What are the risk factors for rupture of abdominal aortic aneurysm (AAA)?

Updated: Jan 08, 2019
  • Author: Saum A Rahimi, MD, FACS; Chief Editor: Vincent Lopez Rowe, MD  more...
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Aneurysm diameter is an important risk factor for rupture. In general, AAAs gradually enlarge (0.2-0.8 mm/year) and eventually rupture. Hemodynamic factors play an important role. Areas of high stress have been found in AAAs and appear to correlate with the site of rupture. Computer-generated geometric models have demonstrated that aneurysm volume is a better predictor of areas of peak wall stress than aneurysm diameter. This may have implications for determining which AAAs require surgical repair.

AAA rupture is believed to occur when the mechanical stress acting on the wall exceeds the strength of the wall tissue. Wall tension can be calculated by applying Laplace’s law, as follows:

  • P × R/W

where P is the mean arterial pressure (MAP), R is the radius of the vessel, and W is the thickness of the vessel wall. AAA wall tension is a significant predictor of pending rupture. The actual tension in the AAA wall appears to be a more sensitive predictor of rupture than aneurysm diameter alone. For these reasons, the clinician may wish to achieve acute blood pressure control in patients with AAA and elevated blood pressure.

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