Branched Stent Grafts for TAAA
Matthew J. Eagleton, MD
Department of Vascular Surgery, Cleveland Clinic
Matthew J. Eagleton, MD
Department of Vascular Surgery, Cleveland Clinic
Patients with thoracoabodminal aortic aneurysms (TAAA) constitute a small proportion of the total population with aortic disease, but the complexity of the pathology has made their study and treatment an area of considerable discussion. Conventional open repair techniques have been refined over the past decade, and centers of excellence now report acceptable pre-operative mortality. The invasiveness of the procedure limits the indications to those who are the most fit. Endovascular repair of aortic aneurysms was first described nearly two decades ago . Since that time, a significant evolution in technology and techniques has been demonstrated. In direct comparison, infra-renal endovascular aneurysm repair demonstrates reduced peri-operative mortality and long-term clinical equipoise with convention surgery [2,3,4]. Similar extensions of endovascular technology to the proximal aorta has allowed for the treatment of thoracic aortic pathology in a similar fashion [5,6]. Endovascular repair, however, has been limited when aneurysms encroach on the visceral vessels, such as in the treatment of juxtarenal AAA and TAAA. The development of fenestrated and branched endograft technology has allowed for the application of this less invasive approach to aneurysm repair in these complex cases. To date, in the United States, placement of these types of grafts has been limited to clinical research trials. Only recently, a device utilizing fenestrations that allows for the treatment of short-necked infrarenal AAA has been approved for commercial use . Treatment of more advanced disease, however, is possible with the use of branched aortic devices, but their application remains restricted to research programs [8,9].
The indication for treatment of TAAAs does not differ from that of conventional surgery despite applying a less-invasive option. The risks of the surgery must be balanced with the benefits of the surgery, carefully evaluating the underlying co-morbidities of the individual patient. In general, repair of TAAA is reserved for patients in whom their aneurysms have reached, or exceeded, 6 cm in maximum diameter. Given its still experimental nature, most fenestrated and branched endograft research programs are limited to treating patients who are considered high risk for conventional surgery . The majority of the devices used are custom designed for a specific patient’s anatomy, and therefore there is little application of this technology currently to the treatment of urgent or emergent cases.
Pre-operative Imaging Studies
Comprehensive aortic assessment is mandatory for procedural planning when using devices that incorporate branched vessels. This is accomplished with the use of high-quality image acquisition, and the ability to manipulate the data in three-dimensional work stations. Longitudinal and/or rotational misalignment can result in critical end-organ loss, with potentially disastrous consequences. Currently available spiral CT technology renders images of excellent quality that can be used to design devices that incorporate the visceral, renal, iliac, internal, and even arch vessels . The author’s current algorithms involve 0.75- to 1.0-mm slice image acquisitions. After acquisition, image reconstruction must be done utilizing multi-planar techniques to allow for accurate measurements of a variety of arterial anatomic criteria. This is accomplished by analyzing renditions of aortic anatomy perpendicular to a centerline of flow. This allows for accurate assessment of the proximal aortic neck, as well as location, distance, and rotational alignment of target branches (Figure 1).
Multiple different anatomic structures and their location must be considered when planning a branched endograft. Initial planning revolves around placement of the stent graft in a location that will allow for adequate proximal fixation and seal. Standard commercial EVAR allows for a proximal landing zone between 10-15 mm by most graft indications for use. With branched aortic endograft placement, we prefer to follow guidelines more akin to those for placement of a thoracic endograft and extend the proximal landing zone to 25 mm. The proximal and distal landing/seal zones should be free of significant atheroma and thrombus, and the aortic walls should be parallel. This can be overcome in more proximal aortic disease through the utilization of elephant trunk grafts and/or debranching procedures, in which a hybrid procedure is performed utilizing both open and endovascular surgery (Figure 2). In addition, the linear and axial location of the target branched vessels must be noted. This will dictate on the graft where the location of the fenestrations or branches will be constructed (Figure 3).
Also to consider when evaluating the patient’s anatomy, is the ability to deliver the graft system. Most fenestrated and branched endografts are delivered through systems that are 20-22 French in diameter, and thus rely on the presence of adequate iliac artery diameters to accommodate placement of such a sheath. While methods to allow for endovascular placement of these larger sheaths have been described , we have tended not to utilize these methods when placing branched endografts. It has been our experience that the presence of stents within the iliac system can reduce the ability to rotationally manipulate the graft delivery system making it more difficult to accurately align the reinforced fenestrations or branches. In these situations, we have preferred to place an ilio-femoral conduit using a 10 mm graft (Figure 4). Historically, we have performed this in a staged fashion at a setting prior to the endovascular procedure .
