Growth Rates of Small Abdominal Aortic Aneurysms Correlate with Clinical Events

Abstract

Conclusions: There is a bimodal growth pattern of abdominal aortic aneurysms (AAAs). AAA-related events are associated with growth rates of at least 2 mm annually. Summary: It is well known there is variation in AAA growth rate, indicating that AAA expansion does not conform to simple mechanics of Laplace's Law. In the United Kingdom Small Aneurysm Trial, growth of AAAs ranged from −1.0 to 6.1 mm/y (Circulation 2004;110:16-21). Peripheral arterial disease and diabetes are known to be associated with slowed AAA growth and smoking with more rapid growth. Elastin peptide, a serum biomarker, appears to be associated with AAA expansion (Eur J Vasc Endovasc Surg 2008;36:273-80). Expansion associations with hypercholesterolemia, sex, and hypertension are less clear, whereas doxycycline, statins, and angiotensin-converting enzyme inhibitors may slow AAA growth. Some have demonstrated an association between increased AAA growth and rupture (J Vasc Surg 2003;37:280-4), whereas others have been unable to demonstrate such a relationship (J Vasc Surg 2002;35:666-71). In this report, the authors examine patterns of AAA growth and the relationship between aneurysm growth and specific risk factors (mean arterial pressure, history of hypertension, hypercholesterolemia, diabetes, smoking, ischemic heart disease, and sex) and aneurysm-related events (surgery or death). From 1984 to 2007, data for 1649 individuals with AAAs were collected prospectively in the Chichester AAA screening program. Data included serial aortic size measurements, blood pressure, risk factors for arterial disease, and medications. The authors adjusted growth rates for risk factor confounders using flexible hierarchical modeling. AAA growth distribution was analyzed using Silverman's test of multimodality. There were 1231 individuals with more than one scan over a surveillance interval of at least 3 months. AAAs demonstrated a bimodal growth pattern, with nearly 50% of all AAAs never progressing to surgery or rupture. Adjusted AAA growth rates >2 mm annually predicted AAA related events (surgery or death). Comment: Many believe the natural history of AAAs is inevitable progressive dilatation until rupture occurs or the patient dies from other causes. The data, however, indicate only 27.2% of monitored AAAs end up requiring repair, and patterns of expansion may relate to clinical events. This information, along with more sophisticated models of stress points on the AAA wall, may eventually allow better selection of patients for AAA repair. Perhaps someday there will be a cohort of patients, even with relatively large AAAs, that can be safely observed. Such knowledge would result in increased peace of mind for the patient and the physician as well as savings for the health care system.