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]

Risk Factors

• The strongest independent acquired risk factor for AAA is smoking.
• In a study by Wilmink et. al wilminkref1, 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.

• Age and family history are the strongest nonreversible risk factors.

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

Other risk factors include:

• Hypertension
• Chronic obstructive pulmonary disease
• Atherosclerotic disease in other vascular beds

  • Coronary artery disease, cerebrovascular disease, peripheral artery disease.

Rapid AAA Expansion

• In small AAAs (3-5.4 cm), the expansion rate appears to be proportional to the initial diameter.
• Other factors related to rapid expansion are:

  • Systolic hypertension
  • Wide pulse pressure
  • Ongoing smoking.

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

AAA Rupture

A ruptured AAA carries a 60 to 90% mortality before the patient reaches hospital and a 30 to 80% operative mortality for those who make it to surgery. The risk of rupture is proportional to the size and rate of growth of the aneurysm. Aneurysms greater than 5 cm diameter or that grow faster than 10 mm 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
  • AAA diameter
  • Current smoker
  • Mean blood pressure
  • 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

    • Small aneurysms 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.

Acknowledgements

The content on this page was first contributed by: C. Michael Gibson M.S., M.D. Template:WH Template:WS