September 18th, 2012

Screening for AAA Comes Under Renewed Scrutiny and Criticism

A 2007 Medicare initiative to increase AAA (abdominal aortic aneurysm) screening in appropriate patients failed to prevent AAA rupture or reduce all-cause mortality, according to a new study published in the Archives of Internal Medicine. The larger implications of the study are unclear, but two accompanying papers, an invited commentary and a perspective, emphasize the darker side of AAA screening.

Jacqueline Baras Shreibati and colleagues examined the effect of the 2007 Screening Abdominal Aortic Aneurysms Very Efficiently (SAAAVE) Act, which provided Medicare coverage for a one-time ultrasound screening for new Medicare patients who were  men and had a history of smoking or were men or women and had a family history of AAA. The SAAAVE Act was based on 2005 U.S. Preventive Services Task Force recommendations.

Using Medicare data from 2004 to 2008, the investigators found a modest increase in AAA screening among eligible 65-year-old men during the study period, from 7.6% in 2004 to 9.6% in 2008. The SAAAVE Act resulted in no significant differences in the rates of AAA repair, AAA rupture, or all-cause mortality, they concluded.

In an invited commentary, Russell Harris, Stacey Sheridan, and Linda Kinsinger write that the evidence about AAA screening has changed since the 2005 USPSTF recommendations. In the past 10 to 15 years, they write, mortality from ruptured AAA has been cut nearly in half. AAA screening, they maintain, has had little to do with this change; rather, the change is more likely due to long-term trends in the reduction of smoking prevalence and the incidence of MI.

An additional trend over this period is the increased use of endovascular aneurysm repair (EVAR) instead of open aneurysm repair (OAR) in patients with AAA. Although EVAR and OAR have had similar long-term outcomes in randomized trials, in clinical practice EVAR is more likely to be performed in patients with AAAs below the 5.5-cm treatment threshold. The authors also point out that even if patients with small AAAs do not undergo an unnecessary procedure, they may suffer from the “negative psychological effects from diagnosis of small AAAs.”

One of the commentary authors, Russell Harris, was a member of the 2005 USPSTF committee and voted in favor of the screening recommendation. A reconsideration of the guidelines may lead to a tightening of these recommendations, the authors suggest:

Sometimes it takes time to fully understand the effects of a new screening policy within the context in which it is introduced. If AAA mortality is declining without much contribution from AAA screening; if EVAR is a technology that is hard to control; if AAA screening leads to substantial harms by labeling and overdiagnosis, then perhaps it is a good thing that the USPSTF will get a chance to reevaluate its positive recommendation before more and more people develop the habit of screening. The outcome this time may be different.

In the accompanying perspective, Vinay Prasad presents the case history of a 65-year-old former smoker with a history of MI who had a 6-cm AAA. After consultation with his physician and his surgeon Mr. R underwent EVAR. After numerous complications causing significant reductions in his quality of life, Mr. R came to regret his decision. Prasad writes that the case raises several difficult issues:

First, Mr R was appropriately consented for surgery; however, in hindsight he wishes different information were presented to him. The informed consent process is often long and complicated, but it remains unclear if it best communicates what some patients want to know. Second, translating data from RCTs to individual patients, who often differ from those participants in the RCTs, remains an uncertain affair. Third, data are often extrapolated from older studies. The data from the cited screening example were collected between 1997 and 1999, prior to the development of endovascular repair. Finally, how quickly should physicians respond to new data, and are data from only 1 or 2 studies sufficient to change practice?

Further reading: Blue light special: AAA screening at Kmart in the disease-mongering aisle.

One Response to “Screening for AAA Comes Under Renewed Scrutiny and Criticism”

  1. Louis Messina, M.D. says:

    The main problem/concern with the new AAA study published in Archives of Internal Medicine is that not enough time has elapsed since 2007 to begin to make any judgments on the effect of screening implementation on outcomes. Screening efforts will invariably detect many small aneurysms. It takes many years for these aneurysms to become large enough to warrant repair.

    The study has serious design flaws, and the interpretation is misleading:

    1. The screening program itself was a failure. Less than 10% of eligible men underwent an AAA screening ultrasound and >3% had the scan as part of the preventive screening program. Thus, with such a low rate of screening, one could not expect to see any clinical impact, i.e., reduction in deaths due to ruptured AAA.
    2. The analysis excluded all patients who had a CT scan. Any patient who would have a large AAA on ultrasound that met criteria for repair would have had a CT scan. Therefore, the study potentially excluded a significant number of patients, if not all patients who had large aneurysm.
    3. In studies which are able to identify those who underwent screening and those who did not, a definite survival and cost benefit was found, but the results of that study would predict that due to the low enrollment, it would take many years to see the benefit of the Medicare program.1 The findings of the latter study show both a reduced death rate from ruptured aneurysms and lower health care costs that held up for ten years.2
    4. Unless a significant proportion of eligible patients undergo screening, one cannot conclude screening is ineffective. To the contrary, the most important finding of this study is that less than 3% of men eligible for an AAA screening underwent the study.
    5. What we learned from this study is that implementation of a program to reduce deaths from ruptured aneurysms by using a screening ultrasound of those at high clinical risk to have an aneurysm failed.

    As a result, in this relatively short time period, we would not expect to see any significant effect on rates of AAA repair, AAA rupture, or all-cause mortality.

    Louis M. Messina, M.D.
    Professor and Chief,
    Division of Vascular Surgery
    Vice Chair, Department of Surgery
    University of Massachusetts Medical School

    Andres Schanzer, MD, FACS
    Associate Professor of Surgery and Quantitative Health Sciences
    Program Director, Vascular Fellowship and Residency
    University of Massachusetts Medical School

    1. Ashton HA, Buxton MJ, Day NE, et al; Multicentre Aneurysm Screening Study Group. The Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomized controlled trial. Lancet. 2002;360(9345):1531-1539.
    2. Ann Intern Med. 2007 May 15;146(10):699-706.