Treating Large/Complex Aneurysms
Techniques and technologies involving branched or fenestrated devices have emerged to offer new EVAR options.
Endovascular aneurysm repair is commonly utilized to treat infrarenal aneurysms with favorable anatomy. This technique has been proven to reduce the acute mortality from between 4.6% and 4.7% to 1.2% and 1.7%1,2 for aneurysms greater than 5 cm or 5.5 cm. This observed risk reduction is significant despite the short-term nature of the benefit and the plethora of described failure modes associated with endovascular grafts.3-11 The mortality risk reduction benefit achieved with endovascular repair of infrarenal aneurysms pales in comparison to the potential for a similar risk reduction in the setting of more proximal aortic aneurysms. The mortality associated with the conventional treatment of such aneurysms ranges from 5% to 34%,12-15 not to mention the relative frequency of major complications, such as paraplegia. Application of endovascular technologies to this patient group will change the face of aortic surgery.
The potential to eliminate the majority of open surgical aneurysm repairs (complex or simple), limit procedural mortality, and offer a treatment option to patients who have long been deemed “inoperable” is enormous. However, the simplicity of an infrarenal endoprosthesis is overshadowed by the intricacy of designing and implanting a device that will accommodate the aortic branches. Critical end organs will then depend on flow through the prosthesis, and thus, device-related complications that manifest after infrarenal aneurysm repair, such as migration16-19 or component separation,19,20 will likely be fatal if encountered after a repair that incorporates critical aortic branches. Therefore, treating aneurysms of the more proximal aorta depends on a stable infrarenal device, and requires proficiency of the interventionalist in (1) planning, (2) sizing, (3) technical issues with implantation of aortic endografts, (4) visceral or brachiocephalic stenting, and (5) in troubleshooting. Despite the obstacles for the development of such technologies, successful early- and intermediate-term results have been achieved in a number of centers using pure endovascular means to treat juxtarenal, thoracoabdominal, and arch aneurysms involving the brachiocephalic vessels.
The use of devices incorporating fixation systems (uncovered bare stents with barbs) that extend across the ostia of the renal arteries has been suggested to improve device stability,21-23 and does not appear to affect renal function. This technique is useful, but it cannot be used in the setting of an aneurysm that is not infrarenal or juxtarenal in nature. Thus, the development of a series of devices to treat aneurysms that abut or incorporate the visceral vessels was undertaken. Initially, devices with holes in the graft synchronized (based on preoperative imaging studies) to the visceral ostia, termed fenestrated grafts, allowed the incorporation of the renal arteries, and thus the endovascular treatment of juxtarenal aneurysms.24-28 The technique is accomplished by placing a balloon-expandable stent through the customized fenestration (Figure 1A), inflating the balloon to the measured diameter of the renal artery (Figure 1B), followed by overdilation or flaring with a compliant balloon to produce the desired result (Figure 1C,D).
In this manner, aneurysms that abut the renal arteries (Figure 2A) can be treated with a device that preserves renal flow bilaterally with a seal in the suprarenal aorta (Figure 2B). Experience with this device has now exceeded approximately 750 cases worldwide. More than 150 patients have been treated with this device at The Cleveland Clinic, and a multicenter trial to evaluate the overall safety and efficacy was initiated a few months ago. The trialists intend to complete the necessary number of implants by June 2005.
The addition of a ring supporting the circumference of the customized fenestration and substitution of the uncovered stent with a stent graft (Figure 3A) represents the simplest form of branch vessel grafting. In this manner, aneurysms that involve the renal arteries or all of the visceral vessels can be treated with an endovascular approach (Figure 3B). Recognize that the seal, in these cases, depends on the joint between the mating stent graft and the nitinol ring reinforcing the fenestration. To enter the intended organ, blood must traverse a right angle to enter the desired branch. This is not optimal from an engineering perspective, but is necessary when working within a small lumen.
