtained by manual compression of the artery against the humerus for 20 minutes.

Problem Solving. Problem prevention comes 1st and is achieved mainly through precise preoperative evaluation that yields accurate measurements and leads to proper planning. Both CT imaging and contrast biplane angiography are used for this purpose. We feel strongly about the desirability of obtaining diagnostic aortography (in addition to CT imaging) whenever possible. Diameter oversizing (4-mm top end, 2-mm distal ends) and modularity are the best friends of the AAA interventionist. The following guidelines are critical: “diameter oversize” at the proximal (mainly) and distal attachment sites; and “length undersize” whenever in doubt (modular grafts can always be extended).

Iliac artery tortuosity is a common cause of technical failure during endoluminal repair of AAA. In the absence of severe calcific disease, straightening the access vessel is possible and quite effective. Use of a Super Stiff wire is thought to be mandatory in every case.

Problems posed by the aneurysm's neck are most often the result of short length or of angulation. Aortic aneurysms with proximal necks as short as 0.7 to 1.0 cm can be repaired with the Talent system through transrenal or suprarenal fixation as described, although this circumstance is less than ideal and carries a greater risk of failure. Diameter oversizing of 4 to 6 mm at the top end is important to maximize sealing in such cases. Aggressive ballooning is another critical component of this procedure, especially when using grafts that are more than 15% oversized. Angulations of less than 60 degrees are manageable, but tilting of the upper segment of the device can cause less predictable (less controllable) placement at the juxta-renal position (Fig. 10). A proximal cuff may need to be added; indeed such a cuff should always be available when embarking upon any AAA implantation, no matter how straightforward the procedure may seem.

Fig. 10 A short, angulated neck can tilt the device and cause a proximal endoleak at the time of deployment.

Extension of the graft with distal landing at the external iliac artery is used to bypass a frankly aneurysmal or very large common iliac artery. In such instances, it is advisable to occlude the ipsilateral internal iliac artery to avoid subsequent reflux and endoleak. Percutaneous coil embolization is most conveniently done as a preliminary outpatient procedure a few days before exclusion of the aneurysm. On occasion, bilateral internal iliac artery occlusion becomes necessary: we feel strongly that this should be done as 2 separate, staged interventions prior to repair of the AAA. We have not thus far seen any ischemic complication from internal iliac artery occlusion, either unilateral or bilateral, and only a handful of patients have developed severe buttock claudication. However, it must be emphasized that the decision to occlude the internal iliac artery should be judicious and dictated by a conservative attitude towards preservation of hypogastric flow.

On occasion, aorto-uni-iliac endoluminal grafting is the best technical approach. This implies the need both for exclusion of the contralateral common iliac artery and for a crossover femoro-femoral bypass to revascularize the contralateral lower extremity. This situation is likely to require use of an iliac conduit for access and device deployment (Fig. 11A). The synthetic conduit thus becomes: 1) the site of distal landing of the endoluminal graft's iliac limb; and 2) the source of inflow for the crossover bypass (Fig. 11B). Additionally, a similar (but temporary) femoral side-graft constitutes a good access option for those occasional patients who present with heavily scarred groins wherein it is difficult to obtain a segment of femoral artery that is long enough for proper control during deployment.

Fig. 11 A, B Artist's depiction of iliac conduit technique for aneurysm exclusion with aorto-uni-iliac stent-graft system.

As we have said above, “aggressive ballooning” is felt to be an important part of the Talent AAA procedure. However, caution must be exercised to avoid dangerous over-dilation at the iliac artery level, especially when the compliant balloon is inflated partly inside the native iliac artery (outside the graft).

Early Results with the Talent™ AAA Device

The Talent stent-graft system for treatment of AAA is an investigational device under an Investigational Device Exemption (IDE) protocol approved by the Food and Drug Administration for use in the United States. Patient enrollment is complete for several Phase II studies on both high-risk and low-risk cohorts. Information on overall technical and clinical results is not yet available. Our own experience at Union Memorial Hospital/MedStar Health in Baltimore now extends to over 120 patients (as of 31 October 1999). Early technical results and acute clinical outcome can be summarized as follows:

• Talent endoluminal graft applicable in nearly 70% of screened AAA patients

• Overall technical success: 94%

• 30-day mortality: 2.5%

• Acute surgical conversion: <1%

• Average length of hospital stay: 3.5 days

• Use of ICU: 10%

• Unable to deliver device during attempted implant: 5%

• Endoleaks

  • At procedure or on initial CT scan: 15%

  • On 30-day CT scan: 8%

Overview and Conclusions

Endovascular grafting of aortic aneurysms is clearly feasible and capable of achieving a high degree of technical success. The question of whether it can justifiably replace surgical treatment will not be answerable for several more years, when the results of on-going trials and long-term follow-up data become available. The essential requirements of a successful stent-graft device have been defined (Table V). Optimal clinical performance (Table VI) will have to be achieved before endovascular grafting becomes standard treatment of aneurysms for the majority of patients.

Table V. Aortic Stent-Grafts: Requirements for Technical Success

Table VI. Aortic Stent-Grafts: Optimal Clinical Performance (Proposed Goals)