The natural history of abdominal aortic aneurysm.

There is now sufficient published evidence to describe with confidence much but not all of the natural history of AAA. AAA of 4.0-5.5 cm in diameter have a rupture rate of 0.7-1.0% per year and for AAA < 4.0 cm this rate is even lower. Women appear to have a higher rupture rate than men for small AAA, but there is no evidence of this for AAA > 5.5 cm. Median enlargement rate of AAA 4.0-5.5 cm is about 0.3 cm per year. Enlargement rate is influenced by AAA diameter, being approximately half this rate for AAA 3.0-4.0 cm and half again faster for AAA > 5.5 cm. There is, however, considerable individual variability in enlargement rates and a variety of diseases and conditions appear to influence these rates. Rupture rates of AAA > 5.5 cm in fit individuals are unknown and unlikely to be known in the future. However, for unfit individuals with AAA > 5.5 cm, the rupture rate is high, starting at about 10% per year and increasing by several fold in the largest AAA. The search is on for drugs to favorably alter this natural history, and if successful, will doubtless shed much light on the pathophysiology of AAA enlargement.