Endoluminal Treatment of AAA

Endovascular repair of abdominal aortic aneurysms (AAA) is performed at OHSU by a multidisciplinary team, some of whom have 10 years of experience with these devices. The team, comprised of interventional radiologists and vascular surgeons, have a collective experience with over 500 endograft procedures.

Endovascular repair of infra-renal AAA with stent-grafts is an alternative to surgical repair. Aortic stent-grafts are available in 3 basic configurations. [Fig 1] Patients must meet anatomic criteria involving the proximal and distal attachment sites, angulation and tortuousity of the aorta and pelvis, and the presence of calcification and occlusive disease in the access arteries. The specific requirements vary for each manufacturer. The majority of devices are modular in construction; i.e the endograft is assembled in the patient. The materials used in construction of endografts are bio-compatible metals such as nitinol, stainless steel, and elgiloy, and proven vascular graft materials. Endografts function by depressurizing the aneurysm sac. Two critical differences from surgery are the absence of sutured anastomoses to blood vessels, and the continued patency of branch vessels from the sac such as lumbar arteries and the inferior mesenteric artery. Most patients treated with current devices receive bifurcated endografts. In general, only ½ to 2/3rds of patients with AAA amenable to surgery can be managed with current endografts. Up to 1/3rd of these patients required pre-implantation embolization of an internal iliac or accessory renal artery, or other percutaneous intervention in order to become anatomically suitable for an endograft. As many as 30% of patients who undergo internal iliac artery embolization develop transient buttock claudication.

Fig.1 a) Bifurcated extending into either the common or external iliac arteries. This is the most common type of endograft. b) Aorto-unilateral iliac (AUNI) graft with surgical femoral-femoral bypass. This type is used when the patient’s anatomy is not suited to a bifurcated graft. c) Tube graft. This is rarely used due to the lack of adequate distal landing zones in the aorta below the aneurysm. (Reproduced with permission from Kaufman JA, Geller SC, Brewster DC, et al. Endovascular repair of abdominal aortic aneurysms: current status and future directions. Am J Roentgenol 2000; 175:289-302)

The exact technique of endograft placement varies with each device, but certain commonalities exist. Most important is careful pre-procedural planning, especially device selection, as none are retrievable. For most manufacturers, the diameters of the device at the attachment sites should be at least 10-15% greater than the artery. Excellent intra-procedural imaging is mandatory. Precise localization of critical branch vessels such as the renal and internal iliac arteries prevents inadvertent occlusion by graft overlay. In general, an aortogram is obtained centered on the renal arteries, followed by deployment of the proximal portion of the device. Once this has been accomplished, the distal portion is deployed after localization of the internal iliac arteries. Most modular bifurcated devices require catheterization of at least on limb, usually from the opposite common femoral artery, to complete construction of the endograft. The device delivery systems range in size from 4 to 8 mm in diameter. Large diameter introduction systems require surgical exposure of the common femoral arteries.

Placement of endografts is successful in more than 95% of attempts, provided patients are carefully selected. In approximately 15-30% of patients additional endovascular procedures are necessary to improve the technical and clinical success of the procedure. The major complication rate is less than 5%, with most complications related to the vascular access. Patients usually are discharged home by the 2nd or 3rd post-procedure day.

Continued opacification of the aneurysm sac by contrast following endograft placement (termed “endoleak”) is found on CT scans in 30-40% of patients acutely, and 20-40% during follow-up. [Fig 2] This finding correlates with sub- or systemic pressures in the aneurysm sac. The etiology of the majority of early and late sac perfusion is Type II, although Types I and III can occur at any time. Type IV perfusion generally resolves spontaneously within 48 hours of endograft placement. Many endoleaks can be treated with percutaneous methods, such as insertion of endograft extensions for Type I leaks, embolization of branch vessels or the sac for Type II leaks, insertion of endograft “patches” for type III leaks.

	Fig.2)

The most important outcome of endografts is freedom from AAA rupture. Delayed rupture is reported in fewer than 0.1% of patients. Most patients have stabilization or decrease in the volume of the aneurysm sac. However, continued sac growth is seen at least 5% of patients. Shrinkage of the peri-aneurysmal fibrosis after endograft placement has been reported in patients with inflammatory aneurysms.

Plain films as well as CT scans (or some other reproducible imaging technique) are essential parts of the follow-up of these patients. Patients must be studied at regular intervals for the remainder of their lives after endograft placement. As the AAA sac decreases in volume, the endograft may become distorted, with limb kinking, separation, and even disengagement from attachment sites. The incidence of complications is increasing as longer follow-up is accumulated. The future role of endografts for AAA remains to be determined as these late outcomes become known.

Link to article: A Northwest First: Aortic Aneurysm Pressure Sensors Implanted (May 4, 2006)