Screening and Management of Abdominal Aortic Aneurysm: The Best Evidence
Am Fam Physician. 2006 Apr 1;73(7):1157-1158.
Deaths related to abdominal aortic aneurysm (AAA) account for less than 1 percent of deaths annually in U.S. men 65 years and older.1 What sets AAA apart from more common causes of death is that it is a preventable problem. Ultrasonographic screening for aortic aneurysms is rapid, accurate, and relatively inexpensive. A single normal ultrasound examination in men 65 years or older virtually excludes future risk of AAA-related death.2 More than 50 years of experience has shown that open surgical repair nearly eliminates the risk of AAA-related death.3 A recent meta-analysis4 found that aneurysm screening reduced AAA-related deaths by 43 percent over four to five years in men 65 years and older.
In 2005, the U.S. Preventive Services Task Force (USPSTF) issued a recommendation for one-time aneurysm screening for all men 65 years and older who have ever smoked (more than 100 lifetime cigarettes).5 The prevalence of AAA in older men ranges from 4.2 to 8.8 percent. The prevalence in men who never smoked is about 30 percent of the prevalence for ever-smokers; aneurysms also are smaller in those who never smoked compared with aneurysms in ever-smokers of the same age. The USPSTF made no recommendation for screening of average-risk men who never smoked.
The prevalence of aortic aneurysms in women ranges from 0.6 to 1.4 percent, or about 15 percent of the prevalence in men. There is also a seven- to 10-year lag in the incidence of aneurysms in women compared with men. Most AAA-related deaths occur before 80 years of age in men and after 80 years of age in women. Because there is no evidence that screening is beneficial in women, the USPSTF recommended against aneurysm screening in average-risk women. The USPSTF noted that physicians should consider other risk factors when individualizing recommendations for specific patients.
The significance of these recommendations was underscored by the recent passage of the Screening Abdominal Aortic Aneurysms Very Efficiently Act. Beginning in January 2007, Medicare will provide coverage to new enrollees for one-time ultrasonography in men with a history of smoking and in men and women 65 to 74 years of age with a family history of AAA.
Once an AAA is identified, the question is how to proceed. Periodic surveillance every two to three years is warranted for those with 3.0- to 3.9-cm AAAs because they rarely rupture.6 For 4.0- to 5.4-cm AAAs, two clinical trials7,8 have demonstrated that immediate surgical repair does not improve overall survival compared with periodic surveillance. Based on these trial outcomes, it is generally safe to refer patients with AAAs of 5.0 cm or larger. For patients with aortic aneurysms 5.5 cm or larger in diameter, the risk of rupture increases progressively with size, and mortality with aneurysm rupture is about 80 percent.9 Elective open surgical repair in those fit for surgery is the accepted standard of care.
In coming years, the more unsettled issue will be the role of endovascular repair in the management of AAA. The impetus for developing this technique was the expectation that for aneurysms 5.5 cm or larger, endovascular repair would reduce postoperative morbidity and mortality, speed recovery, and improve long-term survival compared with open surgical repair. Early results from two European clinical trials10,11 showed that 30-day mortality with endovascular repair in patients with an AAA of 5.5 cm or larger was substantially lower than for surgical repair. However, in follow-up studies12–14 from both trials, these early survival advantages disappeared after one to one and one half years. Because endovascular aneurysm repair has risks of late complications, results after four to five years of follow-up will be needed to determine the long-term outcomes with endovascular repair.
In a 2005 report14 from a U.S. endovascular repair registry, more than one half of endovascular repairs were for aneurysms 5.4 cm or smaller. Because clinical trials have not shown a survival advantage for early surgical repair compared with periodic surveillance, it is not clear whether endovascular repair for small aneurysms is superior to either. Trials are underway in the United States and Europe to examine this question. How will physicians, given what is and is not known about interventions for AAA, provide the patient with informed advice about options? The physician should encourage surveillance when it is prudent. When intervention is indicated, surgical repair is still the standard of care. When advising patients about the option of endovascular repair, long-term outcomes from ongoing clinical trials should provide the best guidance for the appropriate role of this intervention.
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