However, if one is working within a larger lumen (an open sac), or in the setting of marked angulation, it is difficult to plan the fenestration locations and achieve a durable seal with good end-organ perfusion using a simple fenestrated system. Thus, directional branches may be used to provide a more favorable blood flow pattern. The use of such branches creates bulk, either within the device or along the outer border of the primary aortic graft. Therefore, to use such devices, an adequate luminal working area is required. A novel delivery system with wires preloaded into these directional branches greatly simplifies the system. After a device is positioned in close proximity to the desired ostia, the preloaded wire is advanced out of the device tip, and is then snared from a remote location to provide a relatively easy way to place a sheath within the desired branch and visceral vessel. When branching into an internal iliac artery, the modular mating stent graft is advanced through a sheath in the contralateral femoral artery. If all of the visceral vessels are to be incorporated, the celiac and mesenteric are mated with branch grafts in a sequential fashion from the left or right brachial, whereas the renals are treated from a femoral approach.
These techniques, using a variety of designs, have been employed in more than 35 patients at The Cleveland Clinic, with acceptable short-term results. Timothy Chuter, MD, has performed at least 20 cases at UCSF; Eric Verhoeven, MD, has completed 10 cases in Groningen, The Netherlands; Wolf Stelter, MD, has completed 29 cases in Frankfurt, Germany; and John Anderson, MD, Michael Lawrence-Brown, MD, and David Hartley, MD, have done a number of cases in Australia.
A relatively young male had bilateral common iliac aneurysms in the setting of a large juxtarenal aneurysm. The patient had undergone 15 previous abdominal surgeries, the last of which involved a large mesh implant, which subsequently became infected and was treated with long-term intravenous antibiotics. He was not believed to be a surgical candidate. His preoperative imaging demonstrated a proximal neck length of approximately 5 mm, a 5.5-cm AAA, and bilateral common iliac aneurysms >30 mm each. He had two right renal arteries (an anterior and posterior branch arising directly from the aorta), and a single left renal artery (Figure 4A). The treatment included a proximal fenestrated device designed to accommodate the SMA, the left renal artery, and both right renals (Figure 4B-D) with unilateral internal iliac embolization, and preservation of the contralateral internal iliac (Figure 5A) using a helical hypogastric design (Figure 5B) mated with a Viabahn graft to preserve the left internal iliac artery flow (Figure 5C,D).
A 67-year-old man had an aneurysm involving the posterior aspect of the visceral aortic segment, measuring just over 7 cm. Open repair was attempted on two separate occasions, both of which were aborted prior to any incisions being made due to cardiac arrhythmias (asystole) that were refractory to interventional treatment and medical therapy. The endovascular implant procedure was performed using regional anesthesia without complications (Figure 6A,B).
All of this must be accomplished within the confines of a limited aortic segment because extensive aortic coverage has been associated with an increased risk of paraplegia.29
It is quite clear that the entire aorta is within the domain of the aortic interventionalist. Today, there are no true contraindications to endovascular repair, instead it is the risk/benefit ratio of each possible treatment option that must be considered for individual patients. However, several roadblocks will slow the dissemination of this technology. First and foremost is the ability and understanding of the physicians who desire to implement these new technologies. Proficiency with image interpretation, manipulation, endovascular grafting of the infrarenal aorta, and renal and mesenteric stenting is mandatory prior to embarking on complex aortic procedures. Devices will become more complex and costly and will be mated with additional small vessel stent grafts that are in various stages of development. However, clearly, the benefit of these technologies for this patient population are marked, and thus, as physicians, we must place great emphasis on the support of these technological developments and methods by which these skills can be disseminated.
Roy K. Greenberg, MD, is Director of Endovascular Research, The Cleveland Clinic Foundation, Cleveland, Ohio. He has disclosed that he receives research funding from Boston Scientific, Cook, Guidant, Medtronic, Sulzer-Vascutek, and W. L. Gore; he is a paid consultant for Boston Scientific and Cook and receives royalties for patents licensed to Cook. Dr. Greenberg may be reached at (216) 445-5306; firstname.lastname@example.org.
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