When Should an Abdominal Aortic Aneurysm Be Treated?

Medical prevention of progression and rupture. Studies have assessed whether modification of risk factors can delay progression of growth of AAAs. In a small aneurysm trial in the United Kingdom, self-reported smoking status was associated with an incrementally increased growth rate of 0.4 mm per year.⁵ Each year of smoking increases the relative risk of AAA by 4%, and continued smoking leads to more rapid AAA expansion.6 There is no clear relationship between cholesterol levels and AAA expansion rate. Observational studies suggest that aneurysm expansion decreases with statin use, but there is not sufficient evidence to recommend statin therapy for AAA alone.⁶

Many patients with AAA, however, are candidates for statins because of concomitant coronary artery or peripheral vascular disease. Small, randomized controlled trials have shown that macrolides and tetracycline antibiotics might inhibit AAA growth, but prescribing them for this purpose is not currently the standard of care.⁷ Elevated mean blood pressure has been associated with rupture, but there is not good evidence showing delay of progression with treatment of hypertension.⁶ Early observational studies suggested that beta-blocker use would decrease AAA progression, but further evidence has not supported their benefit in slowing progression of size.⁸ Likewise, use of angiotensin-converting enzyme inhibitors has also shown no growth inhibition.⁷ An ongoing Cochrane review is evaluating evidence for these medical treatments of AAA.⁹

Surgical prevention of rupture. There are two surgical methods of AAA repair: open repair and endovascular aneurysm repair (EVAR). Both involve use of a prosthetic graft to prevent the aneurysm from enlarging. The EVAR procedure typically involves entry at the femoral artery, with use of catheters and guide wires to advance a graft to the desired location and anchor it in place. Because this utilizes an endovascular approach, regional rather than general anesthesia can be used.

Multiple investigators have evaluated for differences in outcomes between the two methods of surgical AAA repair. Studies have shown increased 30-day postoperative mortality with open repair, as well as significantly higher rates of postoperative cardiac, pulmonary, and renal complications. One randomized controlled study found 30-day operative mortality of 1.8% in the EVAR group and 4.3% in the open repair group.¹⁰ However, after a median six-year follow-up of patients after EVAR or open repair, there is no difference in total mortality or aneurysm-related mortality.¹⁰ Compared with open repair, the need for long-term surveillance and re-intervention post-EVAR is higher, with endoleak and graft migration the most common complications. This accounts for the loss of early survival advantage in post-EVAR patients. By two years post-operation, complication after repair with either technique is not statistically different. De Bruin et al found that six years after randomization for repair type, cumulative survival rates were 69.9% for patients after open repair and 68.9% with EVAR.¹¹

Studies also have focused on subgroups of patients with a higher operative risk and shorter life expectancy, such as the elderly.¹² A pooled analysis of 13,419 patients aged ≥80 years from six observational studies showed 8.6% immediate mortality after open repair and 2.3% after EVAR (risk difference 6.2%, 95% CI 5.4-7.0%).¹³ Pooled analysis of three longer-term studies showed similar overall survival at three years after EVAR and open repair.¹³ When EVAR is not available, open repair has acceptable short- and long-term survival in patients aged ≥80 years with an AAA at high risk of rupture.¹⁴

Screening. A Cochrane review evaluated the effect of ultrasound screening of asymptomatic AAA on mortality. In 127,891 men and 9,342 women aged 65 to 79, researchers found a significant decrease in mortality in men aged 65 to 79 who were screened (odds ratio 0.6, 95% CI 0.47-0.78) but no benefit to screening of women.15 The current U.S. Preventive Services Task Force (USPSTF) guidelines recommend one-time ultrasound-guided (USG) screening for AAA in men aged 65 to 75 who have any history of tobacco use. For men in this age group who have never smoked, the balance between benefits and harms of screening is too close for the USPSTF to make recommendations. Because of the lower prevalence in women, the USPSTF recommends against screening women for AAA.¹⁸