One of the risks of repair of thoracoabdominal aortic aneurysm repair is the development of spinal cord ischemia [14,15]. In order to help mitigate this catastrophic complication, care must be exercised to maintain all collateral routes of spinal flow as possible. When planning for surgery, we routinely develop a treatment algorithm that will preserve flow to both hypogastric arteries and both subcliavian artery whenever possible. This can be accomplished through the judicious use of ilio-femoral conduits and placement of carotid-subclavian bypass grafts (or subclavian transpositions) . Again, we typically perform these procedures in a staged fashion prior to the endograft procedure.
Currently available devices are based on the Cook Zenith (Cook Medical, Bloomington, IN) platform, but are modified to include one of two types of branches. The first type of design is termed a “reinforced fenestration” (Figure 5). These are essentially holes, customized to the size and location of the target vessel, which are placed in the aortic graft and reinforced with a circumferential nitinol wire (Figure 5). These reinforced fenestrations are then mated with the target vessel with a balloon expandable covered stent, which is flared within the fenestration to obtain a seal. The second type of branch is a “directional branch,” which is a side-arm that is attached directly to the main aortic component (Figure 6). The directional branch allows for easier placement of the mating stent, more flexibility with regards to orientation, and greater amount of overlap with the mating stent. This longer overlap allows for the use of self-expanding covered stents, rather than balloon expandable stents. To assist in access to these directional branches, catheters are preloaded in the delivery system (Figure 7) allowing for direct access into the branch from above. Other graft modifications that assist in the placement of these grafts include diameter reducing ties (Figure 7) and proximal and distal trigger wires, which keep the graft attached to the delivery system and partially constrained after unsheathing the device. This allows for easier manipulation of the graft in aligning the branches with their target vessels. These wires are removed during the deployment process (Figure 7).
While placement of branched endografting can be performed under regional anesthesia , it has been our preference to perform these procedures under a general anesthetic – provided the patients’ co-morbidities are not prohibitive. Monitoring during the case typically involves central venous access and direct arterial blood pressure monitoring. More invasive monitoring is dictated by the underlying co-morbidities of the patient. The use of spinal drainage is employed, with the use of a subarachnoid drain, whenever a group II or III TAAA repair is being performed. In addition, efforts are made to maintain a normal mean arterial pressure. Patients are anticoagulated during the procedure with heparin, with the aim to maintain the activated clotting time (ACT) greater than 250-300 seconds.
Endovascular device implantation requires skill in the orientation of three-dimensional devices based on two-dimensional angiographic imaging equipment. When performing branched endografting for TAAA, it is necessary to have high-quality intraoperative imaging (Figure 8). These are best housed in a hybrid operating room suite that allows for both open and endovascular procedures. While the complexity of the procedure increases, the ability to more accurately evaluate the three-dimensional architecture of the aortic tree before, during and after surgery becomes increasingly important. Flat panel detectors have begun to replace the standard image intensifiers used on conventional fluoroscopy units. The application of this technology provides the ability to perform intraoperative 3D imaging using rotational angiography, termed C-arm cone beam tomography (CBCT). This technology can be used intra-operatively in the form of fusion imaging to guide device implantation. This is similar to traditional road-mapping that is used with conventional angiography. Intraoperative CBCT images can be registered to the preoperative CT images, and these can be superimposed upon the live fluoroscopy images (Figure 9). The superimposed image is updated real-time with movement of the C-arm gantry angle. The superimposed image can help to guide the placement of the fenestrated/branched endograft – utilizing the images to align the branches and fenestrations with their targets. Use of CBCT has been demonstrated to significantly decrease the volume of contrast utilized during these types of contrast .
Patients are positioned supine for the procedure, and the abdomen, pelvis, thighs and the left arm are prepped and draped. The exact procedural steps will vary based on the type of graft construction that is utilized. For the sake of completeness, the author will describe placement of a graft that utilizes both reinforced fenestrated branches and directional branches for treatment of a TAAA. Transverse incisions are performed in the inguinal region, and proximal and distal control of the femoral arteries is obtained. If a directional branch is a part of the graft construction, then an additional incision is made over the distal axillary artery in the upper arm. If this artery is not of adequate size to accommodate a 10 French sheath, then the incision is made more proximally in the infraclavicular location. After the patient is anti-coagulated, intra-arterial access is obtained. Through the ipsilateral femoral artery, stiff wire access is obtained in the ascending aorta. Similar stiff wire access is obtained through the contralateral femoral artery. A large sheath, 20 to 24 French depending on the number of reinforced fenestrations to be stented, is advanced to the aortic bifurcation under fluoroscopic imaging. Multiple smaller sheaths are then advanced into the larger sheath (Figure 10), and this allows for repeated access of multiple distal sites without having to re-access the femoral artery.
