Optimum Treatment

Management guidelines center on evaluation of rupture risk. When the risk of rupture exceeds the risk of surgical repair, replacement of the artery’s aneurysmal segment is indicated. For an asymptomatic AAA, the risk of rupture varies with the diameter of the aneurysm; an AAA of 5 cm has a 5% rupture risk per year, and an AAA of 6 cm has an estimated 10% to 15% rupture risk per year. Patients with saccular aneurysms, chronic obstructive pulmonary disease, or hypertension are thought to have a higher than average risk of aneurysm rupture. Treatment is indicated for aneurysms that are greater than twice the normal artery diameter, that are enlarging rapidly (>0.5 cm in 6 months), or that are symptomatic—the major symptoms being pain or evidence of distal emboli potentially related to the aneurysm.

The number of patients in the United States with the diagnosis of an rAAA has declined in recent years from 23.2 to 12.8 per 100,000 Medicare beneficiaries (P < 0.0001), as did repairs of rAAAs (15.6 to 8.4 per 100,000; P < 0.0001). These data reflect increased surveillance for AAAs and the increased use of endovascular aneurysm repair. With the increasing number of endovascular aneurysm repairs (EVARs), the threshold for intervention based on size has become more controversial. Some evidence suggests that observation of AAAs smaller than 5.5 cm is the proper course, whereas other observers believe that EVAR should be offered to patients earlier in the course of their disease. This question is being addressed in a large randomized study that, when complete, should provide much-needed direction on when to intervene in patients with AAAs.

During the past 50 years the surgical technique for AAA repair has remained essentially unchanged, with outcome improvements resulting from advances in preoperative screening and risk stratification, improved anesthetic practice, and intensive care management. Notably, however, the use of more durable synthetic grafts in recent years (rather than using homografts for AAA repair; Fig. 49-2, upper) has also contributed to the improved long-term outcome following AAA repair. Aneurysmorrhaphy involves mobilization and exposure of the aneurysm and the normal artery above and below the diseased section. Blood flow through the artery is arrested for inline replacement of the diseased artery with an artificial one, resulting in major cardiovascular stress during the procedure and for several days after. The combination of cardiovascular stress and the advanced age and comorbid conditions of the patient increases the procedure-associated morbidity and mortality rates. Patients usually require 7 to 10 days of hospitalization and 6 to 8 weeks to recover. However, once patients fully recover from the procedure, long-term follow-up indicates that few patients need further intervention. When further intervention is needed, generally it is because progression of the disease has occurred in adjacent arteries. Ongoing research focuses on the identification of mechanisms to arrest the disease process to prevent spread and inhibit the inflammatory process.

Figure 49-2 Surgical management of aortic aneurysms.

As general medical care and nutrition have improved, the mean age in the United States and industrialized countries has increased, and with this there is an increasing number of individuals with AAAs. As the age and medical comorbidities of patients with an AAA increased, so did the interest in less-invasive procedures for treatment, resulting in the development of minimally invasive techniques for the treatment of aneurysmal disease. AAA endovascular repair techniques involve the insertion of a new lining into the diseased artery with the use of hooks or stents to secure the lining to the arterial wall. Four devices are approved by the U.S. Food and Drug Administration for the treatment of infrarenal AAAs. The indications for treatment with endovascular devices are identical to those for open surgical repair. The procedure can be performed under local, regional, or general anesthesia, and typically involves exposure of the common femoral arteries for device insertion. Although insertion has been accomplished with percutaneous techniques, most devices are too large for insertion by routine percutaneous treatment methods. Once the aorta is accessed, imaging methods guide device implantation just below the renal arteries, where the aorta and its endothelium are the healthiest. Most patients are hospitalized for 1 day and are fully recovered from the procedure within 1 week. Successful implantation is accomplished in more than 98% of patients.

Patient selection is crucial to outcomes with EVAR. Seal failures (endoleak) are more likely to occur in patients with short, angled, or diseased proximal infrarenal arteries. During follow-up, complications associated with endoleaks or migration develop in 6% to 15% of patients. Many of these complications can be treated with secondary endovascular interventions and do not necessitate conversion to open repair and removal of the device. Iliac artery access issues (smaller or diseased arteries) may also create complications associated with implantation. Although new design techniques and lower profile devices have overcome many of these problems, complications occur in 1% to 2% of patients.

Prospective studies have not shown a reduction in the mortality rate associated with EVAR procedures compared to open surgery, but taken as a whole these studies show the rate of major morbidity is significantly lower (by ~50%) following EVAR. Blood loss and time required to return to an active lifestyle are also significantly reduced. Interim data also suggest that patient survival is greater after EVAR than after traditional open surgical treatment, and this has resulted in the increased use of this approach. Notably, a report from the Agency for Healthcare Research and Quality states that EVAR did not improve longer term overall survival or health status and was associated with greater complications, need for reintervention, long-term monitoring, and costs.

In 2008, approximately 50% of AAAs were treated with endovascular therapy. As branched designs and other innovations are incorporated and durability concerns are addressed, the use of EVAR technology will most likely increase.

Avoiding Treatment Errors

With both the endovascular and open approaches, the anatomy of the aneurysm must be determined. This includes proximity to the renal arteries as well as the angulation of the neck of the aneurysm and the status of the inferior mesenteric artery. Failure to revascularize the inferior mesenteric artery may result in postoperative visceral ischemia, whereas graft impingement on the renal arteries may result in renal failure. Placement of an endograft in a patient with a severely angulated neck can be associated with a type I endoleak.

Optimum Treatment

As is the case for surgical repair of infrarenal disease, surgical repair of thoracic aneurysms usually requires replacement of the diseased artery. However, the risks associated with surgical repair of thoracic and thoracoabdominal aneurysms are significantly higher than those of AAA repair. One major risk associated with thoracoabdominal aneurysm repair is paraplegia, because perfusion to the spinal cord must be interrupted during the repair. Several approaches have been developed to limit the amount of ischemia, including the use of barbiturates, hypothermia, and spinal cord drainage to increase perfusion pressure via collaterals. Even with these protective approaches, for extensive aneurysms involving the area from the left subclavian artery to the aortic bifurcation, the risk of paraplegia is as high as 25%. For small aneurysms involving a short section of the aorta, the risk of paraplegia is not negligible (2% to 8%). Because of the high risk, treatment is delayed until the risk of rupture is greater than the risk of repair, typically when an aneurysm is 6 cm in diameter (Fig. 49-2, lower). Individuals with Marfan’s disease or other collagen vascular diseases represent an important subset in whom the risk of dissection and/or rupture is increased even at smaller aneurysm diameters, requiring earlier surgical intervention.

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