Fit patients with small abdominal aortic aneurysms (AAAs) do not benefit from early intervention

Abstract

The UK Small Aneurysm Trial (UKSAT) and the American Aneurysm Detection and Management (ADAM) trial both concluded that early elective open surgery does not confer any late survival advantage in patients with small abdominal aortic aneurysm (AAA) with diameter 4.0 to 5.5 cm. However, two trials of endovascular aneurysm repair in small AAA have started based upon speculation that a sub-group of particularly fit patients, with low operative mortality, may benefit from early intervention. Here we investigate whether the fittest patients from the UKSAT might have benefited from early intervention. A total of 1090 patients randomized into the UKSAT between 1991 and 1995 were followed for an average of 12 years for mortality. Baseline data were used to calculate the Customized Probability Index (CPI), a validated prognostic risk score for operative mortality after elective open aneurysm repair that assigns risk points for history of cardiac, pulmonary, and renal disease and subtracts risk points for use of statins and beta-blockers. Cox regression was used to assess any differences in all-cause or aneurysm-related mortality between policies of early surgery or surveillance across the fitness spectrum. Tests for interaction used CPI scores as a continuous variable but patients also were stratified into tertile groups for descriptive purposes. Hazard ratios were adjusted for age, gender, and aneurysm diameter. A total of 714 deaths (95 aneurysm-related) occurred in 8485 person-years (number of patients multiplied by average years of conditional follow-up). The mean (standard deviation [SD]) CPI score was 8.1 (9.9) with similar scores between randomized groups. The tertile groups had mean (SD) scores of -1.8 (3.7) for the 389 fittest patients, 8.8 (3.3) for the 438 moderately fit, 21.4 (6.6) for the 261 least fit with missing scores in 2 patients. The tests for interaction were non-significant for both all-cause (P = .176) and aneurysm-related mortality (.178). However, for the least fit patients a survival advantage was seen in the early surgery group; adjusted hazard ratios 0.73 (95% confidence interval [CI] 0.56-0.96) and 0.46 (95% CI 0.22-0.98) for all-cause and aneurysm-related mortality respectively. Early elective surgery did not confer any survival benefit in the fittest patients. On the contrary, the possibility of a survival benefit from early intervention in patients of poor fitness merits further investigation through meta-analysis or validation in other prospective studies.