Abdominal aortic aneurysm risk factors

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Overview

The most significant modifiable risk factor for the development of an abdominal aortic aneurysm is smoking which increases the risk of aneurysm development 8 fold. Advanced age and family history are the strongest non-modifiable risk factors for the development of an abdominal aortic aneurysm. Hypercholesterolemia and hypertension are risk factors as well. Both diabetes mellitus and black race appear to be associated with a lower incidence of abdominal aortic aneurysm. An increased rate of expansion of abdominal aortic aneurysm is related to systolic hypertension, wide pulse pressure, and ongoing smoking. The risk of abdominal aortic aneurysm rupture is proportional to the size and rate of growth of the aneurysm. Abdominal aortic aneurysms greater than 5 cm diameter or those that grow faster than 1 cm per year have a significantly increased risk of rupture and are indications for elective operative repair. Advanced age, female gender, hypertension, active smoking, outpouchings, and mural thrombus are also risk factors for abdominal aortic aneurysm rupture.

Risk Factors for Abdominal Aortic Aneurysm Development

• The strongest independent acquired risk factor for AAA is smoking. In a study by Wilmink et. al , current smokers were shown to be 7.6 times more likely to have an AAA than non smokers. The longer one has smoked, the greater the risk for an AAA, but the number of cigarettes smoked per day did not seem to correlate with risk after adjusting for duration of smoking.
• Advanced age and family history are the strongest nonreversible risk factors.

  • The prevalence of abdominal aortic aneurysms among first-degree relatives of patients with abdominal aortic aneurysms ranges from 15-29%, compared with 2% among relatives of controls.

• Male sex
• Hypertension
• Known atherosclerotic disease - coronary artery disease, cerebrovascular disease, peripheral artery disease
• Hypercholesterolemia
• Chronic obstructive pulmonary disease

Cardiovascular risk factors tend to cluster in certain patients

• Men who smoke and are hypertensive have an incidence of abdominal aortic aneurysm that is 2-5 times than those of the general population
• Similarly, women over the age of 60 with cardiovascular risk factors are 2-3 times more likely to develop aneurysmal disease
• Both diabetes mellitus and black race appear to be associated with a lower incidence of abdominal aortic aneurysm.

Risk Factors for Rapid Abdominal Aortic Aneurysm Expansion

• In small AAAs (3-5.4 cm), the expansion rate appears to be proportional to the initial diameter.
• Independent of the initial diamter of the aneurysm, other factors related to rapid expansion of an abdominal aortic aneurysm are:

• Systolic hypertension
• Wide pulse pressure
• Ongoing smoking

Factors not Associated with more Rapid Expansion of Abdominal Aortic Aneurysm

C-reactive protein levels have also been found to be elevated in larger aneurysms, however do not appear to be linked to rapid expansion.

Risk Factors for Abdominal Aortic Aneurysm Rupture

The risk of rupture is proportional to the size and rate of growth of the aneurysm. Aneurysms greater than 5 cm diameter or those that grow faster than 1 cm per year have a significantly increased risk of rupture and are indications for elective operative repair. In the UK Small Aneurysm Trial, UKref2 important independent variables were identified with abdominal aortic aneurysm rupture:

• Female sex
• Increased diameter of the abdominal aortic aneurysm
• Current smoker
• Mean blood pressure
• Increased age
• Forced expiratory volume in 1 second
• Size at diagnosis is one of the best predictors of rupture.
• The risk increases substantially when the diameter exceeds 6 cm in men and 5 cm in women.
• Small aneurysms can rupture as well, and are threefold more likely to rupture in women
• Localized outpouchings seems to increase the aneurysm's vulnerability for rupture
• It has been suggested that aneurysm growth and rupture correlate with growth of the aneurysm's mural thrombus: the part of the aneurysm wall that is covered with thrombus has been shown to be thinner and showed focal anoxia, inflammation, apoptosis of the smooth muscle cells, and degraded extracellular matrix than wall segments not covered by the thrombus.