LEARNING FROM THE LAST ULTRASOUND - A POPULATION-BASED STUDY OF PATIENTS WITH ABDOMINAL AORTIC-ANEURYSM

Background: Patients with abdominal aortic aneurysm often are followed up with serial ultrasound examinations, but published studies usually describe rupture risk according to the diameter of the abdominal aort ic aneurysm at diagnosis rather than by most recent ultrasound. Inform ation in this form is misleading when used to predict prognosis. Metho ds: We used data from the population-based cohort of residents of Roch ester, Minn, diagnosed as having abdominal aortic aneurysm who have ha d at least 1 ultrasound measurement. Of the 181 patients who were enro lled in this cohort between January 1, 1974, and December 31, 1988, 5 had clinical evidence of rupture at entry. Analysis of a cohort define d by size category at ''last ultrasound'' was undertaken to assess rup ture risk and growth rate. Results: Median overall aneurysmal growth r ate was 0.21 cm/y. Initial growth rate did not correlate with subseque nt growth rate (r=0.18; P=.14) or with initial size (r=-0.12; P=.22). Only 1 aneurysm ruptured when last ultrasound was less than 5 cm, and this occurred 3 1/2 years after this ultrasound. Estimated rupture ris k by last ultrasound was 0% per year (95% confidence interval [CI], 0% -5%) when less than 4.00 cm, 1.0% per year (95% CI, 0%-5%) when 4.00 t o 4.99 cm, and 11% per year (95% CI, 1%-21%) when 5.00 to 5.99 cm. Con clusions: The most clinically useful approach to estimating the risk o f abdominal aortic aneurysm rupture is according to size at last ultra sound. Aneurysm growth rate is predicted neither by size nor by initia l growth rate.