ENDOVASCULAR AORTIC REPAIR

Endovascular surgery is one of the most exciting developments in the treatment of peripheral vascular disease and has the potential to revolutionize current treatment modalities for aortic aneurysm, aortic dissection, and traumatic aortic injury. The use of endoluminal grafts to treat peripheral arterial disease began experimentally in the late 1960s.^[419] The feasibility of this technique for the treatment of abdominal aortic aneurysm was established experimentally some 2 decades later.^[420] In 1991, Parodi and colleagues^[421] reported the first clinical use of the technique in five patients with abdominal aortic aneurysm. They described the transfemoral endoluminal placement of custom-fabricated, aorto-aortic (tube) grafts composed of balloon-expandable stents and a Dacron graft. The technique was satisfactory in three of the five patients. Additional experimental^[422] and clinical reports^[423] continued to demonstrate the feasibility of this innovative endoluminal technique.

Over the past decade, there has been an explosive increase in the use of endoluminal devices to treat aortic disease. This approach can be undertaken without the large incisions, extensive dissections, prolonged aortic cross-clamp times, and significant blood loss and fluid shifts associated with open aortic repair. Endovascular aortic repair is associated with greater hemodynamic stability,^[424] a reduced stress response,^[425] shorter postoperative length of stay,^[426] and improved analgesic control ^[427] compared with open aortic repair. Controlled clinical trials have demonstrated that endovascular aortic aneurysm repair is feasible, safe, and may reduce perioperative morbidity compared with open repair.^{[428] [429] [430]} However, long-term durability has not been established.

The FDA approved the use of two endovascular stent-graft devices in the United States in 1999, with a 5-year surveillance requirement. This surveillance requirement has been extended to the full life of the patient because of reported cases of aneurysm rupture and death.^[431] FDA approval was granted without the usual requirement for a randomized controlled trial. Instead, the FDA allowed a concurrent "matched" group of patients to serve as a control group. Two additional stent-graft devices have received regulatory approval, and several more will likely be approved in the near future. One of the two devices approved for use in 1999 was withdrawn from clinical use in 2003 because of difficulties associated with delivery and deployment. Since regulatory device approval, a rapid increase in endovascular abdominal aortic aneurysm repair has occurred nationwide.^[432] The interest in endoluminal aortic grafting has been expanded to include the thoracic and thoracoabdominal aorta.^{[433] [434]} As experience with endoluminal stent-graft systems and endoluminal techniques increases, along with continued device refinement, this approach will likely be applied to more patients with increasing complex aortic disease.^[435] Endovascular grafting has emerged as a viable alternative to open repair of aortic rupture^[436] and complex aortoiliac occlusive disease. ^[437]

Endovascular Technique

The arterial access site for endovascular stent-graft placement is selected on the basis of vessel size and degree of obstructing atherosclerotic disease. The technique most commonly requires bilateral transverse groin incisions to expose the common femoral arteries. In patients with severely diseased femoral or iliac arteries, balloon angioplasty or local endarterectomy can be performed to allow passage of the delivery system. Adjunctive retroperitoneal procedures may be necessary in up to 20% of patients during endovascular abdominal aortic aneurysm repair.^[438] Indications include small external iliac arteries that limit femoral access and concomitant iliac artery aneurysm that precludes distal fixation of the stent-graft in the common iliac artery. In these cases, a transverse

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Although adjunctive surgical procedures may be needed, the technical skill required for endovascular aortic surgery is primarily catheter based. Appropriately trained cardiologists, radiologists, and vascular surgeons can all deliver endovascular treatment of aortic disease. A multispecialty approach is commonly used and offers patients the expertise of surgical and catheter-based specialists. Although no standard has been set, the requirements for endovascular aortic surgery are the same wherever it is performed. The standard operating room environment is ideal from the surgical and anesthesia standpoints, particularly with regard to conversion to an open repair. The operating room must be equipped with endovascular supplies, portable radiologic imaging tools, and an angiographic table. Angiographic suites often have superior radiographic imaging tools and angiographic tables and are better equipped to deal with ionizing radiation. The superior imaging may reduce radiation exposure and decrease contrast dye loads. In an effort to provide an optimized environment for multispecialty endovascular intervention, many centers are constructing sophisticated operative angiographic suites in or adjacent to the operating room.

Endovascular stent-grafting of the aorta requires preoperative radiologic evaluation to precisely delineate the aortic anatomy. For abdominal aortic aneurysm, length and diameter of the proximal neck, location of important aortic and iliac side branches (i.e., accessory renal arteries, inferior mesenteric artery, and hypogastric arteries), and distal fixation site characteristics must be determined. Significant aneurysm neck angulation, short neck length, large neck diameter, and severe aortic calcification currently exclude many patients from endovascular repair. ^[441] Newer devices incorporating suprarenal proximal fixation^[442] and improved graft design may overcome these exclusions. Stent-grafts with fenestrations to preserve aortic side branch perfusion are one of the most promising design improvements.^[443] Endovascular stent-graft repair of other aortic disease, such as aortic dissection, traumatic aortic disruption, and thoracic and thoracoabdominal aneurysm, also requires precise radiologic delineation of aortic anatomy. TEE and intravascular ultrasound scanning are often used to locate entry and exit sites of dissections and to confirm precise stent-graft placement.^[444]

Endovascular stent-grafts are often custom made for each patient based on aortic anatomy. Each endovascular stent-graft delivery device has a unique method of deployment, and many individual variations of technique are possible. First-generation endografts were not fully stented and required balloon-expansion of the proximal portion at the time of deployment. Metal hooks in the proximal portion were embedded into the aortic wall with balloon inflation, which resulted in complete aortic occlusion, not unlike aortic cross-clamping. These unsupported endografts were prone to complications such as migration and kinking. Distal migration during proximal endograft deployment was particularly troublesome with intrathoracic endograft placement. Induced hypotension,^[445] adenosine-induced asystole,^[446] and induced ventricular fibrillation ^[447] have all been used successfully to reduce endograft migration during deployment. Current-generation endografts are fully stented (i.e., stent-grafts) and self-expanding. Balloon-expansion is not required at the time of deployment. Stent-graft migration at the time of deployment is largely prevented and associated complications are reduced. A unique trilobed aortic balloon can be used to expand the stent-graft for aortic apposition after deployment without complete aortic occlusion.^[433] Although rarely necessary, mild induced hypotension (using nitroglycerin or sodium nitroprusside) can be used selectively during stent-graft deployment.