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Do Very Fit Patients with Small AAA Benefit from Early Intervention? The Impact of Fitness on Patients Enrolled in the UK Small Aneurysm Trial

Louise C. Brown¹, Roger M. Greenhalgh¹, Janet T. Powell¹, Simon G. Thompson² on behalf of The UK Small Aneurysm Trial Participants.
¹Imperial College London, London, United Kingdom²Medical Research Council Biostatistics Unit, Cambridge, United Kingdom.
 
OBJECTIVES: 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 survival advantage. However, two trials of endovascular aneurysm repair in small AAA have started based upon speculation that a sub-group of particularly fit patients may benefit from early intervention with low operative mortality. Here we investigate whether the fittest patients from the UKSAT might have benefited from early intervention.

METHODS: A total of 1090 patients randomized into the UKSAT between 1991 and 1995 were followed for a minimum of 10 years for mortality. Baseline data were used to calculate the Customized Probability Index (CPI) which is a validated prognostic risk score for elective open AAA 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 determine if there was any difference in all-cause or AAA-related mortality between early surgery or surveillance across the fitness spectrum. Tests for interaction used CPI scores as a continuous variable but patients were also stratified into tertile groups for descriptive purposes. Hazard ratios were adjusted for age, sex and AAA diameter.

RESULTS: A total of 714 deaths (95 AAA-related) occurred in 8485 person years follow-up. The mean (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 two patients. The tests for interaction were non-significant for both all-cause (p=0.176) and AAA-related mortality (0.178). However, some benefit was found in the least fit patients where a significant survival advantage was seen in the early surgery group; adjusted hazard ratios 0.73 [95%CI 0.56-0.96] and 0.46 [95%CI 0.22-0.98] for all-cause and AAA-related mortality respectively.

CONCLUSIONS: 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.

AUTHOR DISCLOSURES: L.C. Brown, None; R.M. Greenhalgh, None; J.T. Powell, None; S.G. Thompson, None.