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Management of Small Abdominal Aortic Aneurysms
The introduction and propagation of screening programs for abdominal aortic aneurysm and the more frequent application of cross-sectional imaging has resulted in an increased detection of small-diameter abdominal aortic aneurysms (AAAs). Consequently, the management of these small aneurysms is becoming increasingly relevant in contemporary clinical practice. Recent large screening studies and randomized clinical trials of management of small AAA have improved our knowledge of this topic and informed our management of these patients.
Rupture Risk
The first step in decision making in a patient with an asymptomatic AAA is to estimate the risk of aneurysm rupture. Of the factors known to increase rupture risk, diameter is the most prominent and most useful. AAAs with diameters ranging from 3 to 4 cm have an annual rupture risk of 0%; 4 to 5 cm, 1%; 5 to 6 cm, 1% to 11%; 6 to 7 cm, 10% to 22%; and more than 7 cm, 30% to 33%. The wide range of these estimates reflects variation among patients as well as imprecise data. Observational studies can rarely analyze risk of aneurysm rupture because most AAAs are repaired when they are still intact.
Because not all AAAs rupture at the same diameter, other factors are clearly involved. Factors known to increase rupture risk include rapid expansion, eccentric aneurysm shape, female gender, smoking hypertension, and chronic obstructive pulmonary disease (COPD). Peak wall stress was described to be higher in patients who required subsequent emergency AAA repair and predicted rupture risk at diameters less than 5.5 cm, which demonstrates its potential usefulness in smaller AAAs. At any given diameter, AAAs in women are more likely to rupture than those in men, likely due in part to the smaller initial size of aortas in women. Unfortunately, there is no accurate algorithm that incorporates all of these factors to estimate rupture risk for an individual patient.
Life Expectancy
If AAA rupture risk is average or high, the next step in decision making should be to estimate the patient’s life expectancy. Thus a knowledge of life expectancy by age, sex, and race for patients with AAA becomes important ( Table 1 ). Patients with a short life expectancy as a result of comorbid conditions are less likely to benefit from AAA repair unless the risk of AAA rupture is very high. AAA patients often have multiple comorbid diseases such as coronary artery disease (CAD) and hypertension. Therefore, the late survival rate for patients after elective AAA repair is significantly less than age-matched and sex-matched patients without AAAs (60% versus 79% at 6 years).
TABLE 1
Life Expectancy in Years for Patients with Abdominal Aortic Aneurysms
Adapted from U.S. National Center for Health Statistics: National Vital Statistics Reports (NVSR). Deaths: Final Data for 2007, Vol. 58, No. 19, May 2010.
| NORMAL POPULATION | AAA PATIENTS | |||||||
|---|---|---|---|---|---|---|---|---|
| Male | Female | Male | Female | |||||
| Age (yr) | White | Black | White | Black | White | Black | White | Black |
| 60 | 21.0 | 18.3 | 24.0 | 22.4 | 17.8 | 15.5 | 20.0 | 18.7 |
| 65 | 17.3 | 15.2 | 19.9 | 18.7 | 14.7 | 12.9 | 16.6 | 15.6 |
| 70 | 13.8 | 12.4 | 16.0 | 15.2 | 11.7 | 10.5 | 13.3 | 12.7 |
| 75 | 10.6 | 9.9 | 12.4 | 12.1 | 9.0 | 8.4 | 10.3 | 10.1 |
| 80 | 7.9 | 7.7 | 9.3 | 9.4 | 6.7 | 6.5 | 7.7 | 7.8 |
| 85 | 5.7 | 6.0 | 6.8 | 7.1 | 4.8 | 5.1 | 5.7 | 5.9 |
| 90 | 4.1 | 4.6 | 4.8 | 5.3 | 3.5 | 3.9 | 4.0 | 4.4 |
| 95 | 2.9 | 3.5 | 3.3 | 3.9 | 2.5 | 3.0 | 2.7 | 3.2 |
| 100 | 2.0 | 2.6 | 2.2 | 2.8 | 1.7 | 2.2 | 1.8 | 2.3 |
AAA , Abdominal aortic aneurysm.
In the United Kingdom Small Aneurysm Trial (UKSAT), it was shown that during a mean of 8 years’ surveillance of small AAA, 38% of patients died from non-AAA–related causes, before their AAA reached 5.5 cm, expanded rapidly, or became tender. Estimates of life expectancies for individual patients must be refined by an assessment of their overall health, especially for factors that have substantial influence such as malignancies. In general, the lower the rupture risk, the longer the life expectancy should be to justify AAA repair. Patients with short life expectancies are best managed conservatively unless the risk of rupture is very high.
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