The UK small aneurysm trial

Abstract

The UK Small Aneurysm Trial showed no survival benefit of early surgery compared with surveillance and possible subsequent repair of 4.0- to 5.5-cm diameter AAAs. Using data from this trial, we found that early surgery was, in fact, cost-effective when compared with surveillance if calculated over the entire life expectancy of the population (J Vasc Surg 2000;31:217-26). This was due to a small difference in mortality rates between the two groups (7.0% per year for early surgery vs 7.4% per year for surveillance), which became significant when projected over the patients' entire lifetime, rather than the 6-year follow-up of the UK Trial. Our analysis was intended to show that a small difference in mortality rate can have a substantial impact on decision analysis, even though the clinical trial could not be powered to statistically validate this difference. However, since the mortality rates were not statistically significant between groups in the UK trial, Dr K. Craig Kent, in his thoughtful discussion of our paper, asked us to model the scenario of equal mortality rates between the groups. We have subsequently done this and, in this letter, report the impact of this different assumption on our cost-effectiveness calculation. We used the same model described previously, taking data directly from the published UK Trial.1The UK Small Aneurysm Trial Participants Mortality results for randomized controlled trial of early elective surgery or ultrasonographic surveillance for small abdominal aortic aneurysms.Lancet. 1998; 352: 1649-1655Abstract Full Text Full Text PDF PubMed Scopus (1090) Google Scholar, 2The UK Small Aneurysm Trial Participants Health service costs and quality of life for early elective surgery or ultrasonographic surveillance for small abdominal aortic aneurysms.Lancet. 1998; 352: 1656-1660Abstract Full Text Full Text PDF PubMed Scopus (121) Google Scholar However, rather than using the observed annual mortality rates (7.0% for early surgery and 7.4% for surveillance), we used an annual mortality of 7.0% for both groups. We again subtracted operative mortality from both the early surgery and surveillance groups. As before, we used operative mortality rates taken from the UK trial (5.8% for early surgery and 7.2% for surveillance) for the base case analysis. With sensitivity analysis, operative mortality was again varied across a plausible range (0%-10%); the same relative change in operative mortality was applied to both groups. Our analysis shows that with equal annual mortality rates, in the base case analysis, with an operative mortality of 5.8%, early surgery is not cost-effective (marginal cost-effectiveness ratio $90,400 per quality-adjusted life year [QALY]). However, as shown in the Figure, lower operative mortality renders early surgery cost-effective, with marginal cost-effectiveness ratios below $20,000 per QALY at operative mortality rates below 4%.Such rates are achievable in selected patients. Among US Medicare patients undergoing elective AAA repair in 1995, the 30-day mortality rate was 3.0% for ages 65 to 69, and 4.0% for ages 70 to 74. Thus, even assuming equal long-term mortality rate, our analysis again demonstrates that early surgery for small abdominal aortic aneurysms can be cost-effective, if low operative mortality can be achieved. We would like to thank Dr Kent for prompting this analysis.