Introduction to Abdominal Aortic Aneurysm

Complications of Abdominal Aortic Aneurysm

The most serious and life threatening complication of abdominal aortic aneurysm (AAA) is rupture of the aneurysm which results in profuse internal bleeding. Rupture of an AAA is a serious medical emergency and is associated with a high mortality rate. Massive bleeding from a ruptured abdominal aortic aneurysm into the abdominal cavity can lead to cardiovascular collapse and shock. A ruptured abdominal aortic aneurysm is an acute medical emergency and must be diagnosed and treated urgently to improve the patient's chances of survival.

Approximately 15,000 people die each year in the United States from ruptured abdominal aortic aneurysms and some researchers estimate that the number may be even higher. Up to 15% of people may survive a ruptured aneurysm but their mortality risk increases since only 50% survive the surgical repair.

Risk factors that have been associated with rupture of abdominal aortic aneurysm include:

• AAA Size - The single most important factor that consistently correlates with the risk of rupture of an AAA is its size (diameter and length). The risk of rupture increases with increasing size of AAA and is significantly higher when the aneurysm reaches an average of 5.0 - 5.5 cm. and approaches 6 cm. According to the Joint Council of the American Association for Vascular Surgery (JCAAVS), the most accurate predictor of risk for aneurysmal rupture is the size of the aneurysm. The approximate risk of rupture for AAAs based on size of the aneurysm is as follows:

  • 0% risk below 4 cm. diameter
  • 0.5% - 5% for 4 - 5 cm. diameter
  • 3% - 15% for 5 - 6 cm. diameter
  • 10% - 20% for 6 - 7 cm. diameter
  • 20% - 40% for 7 - 8 cm. diameter
  • 30% - 50% for diameter above 8 cm.

• Female gender

• Current smoker

• Cardiovascular disease

• Chronic Obstructive Pulmonary Disease (COPD)

• Hypertension

• Stroke

• Positive family history of AAA

• Rapid expansion of the diameter of an aneuryms - defined as more than 1cm. per year. Some clinicians use this measure as the basis of decision regarding elective repair of small AAAs (less than 5 cm.). Rapid expansion is thought to be associated with smoking and advanced age.

• Ratio of diameter of the AAA to the normal diameter of the individual's aorta immediately above (proximal) the neck of the aneurysm. There is continued debate regarding the validity or usefulness of this measure.

• Shape of the aneurysm - some surgeons believe that rupture is related to stress on the wall of the artery. Saccular-shaped aneurysms because of their asymmetric shape, exert greater stress on the arterial wall and are, therefore, more likely to rupture.

• Presence of outpouchings in the aneurysm indicates thinning in the arterial wall and this is thought by some researchers to raise the risk of rupture by up to 70%.

• The presence of a thrombus (blood clot) may raise the risk of rupture.

When all these factors are taken into consideration, the risk of rupture of an abdominal aortic aneurysm is determined to be low, average, or high. The JCAAVS notes that for patients with an abdominal aortic aneurysm between the sizes of 4.0 and 5.5, the relative risk of rupture is increased with the following factors:

• Female gender
• Larger diameter at diagnosis
• Current smoker
• Severe COPD

The Joint Council of the American Association for Vascular Surgery (JCAAVS) and Society for Vascular Surgery notes that the risk of rupture of an abdominal aortic aneurysm is substantially increased when the diameter increases from 5 cm. to 6 cm. They recommended that a diameter 5.5 cm. be considered as the threshold for elective surgical repair in the average patient. It should be noted, however, that each individual should be evaluated for relative risk based on factors outlined above as well as body habitus (e.g., for women 4.5 cm. - 5 cm. should be considered as the cutoff whereas for large men, the cutoff may be close to 6 cm.).

In addition to the risk of rupture, other complications of an abdominal aortic aneurysm may include:

• Aortic Dissection - the lining of the artery tears and blood leaks into the wall of the artery

• Hypovolemic shock (decrease in the volume of circulating blood as a result of hemorrhage).

• Arterial embolism - obstruction or occlusion of a vessel by a blood clot.

• Insufficient circulation past the aneurysm leading to intermittent claudication (lameness due to pain in leg muscles because the blood supply is inadequate).

• Kidney damage

• Myocardial infarction (heart attack)

• Stroke