Prior to stent graft placement, it is necessary to localize the target vessels for alignment of the branches or fenestrations. This can be done using a variety of techniques, such as the fusion imaging that was described above. Alternately, aortography can be performed. We prefer, however, to supplement the use of fusion imaging with placement of catheters and wires in at least two of the target vessels to mark their location (Figure 11). These catheters assist, when advancing the endograft, in positioning it along the length of the aortic axis and help to align the branches/fenestrations with the target vessels without the use of contrast.
Prior to insertion of the graft, it is oriented under fluoroscopy (Figure 12). The device is then advanced through the femoral artery on the ipsilateral side. Care must be taken to assess for device rotation as it passes through tortuous iliac systems. When the graft is constructed with direction branches, these utilize preloaded catheter and wire systems as described above. As the device is advanced into the aorta, a wire is advanced through the preloaded catheter system and snared through a sheath advanced through the axillary artery. The fenestrated/branched graft is then advanced until the fenestrations and branches align with their target vessels, and the graft is unsheathed. Given the presence of diameter reducing ties, the graft is not fully deployed and can be manipulated within the aorta. Through the contralateral sheath, access is obtained into the body of the fenestrated/branched endograft, and the shorter, small diameter sheath is exchanged for a larger (7 to 8 French sheath) longer (55 cm) sheath, which is advanced up to the reinforced fenestrations. Using a variety of different catheters and wires, depending on orientation of the graft, the fenestration, and the target vessel, access is obtained through the fenestration and into the target vessel (Figure 13). The corresponding sheath is advanced into the target vessel as well. This process is repeated for all the reinforced fenestrations. The marker catheters and wires are removed as each of the vessels is cannulated through the fenestration.
For the directional branches, the process involves advancing the sheath (10 Fr) from the axillary artery, over the preloaded wire, into the corresponding branch. The sheath is counter-punctured and a catheter and wire are advanced through the sheath, into the branch and into the target vessel (Figure 14). The wire is exchanged for a stiff wire, the through-and-through wire is removed, and the sheath is advanced into the target vessel. Once sheath access is obtained in the target vessels, the graft is completely deployed by releasing the constraining wire and the proximal and distal trigger wires, allowing removal of the delivery system
Angiography is performed in the target vessels prior to stenting. The reinforced fenestrations are stented with balloon-expandable covered stents (Figure 15). These are dilated to a size appropriate for the diameter of the vessel, and then it is flared proximally in the fenestration to obtain a seal. If there is significant tortuosity in the target branch, the distal landing zone of the covered stent is transitioned with the placement of a self-expanding bare metal stent in order to avoid kinking and ultimate occlusion of that branch. Directional branches are stented with self-expanding stent grafts (Figure 16). Aortography is performed to assess for patency of the branches and to assess for the presence of a proximal endoleak.
Depending upon the anatomy, a distal extension may be necessary with either a straight endograft body extension or placement of a modular bifurcated component (Figure 17). The overlap zones undergo balloon angioplasty, as do the distal seal zone. Completion angiography is performed (Figure 18). Sheaths, catheters, and wires are removed, the arteriotomies repaired using 5-0 or 6-0 prolene suture, and the wounds closed in layers.
Patients are managed in the intensive care unit (ICU) following branched endograft repair of TAAA. The duration of time in the ICU is dependent upon a number of factors including the extent of aneurysm that is repaired and the patient’s underlying co-morbidities. Depending on the length of aorta excluded, spinal drains are employed for up to 72 hours. As with any major surgery, urine output, blood pressure, and laboratory values are monitored closely. Most patients are able to eat on the first post-operative day, and they are physically mobilized as soon as possible. Most patients remain hospitalized from 4 to 7 days. Follow up imaging is mandatory to assess for the adequate exclusion of the aneurysm and to assess for continued patency of the branch vessels (Figure 19). Our protocol entails imaging with contrasted cross-sectional imaging (when renal function is not prohibitive) and duplex ultrasonography. These imaging tools are performed within 30 days of surgery, and then repeated annually. Reintervention may be necessary for the presence of an endoleak or branch vessel restenosis, but occur with a very low incidence .
