Surveillance strategies according to the rate of growth of small abdominal aortic aneurysms

Abstract

The management of small abdominal aortic aneurysms (AAA) is by ultrasound surveillance. The study aimed to calculate their growth rate, identify risk factors and determine appropriate screening intervals. The local screening programme and hospital records were used to identify patients with a small (< 5.5 cm) AAA. The dates and maximum diameter of serial scans of patients with two or more scans were obtained. Patients were subdivided by 0.5 cm increments above 3.0 cm. The rate of growth was calculated by linear regression for each patient using both the absolute measurements and logarithmically (ln) transformed measurements. The 95th centile of growth rate within each subgroup was used to estimate the minimum time to grow to 5.5 cm. A total of 252 were included. The mean (± SD) AAA size on the initial scan was 3.9 (± 0.7) cm. Statin use and initial size were predictive factors for the growth rate. The median rate of growth increased according to size from 0.075 to 0.432 cm/year for AAA < 3.5 cm and > 5.0 cm, respectively. It also steadily increased for ln measurements from 0.022 (or 2.2%/year) to 0.078 or (7.8%/year). The minimum time (months) to reach 5.5 cm was 61, 17, 11 and 5 for AAA < 3.5 cm, 3.5–3.9 cm, 4.0–4.4 cm and 4.5–4.9 cm, respectively. Based on ln measurements, the times were similar at 60, 17, 10 and 4 months. In conclusion, the rate of growth increased steadily with AAA size. An aneurysm < 3.5 cm does not require a repeat scan for 5 years, while those measuring 3.5–3.9 cm and 4.0–4.4 cm require a repeat scan after 17 and 11 months.