Thresholds for Abdominal Aortic Aneurysm Repair in England and the United States

Posted by • November 23rd, 2016

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Imagine you are assessing a relatively healthy 85-year-old man who was brought to the hospital after a fall at home. Due to concern for spinal fractures, he underwent CT scans of his head, C-spine, chest, abdomen, and pelvis. Although no traumatic injuries were found, an incidental finding of a 5.5 cm infrarenal abdominal aortic aneurysm (AAA) was noted on the CT scan of the abdomen. The patient is asymptomatic from this aneurysm with no complaints of abdominal pain, back pain, or syncopal episodes. Should he undergo aneurysm repair? Can you watch and wait? Is he at risk for aneurysm rupture if you don’t intervene?

International guidelines recommend aneurysm repair once aneurysm diameter exceeds 5.5 cm for men and 5.0 cm for women. However, these guidelines are not applied universally and there is still uncertainty about the ideal diameter for intervention. In this week’s NEJM, Karthikesalingam et al. compared thresholds for AAA repair in the U.S. and England and differences in rates of aneurysm repair, in-hospital mortality, aneurysm rupture, long-term survival, aneurysm-related mortality, preoperative aneurysm diameter at time of repair, and prevalence of risk factors.  The authors used several unlinked databases and stratified the comparisons by age and gender. Survival comparisons also were adjusted for year of surgery and whether the repair was open or endovascular.

Rates of intact aneurysm repair increased in both countries from 2005–2012, but rates were significantly lower in England (odds ratio, 0.49; P<0.0001). The percentage of repairs that were endovascular was also lower in England (45% vs. 67%, P<0.001).  After controlling for multiple factors, in-hospital mortality and 3-year survival after elective repair were similar in the two countries.

Although rates of hospitalization for aneurysm rupture decreased in both countries from 2005–2012, hospitalization was significantly more common in England (OR, 2.23; P<0.001). Aneurysm –related mortality also declined in both countries, but again was significantly higher in England (OR, 3.60; P<0.001). The mean aneurysm diameter (weighted for age and gender) at intact AAA repair was significantly larger in England than in the U.S. (6.37 vs. 5.83 cm; P<0.001).

The study authors conclude that the rate of intact AAA repair in England is about half as high as in the U.S., likely because surgeons in England repair aneurysms when they are larger than surgeons in the U.S. The higher rate of intact aneurysm repair at a lower diameter in the U.S. did not appear to increase perioperative risk or mortality. In fact, the authors suggest that the higher rate of ruptured aneurysm hospitalization and mortality in England may be due to the higher-diameter aneurysm repair thresholds.

The major weakness of this study is that the authors cannot establish a causal relationship between the increased rates of aneurysm-rupture outcomes in England and the threshold at which they repair aneurysms. In addition, this study is limited by the retrospective design and the use of several unlinked databases during different time periods. Although this study is unlikely to change practice, it does provide more support for the existing international guidelines and may lead some countries to reconsider AAA repair thresholds.

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