1. Parodi JP, JC, Barone, HD;. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms. Annals of vascular surgery. 1991;5(6):491-499.
2. Prinssen M, Verhoeven EL, Buth J, et al. A randomized trial comparing conventional and endovascular repair of abdominal aortic aneurysms. The New England journal of medicine. Oct 14 2004;351(16):1607-1618.
3. United Kingdom ETI, Greenhalgh RM, Brown LC, et al. Endovascular versus open repair of abdominal aortic aneurysm. The New England journal of medicine. May 20 2010;362(20):1863-1871.
4. De Bruin JL, Baas AF, Buth J, et al. Long-term outcome of open or endovascular repair of abdominal aortic aneurysm. The New England journal of medicine. May 20 2010;362(20):1881-1889.
5. Lee WA, Daniels MJ, Beaver TM, Klodell CT, Raghinaru DE, Hess PJ, Jr. Late outcomes of a single-center experience of 400 consecutive thoracic endovascular aortic repairs. Circulation. Jun 28 2011;123(25):2938-2945.
6. Ullery BW, Cheung AT, Fairman RM, et al. Risk factors, outcomes, and clinical manifestations of spinal cord ischemia following thoracic endovascular aortic repair. Journal of vascular surgery. Sep 2011;54(3):677-684.
7. Greenberg RK, Sternbergh WC, 3rd, Makaroun M, et al. Intermediate results of a United States multicenter trial of fenestrated endograft repair for juxtarenal abdominal aortic aneurysms. Journal of vascular surgery. Oct 2009;50(4):730-737 e731.
8. Greenberg R, Eagleton M, Mastracci T. Branched endografts for thoracoabdominal aneurysms. The Journal of thoracic and cardiovascular surgery. Dec 2010;140(6 Suppl):S171-178.
9. Mastracci TM. Endovascular treatment of thoracoabdominal aneurysm. Current treatment options in cardiovascular medicine. Jun 2010;12(3):205-213.
10. Bub GL, Greenberg RK, Mastracci TM, et al. Perioperative cardiac events in endovascular repair of complex aortic aneurysms and association with preoperative studies. Journal of vascular surgery. Jan 2011;53(1):21-27 e21-22.
11. Eagleton MJ. Intraprocedureal imaging: flat panel detectors, rotational angiography, Fluoro CT, IVUS or still the portable C-arm? . Journal of vascular surgery. 2010;52 (4 Suppl):50S-59S.
12. Peterson BG, Matsumura JS. Internal endoconduit: an innovative technique to address unfavorable iliac artery anatomy encountered during thoracic endovascular aortic repair. Journal of vascular surgery. Feb 2008;47(2):441-445.
13. Abu-Ghaida AM, Clair DG, Greenberg RK, Srivastava S, O'Hara P J, Ouriel K. Broadening the applicability of endovascular aneurysm repair: the use of iliac conduits. Journal of vascular surgery. Jul 2002;36(1):111-117.
14. Svensson LG. Paralysis after aortic surgery: in search of lost cord function. The surgeon : journal of the Royal Colleges of Surgeons of Edinburgh and Ireland. Dec 2005;3(6):396-405.
15. Greenberg RK, Lu Q, Roselli EE, et al. Contemporary analysis of descending thoracic and thoracoabdominal aneurysm repair: a comparison of endovascular and open techniques. Circulation. Aug 19 2008;118(8):808-817.
16. Matsumura JS, Lee WA, Mitchell RS, et al. The Society for Vascular Surgery Practice Guidelines: Managment of the left subclavian artery with thoracic endovascular aortic repair. Journal of vascular surgery. 2009;50:1155-1158.
17. Chuter TA, Rapp JH, Hiramoto JS, Schneider DB, Howell B, Reilly LM. Endovascular treatment of thoracoabdominal aortic aneurysms. Journal of vascular surgery. Jan 2008;47(1):6-16.
18. Dijkstra ML, Eagleton MJ, Greenberg RK, Mastracci T, Hernandez A. Intraoperative C-arm cone-beam computed tomography in fenestrated/branched aortic endografting. Journal of vascular surgery. Mar 2011;53(3):583-590.
19. Mastracci TM, Greenberg RK, Eagleton MJ, Hernandez AV. Durability of branches in branched and fenestrated endografts. Journal of vascular surgery. Apr 2013;57(4):926-933; discussion 933.