Abdominal aortic aneurysms are usually asymptomatic until they rupture, at which time they are generally fatal. Unfortunately, most aneurysms are not detected, but in the United Kingdom as many as 3 percent of men older than 60 years are estimated to have small aneurysms (4.0 to 5.9 cm in diameter). Elective surgery is usually advised to repair large aneurysms (6.0 cm or greater) because emergency repair of a ruptured aneurysm has a 30-day mortality rate of 40 to 50 percent, while the mortality rate associated with elective surgery is only 5 to 6 percent. However, there is no consensus on the optimal management of smaller occult aneurysms. The UK Small Aneurysm Trial evaluated elective surgery of small asymptomatic aneurysms to find out if it decreased long-term mortality compared with use of regular ultrasound surveillance (US).
A total of 1,276 otherwise healthy patients between 60 and 75 years of age with small occult abdominal aortic aneurysms were eligible for the four-year study. Patients with aneurysms 4.0 to 4.9 cm in diameter were reviewed every six months, and those with larger lesions were evaluated every three months. Surgical repair was recommended to the patient if the aneurysm exceeded 5.5 cm, if the growth rate exceeded 1 cm per year, if the aneurysm became tender or if other symptoms developed. On average, patients in the study were followed for more than four years.
Of the 1,090 patients who were enrolled in the study, 563 were randomized to receive early surgical intervention and 527 were assigned to surveillance. Of the 563 patients in the surgery group, 452 had surgery within five months of randomization. Of the 527 patients assigned to surveillance, 489 followed the study protocol for surgery. Mortality did not differ between the two groups at two, four or six years, even after adjustment for age, sex or initial size of the aneurysm. After six years, 150 patients in the surveillance group had died and 159 in the surgery group had died. The 30-day mortality rate following surgery was 5.8 percent in the surgery group, compared with 7.1 percent in the surveillance group. Seventeen patients in the surveillance group died from a ruptured abdominal aortic aneurysm, compared with six in the surgery group.
The authors conclude that early surgery does not confer a significant long-term survival advantage in patients with small asymptomatic aortic aneurysms. Use of ultrasonographic surveillance provides a safe alternative for management of this condition. The results of this trial affect screening of patients with small aneurysms. Those with aneurysms smaller than 5.5 cm should be advised to stop smoking and to undergo ultrasonographic surveillance until such a time as surgery is warranted.